Legacy ImageMagick Discussions Archive

IM 6.9.9.35 Q16 Mac OSX Sierra
# ImageMagick pixel enumeration: 4,1,65535,srgba
0,0: (54227,45746,40606,0) #D3B29E00 srgba(211,178,158,0)
1,0: (54227,45746,40606,62708) #D3B29EF4 srgba(211,178,158,0.956863)
2,0: (54227,45489,40606,47288) #D3B19EB8 srgba(211,177,158,0.721569)
3,0: (54227,45746,40606,65535) #D3B29EFF srgba(211,178,158,1)


The above image has 1 fully transparent alpha value, 1 fully opaque alpha value and two partially transparent alpha values.


I want to threshold the alpha channel at 0. So all values but the alpha=0 should go to 1. But the opposite is happening. All values but alpha=1 go to 0.

# ImageMagick pixel enumeration: 4,1,65535,srgba
0,0: (54227,45746,40606,0) #D3B29E00 srgba(211,178,158,0)
1,0: (54227,45746,40606,0) #D3B29E00 srgba(211,178,158,0)
2,0: (54227,45489,40606,0) #D3B19E00 srgba(211,177,158,0)
3,0: (54227,45746,40606,65535) #D3B29EFF srgba(211,178,158,1)


Should not the two alpha values in red actually be 1?


P.S. This goes back at least as far as 6.9.8.3. I have not tested earlier versions

The above seems to work fine in IM 7.0.7.23 Q16 HDRI Mac OSX Sierra
# ImageMagick pixel enumeration: 4,1,65535,srgba
0,0: (54227,45746,40606,0) #D3B29E00 srgba(211,178,158,0)
1,0: (54227,45746,40606,62708) #D3B29EF4 srgba(211,178,158,0.956863)
2,0: (54227,45489,40606,47288) #D3B19EB8 srgba(211,177,158,0.721569)
3,0: (54227,45746,40606,65535) #D3B29EFF srgba(211,178,158,1)

# ImageMagick pixel enumeration: 4,1,65535,srgba
0,0: (54227,45746,40606,0) #D3B29E00 srgba(211,178,158,0)
1,0: (54227,45746,40606,65535) #D3B29EFF srgba(211,178,158,1)
2,0: (54227,45489,40606,65535) #D3B19EFF srgba(211,177,158,1)
3,0: (54227,45746,40606,65535) #D3B29EFF srgba(211,178,158,1)

Correct result: three values of 1 and one value of 0.

The bug in the original post at the top does not seem to be corrected in IM 6.9.9.36 Q16 Mac OSX.

This does not seem to be fixed in IM 6.9.9.37.

convert xc:"#D3B29E00" xc:"#D3B29EF4" xc:"#D3B19EB8" xc:"#D3B29EFF" +append tmp1.png
convert tmp1.png -channel a -threshold 0 +channel tmp2.png
convert tmp2.png txt:
# ImageMagick pixel enumeration: 4,1,65535,srgba
0,0: (54227,45746,40606,0) #D3B29E00 srgba(211,178,158,0)
1,0: (54227,45746,40606,0) #D3B29E00 srgba(211,178,158,0)
2,0: (54227,45489,40606,0) #D3B19E00 srgba(211,177,158,0)
3,0: (54227,45746,40606,65535) #D3B29EFF srgba(211,178,158,1)

The two sets of red 0s should be 1s (or FF)

Thanks for the problem report. We can reproduce it and will have a patch to fix it in GIT master branch @ https://github.com/ImageMagick/ImageMagick later today. The patch will be available in the beta releases of ImageMagick @ https://www.imagemagick.org/download/beta/ by sometime tomorrow.