GraphicsMagick processes options in the order left to right.
GraphicsMagick uses -depth to control the color quantum precision and
not the storage depth and this option is losing the colormap. It is
likely best convert to grayscale before quantizing the colors.
This works with GraphicsMagick 1.3.20:
gm convert input.tif -colorspace GRAY -colors 16 output.tif
To be completely specific about TIFF output bits/sample, do
gm convert input.tif -colorspace GRAY -colors 16 \
-define tiff:bits-per-sample=4 output.tif
When you are specific about bits/sample with a colormapped image, you
need to be careful that the colormap fits the specified bits/sample.
Sorry to hear that the SourceForge web interface is unusable.
Bob
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Bob Friesenhahn
[email protected], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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