Add rtmdet-tiny RTMW/RTMDet HF port

README.md

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+---
+license: apache-2.0
+tags:
+  - object-detection
+  - person-detection
+  - rtmdet
+  - real-time
+  - computer-vision
+pipeline_tag: object-detection
+---
+
+# rtmdet-tiny
+
+This is a Hugging Face-compatible port of **rtmdet-tiny** from [OpenMMLab MMDetection](https://github.com/open-mmlab/mmdetection).
+
+RTMDet is a family of real-time object detectors based on the CSPNeXt architecture. This checkpoint is pretrained on COCO and is particularly well-suited for **person detection** as a first stage before wholebody pose estimation with [RTMW](https://huggingface.co/akore/rtmw-l-384x288).
+
+## Model description
+
+- **Architecture**: CSPNeXt backbone + CSPNeXtPAFPN neck + RTMDetHead
+- **Backbone scale**: deepen=0.167, widen=0.375 (~~5M parameters)
+- **Input size**: 640×640
+- **Classes**: 80 (COCO)
+- **Uses custom code** — load with `trust_remote_code=True`
+
+## Usage
+
+```python
+from transformers import AutoImageProcessor
+from PIL import Image
+import torch
+
+from rtmdet_modules.configuration_rtmdet import RTMDetConfig
+from rtmdet_modules.modeling_rtmdet import RTMDetModel
+
+config = RTMDetConfig.from_pretrained("akore/rtmdet-tiny", trust_remote_code=True)
+model = RTMDetModel.from_pretrained("akore/rtmdet-tiny", trust_remote_code=True)
+model.eval()
+
+processor = AutoImageProcessor.from_pretrained("akore/rtmdet-tiny")
+image = Image.open("your_image.jpg").convert("RGB")
+inputs = processor(images=image, return_tensors="pt")
+
+with torch.no_grad():
+    outputs = model(pixel_values=inputs["pixel_values"])
+
+# outputs["boxes"]:  (N, 4) in [x1, y1, x2, y2]
+# outputs["scores"]: (N,)
+# outputs["labels"]: (N,)  — 0 = person in COCO
+print(outputs)
+```
+
+## Citation
+
+```bibtex
+@misc{lyu2022rtmdet,
+  title={RTMDet: An Empirical Study of Designing Real-Time Object Detectors},
+  author={Chengqi Lyu and Wenwei Zhang and Haian Huang and Yue Zhou and Yudong Wang and Yanyi Liu and Shilong Zhang and Kai Chen},
+  year={2022},
+  eprint={2212.07784},
+  archivePrefix={arXiv},
+  primaryClass={cs.CV}
+}
+```

config.json

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+{
+  "backbone_arch": "P5",
+  "backbone_channel_attention": true,
+  "backbone_deepen_factor": 0.167,
+  "backbone_expand_ratio": 0.5,
+  "backbone_widen_factor": 0.375,
+  "head_exp_on_reg": false,
+  "head_feat_channels": 96,
+  "head_in_channels": 96,
+  "head_pred_kernel_size": 1,
+  "head_share_conv": true,
+  "head_stacked_convs": 2,
+  "head_with_objectness": false,
+  "input_size": [
+    640,
+    640
+  ],
+  "max_detections": 100,
+  "model_type": "rtmdet",
+  "neck_expand_ratio": 0.5,
+  "neck_in_channels": [
+    96,
+    192,
+    384
+  ],
+  "neck_num_csp_blocks": 1,
+  "neck_out_channels": 96,
+  "nms_threshold": 0.6,
+  "num_classes": 80,
+  "score_threshold": 0.05,
+  "strides": [
+    8,
+    16,
+    32
+  ],
+  "transformers_version": "5.2.0",
+  "auto_map": {
+    "AutoConfig": "configuration_rtmdet.RTMDetConfig",
+    "AutoModelForImageProcessing": "modeling_rtmdet.RTMDetModel"
+  }
+}

configuration_rtmdet.py

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+from typing import Dict, List, Optional, Union
+
+from transformers.configuration_utils import PretrainedConfig
+from transformers.utils import logging
+
+
+logger = logging.get_logger(__name__)
+
+
+class RTMDetConfig(PretrainedConfig):
+    """
+    Configuration class for RTMDet models from OpenMMLab.
+    
+    Args:
+        backbone_arch (`str`, *optional*, defaults to `"P5"`):
+            Architecture of the backbone. Can be either "P5" or "P6".
+        backbone_expand_ratio (`float`, *optional*, defaults to `0.5`):
+            Expand ratio of the backbone channels.
+        backbone_deepen_factor (`float`, *optional*, defaults to `1.0`):
+            Factor to deepen the backbone stages.
+        backbone_widen_factor (`float`, *optional*, defaults to `1.0`):
+            Factor to widen the backbone channels.
+        backbone_channel_attention (`bool`, *optional*, defaults to `True`):
+            Whether to use channel attention in the backbone.
+        neck_in_channels (`List[int]`, *optional*, defaults to `[256, 512, 1024]`):
+            Input channels for the neck.
+        neck_out_channels (`int`, *optional*, defaults to `256`):
+            Output channels for the neck.
+        neck_num_csp_blocks (`int`, *optional*, defaults to `3`):
+            Number of CSP blocks in the neck.
+        neck_expand_ratio (`float`, *optional*, defaults to `0.5`):
+            Expand ratio for the neck channels.
+        num_classes (`int`, *optional*, defaults to `80`):
+            Number of classes to predict.
+        head_in_channels (`int`, *optional*, defaults to `256`):
+            Input channels for the detection head.
+        head_stacked_convs (`int`, *optional*, defaults to `2`):
+            Number of stacked convolutions in the head.
+        head_feat_channels (`int`, *optional*, defaults to `256`):
+            Number of feature channels in the head.
+        head_with_objectness (`bool`, *optional*, defaults to `False`):
+            Whether to use objectness in the head.
+        head_exp_on_reg (`bool`, *optional*, defaults to `True`):
+            Whether to use exponential function on the regression branch.
+        head_share_conv (`bool`, *optional*, defaults to `True`):
+            Whether to share convolutions between classes in the head.
+        head_pred_kernel_size (`int`, *optional*, defaults to `1`):
+            Kernel size for the prediction layer in the head.
+        strides (`List[int]`, *optional*, defaults to `[8, 16, 32]`):
+            Strides for multi-scale feature maps.
+        input_size (`List[int]`, *optional*, defaults to `[640, 640]`):
+            Default input image size [width, height].
+        score_threshold (`float`, *optional*, defaults to `0.05`):
+            Score threshold for detections.
+        nms_threshold (`float`, *optional*, defaults to `0.6`):
+            NMS IoU threshold.
+        max_detections (`int`, *optional*, defaults to `100`):
+            Maximum number of detections to return.
+        **kwargs:
+            Additional parameters passed to the parent class.
+    """
+
+    model_type = "rtmdet"
+
+    def __init__(
+        self,
+        backbone_arch: str = "P5",
+        backbone_expand_ratio: float = 0.5,
+        backbone_deepen_factor: float = 1.0,
+        backbone_widen_factor: float = 1.0,
+        backbone_channel_attention: bool = True,
+        neck_in_channels: List[int] = [256, 512, 1024],
+        neck_out_channels: int = 256,
+        neck_num_csp_blocks: int = 3,
+        neck_expand_ratio: float = 0.5,
+        num_classes: int = 80,
+        head_in_channels: int = 256,
+        head_stacked_convs: int = 2,
+        head_feat_channels: int = 256,
+        head_with_objectness: bool = False,
+        head_exp_on_reg: bool = True,
+        head_share_conv: bool = True,
+        head_pred_kernel_size: int = 1,
+        strides: List[int] = [8, 16, 32],
+        input_size: List[int] = [640, 640],
+        score_threshold: float = 0.05,
+        nms_threshold: float = 0.6,
+        max_detections: int = 100,
+        **kwargs
+    ):
+        super().__init__(**kwargs)
+
+        # Backbone config
+        self.backbone_arch = backbone_arch
+        self.backbone_expand_ratio = backbone_expand_ratio
+        self.backbone_deepen_factor = backbone_deepen_factor
+        self.backbone_widen_factor = backbone_widen_factor
+        self.backbone_channel_attention = backbone_channel_attention
+        
+        # Neck config
+        self.neck_in_channels = neck_in_channels
+        self.neck_out_channels = neck_out_channels
+        self.neck_num_csp_blocks = neck_num_csp_blocks
+        self.neck_expand_ratio = neck_expand_ratio
+        
+        # Head config
+        self.num_classes = num_classes
+        self.head_in_channels = head_in_channels
+        self.head_stacked_convs = head_stacked_convs
+        self.head_feat_channels = head_feat_channels
+        self.head_with_objectness = head_with_objectness
+        self.head_exp_on_reg = head_exp_on_reg
+        self.head_share_conv = head_share_conv
+        self.head_pred_kernel_size = head_pred_kernel_size
+        self.strides = strides
+        
+        # Inference config
+        self.input_size = input_size
+        self.score_threshold = score_threshold
+        self.nms_threshold = nms_threshold
+        self.max_detections = max_detections

model.safetensors

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+version https://git-lfs.github.com/spec/v1
+oid sha256:931fc4f5ab39801c5079167c825774f233781c72611104168774bc045d5b92f6
+size 22362944

modeling_rtmdet.py

@@ -0,0 +1,1886 @@
+from typing import List, Optional, Tuple, Union, Sequence, Dict
+from dataclasses import dataclass
+import inspect
+from functools import partial
+import warnings
+
+import math
+import torch
+import torchvision
+import torch.nn as nn
+from torch import Tensor
+import torch.nn.functional as F
+from torch.nn.modules.batchnorm import _BatchNorm, SyncBatchNorm
+
+from transformers.modeling_outputs import  ModelOutput
+from transformers.modeling_utils import PreTrainedModel
+from transformers.utils import logging
+
+from .configuration_rtmdet import RTMDetConfig
+
+
+logger = logging.get_logger(__name__)
+
+@dataclass
+class DetectionOutput(ModelOutput):
+    """
+    Output type for object detection models.
+    
+    Args:
+        boxes (`torch.FloatTensor` of shape `(batch_size, num_boxes, 4)`):
+            Detection boxes in format [x1, y1, x2, y2].
+        scores (`torch.FloatTensor` of shape `(batch_size, num_boxes)`):
+            Detection confidence scores.
+        labels (`torch.LongTensor` of shape `(batch_size, num_boxes)`):
+            Detection class indices.
+        loss (`torch.FloatTensor`, *optional*):
+            Loss value if training.
+    """
+    
+    boxes: torch.FloatTensor = None
+    scores: torch.FloatTensor = None
+    labels: torch.LongTensor = None
+    loss: Optional[torch.FloatTensor] = None
+
+
+# Replace MODELS registry with direct class mappings
+ACTIVATION_LAYERS = {
+    'ReLU': nn.ReLU,
+    'LeakyReLU': nn.LeakyReLU,
+    'PReLU': nn.PReLU,
+    'SiLU': nn.SiLU,
+    'Sigmoid': nn.Sigmoid,
+    'Tanh': nn.Tanh,
+    'GELU': nn.GELU,
+    'Swish': nn.SiLU,  # Swish is equivalent to SiLU
+    'Hardsigmoid': nn.Hardsigmoid,
+    'HSigmoid': nn.Hardsigmoid
+}
+
+# Simple Config Type replacement
+ConfigType = Dict
+OptConfigType = Optional[Dict]
+OptMultiConfig = Optional[Union[Dict, List[Dict]]]
+
+def build_activation_layer(cfg: Dict) -> nn.Module:
+    """Build activation layer.
+    Args:
+        cfg (dict): The activation layer config, which should contain:
+            - type (str): Layer type.
+            - layer args: Args needed to instantiate an activation layer.
+    Returns:
+        nn.Module: Created activation layer.
+    """
+    if not isinstance(cfg, dict):
+        raise TypeError('cfg must be a dict')
+    if 'type' not in cfg:
+        raise KeyError('the cfg dict must contain the key "type"')
+    
+    cfg_ = cfg.copy()
+    layer_type = cfg_.pop('type')
+    
+    if layer_type not in ACTIVATION_LAYERS:
+        raise KeyError(f'Unrecognized activation type {layer_type}')
+    
+    activation = ACTIVATION_LAYERS[layer_type]
+    return activation(**cfg_)
+
+def kaiming_init(module,
+                 a=0,
+                 mode='fan_out',
+                 nonlinearity='relu',
+                 bias=0,
+                 distribution='normal'):
+    assert distribution in ['uniform', 'normal']
+    if hasattr(module, 'weight') and module.weight is not None:
+        if distribution == 'uniform':
+            nn.init.kaiming_uniform_(
+                module.weight, a=a, mode=mode, nonlinearity=nonlinearity)
+        else:
+            nn.init.kaiming_normal_(
+                module.weight, a=a, mode=mode, nonlinearity=nonlinearity)
+    if hasattr(module, 'bias') and module.bias is not None:
+        nn.init.constant_(module.bias, bias)
+
+def constant_init(module, val, bias=0):
+    if hasattr(module, 'weight') and module.weight is not None:
+        nn.init.constant_(module.weight, val)
+    if hasattr(module, 'bias') and module.bias is not None:
+        nn.init.constant_(module.bias, bias)
+
+class _InstanceNorm(nn.modules.instancenorm._InstanceNorm):
+    """Instance Normalization Base Class."""
+    pass
+
+# Custom implementation of methods with asterisks that couldn't be included in the original code
+# These methods need to be renamed without asterisks in actual implementation
+
+def infer_abbr(class_type):
+    """Infer abbreviation from the class name."""
+    if not inspect.isclass(class_type):
+        raise TypeError(
+            f'class_type must be a type, but got {type(class_type)}')
+    if hasattr(class_type, '_abbr_'):
+        return class_type._abbr_
+    if issubclass(class_type, _InstanceNorm):  # IN is a subclass of BN
+        return 'in'
+    elif issubclass(class_type, _BatchNorm):
+        return 'bn'
+    elif issubclass(class_type, nn.GroupNorm):
+        return 'gn'
+    elif issubclass(class_type, nn.LayerNorm):
+        return 'ln'
+    else:
+        class_name = class_type.__name__.lower()
+        if 'batch' in class_name:
+            return 'bn'
+        elif 'group' in class_name:
+            return 'gn'
+        elif 'layer' in class_name:
+            return 'ln'
+        elif 'instance' in class_name:
+            return 'in'
+        else:
+            return 'norm_layer'
+
+# Create mapping from strings to layer classes
+NORM_LAYERS = {
+    'BN': nn.BatchNorm2d,
+    'BN1d': nn.BatchNorm1d,
+    'BN2d': nn.BatchNorm2d,
+    'BN3d': nn.BatchNorm3d,
+    'SyncBN': SyncBatchNorm,
+    'GN': nn.GroupNorm,
+    'LN': nn.LayerNorm,
+    'IN': nn.InstanceNorm2d,
+    'IN1d': nn.InstanceNorm1d,
+    'IN2d': nn.InstanceNorm2d,
+    'IN3d': nn.InstanceNorm3d
+}
+
+CONV_LAYERS = {
+    'Conv1d': nn.Conv1d,
+    'Conv2d': nn.Conv2d,
+    'Conv3d': nn.Conv3d,
+    'Conv': nn.Conv2d
+}
+
+PADDING_LAYERS = {
+    'zero': nn.ZeroPad2d,
+    'reflect': nn.ReflectionPad2d,
+    'replicate': nn.ReplicationPad2d
+}
+
+def build_norm_layer(cfg: Dict,
+                     num_features: int,
+                     postfix: Union[int, str] = '') -> Tuple[str, nn.Module]:
+    """Build normalization layer."""
+    if not isinstance(cfg, dict):
+        raise TypeError('cfg must be a dict')
+    if 'type' not in cfg:
+        raise KeyError('the cfg dict must contain the key "type"')
+    
+    cfg_ = cfg.copy()
+    layer_type = cfg_.pop('type')
+    
+    if layer_type not in NORM_LAYERS:
+        raise KeyError(f'Unrecognized norm type {layer_type}')
+        
+    norm_layer = NORM_LAYERS[layer_type]
+    abbr = infer_abbr(norm_layer)
+    
+    assert isinstance(postfix, (int, str))
+    name = abbr + str(postfix)
+    
+    requires_grad = cfg_.pop('requires_grad', True)
+    cfg_.setdefault('eps', 1e-5)
+    
+    if norm_layer is not nn.GroupNorm:
+        layer = norm_layer(num_features, **cfg_)
+        if layer_type == 'SyncBN' and hasattr(layer, '_specify_ddp_gpu_num'):
+            layer._specify_ddp_gpu_num(1)
+    else:
+        assert 'num_groups' in cfg_
+        layer = norm_layer(num_channels=num_features, **cfg_)
+        
+    for param in layer.parameters():
+        param.requires_grad = requires_grad
+        
+    return name, layer
+
+def build_conv_layer(cfg: Optional[Dict], *args, **kwargs) -> nn.Module:
+    """Build convolution layer."""
+    if cfg is None:
+        cfg_ = dict(type='Conv2d')
+    else:
+        if not isinstance(cfg, dict):
+            raise TypeError('cfg must be a dict')
+        if 'type' not in cfg:
+            raise KeyError('the cfg dict must contain the key "type"')
+        cfg_ = cfg.copy()
+        
+    layer_type = cfg_.pop('type')
+    
+    if layer_type not in CONV_LAYERS:
+        raise KeyError(f'Unrecognized conv type {layer_type}')
+        
+    conv_layer = CONV_LAYERS[layer_type]
+    layer = conv_layer(*args, **kwargs, **cfg_)
+    
+    return layer
+
+def build_padding_layer(cfg: Dict, *args, **kwargs) -> nn.Module:
+    """Build padding layer."""
+    if not isinstance(cfg, dict):
+        raise TypeError('cfg must be a dict')
+    if 'type' not in cfg:
+        raise KeyError('the cfg dict must contain the key "type"')
+        
+    cfg_ = cfg.copy()
+    padding_type = cfg_.pop('type')
+    
+    if padding_type not in PADDING_LAYERS:
+        raise KeyError(f'Unrecognized padding type {padding_type}')
+        
+    padding_layer = PADDING_LAYERS[padding_type]
+    layer = padding_layer(*args, **kwargs, **cfg_)
+    
+    return layer
+
+def efficient_conv_bn_eval_forward(bn: _BatchNorm,
+                                   conv: nn.modules.conv._ConvNd,
+                                   x: torch.Tensor):
+    """
+    Implementation based on https://arxiv.org/abs/2305.11624
+    "Tune-Mode ConvBN Blocks For Efficient Transfer Learning"
+    It leverages the associative law between convolution and affine transform,
+    i.e., normalize (weight conv feature) = (normalize weight) conv feature.
+    It works for Eval mode of ConvBN blocks during validation, and can be used
+    for training as well. It reduces memory and computation cost.
+    Args:
+        bn (_BatchNorm): a BatchNorm module.
+        conv (nn._ConvNd): a conv module
+        x (torch.Tensor): Input feature map.
+    """
+    # These lines of code are designed to deal with various cases
+    # like bn without affine transform, and conv without bias
+    weight_on_the_fly = conv.weight
+    if conv.bias is not None:
+        bias_on_the_fly = conv.bias
+    else:
+        bias_on_the_fly = torch.zeros_like(bn.running_var)
+    if bn.weight is not None:
+        bn_weight = bn.weight
+    else:
+        bn_weight = torch.ones_like(bn.running_var)
+    if bn.bias is not None:
+        bn_bias = bn.bias
+    else:
+        bn_bias = torch.zeros_like(bn.running_var)
+    # shape of [C_out, 1, 1, 1] in Conv2d
+    weight_coeff = torch.rsqrt(bn.running_var +
+                               bn.eps).reshape([-1] + [1] *
+                                               (len(conv.weight.shape) - 1))
+    # shape of [C_out, 1, 1, 1] in Conv2d
+    coefff_on_the_fly = bn_weight.view_as(weight_coeff) * weight_coeff
+    # shape of [C_out, C_in, k, k] in Conv2d
+    weight_on_the_fly = weight_on_the_fly * coefff_on_the_fly
+    # shape of [C_out] in Conv2d
+    bias_on_the_fly = bn_bias + coefff_on_the_fly.flatten() *\
+        (bias_on_the_fly - bn.running_mean)
+    return conv._conv_forward(x, weight_on_the_fly, bias_on_the_fly)
+
+class ConvModule(nn.Module):
+    """A conv block that bundles conv/norm/activation layers."""
+    _abbr_ = 'conv_block'
+    
+    def __init__(self,
+                 in_channels: int,
+                 out_channels: int,
+                 kernel_size: Union[int, Tuple[int, int]],
+                 stride: Union[int, Tuple[int, int]] = 1,
+                 padding: Union[int, Tuple[int, int]] = 0,
+                 dilation: Union[int, Tuple[int, int]] = 1,
+                 groups: int = 1,
+                 bias: Union[bool, str] = 'auto',
+                 conv_cfg: Optional[Dict] = None,
+                 norm_cfg: Optional[Dict] = None,
+                 act_cfg: Optional[Dict] = dict(type='ReLU'),
+                 inplace: bool = True,
+                 with_spectral_norm: bool = False,
+                 padding_mode: str = 'zeros',
+                 order: tuple = ('conv', 'norm', 'act'),
+                 efficient_conv_bn_eval: bool = False):
+        super().__init__()
+        assert conv_cfg is None or isinstance(conv_cfg, dict)
+        assert norm_cfg is None or isinstance(norm_cfg, dict)
+        assert act_cfg is None or isinstance(act_cfg, dict)
+        official_padding_mode = ['zeros', 'circular']
+        self.conv_cfg = conv_cfg
+        self.norm_cfg = norm_cfg
+        self.act_cfg = act_cfg
+        self.inplace = inplace
+        self.with_spectral_norm = with_spectral_norm
+        self.with_explicit_padding = padding_mode not in official_padding_mode
+        self.order = order
+        assert isinstance(self.order, tuple) and len(self.order) == 3
+        assert set(order) == {'conv', 'norm', 'act'}
+        self.with_norm = norm_cfg is not None
+        self.with_activation = act_cfg is not None
+        # if the conv layer is before a norm layer, bias is unnecessary.
+        if bias == 'auto':
+            bias = not self.with_norm
+        self.with_bias = bias
+        
+        if self.with_explicit_padding:
+            pad_cfg = dict(type=padding_mode)
+            self.padding_layer = build_padding_layer(pad_cfg, padding)
+            
+        # reset padding to 0 for conv module
+        conv_padding = 0 if self.with_explicit_padding else padding
+        
+        # build convolution layer
+        self.conv = build_conv_layer(
+            conv_cfg,
+            in_channels,
+            out_channels,
+            kernel_size,
+            stride=stride,
+            padding=conv_padding,
+            dilation=dilation,
+            groups=groups,
+            bias=bias)
+            
+        # export the attributes of self.conv to a higher level for convenience
+        self.in_channels = self.conv.in_channels
+        self.out_channels = self.conv.out_channels
+        self.kernel_size = self.conv.kernel_size
+        self.stride = self.conv.stride
+        self.padding = padding
+        self.dilation = self.conv.dilation
+        self.transposed = self.conv.transposed
+        self.output_padding = self.conv.output_padding
+        self.groups = self.conv.groups
+        
+        if self.with_spectral_norm:
+            self.conv = nn.utils.spectral_norm(self.conv)
+            
+        # build normalization layers
+        if self.with_norm:
+            # norm layer is after conv layer
+            if order.index('norm') > order.index('conv'):
+                norm_channels = out_channels
+            else:
+                norm_channels = in_channels
+            self.norm_name, norm = build_norm_layer(
+                norm_cfg, norm_channels)  # type: ignore
+            self.add_module(self.norm_name, norm)
+            if self.with_bias:
+                if isinstance(norm, (_BatchNorm, _InstanceNorm)):
+                    warnings.warn(
+                        'Unnecessary conv bias before batch/instance norm')
+        else:
+            self.norm_name = None  # type: ignore
+            
+        self.turn_on_efficient_conv_bn_eval(efficient_conv_bn_eval)
+        
+        # build activation layer
+        if self.with_activation:
+            act_cfg_ = act_cfg.copy()  # type: ignore
+            # nn.Tanh has no 'inplace' argument
+            if act_cfg_['type'] not in [
+                    'Tanh', 'PReLU', 'Sigmoid', 'HSigmoid', 'Swish', 'GELU'
+            ]:
+                act_cfg_.setdefault('inplace', inplace)
+            self.activate = build_activation_layer(act_cfg_)
+            
+        # Use msra init by default
+        self.init_weights()
+        
+    @property
+    def norm(self):
+        if self.norm_name:
+            return getattr(self, self.norm_name)
+        else:
+            return None
+            
+    def init_weights(self):
+        if not hasattr(self.conv, 'init_weights'):
+            if self.with_activation and self.act_cfg['type'] == 'LeakyReLU':
+                nonlinearity = 'leaky_relu'
+                a = self.act_cfg.get('negative_slope', 0.01)
+            else:
+                nonlinearity = 'relu'
+                a = 0
+            kaiming_init(self.conv, a=a, nonlinearity=nonlinearity)
+        if self.with_norm:
+            constant_init(self.norm, 1, bias=0)
+            
+    def forward(self,
+                x: torch.Tensor,
+                activate: bool = True,
+                norm: bool = True) -> torch.Tensor:
+        layer_index = 0
+        while layer_index < len(self.order):
+            layer = self.order[layer_index]
+            if layer == 'conv':
+                if self.with_explicit_padding:
+                    x = self.padding_layer(x)
+                # if the next operation is norm and we have a norm layer in
+                # eval mode and we have enabled `efficient_conv_bn_eval` for
+                # the conv operator, then activate the optimized forward and
+                # skip the next norm operator since it has been fused
+                if layer_index + 1 < len(self.order) and \
+                        self.order[layer_index + 1] == 'norm' and norm and \
+                        self.with_norm and not self.norm.training and \
+                        self.efficient_conv_bn_eval_forward is not None:
+                    self.conv.forward = partial(
+                        self.efficient_conv_bn_eval_forward, self.norm,
+                        self.conv)
+                    layer_index += 1
+                    x = self.conv(x)
+                    del self.conv.forward
+                else:
+                    x = self.conv(x)
+            elif layer == 'norm' and norm and self.with_norm:
+                x = self.norm(x)
+            elif layer == 'act' and activate and self.with_activation:
+                x = self.activate(x)
+            layer_index += 1
+        return x
+        
+    def turn_on_efficient_conv_bn_eval(self, efficient_conv_bn_eval=True):
+        # efficient_conv_bn_eval works for conv + bn
+        # with `track_running_stats` option
+        if efficient_conv_bn_eval and self.norm \
+                            and isinstance(self.norm, _BatchNorm) \
+                            and self.norm.track_running_stats:
+            self.efficient_conv_bn_eval_forward = efficient_conv_bn_eval_forward  # noqa: E501
+        else:
+            self.efficient_conv_bn_eval_forward = None  # type: ignore
+            
+    @staticmethod
+    def create_from_conv_bn(conv: torch.nn.modules.conv._ConvNd,
+                            bn: torch.nn.modules.batchnorm._BatchNorm,
+                            efficient_conv_bn_eval=True) -> 'ConvModule':
+        """Create a ConvModule from a conv and a bn module."""
+        self = ConvModule.__new__(ConvModule)
+        super(ConvModule, self).__init__()
+        self.conv_cfg = None
+        self.norm_cfg = None
+        self.act_cfg = None
+        self.inplace = False
+        self.with_spectral_norm = False
+        self.with_explicit_padding = False
+        self.order = ('conv', 'norm', 'act')
+        self.with_norm = True
+        self.with_activation = False
+        self.with_bias = conv.bias is not None
+        # build convolution layer
+        self.conv = conv
+        # export the attributes of self.conv to a higher level for convenience
+        self.in_channels = self.conv.in_channels
+        self.out_channels = self.conv.out_channels
+        self.kernel_size = self.conv.kernel_size
+        self.stride = self.conv.stride
+        self.padding = self.conv.padding
+        self.dilation = self.conv.dilation
+        self.transposed = self.conv.transposed
+        self.output_padding = self.conv.output_padding
+        self.groups = self.conv.groups
+        # build normalization layers
+        self.norm_name, norm = 'bn', bn
+        self.add_module(self.norm_name, norm)
+        self.turn_on_efficient_conv_bn_eval(efficient_conv_bn_eval)
+        return self
+
+class DepthwiseSeparableConvModule(nn.Module):
+    """Depthwise separable convolution module."""
+    def __init__(self,
+                 in_channels: int,
+                 out_channels: int,
+                 kernel_size: Union[int, Tuple[int, int]],
+                 stride: Union[int, Tuple[int, int]] = 1,
+                 padding: Union[int, Tuple[int, int]] = 0,
+                 dilation: Union[int, Tuple[int, int]] = 1,
+                 norm_cfg: Optional[Dict] = None,
+                 act_cfg: Dict = dict(type='ReLU'),
+                 dw_norm_cfg: Union[Dict, str] = 'default',
+                 dw_act_cfg: Union[Dict, str] = 'default',
+                 pw_norm_cfg: Union[Dict, str] = 'default',
+                 pw_act_cfg: Union[Dict, str] = 'default',
+                 **kwargs):
+        super().__init__()
+        assert 'groups' not in kwargs, 'groups should not be specified'
+        # if norm/activation config of depthwise/pointwise ConvModule is not
+        # specified, use default config.
+        dw_norm_cfg = dw_norm_cfg if dw_norm_cfg != 'default' else norm_cfg  # type: ignore # noqa E501
+        dw_act_cfg = dw_act_cfg if dw_act_cfg != 'default' else act_cfg
+        pw_norm_cfg = pw_norm_cfg if pw_norm_cfg != 'default' else norm_cfg  # type: ignore # noqa E501
+        pw_act_cfg = pw_act_cfg if pw_act_cfg != 'default' else act_cfg
+        
+        # depthwise convolution
+        self.depthwise_conv = ConvModule(
+            in_channels,
+            in_channels,
+            kernel_size,
+            stride=stride,
+            padding=padding,
+            dilation=dilation,
+            groups=in_channels,
+            norm_cfg=dw_norm_cfg,  # type: ignore
+            act_cfg=dw_act_cfg,  # type: ignore
+            **kwargs)
+            
+        self.pointwise_conv = ConvModule(
+            in_channels,
+            out_channels,
+            1,
+            norm_cfg=pw_norm_cfg,  # type: ignore
+            act_cfg=pw_act_cfg,  # type: ignore
+            **kwargs)
+            
+    def forward(self, x: torch.Tensor) -> torch.Tensor:
+        x = self.depthwise_conv(x)
+        x = self.pointwise_conv(x)
+        return x
+
+class SPPBottleneck(nn.Module):
+    """Spatial pyramid pooling layer used in YOLOv3-SPP."""
+    def __init__(self,
+                 in_channels,
+                 out_channels,
+                 kernel_sizes=(5, 9, 13),
+                 conv_cfg=None,
+                 norm_cfg=dict(type='BN', momentum=0.03, eps=0.001),
+                 act_cfg=dict(type='Swish'),
+                 init_cfg=None):
+        super().__init__()
+        mid_channels = in_channels // 2
+        self.conv1 = ConvModule(
+            in_channels,
+            mid_channels,
+            1,
+            stride=1,
+            conv_cfg=conv_cfg,
+            norm_cfg=norm_cfg,
+            act_cfg=act_cfg)
+        self.poolings = nn.ModuleList([
+            nn.MaxPool2d(kernel_size=ks, stride=1, padding=ks // 2)
+            for ks in kernel_sizes
+        ])
+        conv2_channels = mid_channels * (len(kernel_sizes) + 1)
+        self.conv2 = ConvModule(
+            conv2_channels,
+            out_channels,
+            1,
+            conv_cfg=conv_cfg,
+            norm_cfg=norm_cfg,
+            act_cfg=act_cfg)
+            
+    def forward(self, x):
+        x = self.conv1(x)
+        with torch.amp.autocast(enabled=False, device_type=x.device.type):
+            x = torch.cat(
+                [x] + [pooling(x) for pooling in self.poolings], dim=1)
+        x = self.conv2(x)
+        return x
+
+class DarknetBottleneck(nn.Module):
+    """The basic bottleneck block used in Darknet."""
+    def __init__(self,
+                 in_channels: int,
+                 out_channels: int,
+                 expansion: float = 0.5,
+                 add_identity: bool = True,
+                 use_depthwise: bool = False,
+                 conv_cfg: OptConfigType = None,
+                 norm_cfg: ConfigType = dict(
+                     type='BN', momentum=0.03, eps=0.001),
+                 act_cfg: ConfigType = dict(type='Swish'),
+                 init_cfg: OptMultiConfig = None) -> None:
+        super().__init__()
+        hidden_channels = int(out_channels * expansion)
+        conv = DepthwiseSeparableConvModule if use_depthwise else ConvModule
+        self.conv1 = ConvModule(
+            in_channels,
+            hidden_channels,
+            1,
+            conv_cfg=conv_cfg,
+            norm_cfg=norm_cfg,
+            act_cfg=act_cfg)
+        self.conv2 = conv(
+            hidden_channels,
+            out_channels,
+            3,
+            stride=1,
+            padding=1,
+            conv_cfg=conv_cfg,
+            norm_cfg=norm_cfg,
+            act_cfg=act_cfg)
+        self.add_identity = \
+            add_identity and in_channels == out_channels
+            
+    def forward(self, x: Tensor) -> Tensor:
+        """Forward function."""
+        identity = x
+        out = self.conv1(x)
+        out = self.conv2(out)
+        if self.add_identity:
+            return out + identity
+        else:
+            return out
+
+class CSPNeXtBlock(nn.Module):
+    """The basic bottleneck block used in CSPNeXt."""
+    def __init__(self,
+                 in_channels: int,
+                 out_channels: int,
+                 expansion: float = 0.5,
+                 add_identity: bool = True,
+                 use_depthwise: bool = False,
+                 kernel_size: int = 5,
+                 conv_cfg: OptConfigType = None,
+                 norm_cfg: ConfigType = dict(
+                     type='BN', momentum=0.03, eps=0.001),
+                 act_cfg: ConfigType = dict(type='SiLU'),
+                 init_cfg: OptMultiConfig = None) -> None:
+        super().__init__()
+        hidden_channels = int(out_channels * expansion)
+        conv = DepthwiseSeparableConvModule if use_depthwise else ConvModule
+        self.conv1 = conv(
+            in_channels,
+            hidden_channels,
+            3,
+            stride=1,
+            padding=1,
+            norm_cfg=norm_cfg,
+            act_cfg=act_cfg)
+        self.conv2 = DepthwiseSeparableConvModule(
+            hidden_channels,
+            out_channels,
+            kernel_size,
+            stride=1,
+            padding=kernel_size // 2,
+            conv_cfg=conv_cfg,
+            norm_cfg=norm_cfg,
+            act_cfg=act_cfg)
+        self.add_identity = \
+            add_identity and in_channels == out_channels
+            
+    def forward(self, x: Tensor) -> Tensor:
+        """Forward function."""
+        identity = x
+        out = self.conv1(x)
+        out = self.conv2(out)
+        if self.add_identity:
+            return out + identity
+        else:
+            return out
+
+class ChannelAttention(nn.Module):
+    """Channel attention Module."""
+    def __init__(self, channels: int, init_cfg: OptMultiConfig = None) -> None:
+        super().__init__()
+        self.global_avgpool = nn.AdaptiveAvgPool2d(1)
+        self.fc = nn.Conv2d(channels, channels, 1, 1, 0, bias=True)
+        self.act = nn.Hardsigmoid(inplace=True)
+        
+    def forward(self, x: Tensor) -> Tensor:
+        """Forward function for ChannelAttention."""
+        with torch.amp.autocast(enabled=False, device_type=x.device.type):
+            out = self.global_avgpool(x)
+        out = self.fc(out)
+        out = self.act(out)
+        return x * out
+
+class CSPLayer(nn.Module):
+    """Cross Stage Partial Layer.
+    Args:
+        in_channels (int): The input channels of the CSP layer.
+        out_channels (int): The output channels of the CSP layer.
+        expand_ratio (float): Ratio to adjust the number of channels of the
+            hidden layer. Defaults to 0.5.
+        num_blocks (int): Number of blocks. Defaults to 1.
+        add_identity (bool): Whether to add identity in blocks.
+            Defaults to True.
+        use_cspnext_block (bool): Whether to use CSPNeXt block.
+            Defaults to False.
+        use_depthwise (bool): Whether to use depthwise separable convolution in
+            blocks. Defaults to False.
+        channel_attention (bool): Whether to add channel attention in each
+            stage. Defaults to True.
+        conv_cfg (dict, optional): Config dict for convolution layer.
+            Defaults to None, which means using conv2d.
+        norm_cfg (dict): Config dict for normalization layer.
+            Defaults to dict(type='BN')
+        act_cfg (dict): Config dict for activation layer.
+            Defaults to dict(type='Swish')
+    """
+    def __init__(self,
+                 in_channels: int,
+                 out_channels: int,
+                 expand_ratio: float = 0.5,
+                 num_blocks: int = 1,
+                 add_identity: bool = True,
+                 use_depthwise: bool = False,
+                 use_cspnext_block: bool = False,
+                 channel_attention: bool = False,
+                 conv_cfg: OptConfigType = None,
+                 norm_cfg: ConfigType = dict(
+                     type='BN', momentum=0.03, eps=0.001),
+                 act_cfg: ConfigType = dict(type='Swish'),
+                 init_cfg: OptMultiConfig = None) -> None:
+        super().__init__()
+        block = CSPNeXtBlock if use_cspnext_block else DarknetBottleneck
+        mid_channels = int(out_channels * expand_ratio)
+        self.channel_attention = channel_attention
+        
+        self.main_conv = ConvModule(
+            in_channels,
+            mid_channels,
+            1,
+            conv_cfg=conv_cfg,
+            norm_cfg=norm_cfg,
+            act_cfg=act_cfg)
+            
+        self.short_conv = ConvModule(
+            in_channels,
+            mid_channels,
+            1,
+            conv_cfg=conv_cfg,
+            norm_cfg=norm_cfg,
+            act_cfg=act_cfg)
+            
+        self.final_conv = ConvModule(
+            2 * mid_channels,
+            out_channels,
+            1,
+            conv_cfg=conv_cfg,
+            norm_cfg=norm_cfg,
+            act_cfg=act_cfg)
+            
+        self.blocks = nn.Sequential(*[
+            block(
+                mid_channels,
+                mid_channels,
+                1.0,
+                add_identity,
+                use_depthwise,
+                conv_cfg=conv_cfg,
+                norm_cfg=norm_cfg,
+                act_cfg=act_cfg) for _ in range(num_blocks)
+        ])
+        
+        if channel_attention:
+            self.attention = ChannelAttention(2 * mid_channels)
+            
+    def forward(self, x: Tensor) -> Tensor:
+        """Forward function."""
+        x_short = self.short_conv(x)
+        x_main = self.main_conv(x)
+        x_main = self.blocks(x_main)
+        x_final = torch.cat((x_main, x_short), dim=1)
+        
+        if self.channel_attention:
+            x_final = self.attention(x_final)
+            
+        return self.final_conv(x_final)
+    
+
+class CSPNeXt(nn.Module):
+    """CSPNeXt backbone used in RTMDet.
+    This is a standalone implementation without requiring the mmdet registry.
+    
+    Args:
+        arch (str): Architecture of CSPNeXt, from {P5, P6}.
+            Defaults to P5.
+        expand_ratio (float): Ratio to adjust the number of channels of the
+            hidden layer. Defaults to 0.5.
+        deepen_factor (float): Depth multiplier, multiply number of
+            blocks in CSP layer by this amount. Defaults to 1.0.
+        widen_factor (float): Width multiplier, multiply number of
+            channels in each layer by this amount. Defaults to 1.0.
+        out_indices (Sequence[int]): Output from which stages.
+            Defaults to (2, 3, 4).
+        frozen_stages (int): Stages to be frozen (stop grad and set eval
+            mode). -1 means not freezing any parameters. Defaults to -1.
+        use_depthwise (bool): Whether to use depthwise separable convolution.
+            Defaults to False.
+        arch_ovewrite (list): Overwrite default arch settings.
+            Defaults to None.
+        spp_kernel_sizes: (tuple[int]): Sequential of kernel sizes of SPP
+            layers. Defaults to (5, 9, 13).
+        channel_attention (bool): Whether to add channel attention in each
+            stage. Defaults to True.
+        conv_cfg (:obj:`ConfigDict` or dict, optional): Config dict for
+            convolution layer. Defaults to None.
+        norm_cfg (:obj:`ConfigDict` or dict): Dictionary to construct and
+            config norm layer. Defaults to dict(type='BN', requires_grad=True).
+        act_cfg (:obj:`ConfigDict` or dict): Config dict for activation layer.
+            Defaults to dict(type='SiLU').
+        norm_eval (bool): Whether to set norm layers to eval mode, namely,
+            freeze running stats (mean and var). Note: Effect on Batch Norm
+            and its variants only.
+    """
+    
+    # From left to right:
+    # in_channels, out_channels, num_blocks, add_identity, use_spp
+    arch_settings = {
+        'P5': [[64, 128, 3, True, False], [128, 256, 6, True, False],
+               [256, 512, 6, True, False], [512, 1024, 3, False, True]],
+        'P6': [[64, 128, 3, True, False], [128, 256, 6, True, False],
+               [256, 512, 6, True, False], [512, 768, 3, True, False],
+               [768, 1024, 3, False, True]]
+    }
+    
+    def __init__(
+        self,
+        arch: str = 'P5',
+        deepen_factor: float = 1.0,
+        widen_factor: float = 1.0,
+        out_indices: Sequence[int] = (2, 3, 4),
+        frozen_stages: int = -1,
+        use_depthwise: bool = False,
+        expand_ratio: float = 0.5,
+        arch_ovewrite: dict = None,
+        spp_kernel_sizes: Sequence[int] = (5, 9, 13),
+        channel_attention: bool = True,
+        conv_cfg: OptConfigType = None,
+        norm_cfg: ConfigType = dict(type='BN', momentum=0.03, eps=0.001),
+        act_cfg: ConfigType = dict(type='SiLU'),
+        norm_eval: bool = False,
+        init_cfg: OptMultiConfig = dict(
+            type='Kaiming',
+            layer='Conv2d',
+            a=math.sqrt(5),
+            distribution='uniform',
+            mode='fan_in',
+            nonlinearity='leaky_relu')
+    ) -> None:
+        super().__init__()
+        arch_setting = self.arch_settings[arch]
+        if arch_ovewrite:
+            arch_setting = arch_ovewrite
+        assert set(out_indices).issubset(
+            i for i in range(len(arch_setting) + 1))
+        if frozen_stages not in range(-1, len(arch_setting) + 1):
+            raise ValueError('frozen_stages must be in range(-1, '
+                             'len(arch_setting) + 1). But received '
+                             f'{frozen_stages}')
+        
+        self.out_indices = out_indices
+        self.frozen_stages = frozen_stages
+        self.use_depthwise = use_depthwise
+        self.norm_eval = norm_eval
+        
+        conv = DepthwiseSeparableConvModule if use_depthwise else ConvModule
+        
+        self.stem = nn.Sequential(
+            ConvModule(
+                3,
+                int(arch_setting[0][0] * widen_factor // 2),
+                3,
+                padding=1,
+                stride=2,
+                norm_cfg=norm_cfg,
+                act_cfg=act_cfg),
+            ConvModule(
+                int(arch_setting[0][0] * widen_factor // 2),
+                int(arch_setting[0][0] * widen_factor // 2),
+                3,
+                padding=1,
+                stride=1,
+                norm_cfg=norm_cfg,
+                act_cfg=act_cfg),
+            ConvModule(
+                int(arch_setting[0][0] * widen_factor // 2),
+                int(arch_setting[0][0] * widen_factor),
+                3,
+                padding=1,
+                stride=1,
+                norm_cfg=norm_cfg,
+                act_cfg=act_cfg))
+                
+        self.layers = ['stem']
+        
+        for i, (in_channels, out_channels, num_blocks, add_identity,
+                use_spp) in enumerate(arch_setting):
+            in_channels = int(in_channels * widen_factor)
+            out_channels = int(out_channels * widen_factor)
+            num_blocks = max(round(num_blocks * deepen_factor), 1)
+            stage = []
+            
+            conv_layer = conv(
+                in_channels,
+                out_channels,
+                3,
+                stride=2,
+                padding=1,
+                conv_cfg=conv_cfg,
+                norm_cfg=norm_cfg,
+                act_cfg=act_cfg)
+            stage.append(conv_layer)
+            
+            if use_spp:
+                spp = SPPBottleneck(
+                    out_channels,
+                    out_channels,
+                    kernel_sizes=spp_kernel_sizes,
+                    conv_cfg=conv_cfg,
+                    norm_cfg=norm_cfg,
+                    act_cfg=act_cfg)
+                stage.append(spp)
+                
+            csp_layer = CSPLayer(
+                out_channels,
+                out_channels,
+                num_blocks=num_blocks,
+                add_identity=add_identity,
+                use_depthwise=use_depthwise,
+                use_cspnext_block=True,
+                expand_ratio=expand_ratio,
+                channel_attention=channel_attention,
+                conv_cfg=conv_cfg,
+                norm_cfg=norm_cfg,
+                act_cfg=act_cfg)
+            stage.append(csp_layer)
+            
+            self.add_module(f'stage{i + 1}', nn.Sequential(*stage))
+            self.layers.append(f'stage{i + 1}')
+    
+    def freeze_stages(self) -> None:
+        """Freeze stages parameters."""
+        if self.frozen_stages >= 0:
+            for i in range(self.frozen_stages + 1):
+                m = getattr(self, self.layers[i])
+                m.eval()
+                for param in m.parameters():
+                    param.requires_grad = False
+    
+    def train(self, mode=True) -> None:
+        """Convert the model into training mode while keeping normalization layer
+        frozen."""
+        super().train(mode)
+        self.freeze_stages()
+        if mode and self.norm_eval:
+            for m in self.modules():
+                if isinstance(m, _BatchNorm):
+                    m.eval()
+    
+    def forward(self, x: Tuple[Tensor, ...]) -> Tuple[Tensor, ...]:
+        outs = []
+        for i, layer_name in enumerate(self.layers):
+            layer = getattr(self, layer_name)
+            x = layer(x)
+            if i in self.out_indices:
+                outs.append(x)
+        return tuple(outs)
+    
+
+class CSPNeXtPAFPN(nn.Module):
+    """Path Aggregation Network with CSPNeXt blocks.
+    This is a standalone implementation that works with the CSPNeXt backbone.
+    
+    Args:
+        in_channels (Sequence[int]): Number of input channels per scale.
+        out_channels (int): Number of output channels (used at each scale)
+        out_indices (Sequence[int]): Output from which stages.
+        num_csp_blocks (int): Number of bottlenecks in CSPLayer.
+            Defaults to 3.
+        use_depthwise (bool): Whether to use depthwise separable convolution in
+            blocks. Defaults to False.
+        expand_ratio (float): Ratio to adjust the number of channels of the
+            hidden layer. Default: 0.5
+        upsample_cfg (dict): Config dict for interpolate layer.
+            Default: `dict(scale_factor=2, mode='nearest')`
+        conv_cfg (dict, optional): Config dict for convolution layer.
+            Default: None, which means using conv2d.
+        norm_cfg (dict): Config dict for normalization layer.
+            Default: dict(type='BN')
+        act_cfg (dict): Config dict for activation layer.
+            Default: dict(type='Swish')
+    """
+
+    def __init__(
+        self,
+        in_channels: Sequence[int],
+        out_channels: int,
+        out_indices=(0, 1, 2),
+        num_csp_blocks: int = 3,
+        use_depthwise: bool = False,
+        expand_ratio: float = 0.5,
+        upsample_cfg: ConfigType = dict(scale_factor=2, mode='nearest'),
+        conv_cfg: OptConfigType = None,
+        norm_cfg: ConfigType = dict(type='BN', momentum=0.03, eps=0.001),
+        act_cfg: ConfigType = dict(type='Swish'),
+        init_cfg: OptMultiConfig = dict(
+            type='Kaiming',
+            layer='Conv2d',
+            a=math.sqrt(5),
+            distribution='uniform',
+            mode='fan_in',
+            nonlinearity='leaky_relu')
+    ) -> None:
+        super().__init__()
+        self.in_channels = in_channels
+        self.out_channels = out_channels
+        self.out_indices = out_indices
+
+        conv = DepthwiseSeparableConvModule if use_depthwise else ConvModule
+
+        # build top-down blocks
+        self.upsample = nn.Upsample(**upsample_cfg)
+        self.reduce_layers = nn.ModuleList()
+        self.top_down_blocks = nn.ModuleList()
+        for idx in range(len(in_channels) - 1, 0, -1):
+            self.reduce_layers.append(
+                ConvModule(
+                    in_channels[idx],
+                    in_channels[idx - 1],
+                    1,
+                    conv_cfg=conv_cfg,
+                    norm_cfg=norm_cfg,
+                    act_cfg=act_cfg))
+            self.top_down_blocks.append(
+                CSPLayer(
+                    in_channels[idx - 1] * 2,
+                    in_channels[idx - 1],
+                    num_blocks=num_csp_blocks,
+                    add_identity=False,
+                    use_depthwise=use_depthwise,
+                    use_cspnext_block=True,
+                    expand_ratio=expand_ratio,
+                    conv_cfg=conv_cfg,
+                    norm_cfg=norm_cfg,
+                    act_cfg=act_cfg))
+
+        # build bottom-up blocks
+        self.downsamples = nn.ModuleList()
+        self.bottom_up_blocks = nn.ModuleList()
+        for idx in range(len(in_channels) - 1):
+            self.downsamples.append(
+                conv(
+                    in_channels[idx],
+                    in_channels[idx],
+                    3,
+                    stride=2,
+                    padding=1,
+                    conv_cfg=conv_cfg,
+                    norm_cfg=norm_cfg,
+                    act_cfg=act_cfg))
+            self.bottom_up_blocks.append(
+                CSPLayer(
+                    in_channels[idx] * 2,
+                    in_channels[idx + 1],
+                    num_blocks=num_csp_blocks,
+                    add_identity=False,
+                    use_depthwise=use_depthwise,
+                    use_cspnext_block=True,
+                    expand_ratio=expand_ratio,
+                    conv_cfg=conv_cfg,
+                    norm_cfg=norm_cfg,
+                    act_cfg=act_cfg))
+
+        if self.out_channels is not None:
+            self.out_convs = nn.ModuleList()
+            for i in range(len(in_channels)):
+                self.out_convs.append(
+                    conv(
+                        in_channels[i],
+                        out_channels,
+                        3,
+                        padding=1,
+                        conv_cfg=conv_cfg,
+                        norm_cfg=norm_cfg,
+                        act_cfg=act_cfg))
+
+    def forward(self, inputs: Tuple[Tensor, ...]) -> Tuple[Tensor, ...]:
+        """
+        Args:
+            inputs (tuple[Tensor]): input features.
+
+        Returns:
+            tuple[Tensor]: YOLOXPAFPN features.
+        """
+        assert len(inputs) == len(self.in_channels)
+
+        # top-down path
+        inner_outs = [inputs[-1]]
+        for idx in range(len(self.in_channels) - 1, 0, -1):
+            feat_high = inner_outs[0]
+            feat_low = inputs[idx - 1]
+            feat_high = self.reduce_layers[len(self.in_channels) - 1 - idx](
+                feat_high)
+            inner_outs[0] = feat_high
+
+            upsample_feat = self.upsample(feat_high)
+
+            inner_out = self.top_down_blocks[len(self.in_channels) - 1 - idx](
+                torch.cat([upsample_feat, feat_low], 1))
+            inner_outs.insert(0, inner_out)
+
+        # bottom-up path
+        outs = [inner_outs[0]]
+        for idx in range(len(self.in_channels) - 1):
+            feat_low = outs[-1]
+            feat_high = inner_outs[idx + 1]
+            downsample_feat = self.downsamples[idx](feat_low)
+            out = self.bottom_up_blocks[idx](
+                torch.cat([downsample_feat, feat_high], 1))
+            outs.append(out)
+
+        if self.out_channels is not None:
+            # out convs
+            for idx in range(len(outs)):
+                outs[idx] = self.out_convs[idx](outs[idx])
+
+        return tuple([outs[i] for i in self.out_indices])
+
+
+class MlvlPointGenerator:
+    """Standard points generator for multi-level feature maps."""
+
+    def __init__(
+        self,
+        strides,
+        offset: float = 0.5
+    ) -> None:
+        if not isinstance(strides, (list, tuple)):
+            strides = [strides]
+            
+        self.strides = strides
+        self.offset = offset
+
+    def grid_priors(
+        self,
+        featmap_sizes,
+        dtype=torch.float32,
+        device='cuda',
+        with_stride=False
+    ):
+        """Generate grid points of multiple feature levels."""
+        num_levels = len(featmap_sizes)
+        multi_level_priors = []
+        
+        for i in range(num_levels):
+            priors = self.single_level_grid_priors(
+                featmap_sizes[i],
+                level_idx=i,
+                dtype=dtype,
+                device=device,
+                with_stride=with_stride)
+            multi_level_priors.append(priors)
+            
+        return multi_level_priors
+
+    def single_level_grid_priors(
+        self,
+        featmap_size,
+        level_idx,
+        dtype=torch.float32,
+        device='cuda',
+        with_stride=False
+    ):
+        """Generate grid points for a single feature level."""
+        feat_h, feat_w = featmap_size
+        stride = self.strides[level_idx]
+        
+        # Create grid coordinates
+        shift_x = (torch.arange(0, feat_w, device=device) + self.offset) * stride
+        shift_y = (torch.arange(0, feat_h, device=device) + self.offset) * stride
+        
+        shift_x = shift_x.to(dtype)
+        shift_y = shift_y.to(dtype)
+        
+        # Create grid
+        shift_yy, shift_xx = torch.meshgrid(shift_y, shift_x, indexing="ij")
+        shift_xx = shift_xx.reshape(-1)
+        shift_yy = shift_yy.reshape(-1)
+        
+        if not with_stride:
+            shifts = torch.stack([shift_xx, shift_yy], dim=-1)
+        else:
+            # Include stride information
+            stride_tensor = torch.tensor(stride, dtype=dtype, device=device)
+            stride_xx = torch.full_like(shift_xx, stride_tensor)
+            stride_yy = torch.full_like(shift_yy, stride_tensor)
+            shifts = torch.stack([shift_xx, shift_yy, stride_xx, stride_yy], dim=-1)
+            
+        return shifts
+
+
+# Helper functions needed for geometric mean sigmoid
+def sigmoid_geometric_mean(x, y):
+    """Compute geometric mean of two sigmoid functions."""
+    x_sigmoid = torch.sigmoid(x)
+    y_sigmoid = torch.sigmoid(y)
+    return torch.sqrt(x_sigmoid * y_sigmoid)
+
+
+def inverse_sigmoid(x, eps=1e-5):
+    """Inverse function of sigmoid."""
+    x = x.clamp(min=0, max=1)
+    x1 = x.clamp(min=eps)
+    x2 = (1 - x).clamp(min=eps)
+    return torch.log(x1 / x2)
+
+
+class RTMDetSepBNHead(nn.Module):
+    """RTMDetHead with separated BN layers and shared conv layers."""
+
+    def __init__(
+        self,
+        num_classes: int,
+        in_channels: int,
+        share_conv: bool = True,
+        use_depthwise: bool = False,
+        pred_kernel_size: int = 1,
+        stacked_convs: int = 2,
+        feat_channels: int = 256,
+        strides: List[int] = [8, 16, 32],
+        with_objectness: bool = False,
+        exp_on_reg: bool = False,
+    ) -> None:
+        super().__init__()
+        self.num_classes = num_classes
+        self.cls_out_channels = num_classes  # For sigmoid
+        self.in_channels = in_channels
+        self.feat_channels = feat_channels
+        self.stacked_convs = stacked_convs
+        self.share_conv = share_conv
+        self.use_depthwise = use_depthwise
+        self.pred_kernel_size = pred_kernel_size
+        self.with_objectness = with_objectness
+        self.exp_on_reg = exp_on_reg
+        self.strides = strides
+        
+        # Number of anchors per grid point
+        self.num_base_priors = 1
+        
+        self._init_layers()
+
+    def _init_layers(self) -> None:
+        """Initialize layers of the head."""
+        self.cls_convs = nn.ModuleList()
+        self.reg_convs = nn.ModuleList()
+
+        self.rtm_cls = nn.ModuleList()
+        self.rtm_reg = nn.ModuleList()
+        if self.with_objectness:
+            self.rtm_obj = nn.ModuleList()
+            
+        for n in range(len(self.strides)):
+            cls_convs = nn.ModuleList()
+            reg_convs = nn.ModuleList()
+            for i in range(self.stacked_convs):
+                chn = self.in_channels if i == 0 else self.feat_channels
+                
+                if self.use_depthwise:
+                    cls_conv = DepthwiseSeparableConvModule(
+                        chn,
+                        self.feat_channels,
+                        3,
+                        stride=1,
+                        padding=1,
+                        bias=False,
+                        act_cfg=dict(type='SiLU'),
+                        norm_cfg=dict(type='BN', momentum=0.03, eps=0.001)
+                        )
+                    reg_conv = DepthwiseSeparableConvModule(
+                        chn,
+                        self.feat_channels,
+                        3,
+                        stride=1,
+                        padding=1,
+                        bias=False,
+                        act_cfg=dict(type='SiLU'),
+                        norm_cfg=dict(type='BN', momentum=0.03, eps=0.001)
+                    )
+                else:
+                    cls_conv = ConvModule(
+                        chn,
+                        self.feat_channels,
+                        3,
+                        stride=1,
+                        padding=1,
+                        bias=False,
+                        act_cfg=dict(type='SiLU'),
+                        norm_cfg=dict(type='BN', momentum=0.03, eps=0.001))
+                    reg_conv = ConvModule(
+                        chn,
+                        self.feat_channels,
+                        3,
+                        stride=1,
+                        padding=1,
+                        bias=False,
+                        act_cfg=dict(type='SiLU'),
+                        norm_cfg=dict(type='BN', momentum=0.03, eps=0.001))
+                # Append conv layers to the list
+                cls_convs.append(cls_conv)
+                reg_convs.append(reg_conv)
+                
+            self.cls_convs.append(cls_convs)
+            self.reg_convs.append(reg_convs)
+
+            self.rtm_cls.append(
+                nn.Conv2d(
+                    self.feat_channels,
+                    self.num_base_priors * self.cls_out_channels,
+                    self.pred_kernel_size,
+                    padding=self.pred_kernel_size // 2))
+            self.rtm_reg.append(
+                nn.Conv2d(
+                    self.feat_channels,
+                    self.num_base_priors * 4,
+                    self.pred_kernel_size,
+                    padding=self.pred_kernel_size // 2))
+            if self.with_objectness:
+                self.rtm_obj.append(
+                    nn.Conv2d(
+                        self.feat_channels,
+                        1,
+                        self.pred_kernel_size,
+                        padding=self.pred_kernel_size // 2))
+
+        if self.share_conv:
+            for n in range(1, len(self.strides)):
+                for i in range(self.stacked_convs):
+                    self.cls_convs[n][i] = self.cls_convs[0][i]
+                    self.reg_convs[n][i] = self.reg_convs[0][i]
+        
+        # Initialize MlvlPointGenerator for anchor-free detection
+        self.prior_generator = MlvlPointGenerator(self.strides, offset=0.0)
+    
+    def init_weights(self):
+        """Initialize weights of the head."""
+        # Initialize conv layers with normal distribution
+        for m in self.modules():
+            if isinstance(m, nn.Conv2d):
+                nn.init.normal_(m.weight, mean=0, std=0.01)
+                if m.bias is not None:
+                    nn.init.constant_(m.bias, 0)
+            if isinstance(m, nn.BatchNorm2d):
+                nn.init.constant_(m.weight, 1)
+                nn.init.constant_(m.bias, 0)
+                
+        # Initialize classification layers with a prior probability
+        bias_init = -torch.log(torch.tensor((1 - 0.01) / 0.01))
+        for rtm_cls in self.rtm_cls:
+            nn.init.normal_(rtm_cls.weight, mean=0, std=0.01)
+            nn.init.constant_(rtm_cls.bias, bias_init)
+            
+        for rtm_reg in self.rtm_reg:
+            nn.init.normal_(rtm_reg.weight, mean=0, std=0.01)
+            nn.init.constant_(rtm_reg.bias, 0)
+            
+        if self.with_objectness:
+            for rtm_obj in self.rtm_obj:
+                nn.init.normal_(rtm_obj.weight, mean=0, std=0.01)
+                nn.init.constant_(rtm_obj.bias, bias_init)
+
+    def forward(self, feats):
+        """Forward features from the upstream network.
+
+        Args:
+            feats (tuple[Tensor]): Features from the upstream network, each is
+                a 4D-tensor.
+
+        Returns:
+            tuple: Usually a tuple of classification scores and bbox prediction
+                - cls_scores (list[Tensor]): Classification scores for all scale
+                  levels, each is a 4D-tensor.
+                - bbox_preds (list[Tensor]): Box energies / deltas for all scale
+                  levels, each is a 4D-tensor.
+        """
+        cls_scores = []
+        bbox_preds = []
+        for idx, (x, stride) in enumerate(
+                zip(feats, self.strides)):
+            cls_feat = x
+            reg_feat = x
+
+            for cls_layer in self.cls_convs[idx]:
+                cls_feat = cls_layer(cls_feat)
+            cls_score = self.rtm_cls[idx](cls_feat)
+
+            for reg_layer in self.reg_convs[idx]:
+                reg_feat = reg_layer(reg_feat)
+
+            if self.with_objectness:
+                objectness = self.rtm_obj[idx](reg_feat)
+                cls_score = inverse_sigmoid(
+                    sigmoid_geometric_mean(cls_score, objectness))
+                    
+            if self.exp_on_reg:
+                # Convert anchor-free to distance prediction, with stride scale
+                reg_dist = self.rtm_reg[idx](reg_feat).exp() * stride
+            else:
+                reg_dist = self.rtm_reg[idx](reg_feat) * stride
+                
+            cls_scores.append(cls_score)
+            bbox_preds.append(reg_dist)
+            
+        return tuple(cls_scores), tuple(bbox_preds)
+    
+    def predict(self, cls_scores, bbox_preds, batch_img_metas=None, cfg=None,
+               rescale=False, with_nms=True, score_thr=0.05, 
+               nms_iou_threshold=0.6, max_per_img=100):
+        """Transform network outputs into bbox predictions.
+        
+        This is a simplified version for inference only.
+        """
+        assert len(cls_scores) == len(bbox_preds)
+        num_levels = len(cls_scores)
+        device = cls_scores[0].device
+        batch_size = cls_scores[0].shape[0]
+        
+        # If no image metadata is provided, create default ones
+        if batch_img_metas is None:
+            # Use input feature size to estimate image size
+            featmap_sizes = [cls_scores[i].shape[-2:] for i in range(num_levels)]
+            strides = self.strides
+            
+            # Calculate original image size based on feature map sizes and strides
+            # This is approximate but works for most cases
+            upscaled_sizes = []
+            for i, featmap_size in enumerate(featmap_sizes):
+                h, w = featmap_size
+                upscaled_sizes.append((h * strides[i], w * strides[i]))
+            
+            # Use the maximum size across levels
+            img_h = max(s[0] for s in upscaled_sizes)
+            img_w = max(s[1] for s in upscaled_sizes)
+            
+            batch_img_metas = [{
+                'img_shape': (img_h, img_w, 3),
+                'scale_factor': [1.0, 1.0, 1.0, 1.0]
+            } for _ in range(batch_size)]
+        
+        # Get feature map sizes
+        featmap_sizes = [cls_scores[i].shape[-2:] for i in range(num_levels)]
+        
+        # Generate grid points for each level
+        mlvl_priors = self.prior_generator.grid_priors(
+            featmap_sizes,
+            dtype=cls_scores[0].dtype,
+            device=device,
+            with_stride=True)
+
+        result_list = []
+        for img_id in range(batch_size):
+            img_meta = batch_img_metas[img_id]
+            cls_score_list = [
+                cls_scores[i][img_id].detach() for i in range(num_levels)
+            ]
+            bbox_pred_list = [
+                bbox_preds[i][img_id].detach() for i in range(num_levels)
+            ]
+            
+            results = self._predict_by_feat_single(
+                cls_score_list,
+                bbox_pred_list,
+                mlvl_priors,
+                img_meta,
+                score_thr=score_thr,
+                nms_iou_threshold=nms_iou_threshold,
+                max_per_img=max_per_img,
+                rescale=rescale,
+                with_nms=with_nms
+            )
+            result_list.append(results)
+        
+        # Convert the results to a more standardized format
+        boxes_batch = []
+        scores_batch = []
+        labels_batch = []
+        
+        for result in result_list:
+            boxes = result['bboxes']
+            scores = result.get('scores', boxes[:, -1])
+            labels = result['labels']
+            
+            # Ensure boxes have only coordinates (some implementations add score as 5th column)
+            if boxes.shape[1] > 4:
+                boxes = boxes[:, :4]
+                
+            boxes_batch.append(boxes)
+            scores_batch.append(scores)
+            labels_batch.append(labels)
+        
+        # Stack results if there's at least one detection in each image
+        if all(len(boxes) > 0 for boxes in boxes_batch):
+            return DetectionOutput(
+                boxes=torch.stack(boxes_batch),
+                scores=torch.stack(scores_batch),
+                labels=torch.stack(labels_batch)
+            )
+        
+        # Handle case where some images have no detections
+        max_num = max(len(boxes) for boxes in boxes_batch)
+        if max_num == 0:
+            # No detections at all
+            dummy = torch.zeros((batch_size, 0, 4), device=device)
+            return DetectionOutput(
+                boxes=dummy,
+                scores=torch.zeros((batch_size, 0), device=device),
+                labels=torch.zeros((batch_size, 0), dtype=torch.long, device=device)
+            )
+        
+        # Pad results to have consistent tensor shapes
+        padded_boxes = []
+        padded_scores = []
+        padded_labels = []
+        
+        for boxes, scores, labels in zip(boxes_batch, scores_batch, labels_batch):
+            num_dets = len(boxes)
+            if num_dets == 0:
+                padded_boxes.append(torch.zeros((max_num, 4), device=device))
+                padded_scores.append(torch.zeros(max_num, device=device))
+                padded_labels.append(torch.zeros(max_num, dtype=torch.long, device=device))
+            else:
+                padding = torch.zeros((max_num - num_dets, 4), device=device)
+                padded_boxes.append(torch.cat([boxes, padding], dim=0))
+                
+                padding = torch.zeros(max_num - num_dets, device=device)
+                padded_scores.append(torch.cat([scores, padding], dim=0))
+                
+                padding = torch.zeros(max_num - num_dets, dtype=torch.long, device=device)
+                padded_labels.append(torch.cat([labels, padding], dim=0))
+        
+        return DetectionOutput(
+            boxes=torch.stack(padded_boxes),
+            scores=torch.stack(padded_scores),
+            labels=torch.stack(padded_labels)
+        )
+
+    def _predict_by_feat_single(self, cls_score_list, bbox_pred_list, mlvl_priors,
+                               img_meta, score_thr=0.05, nms_iou_threshold=0.6,
+                               max_per_img=100, rescale=False, with_nms=True):
+        """Transform outputs of a single image into bbox predictions.
+        
+        This is a simplified version for inference only.
+        """
+        # For each scale level
+        mlvl_bboxes = []
+        mlvl_scores = []
+        
+        for level_idx, (cls_score, bbox_pred, priors) in enumerate(
+                zip(cls_score_list, bbox_pred_list, mlvl_priors)):
+            assert cls_score.size()[-2:] == bbox_pred.size()[-2:]
+            
+            # Reshape
+            cls_score = cls_score.permute(1, 2, 0).reshape(-1, self.cls_out_channels)
+            bbox_pred = bbox_pred.permute(1, 2, 0).reshape(-1, 4)
+            
+            # Get scores
+            scores = torch.sigmoid(cls_score)
+            
+            # Find high-scoring predictions
+            max_scores, _ = scores.max(dim=1)
+            keep_mask = max_scores > score_thr
+            scores = scores[keep_mask]
+            bbox_pred = bbox_pred[keep_mask]
+            priors = priors[keep_mask]
+            
+            # If no valid predictions for this level, continue
+            if scores.numel() == 0:
+                continue
+                
+            # Decode bboxes
+            bboxes = self._decode_bboxes(priors, bbox_pred, img_meta.get('img_shape'))
+            
+            mlvl_bboxes.append(bboxes)
+            mlvl_scores.append(scores)
+            
+        # Combine all levels
+        if len(mlvl_bboxes) == 0:
+            # Return empty result if no valid predictions
+            return {
+                'bboxes': torch.zeros((0, 4), device=cls_score_list[0].device), 
+                'scores': torch.zeros((0,), device=cls_score_list[0].device),
+                'labels': torch.zeros((0,), device=cls_score_list[0].device, dtype=torch.long)
+            }
+            
+        bboxes = torch.cat(mlvl_bboxes)
+        scores = torch.cat(mlvl_scores)
+        
+        # Optional rescaling to original image size
+        if rescale and 'scale_factor' in img_meta:
+            bboxes /= bboxes.new_tensor(img_meta['scale_factor']).repeat((1, 2))
+        
+        # Apply NMS for each class
+        if with_nms:
+            det_bboxes, det_labels = self._nms(bboxes, scores, 
+                                              nms_iou_threshold, 
+                                              max_per_img)
+        else:
+            # Just return top k scores without NMS
+            scores_flattened = scores.flatten()
+            if scores_flattened.size(0) > max_per_img:
+                top_scores, indices = scores_flattened.topk(max_per_img)
+                scores_top_k = scores.view(-1, self.num_classes).index_select(0, indices)
+                bboxes_top_k = bboxes.index_select(0, indices)
+                labels_top_k = indices % self.num_classes
+                det_bboxes = torch.cat([bboxes_top_k, top_scores.unsqueeze(-1)], dim=1)
+                det_labels = labels_top_k
+            else:
+                # Convert to the same format with NMS
+                num_bboxes = bboxes.size(0)
+                max_scores, labels = scores.max(dim=1)
+                det_bboxes = torch.cat([bboxes, max_scores.unsqueeze(-1)], dim=1)
+                det_labels = labels
+            
+        return {
+            'bboxes': det_bboxes, 
+            'scores': det_bboxes[:, -1],
+            'labels': det_labels
+        }
+    
+    def _decode_bboxes(self, priors, distance, max_shape=None):
+        """Decode distance predictions to bounding box coordinates."""
+        # Get xy coordinates of priors (grid points)
+        xy = priors[..., :2]
+        
+        # Distance predictions to 4 boundaries (left, top, right, bottom)
+        # distances = [l, t, r, b]
+        
+        # Calculate bbox coordinates
+        x1 = xy[..., 0] - distance[..., 0]
+        y1 = xy[..., 1] - distance[..., 1]
+        x2 = xy[..., 0] + distance[..., 2]
+        y2 = xy[..., 1] + distance[..., 3]
+        
+        bboxes = torch.stack([x1, y1, x2, y2], -1)
+        
+        # Clip boxes to image boundaries if needed
+        if max_shape is not None:
+            bboxes[..., 0].clamp_(min=0, max=max_shape[1])
+            bboxes[..., 1].clamp_(min=0, max=max_shape[0])
+            bboxes[..., 2].clamp_(min=0, max=max_shape[1])
+            bboxes[..., 3].clamp_(min=0, max=max_shape[0])
+            
+        return bboxes
+    
+    def _nms(self, bboxes, scores, iou_threshold, max_per_img):
+        """Apply NMS to detection results."""
+        # For each class
+        num_classes = scores.shape[1]
+        det_bboxes = []
+        det_labels = []
+        
+        for cls_idx in range(num_classes):
+            cls_scores = scores[:, cls_idx]
+            keep_idx = cls_scores > 0.05  # Apply score threshold
+            
+            if not keep_idx.any():
+                continue
+                
+            cls_bboxes = bboxes[keep_idx]
+            cls_scores = cls_scores[keep_idx]
+            
+            # Apply NMS for this class
+            keep = self._batched_nms(cls_bboxes, cls_scores, iou_threshold)
+            keep = keep[:max_per_img]
+            
+            det_bboxes.append(torch.cat([cls_bboxes[keep], cls_scores[keep].unsqueeze(-1)], dim=1))
+            det_labels.append(cls_bboxes.new_full((keep.size(0),), cls_idx, dtype=torch.long))
+            
+        if len(det_bboxes) > 0:
+            det_bboxes = torch.cat(det_bboxes, dim=0)
+            det_labels = torch.cat(det_labels, dim=0)
+            
+            # Sort by score
+            _, indices = det_bboxes[:, -1].sort(descending=True)
+            det_bboxes = det_bboxes[indices]
+            det_labels = det_labels[indices]
+            
+            # Limit to max_per_img
+            det_bboxes = det_bboxes[:max_per_img]
+            det_labels = det_labels[:max_per_img]
+        else:
+            # Return empty tensors if no detections
+            det_bboxes = bboxes.new_zeros((0, 5))
+            det_labels = bboxes.new_zeros((0,), dtype=torch.long)
+            
+        return det_bboxes, det_labels
+    
+    def _batched_nms(self, boxes, scores, iou_threshold):
+        """Performs non-maximum suppression on a batch of boxes."""
+        if boxes.shape[0] == 0:
+            return boxes.new_zeros(0, dtype=torch.long)
+        
+        try:
+            # Try to use torchvision NMS for speed if available
+            return torchvision.ops.nms(boxes, scores, iou_threshold)
+        except:
+            # Fall back to manual NMS implementation
+            x1 = boxes[:, 0]
+            y1 = boxes[:, 1]
+            x2 = boxes[:, 2]
+            y2 = boxes[:, 3]
+            areas = (x2 - x1) * (y2 - y1)
+            _, order = scores.sort(descending=True)
+            
+            keep = []
+            while order.size(0) > 0:
+                i = order[0].item()
+                keep.append(i)
+                
+                if order.size(0) == 1:
+                    break
+                    
+                xx1 = torch.max(x1[order[1:]], x1[i])
+                yy1 = torch.max(y1[order[1:]], y1[i])
+                xx2 = torch.min(x2[order[1:]], x2[i])
+                yy2 = torch.min(y2[order[1:]], y2[i])
+                
+                w = torch.clamp(xx2 - xx1, min=0)
+                h = torch.clamp(yy2 - yy1, min=0)
+                inter = w * h
+                
+                iou = inter / (areas[i] + areas[order[1:]] - inter)
+                
+                inds = torch.where(iou <= iou_threshold)[0]
+                order = order[inds + 1]
+                
+            return torch.tensor(keep, dtype=torch.long, device=boxes.device)
+
+
+class RTMDetModel(PreTrainedModel):
+    """
+    RTMDet object detection model compatible with Hugging Face transformers.
+    Updated implementation using PyTorch only with no NumPy or OpenCV dependencies.
+    
+    This model consists of a backbone, neck, and detection head for object detection.
+    """
+    
+    config_class = RTMDetConfig
+    base_model_prefix = "rtmdet"
+    main_input_name = "pixel_values"
+    
+    def __init__(self, config):
+        super().__init__(config)
+        
+        # Build backbone
+        self.backbone = CSPNeXt(
+            arch=config.backbone_arch,
+            deepen_factor=config.backbone_deepen_factor,
+            widen_factor=config.backbone_widen_factor,
+            expand_ratio=config.backbone_expand_ratio,
+            channel_attention=config.backbone_channel_attention,
+            use_depthwise=False,
+        )
+        
+        # Build neck
+        self.neck = CSPNeXtPAFPN(
+            in_channels=config.neck_in_channels,
+            out_channels=config.neck_out_channels,
+            num_csp_blocks=config.neck_num_csp_blocks,
+            expand_ratio=config.neck_expand_ratio,
+            use_depthwise=False,
+        )
+        
+        # Build head
+        self.bbox_head = RTMDetSepBNHead(
+            num_classes=config.num_classes,
+            in_channels=config.head_in_channels,
+            stacked_convs=config.head_stacked_convs,
+            feat_channels=config.head_feat_channels,
+            with_objectness=config.head_with_objectness,
+            exp_on_reg=config.head_exp_on_reg,
+            share_conv=config.head_share_conv,
+            pred_kernel_size=config.head_pred_kernel_size,
+            strides=config.strides,
+            use_depthwise=False
+        )
+        
+        # Initialize weights
+        self.init_weights()
+    
+    def init_weights(self):
+        """Initialize the weights of the model."""
+        # Backbone is usually initialized from pre-trained weights
+        # so we don't need special initialization
+        
+        # Initialize head
+        self.bbox_head.init_weights()
+    
+    def forward(
+        self,
+        pixel_values=None,
+        labels=None,
+        output_hidden_states=None,
+        return_dict=None,
+    ):
+        """
+        Forward pass of the model.
+        
+        Args:
+            pixel_values (`torch.FloatTensor` of shape `(batch_size, channels, height, width)`):
+                Pixel values. Pixel values can be obtained using 
+                RTMDetImageProcessor.
+            labels (`List[Dict]`, *optional*):
+                Labels for computing the detection loss. Expected format:
+                List of dicts with 'boxes' and 'labels' keys.
+            output_hidden_states (`bool`, *optional*):
+                Whether or not to return the hidden states of all layers.
+            return_dict (`bool`, *optional*):
+                Whether or not to return a ModelOutput instead of a plain tuple.
+                
+        Returns:
+            `DetectionOutput` or `tuple`:
+                If return_dict=True, `DetectionOutput` is returned.
+                If return_dict=False, a tuple is returned where the first element
+                is the detection output tensor.
+        """
+        return_dict = return_dict if return_dict is not None else self.config.use_return_dict
+        
+        # Get inputs
+        if pixel_values is None:
+            raise ValueError("You have to specify pixel_values")
+            
+        batch_size, channels, height, width = pixel_values.shape
+        
+        # Extract features from backbone
+        backbone_features = self.backbone(pixel_values)
+        
+        # Process features through neck
+        neck_features = self.neck(backbone_features)
+        
+        # Get cls_scores and bbox_preds from head
+        cls_scores, bbox_preds = self.bbox_head(neck_features)
+        
+        if labels is not None:
+            # Training mode: calculate loss (not implemented in this simplified version)
+            loss = torch.tensor(0.0, device=pixel_values.device)
+            if return_dict:
+                return DetectionOutput(loss=loss)
+            else:
+                return (loss,)
+        
+        # Inference mode: Get detection results
+        # Create default batch_img_metas for prediction
+        batch_img_metas = [{
+            'img_shape': (height, width, 3),
+            'scale_factor': [1.0, 1.0, 1.0, 1.0]
+        } for _ in range(batch_size)]
+        
+        # Call predict method with parameters from config
+        results = self.bbox_head.predict(
+            cls_scores=cls_scores,
+            bbox_preds=bbox_preds,
+            batch_img_metas=batch_img_metas,
+            rescale=False,
+            with_nms=True,
+            score_thr=self.config.score_threshold,
+            nms_iou_threshold=self.config.nms_threshold,
+            max_per_img=self.config.max_detections
+        )
+        
+        if return_dict:
+            return results
+        else:
+            # Return as tuple (boxes, scores, labels)
+            return (results.boxes, results.scores, results.labels)
+

preprocessor_config.json

@@ -0,0 +1,39 @@
+{
+    "_valid_processor_keys": [
+      "images",
+      "do_resize",
+      "size",
+      "keep_aspect_ratio",
+      "ensure_multiple_of",
+      "resample",
+      "do_rescale",
+      "rescale_factor",
+      "do_normalize",
+      "image_mean",
+      "image_std",
+      "do_pad",
+      "size_divisor",
+      "return_tensors",
+      "data_format",
+      "input_data_format"
+    ],
+    "do_normalize": true,
+    "do_rescale": false,
+    "do_resize": true,
+    "image_mean": [
+      123.675,
+      116.28,
+      103.53
+    ],
+    "image_processor_type": "DPTImageProcessor",
+    "image_std": [
+      58.395,
+      57.12,
+      57.375
+    ],
+    "size": {
+      "height": 640,
+      "width": 640
+    }
+  }
+