On 2015/05/23 8:49 AM, Matteo Niccoli wrote:
> Hi Eric
>
> If you look at the two attached images, both have the shading as expected,
> but in one case the colours have changed, from the cubehelix colors, to
> rainbow colors.
Yes, the result looks more like a rainbow set, but that doesn't mean
anything is incorrect. The algorithm is doing what you are telling it
to do. The "alter V" algorithm will *always* generate colors that are
outside the original colormap. It happens that superimposing wild
variations in V on something mapped with cubehelix yields a result that
looks more rainbow-ish than if you started with some other map. This is
just because of the character of cubehelix. It doesn't mean the code is
failing--it means the algorithm is not the right one for the result you
want to achieve, or cubehelix is not a good choice for the result you
want, or both.
You might get something more to your liking if you were to start with a
colormap in which V is uniform--all variation is in H and S--and then
impose the shading on the V. Cubehelix starts with a full range of V,
so replacing V with your shading channel completely changes the set of
colors you end up with.
Eric
>
> Matteo
>
> On Sat, May 23, 2015 2:19 pm, Eric Firing wrote:
>> On 2015/05/22 9:33 AM, Matteo Niccoli wrote:
>>
>>> The second method suggested by titusjan replaces value in hsv space
>>> with intensity as suggested. Eric you will notce I did include the line
>>> img_array = plt.get_cmap('cubehelix')(data_n) and yet the colormapping
>>> is not working.
>>
>> I don't understand your conclusion that the colormapping is not working.
>> I don't see anything wrong with any of these plots. The two
>> algorithms appear to be doing exactly what they are supposed to do.
>>
>> Eric
>>
>>
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