Copy a certain CMYK color from one image to another image

[R4C3R]

I try to combine two CMYK based images into one image. The first image serves as background, the 2nd image as overlay. However, from the second image I only want to use pixels that have a certain pre-defined colour.

image1.jpg JPEG 7121x1434 7121x1434+0+0 8-bit CMYK 918KB 0.000u 0:00.000
image2.eps EPT 6008x298 6008x298+0+0 16-bit ColorSeparation CMYK 7.162MB 0.000u 0:00.000

from image2 I only want to use pixels with CMYK colour 60 30 20 80 for the overlay.

the images should be center aligned (-gravity center)

How can this be accomplished using imagemagick?

[snibgo]

I think you want to composite the second image over the first, but only after making other colours transparent, like this:

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magick in1.jpg ( in2.jpg -alpha set -fuzz 0.5% +transparent icc-color(cmyk,0,0,0,0) ) -composite out.jpg

The icc-color numbers are in the range 0.0 to 1.0. I'm not sure how you would specify 60 30 20 80 which I assume are out of 255.

[R4C3R]

I'm also unsure about the icc-colours & CMYK relation.

The second image has only two colours, CMYK 60 30 20 80 and white. Maybe this information helps solving the problem.

What I used sofar was:

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composite -compose multiply image2.eps -gravity center image1.jpg output.jpg

But the colours CMYK of output.jpg seem to be slightly different from the image2.jpg, probably because it is the result of a pixel multiplication process of both images.

[snibgo]

What version of IM, on what platform?

I suggest you don't use the "composite" command. Instead, use "convert" in v6 or "magick" in v7, with a "-composite" option.

Why are you multiplying pixels?

[R4C3R]

I'm using

Version: ImageMagick 6.9.7-4 Q16 x86_64 20170114 http://www.imagemagick.org

on

Ubuntu 18.10 LTS

I multiplied the pixels because optically it came close to what I was looking for. Image2 has only two colours white and CMYK 60 30 20 80 (which comes close to black)

[snibgo]

If image2 has only white and some other colour, and you don't want the white copied, then...

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convert in1.jpg ( in2.eps -alpha set -transparent icc-color(cmyk,0,0,0,0) ) -composite out.tiff

I write to tiff instead of jpg because tiff is by default lossless.

[R4C3R]

This command does the trick for me, everything in image 2 that is white (cmyk,0,0,0,0) is made transparant before using image2 as an overlay on top of image1:

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convert image1.jpg -gravity center \( image2.eps -alpha set -transparent icc-color\(cmyk,0,0,0,0\) \) -composite output.tiff

Thank you for all your support!

PS:

Finding 1) I also found out that imagemagick reports the CMYK colours on a scale from 0 to 255. The CMYK colour I was using (60 30 20 80) translated to image magicks definition of CMYK as cmyk,153,76,51,204

To determine the colour of a certain pixel I used the following command:

convert image2.tiff -format '%[pixel:p{1,149}]' info:-;echo

with the following result: cmyk(153,76,51,204), the same pixel is reported in Photoshop as CMYK 60,30,20,80.

Finding 2) However converting the command like this (making everything transparant that has not the pre-defined cmyk colour) didn't work for some reason.

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convert image1.jpg -gravity center \( image2.eps -alpha set +transparent icc-color\(cmyk,153,76,51,204\) \) -composite output.tiff