Encode 32bit float into three 8bit RGBA channels

float_to_rgba.py

#!/usr/bin/env python
# Store 32-bit floating point number within three 8bit channels of a 32-bit RGBA pixel.
# Only suitable for normalised input values in the range [0.0, 1.0).
#
# Refer: https://aras-p.info/blog/2009/07/30/encoding-floats-to-rgba-the-final/

import numpy as np

def frac(x):
    return x - np.floor(x)

def encode(v):
    enc = np.float32((1.0, 256.0, 256.0**2, 256.0**3)) * v
    enc = frac(enc)
    enc -= (enc[1], enc[2], enc[3], enc[3]) * np.float32((1/256.0, 1/256.0, 1/256.0, 0.0))
    return enc

def decode(rgba):
    return np.dot(rgba, np.float32((1.0, 1/256.0, 1/(256.0**2), 1/(256.0**3))))

if __name__ == "__main__":
    max_diff = 0.0
    for x in np.linspace(0.0, 1.0, 1000, endpoint=False):
        enc = encode(x)
        enc8 = np.uint8(enc * 256.0)
        dec8 = enc8 / 256.0
        dec = decode(dec8)
        max_diff = np.maximum(max_diff, x - dec)
        print(f"{x}: {x - dec}")
    print(f"Max diff {max_diff}")