[squeak-dev] Colour visualisation & mapping info

Tobias Pape Das.Linux at gmx.de
Mon May 30 18:57:09 UTC 2022


> On 18. May 2022, at 21:33, tim Rowledge <tim at rowledge.org> wrote:
> From time to time we have to think about how we handle colours and gradients; it's a quite complex subject that mixes physics and biology.

That's fun!

This reminded me that the matplotlib people did a very good job (that is in line with the stuff below) for
their color schemes:

Best regards

> An acquaintance at UBC teaches this subject and recently posted to another list, and gave me permission to share -
>> Hi folks,
>> Delurking for the first time in quite a while to weigh in, I do teach about
>> color and color perception.
>> In short:  The right color space to use for interpolating colors is CIELAB
>> (aka L*a*b* or LAB or Lab), which is carefully designed to be perceptually
>> uniform.  RGB is dramatically non-uniform, do not interpolate in that color
>> space because you're in for a world of hurt. Unfortunately, while HSV/HSL
>> is more uniform than RGB in the colorful dimensions, it isn't truly uniform
>> either in the black-and-white dimension, so it's not a good bet. If you do
>> the math in the CIELAB space you don't need to think about gamma
>> correction, that will just confuse the issue.
>> Tools:
>> Example D3 code plus explanations from Mike Bostock at
>> https://bl.ocks.org/mbostock/3014589
>> Observable notebook with some examples and analysis of interpolation in
>> different color spaces from Zan Armstrong at
>> https://observablehq.com/@zanarmstrong/comparing-interpolating-in-different-color-spaces
>> Interactive demos from Carlos Scheidegger at
>> https://cscheid.net/projects/color-interpolation/
>> LAB/Lch  color gradient generator at
>> https://davidjohnstone.net/lch-lab-colour-gradient-picker
>> Older but in-depth post from Gregor Aisch (with a lot of commentary from
>> experts below) at
>> https://www.vis4.net/blog/2011/12/avoid-equidistant-hsv-colors/
>> In long: For more on color here's the three relevant videos from my
>> visualization course. The third one goes a bit into the question of color
>> spaces in the first seven minutes, but it might make more sense if you
>> watch the first one to establish some basics first. The second one is
>> mostly focused on the issue of colorblindness.
>> Color I (19 min)
>> https://www.youtube.com/watch?v=QNDd_hvdORw&list=PLT4XLHmqHJBeB5LwmRmo6ln-m7K3lGvrk&index=15
>> Color II (6 min)
>> https://www.youtube.com/watch?v=yUsL6a1d9n0&list=PLT4XLHmqHJBeB5LwmRmo6ln-m7K3lGvrk&index=16
>> Color III (18 min)
>> https://www.youtube.com/watch?v=zt8uIbSMeFg&list=PLT4XLHmqHJBeB5LwmRmo6ln-m7K3lGvrk&index=17
>> Cheers, Tamara
>> ----
>> Tamara Munzner
>> Professor, Department of Computer Science, University of British Columbia
> tim

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