Answer
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Open your file into Photoshop, open the channels panel, you will notice that the black and white areas are presented in all RGB channels.
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Go to
Edit > Convent Profile
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In the convert to profile dialogue box go to the section
Destination space
and dropdown the list toCustom CMYK
. -
A warning dialogue will appear just click OK .
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In the custom CMYK dialogue box in the separation options section select the Black Generation to
Maximum
, you will notice that the colored curves disappeared and we preserve the black curve only in the gray ramp chart. -
Click OK for applying the black and change the profile custom name to your own and press OK to applying our custom color profile.
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Now open the channels panel, you should see the black and white background are dropped in the black channel only.
That’s it.
Attribution
Source : Link , Question Author : user7343079 , Answer Author : hsawires