CMYK to CMYK conversions? Best Plug-In? Best way to lower TAC?

[Gregg]

What do you feel is the best way to lower the TAC of a CMYK image while maintaining all layers and adjustment layers? For arguments sake, let's say you are unable to lower the TAC with a selective color adjustment, or any other adjustment. How would you go about doing it?

Are there plug-ins that allow CMYK - CMYK conversions?

I often go CMYK–LAB–CMYK to achieve this, but the end result is a flattened file.

Thanks in advance for any feedback.

 

[gordo]

Would converting to a profile that had a different TAC do this? (PShop--->Convert to profile)?

gordo

 

[Gregg]

Hi, Gordo. Yes, that seems to work. For some reason I thought you could not go CMYK-CMYK in Photoshop (without a plug-in). I even went back to CS2, thinking it was older versions that didn't allow it, and it worked in CS2 as well.

Thanks.

 

[Stephen Marsh]

Was it CS4 or CS5 that introduced a DeviceLink conversion option in the advanced view of convert to profile (I know it is in CS5)?

For many, the issue is not that a later version of Photoshop can't perform a DVL conversion (it can), it is that they don't have a devicelink profile in the first place. These are not usually freely distributed and are created as part of paid colour service for those that don't have the ability to make such a profile.

The problem with a regular profile is that solid primary and secondary overprints and black channel data will be lost as the Profile Connection Space (usually L*a*b*) will be used in the transform.

A devicelink can be created so that the K channel and solid primary colours are not affected, there is no PCS and the transform is a true CMYK to CMYK move.


Stephen Marsh

 

[Stephen Marsh]

Hi, Gordo. Yes, that seems to work. For some reason I thought you could not go CMYK-CMYK in Photoshop (without a plug-in). I even went back to CS2, thinking it was older versions that didn't allow it, and it worked in CS2 as well.

Thanks.

If you don't have a suitable DVL and must use a regular ICC to reduce TAC/TIL - then I would only apply the ICC conversion to the deep shadows that are over the ink limit (rather than hosing the entire file's colour builds when all you really need is a total ink reduction).

VIGC offer a great range of ISO profiles at different ink limits which can be very useful for this task:

http://www.vigc.org/vigc-max-tac-icc-profielen/download-vigc-max-tac-icc-profiles/

These profiles are huge in file size, so don't embed them into the Photoshop file, just assign a regular F39/ISO Coated profile after converting to the VIGC ISO Coated version using a lower total ink coverage.


Stephen Marsh

 

[Gregg]

Thanks, Stephen. I'll check out those profiles.

 

[Tommyjt]

I agree with Stephen that you should be using a Device Link Profile for the conversions for the reasons he stated.
The other thing that I would do is create a smart object from your original layers, then convert.
This is a non-destructive method that will keep all your layers intact for future editing and allow you to convert to any TAC (or color mode) you want any time you want.

Tom

 

[rich apollo]

If you don't have a suitable DVL and must use a regular ICC to reduce TAC/TIL - then I would only apply the ICC conversion to the deep shadows that are over the ink limit (rather than hosing the entire file's colour builds when all you really need is a total ink reduction).

How are you going to do that, Stephen? An ICC color transform on an image is kind of all or nothing, isn't it?

These profiles are huge in file size, so don't embed them into the Photoshop file, just assign a regular F39/ISO Coated profile after converting to the VIGC ISO Coated version using a lower total ink coverage.

But, the assigned profile is not representative of the colorspace of the file.

 

[Stephen Marsh]

How are you going to do that, Stephen? An ICC color transform on an image is kind of all or nothing, isn't it?

Hi Rich, you are correct - however Photoshop gives the end user many flexible options. I was thinking of making an action to pin to this topic (and probably still will), however it is easy enough to explain the broad steps in text form...

1. Create a new layer, move it to the top of the layer stack.
2. Stamp all visible data as a merged copy into this new layer.
3. Copy layer data to clipboard, create a new temp document.
4. Paste data in to new temp doc, convert to the profile that reduces total ink.
5. Copy data to clipboard, close down the temp doc without saving.
6. Paste the converted data into the new top layer, preserving colour numbers/values (perhaps purge clipboard data).
7. Use layer option blend-if sliders and or a layer mask to limit the contribution of this layer to only the darkest areas of the image (probably also including some three quarter tone transitions for safety).

Of course, if any of the underlying layers change, you would have to run the action again.

There is no real need to convert the whole document's colour builds to a different CMYK recipe, when all that is required is the reduction of total ink (throwing the baby out with the bath water and all that). I have compared making masked edits to reduce total ink, however the results have never been as good as when using a profile conversion.

But, the assigned profile is not representative of the colorspace of the file.

Sure it is still representative, it is still the same colorimetric description, just a different profile created from the same characterisation data. As long as the two different profiles are created from the same measurement data, for all intents and purposes the colour is exactly the same. It does not matter that the ink reduced image was converted to the "ISO Coated VIGC 260" profile, and that the assigned profile was "Fogra 39 320", the L*a*b* values of the pixels all remain the same (sometimes for some colours, there may be an acceptable +/- 1 Lab value shift). A conversion out of CMYK will still provide exactly the same conversion, it does not matter than one profile is ISO Coated 320% and the other profile is ISO Coated 280%, or Fogra 39 300% etc.

Why embed a 30mb VIGC profile into a 2mb image, when one can embed a 2mb profile that describes exactly the same colorimetric intent? Depending on the workflow, one may not even wish to tag a profile to the image at all.


Stephen Marsh

 

[Gregg]

I grabbed those VIGC profiles that you mentioned, Stephen. I am struggling with the Device Link option in Photoshop though. I can convert to one of the VIGC profiles, for example ISOcoated_VIGC_39L_300_v2.icc. However, I cannot make use of the Device Link option. The only option I have is Total Ink Preview, which when applied to a test image of 100/100/100/100, results in 0/0/0/100.

I did some googling and watched some YouTube vids. Do you need a Plug-In from VIGC to access the Device Link options?

Somewhat lost here.

 

[Stephen Marsh]

The VIGC profiles are not devicelink icc profiles, they are just standard device icc profiles (they still use a L*a*b* PCS and are not a direct connection between two CMYK spaces).

The reason that I mentioned those profiles is that they do have a range of various total ink limits. The only other ISO profiles that are around the net have 340-320% and 300% total ink.

If you don't have a CMYK to CMYK devicelink profile installed on your system, then Photoshop can't do anything with the devicelink conversion option.

I'll see if I can put that action together today... What is the exact tagged profile or assumed working space profile names of the condition that has too much ink? Which profile are you converting to in order to lower the total ink?


Stephen Marsh

 

[Gregg]

I see. I knew I was missing something.

There are a couple of profiles we work with. The only standard one is U.S. Web Coated SWOP v2, the others are profiles provided by our domestic or Asian partners (which is a modified F39 with 300 TAC).

When converting I will go from the current working space (e.g. SWOP v2), then convert to Lab, then back to SWOP v2.

This method is not used all of the time. It's only when I am unable to lower TAC successfully through various methods in Photoshop.

I've been using this method for many years, and if memory serves me correctly, it was when you could not convert CMYK to CMYK, but I have no idea what version of Photoshop introduced that functionality.

 

[Stephen Marsh]

As your destination is SWOP 300%, you probably would not wish to use those VIGC profiles as the destination as they are intended for ISO coated and uncoated conditions (one might be able to get away with using them for GRACoL though).

When converting out of the source CMYK to the destination CMYK profile, you really need to know what profile describes the current CMYK image (do you trust the embedded profile, and if there is no profile then assign what you think is the correct description).

There is probably no advantage or need to go from CMYK to Lab to CMYK, when you just go "direct" from CMYK to CMYK (through the PCS of course).

The profile that you are converting to seems to be a no brainer (SWOP v2).

I personally have tried many methods of lowering total ink that was too high. Methods that directly adjust the darkest areas of the image in theory are the best, however in practice I have never been happy with the transitions from three quarter tones to deep shadows. Of course, it really depends on the image content and what works well for one image may not work so well for another.

I have had better success with profile conversions, however these also have issues to. One is re-separating the entire image's colour builds (which may no longer match vector colour builds for example). One really only wishes to lower the total ink, not re-separate the entire images full range of colours and tones. By converting a dupe of the original to the required profile to lower total ink, one can then mask in the darker tones and transitional areas so that other colours and tones are not adversely altered.


Stephen Marsh

 

[rich apollo]

I have had better success with profile conversions, however these also have issues to. One is re-separating the entire image's colour builds (which may no longer match vector colour builds for example).

That's EXACTLY why I'm a fan of PDF color management.

 

[Stephen Marsh]

Gregg, I forgot to ask - what type of printing do you do?

Are you really sending work to a web press in US magazine printing conditions, where SWOP rules?

Or are you really a flat sheet offset printer, where GRACoL would probably be a better description of your work - however you wish to have a lower total ink than the GRACoL profile, which is why you have elected to use SWOP as it has a 300% limit?


Stephen Marsh

 

[Gregg]

Gregg, I forgot to ask - what type of printing do you do?

Are you really sending work to a web press in US magazine printing conditions, where SWOP rules?

Or are you really a flat sheet offset printer, where GRACoL would probably be a better description of your work - however you wish to have a lower total ink than the GRACoL profile, which is why you have elected to use SWOP as it has a 300% limit?


Stephen Marsh

Hi, Stephen. We are using SWOP (for our titles printed in the States), mainly because of it's 300% limit. What I'd like to find a solution for is when a CMYK file in SWOP is pushed passed 300%. This is when I have used the CMYK-LAB-CMYK method. Sometimes I can achieve good results with a selective color adjustment, but not always. I tried your suggested method in one of your earlier posts, that worked quite well. For the situation i described, is there any Device Link solution?

 

[Stephen Marsh]

Hi, Stephen. We are using SWOP (for our titles printed in the States), mainly because of it's 300% limit. What I'd like to find a solution for is when a CMYK file in SWOP is pushed passed 300%. This is when I have used the CMYK-LAB-CMYK method. Sometimes I can achieve good results with a selective color adjustment, but not always. I tried your suggested method in one of your earlier posts, that worked quite well. For the situation i described, is there any Device Link solution?

What would be best is to use a GRACoL profile with a 300% total ink limit, a bit like ISO Coated v2 that also has a 300% version (if the files are prepared for GRACoL and you are printing closer to GRACoL than SWOP). For files prepared for SWOP that are over 300%, you can simply convert to Lab/RGB then back to SWOP.

There are of course DeviceLink solutions available, for pay. For free, that is a bit harder… Download the demo of the Heidelberg Prinect PDF Toolbox 2013 and look for the CmykMaxDot??? devicelinks.


Stephen Marsh