[Matplotlib-devel] [rfc] a better interchange format for colormaps

[kthyng]

Columns of rgb points that I have been using for sharing colormaps have
been pretty easy and straight-forward (easily extended to 4 columns for
alpha). Is the main problem the lack of meta data?

Kristen

On Thu, Apr 21, 2016 at 2:24 PM, Chris Barker - NOAA Federal [via
matplotlib] <ml-node+s1069221n46987h22 at n5.nabble.com> wrote:

> Great idea!
>
> AS it happens, we're messing with colormaps ourselves here, and indeed to
> need to have consistent ones across browser-JS and python -- so great
> timing!
>
> I'm not so sure about the encoding of the colors -- I read the
> justification (nicely written), but I still think file size is pretty much
> a non-issue -- these are not going to be gigabytes no matter how you slice
> it. and the compressed file sizes are definitely close enough in size to
> make no difference. So I would much prefer:
>
> [ [r, g, b], [r,g,b], ....]
>
> However, maybe that's because I still can't wrap my head easily around hex
> :-)
>
> I think compatibility with D3 per se should be a minor influence, but if
> Javascript itself "likes" to use hex colors and could more easily deal with
> this, then I guess that might be a driver (or do I think that because I'm a
> pythonista that could easily write the conversion code in Python than JS
> ...)
>
> Also for discrete colormaps, might there be a use case for transparency?
> i.e. RGBA ? In which case, the encoding should be able to handle  either
> three or four channels per color with no ambiguity. Would that be two hex
> values per color for a 32 bit color (then you have to have a clean
> endianness, yes?) or commas or something separating the colors.
>
> As for specifying the number of colors somewhere else, I agree that that's
> just a recipe for inconsistency with no gain -- is anyone going to have to
> write a parser where they have to alocate teh memory ahead of time???
>
> -CHB
>
>
> On Wed, Apr 20, 2016 at 4:22 PM, Nathaniel Smith <[hidden email]
> <http:///user/SendEmail.jtp?type=node&node=46987&i=0>> wrote:
>
>> Hi matplotters,
>>
>> We've been working on improving our tool for building custom
>> viridis-like colormaps (e.g. adding support for diverging colormaps),
>> and one of the things that we got frustrated by is how there's no
>> compelling way to save and distribute the resulting colormaps so that
>> people can actually use them. So, I wrote up a little spec to
>> standardize a way of storing and distributing colormaps in JSON, with
>> the hope that we can convince everyone to implement this and stop
>> writing silly little conversion scripts all the time.
>>
>> The v0.1 draft is here:
>>     https://github.com/njsmith/json-cm/blob/master/json-cm-spec.md
>>
>> Any comments? There are always a lot of fiddly details to get right in
>> this kind of thing -- I made a bunch of guesses about what kind of
>> stuff is important and how to represent it, but it can only benefit
>> from review from different perspectives. I would equally love to get
>> nitpicky critiques and high-level queries.
>>
>> Thanks!
>> -n
>>
>> --
>> Nathaniel J. Smith -- https://vorpus.org
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>>
>
>
>
> --
>
> Christopher Barker, Ph.D.
> Oceanographer
>
> Emergency Response Division
> NOAA/NOS/OR&R            (206) 526-6959   voice
> 7600 Sand Point Way NE   (206) 526-6329   fax
> Seattle, WA  98115       (206) 526-6317   main reception
>
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-- 
Kristen M. Thyng
Assistant Research Scientist
Department of Oceanography
Texas A&M University
Eller O&M 607
http://kristenthyng.com




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