Given a LUT file, plot its luma EOTF to a tiny image

plot_lut

#! /usr/bin/env python

import argparse

import OpenImageIO as oiio


LUMA = (0.2126, 0.7152, 0.0722)


def plot_lut(lutpath, outpath):
    size = None
    mult = None
    out = None
    count = 0
    with open(lutpath) as lut:
        for line in lut:
            line = line.strip()
            if not line:
                continue
            if size:
                if count % mult == 0:
                    v = sum(c * l for c, l in zip((float(s) for s in line.split(' ')), LUMA))
                    out.setpixel(count / mult, size - int(round(v * (size - 1))), (1.0, 1.0, 1.0))
                count += 1
                continue
            if not size and line.startswith('LUT_3D_SIZE'):
                size = int(line[11:].lstrip())
                mult = size ** 3 / size + size + 1
                out = oiio.ImageBuf(oiio.ImageSpec(size, size, 3, oiio.FLOAT))
                oiio.ImageBufAlgo.fill(out, (0, 0, 0))
    out.write(outpath)


if __name__ == '__main__':
    parser = argparse.ArgumentParser(epilog='The paths can have any extension understood by OpenImageIO')
    parser.add_argument('lutpath', metavar='/path/to/lut.cube')
    parser.add_argument('outpath', metavar='/path/to/output.png')
    args = parser.parse_args()
    plot_lut(args.lutpath, args.outpath)