vggt/utils/helper.py

# Copyright (c) Meta Platforms, Inc. and affiliates.
# All rights reserved.
#
# This source code is licensed under the license found in the
# LICENSE file in the root directory of this source tree.

import numpy as np


def randomly_limit_trues(mask: np.ndarray, max_trues: int) -> np.ndarray:
    """
    If mask has more than max_trues True values,
    randomly keep only max_trues of them and set the rest to False.
    """
    # 1D positions of all True entries
    true_indices = np.flatnonzero(mask)  # shape = (N_true,)

    # if already within budget, return as-is
    if true_indices.size <= max_trues:
        return mask

    # randomly pick which True positions to keep
    sampled_indices = np.random.choice(true_indices, size=max_trues, replace=False)  # shape = (max_trues,)

    # build new flat mask: True only at sampled positions
    limited_flat_mask = np.zeros(mask.size, dtype=bool)
    limited_flat_mask[sampled_indices] = True

    # restore original shape
    return limited_flat_mask.reshape(mask.shape)


def create_pixel_coordinate_grid(num_frames, height, width):
    """
    Creates a grid of pixel coordinates and frame indices for all frames.
    Returns:
        tuple: A tuple containing:
            - points_xyf (numpy.ndarray): Array of shape (num_frames, height, width, 3)
                                            with x, y coordinates and frame indices
            - y_coords (numpy.ndarray): Array of y coordinates for all frames
            - x_coords (numpy.ndarray): Array of x coordinates for all frames
            - f_coords (numpy.ndarray): Array of frame indices for all frames
    """
    # Create coordinate grids for a single frame
    y_grid, x_grid = np.indices((height, width), dtype=np.float32)
    x_grid = x_grid[np.newaxis, :, :]
    y_grid = y_grid[np.newaxis, :, :]

    # Broadcast to all frames
    x_coords = np.broadcast_to(x_grid, (num_frames, height, width))
    y_coords = np.broadcast_to(y_grid, (num_frames, height, width))

    # Create frame indices and broadcast
    f_idx = np.arange(num_frames, dtype=np.float32)[:, np.newaxis, np.newaxis]
    f_coords = np.broadcast_to(f_idx, (num_frames, height, width))

    # Stack coordinates and frame indices
    points_xyf = np.stack((x_coords, y_coords, f_coords), axis=-1)

    return points_xyf