Change color for clean black channel

[MHRabbani]

I have an image (one layer tiff) with 8 solid color.

Only one of these colors has a black layer (0,0,0,100).

I want to change this color (0,0,0,100) to (100,100,100,0) to clean the black layer of image.

when I use replace color tools, the texts are thinner.

How can I change color without changing the texts thickness?

[D Fosse · Accepted solution]

You can copy>paste between color channels, so technically it's no more difficult than that. Note that 100-100-100-0 won't give you a neutral black! Inks have different densities.

Since these are CMYK numbers I assume this is going to an offset press? You need to watch the total ink limit. If you end up with 100-100-100-100 in some areas, you have a problem. The ink will smear and not dry properly.

Most CMYK profiles have an ink limit in the 280% - 320% range. This is built into the profile. A so-called rich black, printed on all four plates, maximizes ink on each plate to give the deepest black possible without exceeding the limit.

[Stephen_A_Marsh]

As only one image has black values, you could use Apply Image to “stamp” the K data to the CMY channels, then a curve to the K channel can easily remove all K data. Channel mixer may also be an option, however a CMYK test image would be needed.