Help! Grayscale picture in CMYK Mode => not only K

Discussion in 'Photoshop' started by Gerry Kunz, Dec 2, 2005.

  1. Gerry Kunz

    Gerry Kunz Guest

    Hello,

    I have a grayscale picture which I have top build in into a folder. The
    folder will be printed in a printing house via offset-print. In the folder
    there are color elements too (CMYK photos, etc.) and this greyscale picture.
    When I change the mode in Photoshop from grayscale to CMYK, I realized,
    that there are not only K values in the picture, but also CMY values. When I
    import the picture in my graphics software od print it out, I can see a
    slight color cast. What can I do with the picture to transform it into a
    picture which has only K values (CMY=0)? The picture should be printed in K
    process color only.

    Thanks
    Gerry.
     
    Gerry Kunz, Dec 2, 2005
    #1
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  2. Gerry Kunz

    edjh Guest

    On the layer(s) that you want grayscale go to Image>Adjustments>Channel
    Mixer and check Monochrome. Use the sliders (leave Constant at zero) to
    get the look you want. Other layers will not be affected.

    You can do this with an Adjustment Layer as well. Group layer with
    Adjustment Layer to make sure layers below aren't affected if necessary.
     
    edjh, Dec 2, 2005
    #2
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  3. First select the entire picture and copy it. Then select the K channel
    only an paste the picture. Now your entire picture is in the K channel.
    Next, go to the other channels one by one, choose menu "Select all' and
    hit delete.
     
    Johan W. Elzenga, Dec 2, 2005
    #3
  4. Gerry Kunz

    edjh Guest

    You can do that but I think you'll lose a lot of the tonal quality that
    is provided by those other channels.
     
    edjh, Dec 2, 2005
    #4
  5. Gerry Kunz

    tacit Guest

    You can use the Channel Mixer or Copy->Paste as others have suggested,
    but I've found the fastest way to force a CMYK grayscale image to the K
    channel only is to use the Hue and Saturation command. Turn on
    "colorize" and turn the saturation to 0.
     
    tacit, Dec 2, 2005
    #5
  6. Gerry Kunz

    Mike Russell Guest

    Reseparate your grayscale image specifying Max GCR, and the correct dot gain
    value for your press. This will give you a K only version of your image.
    Pasting the grayscale image directly into the K channel is almost certain to
    produce too dark a result because of the lack of dot gain compensation.

    Tacit is correct that you will lose subtle gradations by printing only to
    the K channel. You can retain some of this gradation, while minimizing
    color casts, by separating with GCR set to heavy or medium. This puts more
    of the image into the K plate, and reduces the chance of any color cast in
    the final printing.

    BTW - the color cast you see in your graphics software may not be
    significant. Illustrator and Quark, for example, use a quick and dirty
    preview method for placement purposes only. In certain versions of these
    programs, the CMYK looks bad on screen, and bears little relation to what is
    finally printed.

    The best, and only, book that deals with these issues in a digital setting
    is Dan Margulis's Professional Photoshop.
     
    Mike Russell, Dec 2, 2005
    #6
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