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I read that answers at this question: Preparing design for duotone printing?

I need it to be more specific about the step: use the complementary RGB channel, in this case Red (E) Play with the contrast.

Where can I find the compl. RGB channel while working in grayscale? Also, in which way do I combine these two layers?

The result is fantastic and I wish to make it myself!

  • I almost rewrite entirely the other post so it is more clear the concept behind duotones. For the specific process on Photoshop, these answers are fine. More examples added! – Rafael Oct 19 '18 at 22:36
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I guess the answer is talking about the complementary color of the image main color: cyan, which is red, the opposite.

The step by step is:

  1. Search the complementary channel (at the gif example is the Green Channel)
  2. Duplicate it and rename it (COMPLEMENTARY)
  3. Invert it
  4. Set the image to grayscale
  5. Set the image back to RGB
  6. Load the COMPLEMENTARY channel selection
  7. Create a Color Fill Layer with the ink content
  8. Change the blend mode to Multiply

Animation

This gif follows the step by step of the answer included in the question. It is not the right method for a two-ink printing, it's only the creation of a RGB image in duotone such as the explanation. This other answer shows more details about how to make a Photoshop Duotone.

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    Curious why RGB mode is used when the goal is offset printing? Had the same curiosity about Rafael's answer in the linked question. If you work in RGB to do this it inevitably gets converted to CMYK, not 2 color (duotone). – Scott Oct 18 '18 at 20:50
  • @Scott I was writing (and translating) the clarification to insert in the answer. It's a wrong answer for me too. – Danielillo Oct 18 '18 at 20:53
  • Dear Scott and dear Danielillo wow! thank you so much, very helpful. I thought that by exporting a file as duotone I could print only two colours and save money at the printing step of an edition. What about digital printing? Is it OK to print duotone? – Christos Oct 19 '18 at 8:56
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    ΟΚ! In Greece, every plate is charged so less plates less cost, but I'm gonna talk to my printer. Thanks again, so much! – Christos Oct 19 '18 at 9:24
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    @Danielillo, that is only the case for offset printers who focus primarily on CMYK printing. For small print shops that have 2-color presses, this method is far cheaper than full CMYK process printing, and has saved my clients a lot on production costs over the years. – 13ruce Oct 19 '18 at 19:27
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I'm not one to use RGB color more for Offset printing, and especially for duotones. If you work on RGB to create the perfect duotone, well.. that image will need to be converted to CMYK for printing. When it's converted, your (visual) 2 colors gets split across the CMYK channels and it's no longer a duotone technically. It may still look like 2 colors, but it's a 4 color image, not 2 color.

There are options for real duotones....


1 Standard Duotone

Start with a greyscale image:

enter image description here

Choose Image > Mode > Duotone. This allows you to pick a second color:

enter image description here

If you want to adjust the amount of color you can alter the Duotone Curve for either color:

enter image description here

This creates a real duotone. Save as DCS 2.0 (or PSD) and place in a layout application.

enter image description here


2 Duotone with different pixel data per color

if you want different pixel data in a two-color image (still a duotone)...

Start with the same Greyscale image;

enter image description here

Convert the image to CMYK - Image > Mode >CMYK . Look at the Channels Panel and highlight the channel with the most contrast (often the Y channel). Select all and Edit > Copy. Then highlight the K channel and Edit > Paste. Now fill the C, M, and Y channels with 100% white, so they are "empty".

enter image description here

You may then need to highlight the K channel and adjust Levels/Curves to bring the contrast back to normal:

enter image description here

Now, from the Channels Panel, choose New Spot Channel and pick your color:

enter image description here

Then, if you want you can copy the K channel and paste it on the Spot Color channel:

enter image description here

And any changes you make to either channel with alter that color specifically rather than the entire image:

enter image description here

(Leave the blank CMY channels there.)

Save as DCS2.0 (or PSD) for placement in a Layout Application.

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