-colors does not work with RGBA PNG

[Juce]

sphere.png:


convert sphere.png -colors 50 spherecolors50.png


convert sphere.png PNG8:spherepng8.png


This works:
convert sphere.png spheregif.gif


ImageMagick 6.6.8-6 2011-03-21 Q16
Windows XP 32-bit

[glennrp]

For the first conversion I'm seeing the same result whether the output is .png or .txt so I don't think it's a PNG bug.

For the second conversion, it is to be expected that the quantization is lousy because we are simply dropping
the low 5 bits of the Red and Green samples and the low 6 bits of blue.

Converting spheregif.gif to spheregif.png looks pretty good, exactly the same as spheregif.gif but smaller file size.