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preparing duotone images

Feb 20, 2012 2:14 AM

Hello guys,

 

I want to create duotone (or tritone) images for offset printing. I am not going to use special inks for these. I will just create duotone image from the photoshop Duotone setting and choose Black for the first ink and Yellow for the second. My common sense suggests that this way I don't have to pay for the extra ink but still will be able to create duotone/tritone effect images. Of course I will tweak the percentage of each color. For example: 100% black with 30 % yellow (may be add 15% magenta if I want to go tritone).

But one thing I don't understand is that when I print this kind of image from my laser-jet printer, the colors don't look right. If I convert this image from duotone to CMYK, the color comes out right. But the channels go back to 4 color CMYK.

 

Again, how do I prepare duotone image for offset printing?

Thanks.

 
Replies
  • Currently Being Moderated
    Feb 20, 2012 6:43 PM   in reply to generalbatzorig

    Duotones are always going to be considered spot color channels.  So, when you print them on your desktop laser, the driver has difficulty converting the spot color channels to whatever the driver reads for output.  Even if you assign a Black and a yellow, those are not process colors, but spot color.  If your file is heading for offset printing, you have 2 options: option #1 = print a 2 color spot color job consisting of Spot Black and Spot yellow.  Option #2 = print a converted duotone to a CMYK image and print your average process color on press.  You have to decide.  Do I want a 2-color job or do I want a 4-color job?  If you add another spot color in Photoshop ( i.e., a tritone ), then you will have to decide on a 3-color job vs. a 4-color job.  I've done similar projects where I use Photoshop to create a duotone.  I then convert a copy of the duotone to CMYK and adjust the curves to get the look I want and still be able to print process color.  This sounds like it will work for you.

     
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  • Currently Being Moderated
    Feb 21, 2012 6:56 PM   in reply to generalbatzorig

    Photoshop creates 2 channels when you create a duotone.  Channel #1 = Black.  Channel #2 = Yellow.  These are probably spot process color channels.  Not process color, which is CMYK.  Now, I think you'd have to convert a copy of the duotone to CMYK, call it something like DUOc.  Name your duotone DUO.  What I would do, since you want to manipulate the entire process with these few must-have duotones, is copy the Black channel from your DUO ( duotone ) file and paste it into the Black channel of your DUOc ( process color file ).  Then, copy the Yellow channel form your DUO file and paste it into the Yellow channel of your CMYK DUOc file.  Delete ( but leave blank ) the M and C channels in your DUOc file.  You will then have a CMYK duotone that will fit into your existing CMYK file structure.  But, the important distinction here is that you cannot use a duotone in a CMYK file structure without adding 2 colors to the process color which will have an end result of a 6-color job.  This is why Photoshop creates just a 2-channel file in their duotone or a 3-channel file in their tritone.  Those color channels are considered spot color channels that are always interpreted as separate or additional colors in the process.  So, in your case, when the job is RIP'd, the additional duotone channels would output on their own, separate from the rest of the job.

     
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  • Currently Being Moderated
    Feb 26, 2012 8:42 AM   in reply to generalbatzorig

    Alternate method to convert a black and yellow duotone to CMYK with no copy/pasting:

     

    1. Set up your duotone as desired.

    2. Image > Mode > Multichannel. This gives you separate channels for your yellow and black.

    3. Add two blank channels. These can be alpha channels or spot channels, doesn't matter. Just make sure they are blank (filled entirelry with white).

    4. Move the two blank channels to the top of the list.

    5. Image > Mode > CMYK. When converting multichannel to CMYK Photoshop will assume the top channel to be cyan, the second to be magenta, the third yellow and the fourth black. (Five and up will remain as spot channels).

     

    This is what I would do. This way you're sending the printer CMYK files with no cyan or magenta data. These can be used alongside of the other full-color images in your layout without any futzing on the part of the printer's prepress folks.

     
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  • Currently Being Moderated
    Oct 31, 2012 9:29 AM   in reply to generalbatzorig

    As a graphic designer and prepress guy it sounds like your best option is to send it as CMYK and ask the prepress department to only run the three plates. From what I understand you are looking for only Y, M, K?  Another alternative and a cheap and dirty trick is to substitute your spot colors with a process color and avoid messing with channels. If the artwork isn't too complicated you can just recolor it for the proof and revert to the process colors for production. The print file will look strange but the final product should look alright.

     

    I use to mess around with dual tones and tri tones in .psd using channels to assign spot colors then saving a Photoshop DCS 2.O. You then link that to a .indd file (the preview always looked strange but once printed it was perfect) that was back a few versions ago perhaps the preview works now for a DCS file but I'm not sure if its the best route anymore. It worked great and the colors separated exactly how I wanted however its a lengthy process, difficult to edit and typically not worth the time. Usually there isn't a huge savings between 3-4 colors.

     

    If you are still trying to figure it out let me know and I can explain the process I would use.

     

    Good luck,

    Victor

    Graphic Designer

    http://www.earlepress.com

     
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