Re: [matplotlib-devel] proposed change to colors.py

[Phillip M. F. <pfe...@ve...>]

I'm not sure whether I'm correctly understanding you. Let's consider a 
hypothetical engineering performance-versus-requirements scatter plot or 
contour plot of a performance metric that takes positive values. I'd 
like to map values to colors so that anything below 50 gets solid red, 
values from 50 to 70 get a color between red and orange (linear 
interpolation), values from 70 to 90 get a color between orange and 
yellow, values from 90 to 105 get a color between yellow and green, and 
anything greater than or equal to 105 gets solid green. Is this 
considered "smooth variation"? If so, how would I implement something 
like this?

Thanks!

Phillip

Eric Firing wrote:
> Phillip M. Feldman wrote:
>> Eric and Reinier-
>>
>> It seems to me that continuous (piecewise-linear) colormaps could 
>> work in much the same fashion.  One would specify n boundary colors 
>> and n thresholds (for continuous colormaps, I believe that the number 
>> of thresholds and colors must be the same), and for any value between 
>> two thresholds, the colors associated with the bounding thresholds 
>> would be automatically interpolated.  What do you think?
>
> How does this differ from LinearSegmentedColormap.from_list()?  I 
> guess what you are getting at is the quantization problem I mentioned 
> in connection with discrete colormaps.  But it is not a problem when 
> the colors are linearly interpolated--that is, smoothly varying from 
> one end of the map to the other.  It is only a problem when there are 
> jumps.
>
> Eric
>
>>
>> Phillip
>>
>> Eric Firing wrote:
>>> What does allow you to specify the transitions exactly (to within 
>>> the limits of double precision) is this:
>>>
>>> cmap = ListedColormap(['r','g','b'])
>>> norm = BoundaryNorm([1.5+1.0/3, 1.5+2.0/3], cmap.N)
>>
>
>