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# Copyright 2025 The HuggingFace Team. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import math
from typing import TYPE_CHECKING, Dict, List, Optional, Tuple, Union
import torch
from ..configuration_utils import register_to_config
from .guider_utils import BaseGuidance, GuiderOutput, rescale_noise_cfg
if TYPE_CHECKING:
from ..modular_pipelines.modular_pipeline import BlockState
class AdaptiveProjectedGuidance(BaseGuidance):
"""
Adaptive Projected Guidance (APG): https://huggingface.co/papers/2410.02416
Args:
guidance_scale (`float`, defaults to `7.5`):
The scale parameter for classifier-free guidance. Higher values result in stronger conditioning on the text
prompt, while lower values allow for more freedom in generation. Higher values may lead to saturation and
deterioration of image quality.
adaptive_projected_guidance_momentum (`float`, defaults to `None`):
The momentum parameter for the adaptive projected guidance. Disabled if set to `None`.
adaptive_projected_guidance_rescale (`float`, defaults to `15.0`):
The rescale factor applied to the noise predictions. This is used to improve image quality and fix
guidance_rescale (`float`, defaults to `0.0`):
The rescale factor applied to the noise predictions. This is used to improve image quality and fix
overexposure. Based on Section 3.4 from [Common Diffusion Noise Schedules and Sample Steps are
Flawed](https://huggingface.co/papers/2305.08891).
use_original_formulation (`bool`, defaults to `False`):
Whether to use the original formulation of classifier-free guidance as proposed in the paper. By default,
we use the diffusers-native implementation that has been in the codebase for a long time. See
[~guiders.classifier_free_guidance.ClassifierFreeGuidance] for more details.
start (`float`, defaults to `0.0`):
The fraction of the total number of denoising steps after which guidance starts.
stop (`float`, defaults to `1.0`):
The fraction of the total number of denoising steps after which guidance stops.
"""
_input_predictions = ["pred_cond", "pred_uncond"]
@register_to_config
def __init__(
self,
guidance_scale: float = 7.5,
adaptive_projected_guidance_momentum: Optional[float] = None,
adaptive_projected_guidance_rescale: float = 15.0,
eta: float = 1.0,
guidance_rescale: float = 0.0,
use_original_formulation: bool = False,
start: float = 0.0,
stop: float = 1.0,
):
super().__init__(start, stop)
self.guidance_scale = guidance_scale
self.adaptive_projected_guidance_momentum = adaptive_projected_guidance_momentum
self.adaptive_projected_guidance_rescale = adaptive_projected_guidance_rescale
self.eta = eta
self.guidance_rescale = guidance_rescale
self.use_original_formulation = use_original_formulation
self.momentum_buffer = None
def prepare_inputs(
self, data: "BlockState", input_fields: Optional[Dict[str, Union[str, Tuple[str, str]]]] = None
) -> List["BlockState"]:
if input_fields is None:
input_fields = self._input_fields
if self._step == 0:
if self.adaptive_projected_guidance_momentum is not None:
self.momentum_buffer = MomentumBuffer(self.adaptive_projected_guidance_momentum)
tuple_indices = [0] if self.num_conditions == 1 else [0, 1]
data_batches = []
for i in range(self.num_conditions):
data_batch = self._prepare_batch(input_fields, data, tuple_indices[i], self._input_predictions[i])
data_batches.append(data_batch)
return data_batches
def forward(self, pred_cond: torch.Tensor, pred_uncond: Optional[torch.Tensor] = None) -> GuiderOutput:
pred = None
if not self._is_apg_enabled():
pred = pred_cond
else:
pred = normalized_guidance(
pred_cond,
pred_uncond,
self.guidance_scale,
self.momentum_buffer,
self.eta,
self.adaptive_projected_guidance_rescale,
self.use_original_formulation,
)
if self.guidance_rescale > 0.0:
pred = rescale_noise_cfg(pred, pred_cond, self.guidance_rescale)
return GuiderOutput(pred=pred, pred_cond=pred_cond, pred_uncond=pred_uncond)
@property
def is_conditional(self) -> bool:
return self._count_prepared == 1
@property
def num_conditions(self) -> int:
num_conditions = 1
if self._is_apg_enabled():
num_conditions += 1
return num_conditions
def _is_apg_enabled(self) -> bool:
if not self._enabled:
return False
is_within_range = True
if self._num_inference_steps is not None:
skip_start_step = int(self._start * self._num_inference_steps)
skip_stop_step = int(self._stop * self._num_inference_steps)
is_within_range = skip_start_step <= self._step < skip_stop_step
is_close = False
if self.use_original_formulation:
is_close = math.isclose(self.guidance_scale, 0.0)
else:
is_close = math.isclose(self.guidance_scale, 1.0)
return is_within_range and not is_close
class MomentumBuffer:
def __init__(self, momentum: float):
self.momentum = momentum
self.running_average = 0
def update(self, update_value: torch.Tensor):
new_average = self.momentum * self.running_average
self.running_average = update_value + new_average
def normalized_guidance(
pred_cond: torch.Tensor,
pred_uncond: torch.Tensor,
guidance_scale: float,
momentum_buffer: Optional[MomentumBuffer] = None,
eta: float = 1.0,
norm_threshold: float = 0.0,
use_original_formulation: bool = False,
):
diff = pred_cond - pred_uncond
dim = [-i for i in range(1, len(diff.shape))]
if momentum_buffer is not None:
momentum_buffer.update(diff)
diff = momentum_buffer.running_average
if norm_threshold > 0:
ones = torch.ones_like(diff)
diff_norm = diff.norm(p=2, dim=dim, keepdim=True)
scale_factor = torch.minimum(ones, norm_threshold / diff_norm)
diff = diff * scale_factor
v0, v1 = diff.double(), pred_cond.double()
v1 = torch.nn.functional.normalize(v1, dim=dim)
v0_parallel = (v0 * v1).sum(dim=dim, keepdim=True) * v1
v0_orthogonal = v0 - v0_parallel
diff_parallel, diff_orthogonal = v0_parallel.type_as(diff), v0_orthogonal.type_as(diff)
normalized_update = diff_orthogonal + eta * diff_parallel
pred = pred_cond if use_original_formulation else pred_uncond
pred = pred + guidance_scale * normalized_update
return pred
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