[Octave-bug-tracker] [bug #41851] ind2rgb tests

[Rik]

Follow-up Comment #3, bug #41851 (project octave):

I don't know what Matlab is doing, but I think Octave is correct in rejecting
the variable img as not being an indexed image.

When the img is of type double, a 1 in the matrix points to the first row in
the colormap.  When the img is an integer type, such as uint8, then an offset
of 1 is used such that a 0 in the matrix points to the first row in the
colormap.  See Matlab's own documentation for more information
(http://www.mathworks.com/help/matlab/creating_plots/image-types.html).

In the posted code, the image is originally in uint8 format and thus has 0
values.  Using double() to convert a uint8 image is not correct.  You actually
need to do


img_double = double (img) + 1;




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