Separating alpha channel yields values that are too low.
Posted: 2014-02-18T17:42:59-07:00
Hello,
So I have a PNG with alpha in it.
Created with inkscape, I created a white 64x64 image with alpha value 90.
When I extract the alpha channel with NetPBM, I get a proper result: value 90.
When I extract the alpha channel with ImageMagick, I get the value 26 instead, far too low.
Why doesn't ImageMagick output the proper values?
Version: ImageMagick 6.7.7-10 2013-09-10 Q16
Thanks,
Bram
So I have a PNG with alpha in it.
Created with inkscape, I created a white 64x64 image with alpha value 90.
When I extract the alpha channel with NetPBM, I get a proper result: value 90.
When I extract the alpha channel with ImageMagick, I get the value 26 instead, far too low.
Code: Select all
$ pngtopnm -alpha white.png > white.pgm
$ pgmhist white.pgm
value count b% w%
----- ----- -- --
90 4096 100% 100%
$ convert white.png -channel A -separate out.pgm
$ pgmhist out.pgm
value count b% w%
----- ----- -- --
26 4096 100% 100%
Version: ImageMagick 6.7.7-10 2013-09-10 Q16
Thanks,
Bram