[Image-SIG] BUG: convert to greyscale errors

[David Austin]

Hi all,

I've found an incorrect dependency upon neighbouring pixels in conversion
to
greyscale.  Running this simple script (against attached images):

import Image
im1 = Image.open('a.png')
im2 = Image.open('b.png')
pt = (301, 72)
print "Before", im1.getpixel(pt), im2.getpixel(pt)
im1 = im1.convert("P")
im2 = im2.convert("P")
print "After", im1.getpixel(pt), im2.getpixel(pt)

Gives:

Before (63, 73, 50) (63, 73, 50)
After 60 59

i.e. before conversion the RGB values are identical, after the greyscale
values are not.

Regards,
David
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