lib/pixielib/utils/tensor_cropper.py

"""
crop
for torch tensor
Given image, bbox(center, bboxsize)
return: cropped image, tform(used for transform the keypoint accordingly)

only support crop to squared images
"""
import torch
from kornia.geometry.transform.imgwarp import (
    warp_perspective,
    get_perspective_transform,
    warp_affine,
)


def points2bbox(points, points_scale=None):
    if points_scale:
        assert points_scale[0] == points_scale[1]
        points = points.clone()
        points[:, :, :2] = (points[:, :, :2] * 0.5 + 0.5) * points_scale[0]
    min_coords, _ = torch.min(points, dim=1)
    xmin, ymin = min_coords[:, 0], min_coords[:, 1]
    max_coords, _ = torch.max(points, dim=1)
    xmax, ymax = max_coords[:, 0], max_coords[:, 1]
    center = torch.stack([xmax + xmin, ymax + ymin], dim=-1) * 0.5

    width = xmax - xmin
    height = ymax - ymin
    # Convert the bounding box to a square box
    size = torch.max(width, height).unsqueeze(-1)
    return center, size


def augment_bbox(center, bbox_size, scale=[1.0, 1.0], trans_scale=0.0):
    batch_size = center.shape[0]
    trans_scale = (torch.rand([batch_size, 2], device=center.device) * 2.0 - 1.0) * trans_scale
    center = center + trans_scale * bbox_size    # 0.5
    scale = (torch.rand([batch_size, 1], device=center.device) * (scale[1] - scale[0]) + scale[0])
    size = bbox_size * scale
    return center, size


def crop_tensor(image, center, bbox_size, crop_size, interpolation="bilinear", align_corners=False):
    """for batch image
    Args:
        image (torch.Tensor): the reference tensor of shape BXHxWXC.
        center: [bz, 2]
        bboxsize: [bz, 1]
        crop_size;
        interpolation (str): Interpolation flag. Default: 'bilinear'.
        align_corners (bool): mode for grid_generation. Default: False. See
          https://pytorch.org/docs/stable/nn.functional.html#torch.nn.functional.interpolate for details
    Returns:
        cropped_image
        tform
    """
    dtype = image.dtype
    device = image.device
    batch_size = image.shape[0]
    # points: top-left, top-right, bottom-right, bottom-left
    src_pts = (
        torch.zeros([4, 2], dtype=dtype, device=device).unsqueeze(0).expand(batch_size, -1,
                                                                            -1).contiguous()
    )

    src_pts[:, 0, :] = center - bbox_size * 0.5    # / (self.crop_size - 1)
    src_pts[:, 1, 0] = center[:, 0] + bbox_size[:, 0] * 0.5
    src_pts[:, 1, 1] = center[:, 1] - bbox_size[:, 0] * 0.5
    src_pts[:, 2, :] = center + bbox_size * 0.5
    src_pts[:, 3, 0] = center[:, 0] - bbox_size[:, 0] * 0.5
    src_pts[:, 3, 1] = center[:, 1] + bbox_size[:, 0] * 0.5

    DST_PTS = torch.tensor(
        [[
            [0, 0],
            [crop_size - 1, 0],
            [crop_size - 1, crop_size - 1],
            [0, crop_size - 1],
        ]],
        dtype=dtype,
        device=device,
    ).expand(batch_size, -1, -1)
    # estimate transformation between points
    dst_trans_src = get_perspective_transform(src_pts, DST_PTS)
    # simulate broadcasting
    # dst_trans_src = dst_trans_src.expand(batch_size, -1, -1)

    # warp images
    cropped_image = warp_affine(
        image,
        dst_trans_src[:, :2, :],
        (crop_size, crop_size),
        mode=interpolation,
        align_corners=align_corners,
    )

    tform = torch.transpose(dst_trans_src, 2, 1)
    # tform = torch.inverse(dst_trans_src)
    return cropped_image, tform


class Cropper(object):
    def __init__(self, crop_size, scale=[1, 1], trans_scale=0.0):
        self.crop_size = crop_size
        self.scale = scale
        self.trans_scale = trans_scale

    def crop(self, image, points, points_scale=None):
        # points to bbox
        center, bbox_size = points2bbox(points.clone(), points_scale)
        center, bbox_size = augment_bbox(
            center, bbox_size, scale=self.scale, trans_scale=self.trans_scale
        )
        # crop
        cropped_image, tform = crop_tensor(image, center, bbox_size, self.crop_size)
        return cropped_image, tform

    def transform_points(self, points, tform, points_scale=None, normalize=True):
        points_2d = points[:, :, :2]

        #'input points must use original range'
        if points_scale:
            assert points_scale[0] == points_scale[1]
            points_2d = (points_2d * 0.5 + 0.5) * points_scale[0]

        batch_size, n_points, _ = points.shape
        trans_points_2d = torch.bmm(
            torch.cat(
                [
                    points_2d,
                    torch.ones(
                        [batch_size, n_points, 1],
                        device=points.device,
                        dtype=points.dtype,
                    ),
                ],
                dim=-1,
            ),
            tform,
        )
        trans_points = torch.cat([trans_points_2d[:, :, :2], points[:, :, 2:]], dim=-1)
        if normalize:
            trans_points[:, :, :2] = trans_points[:, :, :2] / self.crop_size * 2 - 1
        return trans_points


def transform_points(points, tform, points_scale=None):
    points_2d = points[:, :, :2]

    #'input points must use original range'
    if points_scale:
        assert points_scale[0] == points_scale[1]
        points_2d = (points_2d * 0.5 + 0.5) * points_scale[0]

    batch_size, n_points, _ = points.shape
    trans_points_2d = torch.bmm(
        torch.cat(
            [
                points_2d,
                torch.ones([batch_size, n_points, 1], device=points.device, dtype=points.dtype),
            ],
            dim=-1,
        ),
        tform,
    )
    trans_points = torch.cat([trans_points_2d[:, :, :2], points[:, :, 2:]], dim=-1)
    return trans_points