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Thread: CMYK to Duotone "best practice" steps?

  1. #1
    stedders is offline Junior Member
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    Default CMYK to Duotone "best practice" steps?

    This is similar to (but not exactly the same) to a post of mine from yesterday.

    I now have this image, which is CMYK, and need to create a (green and black) duotone.

    Could anyone walk me through the "best practice" steps that I need to take with this.
    I am not sure what PMS green I want at this stage.
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  2. #2
    Stephen Marsh is offline Senior Member
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    Using Photoshop to create a Duotone, the source image is a single channel grayscale - then the two duotone plates are curved to create the differences. Looking at the image, I don't think that this is what you wish to do though...

    I think that you require a Multichannel image that has two spot colour channels, one black and one green. Or you could have a greyscale mode document with a spot green channel. There used to be an old plug-in called "Powertone" that automated the process of creating "extended duotones", however it is no longer available and they were not really duotones in the same way as Photoshop Duotone mode files. Don't worry though, it is not too hard to do this manually.

    As you need green and black, it would be safe to assume that the K channel would be a good place to start for the K data. That being said, you may need to use channel mixer or apply image to add in some data from the CMY channels to the K channel.

    As green is mostly created from Cyan and Yellow, you would need to base the spot green separation off these two channels. Again, you may have to blend the detail from the C and Y channels together, perhaps with some M or K data (unless say the Y channel did not contribute a great deal of useful image content).

    It would be more useful to have a crop of the original CMYK data than an RGB screenshot. I could record an action for you that would do the conversion.


    Regards,

    Stephen Marsh
    Last edited by Stephen Marsh; 01-09-2013 at 07:03 PM.

  3. #3
    DCurry is offline Senior Member
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    Assuming that Stephen is correct and you really want a 2-color image, not a traditional duotone, go back and check out Erik's reply to your other post. Convert to Lab or RGB, then convert back to CMYK using Max Black Generation. This will pretty much get your black all on the K channel.

    Then I would add your Spot channel, go to your Yellow channel and Select All>Copy and then paste into the new Spot channel, then go back and delete everything off the CMY channels just like in the other post.

    If you have to do this every now and then, it is worthwhile to save your Max GCR setting as a profile. Then you can simply convert to that profile as your first step and not worry about messing with your CMYK separation settings.
    Dan Curry
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  4. #4
    Stephen Marsh is offline Senior Member
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    Dan is correct, I am assuming that a standard Photoshop Duotone mode file is not what the OP is after.

    I agree with Dan, a Max GCR conversion for the K channel data and or other channel data could be a good place to start, over and above existing CMYK data. I am not sure if going from your current CMYK to an intermediate space such as RGB or Lab would help if you are not going to made intermediate edits such as making the K background 0r0g0b etc., you should be able to go from CMYK direct to CMYK with later versions of Photoshop.


    Stephen Marsh

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    DCurry is offline Senior Member
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    Quote Originally Posted by Stephen Marsh View Post
    you should be able to go from CMYK direct to CMYK with later versions of Photoshop.
    Yes, you can do a Profile-to-Profile conversion,provided you have already built a Max GCR ICC profile.
    Dan Curry
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    Stephen Marsh is offline Senior Member
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    One can make a legacy Custom CMYK engine Max GCR conversion "on the fly" without having one pre-built and saved as an ICC profile. Either way it would be important to ensure that the final file has a solid black background if this is what is required (otherwise one may get 92% or some other tint value rather than 100%).


    Stephen Marsh

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    DCurry is offline Senior Member
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    Yes, but wouldn't that entail going in and setting your CMYK to Mac GCR, then doing the conversion, and then having to remember to go back and change the settings back to one's normal settings, lest you forget and future conversions unintentionally get the Max GCR. I've been burned by forgetting to do that before, hence the ICC idea which lets me do it anytime with no risk of forgetting to return to my normal CMYK setup.

    Also, how could one do this CMYK-to-CMYK without a profile-to-profile conversion and without stopping in Lab or RGB first?
    Dan Curry
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    buckeye is offline Senior Member
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    stedders,

    Here's a very quick and easier way that I used to do in the past. Not sure if it's what you're looking for, but give it a try.

    1. Convert your RGB or CMYK file to Grayscale.

    2. Now convert it to Duotone mode and apply these settings that I uploaded.
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  9. #9
    stedders is offline Junior Member
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    Thanks very much everyone for replying. Yes, it's a two-colour image that is needed – not necessarily a duotone (lazy language on my behalf)
    If it's any use – attached is the image in CMYK with the relevant channels.
    I think I have got a hang of what to do – but it's just useful to listen to other ideas.
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    Last edited by stedders; 01-10-2013 at 02:38 PM.

  10. #10
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    You could just use the black and yellow channels in your cmyk image. Delete the magenta and cyan.

    best, gordo


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