[Matplotlib-users] getting extra colors in figure

[Eric Firing]

On 2016/07/22 8:24 AM, Smit, Christine E. (GSFC-610.2)[TELOPHASE CORP] 
wrote:
> Hi! I’m trying to plot data using imshow and ending up with more colors
> than I specify in the colormap. This is causing problems with a downstream
> user who is machine reading images to determine approximate data values
> based on colors. I think the issue has something to do with rounding
> because many colors in the image are only slightly off from the colors I
> specified. My plots have exactly one pixel per data value, so each pixel¹s
> color should be exactly a color in the colormap.

Christine,

To solve the problem, try using interpolation = 'nearest' rather than 
'none'.  The distinction between these is two is endlessly confusing, 
but 
http://matplotlib.org/examples/images_contours_and_fields/interpolation_none_vs_nearest.html 
is an attempt to illustrate it.

In your example, with "nearest" I get 5 unique colors, not 6.

Eric