# CMYK separation on black background?



## Stevistkrieg (Mar 6, 2008)

CMYK separations are normally based on having a white background on which the 4 colors are printed. 

Is there a way to print 4 color process on a black shirt without a white base layer?

I was thinking it might be possible to use the K channel for a white layer instead of black, adjusting the 4 channels to compensate for the change, thereby making all the negative space in the image filled by the black background of the shirt. So it would be 4 colors (screens) total: cyan, magenta, yellow and white.

Has anyone attempted this type of separation? How exactly do the c, m and y channels need to be adjusted to account for the printed white layer and the missing black layer? 

I understand the final print would probably be very faint and dark. It would probably be better used for printing cmyk on black paper. thanks!


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## Naga (Mar 11, 2008)

The short answer is: no way.
You must apply a solid layer of white (or bleach away the black) before printing colors.

The colors must be somewhat transparent to function when applied in layers.
In Photoshop channels, this is simulated with a solidity number, which is typically in the area 5% - 20% for colors and 85% - 100% for white and black.

When the base is black, *no* light is reflected to go back thru the color layers and illuminate them.
Only a tiny bit of light is reflected at the color layers giving a resulting color, which is almost black.


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## Stevistkrieg (Mar 6, 2008)

i see.. makes sense. thanks!


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## HMD10 (Feb 17, 2008)

Yes you can use the K (black) as the white and use the color of the shirt for Black. You are going to have to play around a little with the image.


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## HMD10 (Feb 17, 2008)

The Black on the press would be white. You can't use the black output as your white you have to make a separate white output for under the image Just wanted to clear that up.


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## Brian Danka (Nov 6, 2009)

JMclothing said:


> The Black on the press would be white. You can't use the black output as your white you have to make a separate white output for under the image Just wanted to clear that up.



Can you explain this a little further... Also what are other similar methods that can make printing on a black shirt possible?


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