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Thread: Photoshop – problems convering colours

  1. #1
    stedders is offline Junior Member
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    Default Photoshop – problems convering colours

    I have been supplied with the attached image.
    I am working in a commercial print environment – this needs to print two colours (green uncertain of what PMS – but just call it custom green for the time being) and black – ideally it needs to be on transparent background.


    The image I have been supplied has traces, very small traces, of the other process colours. Obviously I could just indicate to suppress these extra colours – but I would rather get it right. Could anyone advise on what would be the best strategy for removing these colours.


    This is not really my line of work (in normal circumstances) – but I have tried deleting the other channels (which sort of works, but I lose my transparency) – I feel there is an obvious answer staring at me.


    I just wish I knew what it was.


    Help anyone?
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  2. #2
    DCurry is offline Senior Member
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    Use Curves to remove the traces of ink in the CMY channels. Click on the CMYK composite channel, go to Curves, then on each individual channel (C,M,Y only) grab the upper right point and drag it straight down, so it will read Input: 100 and Output: 0.

    This will remove all traces of ink on those channels.

    Another way is to go to each channel and Select All>Delete. Don't delete the actual channels, just the pixels in the channels.
    akalaray likes this.
    Dan Curry
    Prinergy 5.3 • Preps 5.3.3 + 6.3

  3. #3
    buckeye's Avatar
    buckeye is offline Senior Member
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    What I like to do in instances like this is apply Maximum Black Generation to the file which will help separate the Custom Green from the Black.

    It's fairly easy to do and it will still keep your transparency.

    1. Go to Edit > Color Settings, and where it says Working Spaces, click the CMYK pulldown menu and at the top will be a "Custom CMYK" setting. You'll get another dialog box in which you'll select "Maximum" for the Black Generation.

    2. Open the file and convert it to Lab or RGB and then convert it back to CMYK.

    3. Copy the Yellow channel and then double click on it so you can make it a spot color of your choice.

    4. As DCurry said, do a Select All and delete all of the pixels on the Cyan, Magenta and Yellow channels.

    Caution! After fixing your file, make sure you go back to your original CMYK Color Settings profile. If not, the next time you convert an RGB file to CMYK, it will desaturate the file and lose most of its color.

    Hope this helps,

    Erik
    OS X 10.8.3 • Rampage 11.3 • Preps 5.3.3 • Javelin 8300 • Epson 9900 • KM C8000

  4. #4
    DCurry is offline Senior Member
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    Erik - great idea. In fact, I was going to suggest a similar approach when I looked at the OP's screenshot and he already has the K and Spot channels in place - he's just trying to eliminate all pixel data that remains on the CMY channels (seems there's a few rogue pixels hanging around.)
    Dan Curry
    Prinergy 5.3 • Preps 5.3.3 + 6.3

  5. #5
    buckeye's Avatar
    buckeye is offline Senior Member
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    DCurry,

    Guess I kind of convoluted your solution, which is what I would have done also to eliminate the rogue pixels.

    Oh well, if he or anyone else who reads this thread needs to convert a CMYK file to a 2C file, there you go.

    Erik
    OS X 10.8.3 • Rampage 11.3 • Preps 5.3.3 • Javelin 8300 • Epson 9900 • KM C8000


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