PIL: How to use a palette?

[Antoon Pardon]

Is it possible to know how many colors are in a palette and
which ones?

 

[Fredrik Lundh]

Is it possible to know how many colors are in a palette

get the histogram, and count the number of non-zero bins
(len(filter(None, im.histogram())) usually does the trick).

and which ones?

quickest solution: resize the image to (256, 1), convert to RGB,
and use getpixel((i, 0)) to get the color for color index i.

lut = im.resize((256, 1)).convert("RGB")
print lut.getpixel((0, 0)) # get color #0

or use getdata() to get an array of color indices:

lut = im.resize((256, 1)).convert("RGB").getdata()
print lut

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