[ncl-talk] colorbar that's part grayscale, part color?

[Jared Lee]

Rashed: Thanks for that example! That's quite helpful.

Adam: When I use getvalues plot at contour like you suggested, the fill_colors
array is full of 30-bit integers. Is there a handy function or translation
tool to convert those back to RGBA values and/or string color names, or
would I have to write my own? The rgb.txt file on NCL's named colors page
provides a way to compare named colors to RGB values, but does not include
the corresponding 30-bit integers that would allow for quick string parsing
and pattern matching.

Jared

On Tue, Feb 13, 2018 at 2:41 PM, Adam Phillips <asphilli at ucar.edu> wrote:

> Hi Jared,
> To add to Rashed's suggestions:
> You can set cnFillColors to exactly the colors you want, via named colors,
> indexes from a color map, or RGB or RGBA values.
> http://www.ncl.ucar.edu/Document/Graphics/Resources/cn.shtml#cnFillColors
>
> See numerous examples here: (Search on the page for "cnFillColors")
> http://www.ncl.ucar.edu/Applications/res_list.shtml
>
> To answer your query: You can use getvalues to return the colors used in a
> specific plot:
> plot = gsn_csm_contour_map(.....
> getvalues plot at contour       ; use plot at contour for contour plots created
> using gsn_*_map, otherwise just use "plot"
>  "cnFillColors" : fill_colors
> end getvalues
> print(fill_colors)
>
> Hope that helps!
> Adam
>
> On Tue, Feb 13, 2018 at 1:51 PM, Jared Lee <jaredlee at ucar.edu> wrote:
>
>> Hi Rashed,
>>
>> Thanks for the example! That method works fine if you have your threshold
>> contour line (0ºC, say) is exactly in the middle of your set of contour
>> lines, but not if you have different numbers of contours above and below
>> your threshold value to split the colorbars/colormaps, unfortunately. And
>> it also limits you to combining colormaps that would total no more than 256
>> colors.
>>
>> What I ended up doing to get a similar effect (though not explicitly
>> blending two colormaps) was to play with cnFillPatterns and make the
>> contour intervals below 0ºC be either cross-hatched or stippled (and
>> cnFillScaleF changes the stipple density), as in the attached image (note
>> that cnFillMode must be set to "AreaFill" to use fill patterns). That might
>> be my compromise solution, at least for now.
>>
>> It would still be nice to be able to return the names of colors (or RBGA
>> values) that are assigned to the various contour levels (after setting
>> cnFillPalette to a named colormap and setting cnMinLevelValF,
>> cnMaxLevelValF, and cnLevelSpacingF), and then explicitly supply different
>> color names (or opacities) for some of the intervals. I'm not sure how to
>> return the names of colors that are actually being used with a given set of
>> contour levels, though.
>>
>> Jared
>>
>> On Mon, Feb 12, 2018 at 6:50 PM, Rashed Mahmood <rashidcomsis at gmail.com>
>> wrote:
>>
>>> Hi Jared,
>>> I think it's easy combine two color maps to get what you want. See
>>> attached script and the figure. the input file is NCEP surface air
>>> temperature.
>>>
>>> Cheers,
>>> Rashed
>>>
>>>
>>> On Mon, Feb 12, 2018 at 4:33 PM, Jared Lee <jaredlee at ucar.edu> wrote:
>>>
>>>> Hi all,
>>>>
>>>> Has anyone out there made any plots where the colorbar/colormap is part
>>>> grayscale, part color? For example, what I'd like to do for one application
>>>> is make some plots with a color palette like "NCV_bright," for instance,
>>>> where temperatures below 0ºC (say) get plotted in a grayscaled version of
>>>> the color palette, but grid cells with values above 0ºC get plotted with
>>>> the regular full-color palette. How would I go about doing that? Would I
>>>> have to manually replace the sub-zero part of my color palette with various
>>>> named gray colors? Thanks for any tips or ideas!
>>>>
>>>> Jared
>>>>
>>>> --
>>>> ===============================
>>>> Jared A. Lee, Ph.D.
>>>> Project Scientist I
>>>> Research Applications Laboratory
>>>> National Center for Atmospheric Research
>>>> Boulder, Colorado, USA
>>>>
>>>> Member, AMS Planning Commission
>>>>
>>>> Email: jaredlee at ucar.edu (w)
>>>> Phone: 303.497.8485 <(303)%20497-8485> (w)
>>>> Web: https://staff.ucar.edu/users/jaredlee
>>>> ===============================
>>>>
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>>>>
>>>
>>
>>
>> --
>> ===============================
>> Jared A. Lee, Ph.D.
>> Project Scientist I
>> Research Applications Laboratory
>> National Center for Atmospheric Research
>> Boulder, Colorado, USA
>>
>> Member, AMS Planning Commission
>>
>> Email: jaredlee at ucar.edu (w)
>> Phone: 303.497.8485 <(303)%20497-8485> (w)
>> Web: https://staff.ucar.edu/users/jaredlee
>> ===============================
>>
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>>
>
>
> --
> Adam Phillips
> Associate Scientist,  Climate and Global Dynamics Laboratory, NCAR
> www.cgd.ucar.edu/staff/asphilli/   303-497-1726 <(303)%20497-1726>
>
> <http://www.cgd.ucar.edu/staff/asphilli>
>



-- 
===============================
Jared A. Lee, Ph.D.
Project Scientist I
Research Applications Laboratory
National Center for Atmospheric Research
Boulder, Colorado, USA

Member, AMS Planning Commission

Email: jaredlee at ucar.edu (w)
Phone: 303.497.8485 (w)
Web: https://staff.ucar.edu/users/jaredlee
===============================
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