Converting duotone to CMYK for print

[Guest]

I have a full colour RGB image of an explosion of mulitple paint colours on a black background. I want to change the explosion of colours to our brand teal green colour, with the background C 0%, M 0%, Y 0%, B 100%.

I have converted the RGB image to greyscale and then to duotone. Then set up my two inks. A 100% black and a CMYK teal green colour.

The image will be professionally printed. To avoid any problems with the duotone I want to convert it to CMYK. But when I do this, the black background becomes C 91%, M 79%, Y 62%, B 97%.

This is way too much ink density.

I was hoping that the the black would simply stay C 0, M 0, Y 0, B 100%.  i.e. overprint / knockout the teal green that is 'behind' it. Instead the two inks (the black and teal green) and combining, making the black unprintable.

1. Any idea how I convert the duotone to CMYK without the black ink density becoming unprintable?

2. Or how I change the colours in the explosion to our brand colour (without using a duotone) and the rgb background to a solid CMYK (100%K) black

Thank you

ps. I've tried converting the RGB image to greyscale and then importing it into InDesign and then changing the background colour to our brand teal green. This works, but it doesn't look at good as the duotone.

[c.pfaffenbichler]

1. Any idea how I convert the duotone to CMYK without the black ink density becoming unprintable?

You could use max GCR but you are probably better off doing the separation manually.

Please post meaningful screenshots including all pertinent Panels and dialogs of the duotone- and the RGB-image.

[Test Screen Name]

Which CMYK profile are you using? The ink density limits come from that.

[Guest]

I don't know what CMYK profile I'm using. But I do know that a printer won't want to print large, solid, background colour of:

C 91%, M 79%, Y 62%, B 97%

[c.pfaffenbichler]

But I do know that a printer won't want to print large, solid, background colour of:

C 91%, M 79%, Y 62%, B 97%

A TAC of 329% hardly seems a problem for sheetfed offset printing.

I don't know what CMYK profile I'm using.

What are the Edit > Colour Settings?

Please read up on Color Management.

Set up color management

COLOR MANAGEMENT PHOTOSHOP CC CS6 Basic ColorManagement Theory ICC Profiles Color Spaces Calibrated ...

[Guest]

A TAC of 329% hardly seems a problem for sheetfed offset printing.

Oh, okay. Yes this website supports that (Total ink or area coverage | What is TIC and how to check it ).

The image will be going on a number of different materials, including digital printing for business cards and digital printing for a large banner. Do you think the TAC/TIC of 329% will be a problem for this?

Thank you

[c.pfaffenbichler]

Do you think the TAC/TIC of 329% will be a problem for this?

That may well be, but you should clear the CMYK Colour Space with the printers beforehand.

For digital and banners you should be fine with »C 100%, M 0, Y 45%, K 40%« but some media may require some adaption.

Limiting the TAC certainly is no bad idea in principle, I usually go for something like 50/40/40/100 – and a pure 0/0/0/100-black might end up paler than necessary.

But (more problems) a 4C CMYK might be problematic with small white texts if the registration varies too much.

You may have seen ads in newspapers where, due to the »poor« registration, small white texts’ legibility suffered on images or colourful backgrounds.

Is the green intended to be flat or should it feature brighter highlights?

You could (more or less) simulate the duotone result by

• pasting the grayscale image in every Channel of a CMYK image and using a Curves Layer corresponding to the settings in the Duotone dialog and a Solid Colour Layer set to Screen for each Color

• and multiplying those. 

• Then you could knock out the »background« with whichever color (pure  black or a 4C black) you decide on.

[Guest]

Original full colour RGB image.

Duotone image

I need the black background to be C 0, M 0, Y 0, K 100%

And the explosion to be our brand green C 100%, M 0, Y 45%, K 40%

But when I convert from duotone to CMYK the black background ends up as C 91%, M 79%, Y 62%, B 97%

which no printer will want to print cos' there is too much ink.

[c.pfaffenbichler]

I asked for meaningful screenshots and the TAC seems unproblematic unless you have specific, conflicting information about the actual print process that you have not divulged. 

[c.pfaffenbichler]

I recommend you do the separation manually in a CMYK file but the trapping might be a slight issue.

Is the green intended to be flat or should it feature brighter highlights?

[Test Screen Name]

If you don't know what CMYK profile you're using you have a problem. You need to use one designed for your press conditions. CMYK isn't a generic thing.

[c.pfaffenbichler]

Test Screen Name makes a valid point.

While the pure »green« might appear similar in several print processes (at least while one does not actually hold one product directly up against another) the different gains may affect the appearance of the image’s brightness differently and thus affect the overall impression.

[Guest]

Wow thank you for your help. This is well outside my comfort zone and I don't understand how to do your suggestions.

Could I simply create a CMYK file and two layers. The bottom layer would be solid teal green C100, M0, Y45 K40. I would then paste into the top layer the greyscale image. Then remove all the CMY from this layer (using Curves??).

Then set the blending mode for the top layer to be Multiply. Then flatten the image. The background colour is now (as expected) C100 M0 Y45 K100. A combined TIC of 245%. Considerably less than the previous 329% and therefore much more likely to print and dry okay?

[c.pfaffenbichler]

Could I simply create a CMYK file and two layers. The bottom layer would be solid teal green C100, M0, Y45 K40. I would then paste into the top layer the greyscale image. Then remove all the CMY from this layer (using Curves??).

That might, depending on your CMYK Working Space, leave a somewhat »skeletal« black.

You could select the CMYK layer’s black Channel in the Channels Panel and paste the copied grayscale image into that.

Then you can use a Curves Layer Clipping Masked to that Layer to edit the contrast if necessary.

The background colour is now (as expected) C100 M0 Y45 K100. A combined TIC of 245%. Considerably less than the previous 329% and therefore much more likely to print and dry okay?

But this may result in a greenish black, so you could add a 50/40/40/100-Solid Colour Layer and use the grayscale image as the basis for a Layer Mask that limits its effect to the darkest areas.

Mind you: All this is »old-time« technique that circumvents proper Colour Management and can lead to problems of its own.

Ideally you should have the image proofed, in any case you should check out the Channels to see if any noticeable break-offs or banding occur.

[Guest]

I think what I'm going to do is:

Convert the image to greyscale and then duotone. Save as a .PSD file. Use in InDesign and then save as a PDF converting the colours to CMYK (FOGR39). This will convert the extra "spot" colour 'teal green' in the duotone image to CMYK.

Send to printers, ask to see a proof and hope that the registration is fine and that the 329% TIC isn't a problem.

How does this sound?

[c.pfaffenbichler]

This might be a bit of a problem if you really want to achieve the specific CMYK values for the pure green you mentioned.

[Guest]

I've been playing around with this and one of your suggestions:

Convert the image to greyscale.

increase the contrast.

Make a new CMYK file.

Import the greyscale image into the black Channel in the Channels Panel

Make a new layer.

Move layer to below the 'greyscale' image.

Make the layer solid teal green C100 M0 Y45 K40.

Set the top layer blending mode to Multiply.

Then flatten the image.

The background "black" colour is now (as expected) C100 M0 Y45 K100. A combined TIC of 245%. Considerably less than the previous 329% and therefore much more likely to print and dry okay.

From print outs on my office laser printer the "black" background is a nice solid black. And not too green.

And our brand teal green stays the correct CMYK colour.

What do you think?

Thank you for all your help

[JJLAPIN]

The Black in this file will print fine in all the mediums you listed.

[c.pfaffenbichler]

The image seems to show traces of previous editing:

[Guest]

I've just had a quick look. I think that is the only example of something odd. I bought the image from Adobe Stock, so I'd be upset if there were more issues with the image

[JJLAPIN]

The image I played with came from a Google search and then I manipulated it. Simple airbrush will clean that up. Made it a little more teal also.