CMYK to Duotone "best practice" steps?

[stedders]

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.

 

[Stephen Marsh]

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

 

[DCurry]

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.

 

[Stephen Marsh]

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

 

[DCurry]

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.

 

[Stephen Marsh]

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

 

[DCurry]

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?

 

[buckeye]

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.

 

[stedders]

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.

 

[gordo]

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

best, gordo

 

[Stephen Marsh]

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?

Hi Dan, the *convert to profile* option will let you select "custom CMYK" and one can make on the fly changes to the parameters, without having to actually change your CMYK working space in color settings. This is not to be confused with *image/mode/CMYK* which does use your CMYK color settings and is not an "on the fly" operation.

The CMYK image/profile to CMYK image/profile conversion will naturally use the profile PCS (Lab), which is not the same thing as actually converting the CMYK image to RGB/LAB and then converting to CMYK. This extra mode change to an intermediate mode is not really needed, unless one wishes to perform intermediate edits.

So CMYK -> CMYK is technically better than CMYK -> RGB/LAB -> CMYK. Of course, if one does go to RGB/LAB one has the option to make edits to tone and colour in that intermediate space before converting to CMYK.


Stephen Marsh

 

[DCurry]

Cool - never did it that way before. Thanks!

 

[buckeye]

Dan, thanks for asking the question of how to convert CMYK to CMYK, and thank you Stephen for providing us the quicker way. I obviously never did it that way either, but will from here on out.

Erik

 

[buckeye]

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

best, gordo

stedders,

Many ways to skin a cat in this instance but Gordo's way is far and away the simplest. To further what he suggested, after deleting the cyan and magenta channel, double click the yellow channel and change it to the spot color of your choice and you'll have what I would consider, an output/print friendly file that wouldn't need any remapping or omitting of any colors.

Erik

 

[Stephen Marsh]

Erik, I agree, many ways to skin a cat, which is what this topic thread is all about! The OP was after some "best practice" tips, which means that this issue should be looked at from all sides, not just the current image in question. What works well for one image will not always work well for another.

We only have a small RGB screen capture of what appears to be a part of the image - is there more image that is not visible that may be very different from the area in the screen capture? Additionally, what is the actual CMYK channel data like?

What type of GCR has been used in this image, in what channels has the detail be placed? As the image detail is green, one can assume that there may be critical detail in the magenta and black channels. It is hard to know from the screen capture, what we can see appears to be a simple graphic with hardly any detail, however is there more image that is not visible and would this change the evaluation and conversion process? Re-separating to a Max GCR conversion would place most of the detail in the K channel, if it was not there originally. This would also simplify the GCR issue and colour would only be where colour was needed - rather than creating grey component data.

So once one have the K channel all sorted, the green channel needs to be created from the C/Y channels. For most natural green colours such as foliage, the Y channel will usually be stronger than the C channel, so the Y channel may be a good place to start. For a simple graphic, this may be all one requires with minor edits. That being said, the Y channel may often have less detail than the C channel (if this is important for the image at hand) and the Y channel can often show major JPEG compression artefacts. Sometimes one has to use the Y and use apply image to blend in the C data, or vice versa (using different blend modes, opacity, inversion, a channel as a mask etc). Sometimes channel mixer may get one there, combining the data from the CY channels. Sometimes one may wish to add in some detail from the MK channels to the CY when making a spot green. Sometimes one may get the channel data from an RGB or the a*b* channels of a Lab mode conversion if that provides better data for the final spot colour channels. One last point is that sometimes one may have to build in some trapping/fit into such graphics.

Sometimes the image at hand lends itself to a "simple" conversion method, other times an image requires one to use "complex" methods.


Stephen Marsh

 

[buckeye]

Stephen,

Agreed 100%. I understand completely the complex methods you speak of and that no one method can be used for all files - was just trying to keep it simple for the OP.

Erik

 

[stedders]

I just wanted to pass on my thanks to everyone for contributing to this thread.

I have certainly had more than my "money's worth".

This was an old job that I worked on a few weeks back, that I felt could have gone better – and it's my new year's resolution to make a note of such things and "revisit" jobs to see where improvements could have been made.

I particularly appreciated Erik's point about creating the "Maximum Black" – that was certainly not something I had used before, and I can think of a number of areas where this could come in useful.

Many thanks to everyone for contributing. All the points have been relevant and well made and – by me at least – much appreciated.

Thanks.