Promote greys to cmyk black?

[cg433n]

Is there a way to move all gray colors of a CMYK image (e.g. a cmyk .tiff) into the black (K) plate with Imagemagick?
(In Adobe Acrobat Pro, this functionality is labeled: "Promote grays to CMYK black")

[snibgo]

Converting it to CMY than back to CMYK seems to do the trick.

Code: Select all

convert incmyk.tiff -colorspace CMY -colorspace CMYK outcmyk.tiff

[cg433n]

While the command works, it looks like the colors of the result are significantly altered.
I'm trying separate the channels of an image like this: http://en.wikipedia.org/wiki/File:Barns ... tetons.jpg,
so that all black and gray color data lies on one plate http://en.wikipedia.org/wiki/File:CMYK_ ... _black.jpg, thereby conserving for four color process newsprint printing.

[snibgo]

The main image on your linked page is sRGB, not CMY or CMYK.

For printing, it's better to use profiles tuned to your printer/inks/paper.

[snibgo]

Can you put up the source image and results? Put them somewhere like dropbox.com and paste the links here. Also say what version IM you are using, and the exact commands.