ocio_v1_gpu.py

import colour
import numpy as np
import matplotlib.pyplot as plt

np.set_printoptions(suppress=True)


"""
Example shader generated by ocio v1, using Troy's config untouched, lutsize is 32

vec4 OCIODisplay(vec4 inPixel, sampler3D lut3d)
{
    vec4 out_pixel = inPixel;
    out_pixel.rgb = max(
        vec3(1.17549e-38, 1.17549e-38, 1.17549e-38),
        vec3(1, 1, 1) * out_pixel.rgb + vec3(0, 0, 0)
    );

    // log2 (log base convert) => 1.4427 == 1 / log(2)
    out_pixel.rgb = vec3(1.4427, 1.4427, 1.4427) * log(out_pixel.rgb) + vec3(0, 0, 0);

    // scale to range => 0.04 == 1 / (lg2max - lg2min)
    out_pixel = vec4(0.04, 0.04, 0.04, 1) * out_pixel;
    // offset to range => 0.498956 == |lg2min / (lg2max - lg2min)|
    out_pixel = vec4(0.498956, 0.498956, 0.498956, 0) + out_pixel;

    // sample using opengl coordinate system
    // 0.96875 == (lutsize - 1 / lutsize)
    // 0.015625 == (1.0 / 2 * lutsize)
    out_pixel.rgb = texture3D(lut3d, 0.96875 * out_pixel.rgb + 0.015625).rgb;
    return out_pixel;
}

"""

lg2_min = -12.4739
lg2_max = 12.5261
scale = 1.0 / (lg2_max - lg2_min)
offset = abs(lg2_min / (lg2_max - lg2_min))

lut_size = 32
lut = colour.LUT3D(size=lut_size)

lut.table = (lut.table - offset) / scale
lut.table = np.power(2, lut.table)
lut.table = np.clip(lut.table, 0.0, 1.0)
lut.table = colour.models.sRGB_COLOURSPACE.cctf_encoding(lut.table)

input_rgb = [1.0, 1.0, 1.0]
rgb = np.log2(input_rgb)
rgb = scale * rgb + offset
output_rgb = colour.table_interpolation(rgb, lut.table, method='Trilinear')

print("Allocation lg2 {}".format([lg2_min, lg2_max]))
print("Input {} => Output {}".format(input_rgb, np.rint(output_rgb * 255)))