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I have .tiff. Part of the .tiff is a bar code. My printer is insisting the bar code be converted to 100%K - CMYK "pure black". (Their words)

A couple obstacles: 1) The Bar Code has been scaled up. Since it got resampled in that process, the edges aren't pure black anymore. Just selecting the black area by color is tricky now, since the outermost pixels might or might not be included.

2) The .tiff is in RGB8, and my printer wants CMYK. RGB rich black does not translate to 100% K in CMYK.

How would you go about changing this one part of the image to 100%K CMYK, to make the printer happy.

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up vote 7 down vote accepted

The easiest way would be to create a selection around the bar code (I assume it's got the white background), then using the Channels Panel -

Hightlight the black channel and use Levels to boost the tone to 100%. Then Highlight the C channel and fill the selection with white. Then fill the selection on the M and Y channels with white as well.

Double check the K channel again and ensure the values are 100%.

That should give you only a 100%K bar code.

The preferable method is really to use a vector bar code. There are several online barcode converters which provide downloadable .eps files. Here is a link to a good one.

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For good measure, I converted the .tif to CMYK before pasting the bar code in. –  baudot Feb 9 '12 at 2:17
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Yea, even though barcodes are fault-tolerant by design, you should always generate a new barcode instead of blowing up a raster image. That's never a good idea to do on any professional project. As long as you know the code type, you can easily generate a new one, and in vector format that you can scale however you want. –  Lèse majesté Feb 9 '12 at 3:16
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