Package: gimp Version: 2.6.8-2 When converting an RGB image to indexed, the GIMP sometimes fails to choose as accurately as it could between similar colors in a chosen palette, even when each pixel has an exact match somewhere in the palette.
The enclosed colormaptest.ppm and Colormap_test files together form a
test case to reproduce this bug, as follows:
1. Compare colormaptest.ppm (a text PPM image) and Colormap_test (a GIMP
palette) to verify that each contains the same RGB triples in the
same order.
2. Move or copy Colormap_test into a directory for GIMP palettes, e.g.,
the ~/.gimp-2.6/palettes/ directory.
3. Start the GIMP and open colormaptest.ppm, then zoom in enough that
you can see each individual pixel.
4. Right-click image -> Image -> Mode -> Indexed... to open the Indexed
Color Conversion dialogue, and set it as follows:
a. Under "Colormap", select "Use custom palette", then click the
button below that selection to pop up the list of
available palettes. From this list select "Colormap_test".
Uncheck the "Remove unused colors from colormap" checkbox if it's
checked.
b. Under "Dithering", for "Color dithering:" select "None". Uncheck
the "Enable dithering of transparency" checkbox if it's checked.
c. Click "Convert".
5. Observe that while the leftmost and middle pixels have been mapped to
their exact matches in the palette, the rightmost pixel has been
mapped to the same color as the middle pixel. (Try pressing ^Z to
undo and ^Y to redo repeatedly if you don't see it at first.)
<<attachment: colormaptest.ppm>>
GIMP Palette 103 79 59 95 71 55 87 67 51
