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import numpy as np
import torch
def rgb2ycbcr(img, y_only=False):
"""Convert a RGB image to YCbCr image.
This function produces the same results as Matlab's `rgb2ycbcr` function.
It implements the ITU-R BT.601 conversion for standard-definition
television. See more details in
https://en.wikipedia.org/wiki/YCbCr#ITU-R_BT.601_conversion.
It differs from a similar function in cv2.cvtColor: `RGB <-> YCrCb`.
In OpenCV, it implements a JPEG conversion. See more details in
https://en.wikipedia.org/wiki/YCbCr#JPEG_conversion.
Args:
img (ndarray): The input image. It accepts:
1. np.uint8 type with range [0, 255];
2. np.float32 type with range [0, 1].
y_only (bool): Whether to only return Y channel. Default: False.
Returns:
ndarray: The converted YCbCr image. The output image has the same type
and range as input image.
"""
img_type = img.dtype
img = _convert_input_type_range(img)
if y_only:
out_img = np.dot(img, [65.481, 128.553, 24.966]) + 16.0
else:
out_img = np.matmul(
img, [[65.481, -37.797, 112.0], [128.553, -74.203, -93.786], [24.966, 112.0, -18.214]]) + [16, 128, 128]
out_img = _convert_output_type_range(out_img, img_type)
return out_img
def bgr2ycbcr(img, y_only=False):
"""Convert a BGR image to YCbCr image.
The bgr version of rgb2ycbcr.
It implements the ITU-R BT.601 conversion for standard-definition
television. See more details in
https://en.wikipedia.org/wiki/YCbCr#ITU-R_BT.601_conversion.
It differs from a similar function in cv2.cvtColor: `BGR <-> YCrCb`.
In OpenCV, it implements a JPEG conversion. See more details in
https://en.wikipedia.org/wiki/YCbCr#JPEG_conversion.
Args:
img (ndarray): The input image. It accepts:
1. np.uint8 type with range [0, 255];
2. np.float32 type with range [0, 1].
y_only (bool): Whether to only return Y channel. Default: False.
Returns:
ndarray: The converted YCbCr image. The output image has the same type
and range as input image.
"""
img_type = img.dtype
img = _convert_input_type_range(img)
if y_only:
out_img = np.dot(img, [24.966, 128.553, 65.481]) + 16.0
else:
out_img = np.matmul(
img, [[24.966, 112.0, -18.214], [128.553, -74.203, -93.786], [65.481, -37.797, 112.0]]) + [16, 128, 128]
out_img = _convert_output_type_range(out_img, img_type)
return out_img
def ycbcr2rgb(img):
"""Convert a YCbCr image to RGB image.
This function produces the same results as Matlab's ycbcr2rgb function.
It implements the ITU-R BT.601 conversion for standard-definition
television. See more details in
https://en.wikipedia.org/wiki/YCbCr#ITU-R_BT.601_conversion.
It differs from a similar function in cv2.cvtColor: `YCrCb <-> RGB`.
In OpenCV, it implements a JPEG conversion. See more details in
https://en.wikipedia.org/wiki/YCbCr#JPEG_conversion.
Args:
img (ndarray): The input image. It accepts:
1. np.uint8 type with range [0, 255];
2. np.float32 type with range [0, 1].
Returns:
ndarray: The converted RGB image. The output image has the same type
and range as input image.
"""
img_type = img.dtype
img = _convert_input_type_range(img) * 255
out_img = np.matmul(img, [[0.00456621, 0.00456621, 0.00456621], [0, -0.00153632, 0.00791071],
[0.00625893, -0.00318811, 0]]) * 255.0 + [-222.921, 135.576, -276.836] # noqa: E126
out_img = _convert_output_type_range(out_img, img_type)
return out_img
def ycbcr2bgr(img):
"""Convert a YCbCr image to BGR image.
The bgr version of ycbcr2rgb.
It implements the ITU-R BT.601 conversion for standard-definition
television. See more details in
https://en.wikipedia.org/wiki/YCbCr#ITU-R_BT.601_conversion.
It differs from a similar function in cv2.cvtColor: `YCrCb <-> BGR`.
In OpenCV, it implements a JPEG conversion. See more details in
https://en.wikipedia.org/wiki/YCbCr#JPEG_conversion.
Args:
img (ndarray): The input image. It accepts:
1. np.uint8 type with range [0, 255];
2. np.float32 type with range [0, 1].
Returns:
ndarray: The converted BGR image. The output image has the same type
and range as input image.
"""
img_type = img.dtype
img = _convert_input_type_range(img) * 255
out_img = np.matmul(img, [[0.00456621, 0.00456621, 0.00456621], [0.00791071, -0.00153632, 0],
[0, -0.00318811, 0.00625893]]) * 255.0 + [-276.836, 135.576, -222.921] # noqa: E126
out_img = _convert_output_type_range(out_img, img_type)
return out_img
def _convert_input_type_range(img):
"""Convert the type and range of the input image.
It converts the input image to np.float32 type and range of [0, 1].
It is mainly used for pre-processing the input image in colorspace
conversion functions such as rgb2ycbcr and ycbcr2rgb.
Args:
img (ndarray): The input image. It accepts:
1. np.uint8 type with range [0, 255];
2. np.float32 type with range [0, 1].
Returns:
(ndarray): The converted image with type of np.float32 and range of
[0, 1].
"""
img_type = img.dtype
img = img.astype(np.float32)
if img_type == np.float32:
pass
elif img_type == np.uint8:
img /= 255.
else:
raise TypeError(f'The img type should be np.float32 or np.uint8, but got {img_type}')
return img
def _convert_output_type_range(img, dst_type):
"""Convert the type and range of the image according to dst_type.
It converts the image to desired type and range. If `dst_type` is np.uint8,
images will be converted to np.uint8 type with range [0, 255]. If
`dst_type` is np.float32, it converts the image to np.float32 type with
range [0, 1].
It is mainly used for post-processing images in colorspace conversion
functions such as rgb2ycbcr and ycbcr2rgb.
Args:
img (ndarray): The image to be converted with np.float32 type and
range [0, 255].
dst_type (np.uint8 | np.float32): If dst_type is np.uint8, it
converts the image to np.uint8 type with range [0, 255]. If
dst_type is np.float32, it converts the image to np.float32 type
with range [0, 1].
Returns:
(ndarray): The converted image with desired type and range.
"""
if dst_type not in (np.uint8, np.float32):
raise TypeError(f'The dst_type should be np.float32 or np.uint8, but got {dst_type}')
if dst_type == np.uint8:
img = img.round()
else:
img /= 255.
return img.astype(dst_type)
def rgb2ycbcr_pt(img, y_only=False):
"""Convert RGB images to YCbCr images (PyTorch version).
It implements the ITU-R BT.601 conversion for standard-definition television. See more details in
https://en.wikipedia.org/wiki/YCbCr#ITU-R_BT.601_conversion.
Args:
img (Tensor): Images with shape (n, 3, h, w), the range [0, 1], float, RGB format.
y_only (bool): Whether to only return Y channel. Default: False.
Returns:
(Tensor): converted images with the shape (n, 3/1, h, w), the range [0, 1], float.
"""
if y_only:
weight = torch.tensor([[65.481], [128.553], [24.966]]).to(img)
out_img = torch.matmul(img.permute(0, 2, 3, 1), weight).permute(0, 3, 1, 2) + 16.0
else:
weight = torch.tensor([[65.481, -37.797, 112.0], [128.553, -74.203, -93.786], [24.966, 112.0, -18.214]]).to(img)
bias = torch.tensor([16, 128, 128]).view(1, 3, 1, 1).to(img)
out_img = torch.matmul(img.permute(0, 2, 3, 1), weight).permute(0, 3, 1, 2) + bias
out_img = out_img / 255.
return out_img
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