CIELAB color range for Scikit-image?

Question

I am working on CIELAB colour space but cannot find any information about the range of each channel produced by skimage.color.rgb2lab .

Thanks.

Thank you for bringing the lack of documentation to our attention. There is now an open issue to track this bug: https://github.com/scikit-image/scikit-image/issues/1185 — Stefan van der Walt, Oct 09 '14 at 18:15
And to answer your question: L: 0 to 100, a: -127 to 128, b: -128 to 127. — Stefan van der Walt, Oct 09 '14 at 18:16
@StefanvanderWalt are you sure the value range is different for a and b. Shouldn't it be -128 to 127 for a as well? — Benedikt, Sep 05 '18 at 13:34

TinyEpic · Accepted Answer · 2015-01-20T14:51:20.017

5

Just would like to post the answer from @Stefan

L: 0 to 100, a: -127 to 128, b: -128 to 127.

edited Jan 20 '15 at 14:51

answered Jan 20 '15 at 14:41

TinyEpic

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score 1 · Answer 2 · answered Mar 12 '20 at 08:54

Quote from wiki, https://en.wikipedia.org/wiki/CIELAB_color_space

The scaling and limits of the a* and b* axes will depend on the specific implementation, as described below, but they often run in the range of ±100 or −128 to +127 (signed 8-bit integer).

In skimage, xxx2lab() usually return a float point array, thus it is more likely that the range of a* and b* is [-100,100].

PS:

I have tried image with value > 100 or < -100 in lab color, and I think the warnings I got from lab2rgb() in skimage could prove this point.

UserWarning: Color data out of range: Z < 0 in 30 pixels return xyz2rgb(lab2xyz(lab, illuminant, observer))

CIELAB color range for Scikit-image?

2 Answers2