Legacy ImageMagick Discussions Archive

Hello,

I try to convert rgb.png files to cmyk.tiff. (convert -colorspace CMYK rbg.png cmyk.tiff). The problem is that black channel is zero and all black pixels are mixture of cyan, magenta and yellow. How can I make CMYK files, where black pixels are only in the K-channel and all other colors are zero at these points.

Regards,
Arto

What version of IM are you using?

can you give a link to an example image (small example).

anthony wrote:What version of IM are you using?

Examples are made by the latest version 6.3.5-Q8 (Windows).

anthony wrote:can you give a link to an example image (small example).

Small example of the original .png can be found from:

http://www.keskiespoo.net/~arinkala/im/rgb.png

at the same directory cmyk.tif is made by command

convert -colorspace CMYK rgb.png cmyk.tif

after that color channels are separated by both images.

convert rgb.png -colorspace CMYK -separate rgb_sep_%d.tif
convert cmyk.tif -colorspace CMYK -separate cmyk_sep_%d.tif

The files separated from rgb.png seems to be fine, but from cmyk.tif K-channel is zero.

Okay so reading in a CMYK version of TIFF then applying -colorspace CMYK
stuffs up the image.

I would report exactly that in the bugs section.

The error might appear already in the conversion from .png. So, that the colorspace in the .tif file is CMY instead of CMYK.