81 lines
2.9 KiB
Python
81 lines
2.9 KiB
Python
"""Precompute CAM16-UCS colour tuples for all 2^24 RGB tuples.
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This 192MB data file is used to convert from RGB to CAM16-UCS colour space
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for purposes of computing (approximate) perceptual difference between pairs of
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colours when optimizing the image conversion (since this perceptual
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difference corresponds to the Euclidean distance in this colour space)
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"""
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import os
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import colour
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import numpy as np
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def srgb_to_linear_rgb_array(a: np.ndarray, gamma=2.4) -> np.ndarray:
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return np.where(a <= 0.04045, a / 12.92, ((a + 0.055) / 1.055) ** gamma)
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DATA_DIR = 'data'
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def main():
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try:
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os.mkdir(DATA_DIR, mode=0o755)
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except FileExistsError:
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pass
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print("Precomputing conversion matrix from 24-bit RGB to CAM16UCS colour "
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"space")
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# Compute matrix of all 24-bit RGB values, normalized to 0..1 range
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bits24 = np.arange(2 ** 24, dtype=np.uint32).reshape(-1, 1)
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all_rgb24 = np.concatenate(
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[bits24 >> 16 & 0xff, bits24 >> 8 & 0xff, bits24 & 0xff],
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axis=1).astype(np.float32) / 255
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del bits24
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with colour.utilities.suppress_warnings(colour_usage_warnings=True):
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# Compute matrix of corresponding CAM16UCS colour values, indexed
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# by 24-bit RGB value
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rgb24_to_cam16ucs = colour.convert(all_rgb24, "RGB", "CAM16UCS").astype(
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np.float32)
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del all_rgb24
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np.save("%s/rgb24_to_cam16ucs.npy" % DATA_DIR, np.ascontiguousarray(
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rgb24_to_cam16ucs))
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del rgb24_to_cam16ucs
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print("Precomputing conversion matrix from 12-bit //gs RGB to CAM16UCS "
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"colour space")
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# Compute matrix of all 12-bit RGB values, normalized to 0..1 range
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bits12 = np.arange(2 ** 12, dtype=np.uint32).reshape(-1, 1)
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r = bits12 >> 8
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g = (bits12 >> 4) & 0xf
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b = bits12 & 0xf
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all_rgb12 = np.concatenate(
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[(r << 4) | r, (g << 4) | g, (b << 4) | b], axis=1).astype(
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np.float32) / 255
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del bits12, r, g, b
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# //gs RGB values use gamma-corrected Rec.601 RGB colour space. We need to
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# convert to Rec.709 RGB as preparation for converting to CAM16UCS. We
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# do this via the YCbCr intermediate color model.
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rgb12_iigs = np.clip(srgb_to_linear_rgb_array(
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np.clip(colour.YCbCr_to_RGB(
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colour.RGB_to_YCbCr(
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all_rgb12, K=colour.WEIGHTS_YCBCR[
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'ITU-R BT.601']),
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K=colour.WEIGHTS_YCBCR['ITU-R BT.709']), 0, 1)), 0, 1)
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with colour.utilities.suppress_warnings(colour_usage_warnings=True):
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# Compute matrix of corresponding CAM16UCS colour values, indexed
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# by 12-bit //gs RGB value
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rgb12_iigs_to_cam16ucs = colour.convert(
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rgb12_iigs, "RGB", "CAM16UCS").astype(np.float32)
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del rgb12_iigs
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np.save("%s/rgb12_iigs_to_cam16ucs.npy" % DATA_DIR, np.ascontiguousarray(
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rgb12_iigs_to_cam16ucs))
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del rgb12_iigs_to_cam16ucs
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if __name__ == "__main__":
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main()
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