PNG predictor added
parent
18a5058af6
commit
0278076ea8
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@ -25,15 +25,22 @@ def apply_png_predictor(pred, colors, columns, bitspercomponent, data):
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# PNG none
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buf += line1
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elif pred == '\x01':
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# PNG sub
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b = 0
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for c in line1:
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b += ord(c)
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buf += chr(b & 255)
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# PNG sub (UNTESTED)
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c = 0
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for b in line1:
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c = (c+ord(b)) & 255
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buf += chr(c)
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elif pred == '\x02':
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# PNG up
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for (a,b) in zip(line0,line1):
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buf += chr((ord(a)+ord(b)) & 255)
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c = (ord(a)+ord(b)) & 255
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buf += chr(c)
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elif pred == '\x03':
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# PNG average (UNTESTED)
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c = 0
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for (a,b) in zip(line0,line1):
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c = ((c+ord(a)+ord(b))/2) & 255
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buf += chr(c)
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else:
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# unsupported
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raise ValueError(pred)
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