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reduce PNG palette size for images <255 colors

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limit color and trancparency palette to 2^bits entries, when a PNG is
saved with the 'bits' PNG encoder option
This commit is contained in:
Oliver Tonnhofer 2013-03-11 20:58:54 +01:00
parent 6537ba19c3
commit 6a450e303d
1 changed files with 8 additions and 3 deletions
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11
PIL/PngImagePlugin.py
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@ -545,12 +545,16 @@ def _save(im, fp, filename, chunk=putchunk, check=0):
b'\0') # 12: interlace flag
if im.mode == "P":
chunk(fp, b"PLTE", im.im.getpalette("RGB"))
palette_bytes = (2 ** bits) * 3
chunk(fp, b"PLTE", im.im.getpalette("RGB")[:palette_bytes])
if "transparency" in im.encoderinfo:
if im.mode == "P":
transparency = max(0, min(255, im.encoderinfo["transparency"]))
chunk(fp, b"tRNS", b'\xFF' * transparency + b'\0')
alpha = b'\xFF' * transparency + b'\0'
# limit to actual palette size
alpha_bytes = 2**bits
chunk(fp, b"tRNS", alpha[:alpha_bytes])
elif im.mode == "L":
transparency = max(0, min(65535, im.encoderinfo["transparency"]))
chunk(fp, b"tRNS", o16(transparency))
@ -562,7 +566,8 @@ def _save(im, fp, filename, chunk=putchunk, check=0):
else:
if im.mode == "P" and im.im.getpalettemode() == "RGBA":
alpha = im.im.getpalette("RGBA", "A")
chunk(fp, "tRNS", alpha)
alpha_bytes = 2**bits
chunk(fp, b"tRNS", alpha[:alpha_bytes])
if 0:
# FIXME: to be supported some day