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quag / JzAzBz

Implementations of JzAzBz based colorspace conversions.
MIT License
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range of JzAzBz coordinates #1

Open eonadler opened 5 years ago

eonadler commented 5 years ago

We have encountered the following issue, which has been reproduced using a few independent RGB --> JzAzBz implementations (including this and colorio) ---

The JzAzBz paper (https://www.osapublishing.org/DirectPDFAccess/77717F83-F893-C8C0-B2B48451182A4DFC_368272/oe-25-13-15131.pdf?da=1&id=368272&seq=0&mobile=no) seems to suggest that the coordinates should span roughly Jz in (0,1), Az in (-0.5, 0.5), Bz in (-0.5,0.5). However, when we explicitly map all RGB tuples in (0,255) x (0,255) x (0,255) to JzAzBz as follows, we find that (Jz, Az, Bz) span (0,0.167), (-0.09,1.09), (-0.156,0.115).

So we're wondering if the original paper renormalized their coordinates, or if there's a mistake on our end.

Extremely simplified code that demonstrates the basic issue:

import numpy as np import colorio

jzazbz_test[i][j][k] = jzazbz_test = np.zeros((256,256,256,3)) for i in range(0,255): for j in range(0,255): for k in range(0,255): jzazbz_test[i][j][k] = np.array(srgb255ToJzAzBz_(1.*i,1.*j,1.*k))

print('min Jz={}'.format(np.min(jzazbz_test[:,:,:,0]))) print('max Jz={}'.format(np.max(jzazbz_test[:,:,:,0])))

print('min Az={}'.format(np.min(jzazbz_test[:,:,:,1]))) print('max Az={}'.format(np.max(jzazbz_test[:,:,:,1])))

print('min Bz={}'.format(np.min(jzazbz_test[:,:,:,2]))) print('max Bz={}'.format(np.max(jzazbz_test[:,:,:,2])))

andersk commented 4 years ago

Jzazbz is designed to support HDR and wide-gamut colors. The [0, 255] × [0, 255] × [0, 255] sRGB space does not cover the domain of possible inputs.

quag commented 4 years ago

Yes, JzAzBz is designed to support HDR and wide gamut. JzAzBz research came out of Dolby specifically for future standards for displays.

On Sun, Jan 12, 2020 at 4:37 PM Anders Kaseorg notifications@github.com wrote:

JzAzBz is designed to support HDR and wide-gamut colors. The [0, 255] × [0, 255] × [0, 255] sRGB space does not cover the domain of possible inputs.

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