Re: [matplotlib-devel] Possible bug in LinearSegmentedColormap

2011/1/17 Eoghan Harrington <eo...@gm...>

> Hi,
>
> I noticed some erroneous behaviour when using a
> LinearSegmentedColormap with an "under" color and different numbers of
> color levels. The attached script replicates the behaviour, whereby
> lowering the number of colors causes less of the values to be
> considered "under" the vmin. I tracked the problem back to the
> Colormap class where the results of Normalize are multiplied by the
> number of color levels (N) and casted as an int to be used as indices
> in the color array. The expected behaviour would be that all negative
> values should be considered "under", however the results of the cast
> means that anything between 0 and -0.5 will be set to 0 and therefore
> will be in the normal color range for the colormap. The attached patch
> overcomes this by setting all negative values to -1 before applying
> the cast.
>
> Thanks for your help,
> Eoghan
>
>
Thanks for catching this one.  Blindly casting to int is wrong (which has a
problem for values between -1 and 0, not just -0.5 and 0).  This has been
committed in v1_0_maint as r8931 and in the development trunk as r8932.

Ben Root