How to find pixel with highest ink total in C+M+Y+K = highest in image

[aymanzone]

hi Guys,

Anyone know if there Is there's a way to find highest ink total (C+M+Y+K=? highest) for a pixel in a CMYK image in Affinity Photo? Perhaps there is a graph too?

Context: my image is in Fogra39, I'm using Affinity Photo. I'm newbie  in CMYK.

Why would I want look for highest ink total? To prevent ink blots (I think)

I've noticed that standard black can have lower ink total than very light colors... wow!

see total ink in imgur for proof https://i.imgur.com/VZ3iTrr.png
Total ink for black (1) is CMYK = 0+0+0+99 = 99%
Total ink for light color (2) IS CMYK = 63+34+0+37 =130%

I think some factories prefer to have 250% or 280% maximum, it depends.

I'm familiar with standard black and rich black but I'm asking about total ink.
If you don't know what standard black vs rich black, check out this nice link: https://printninja.com/printing-resource-center/printninja-file-setup-checklist/offset-printing-guidelines/offset-color-requirements/standard-black-vs-rich-black

Hope I'm not spamming forums, thanks for reading this. I had a different topic post earlier and had a lot of very informative replies.

Thanks.

Edited October 6, 2020 by aymanzone

[thomaso]

A good thing first: In a CMYK document the color profile always contains a limitation of the total ink, which varies with the profile. For instance your Fogra39 has a limit of max. 330 %. So you can limit the TAC (Total Amount of Color = Total Area Coverage) by an according profile, which usually is related to the specific print process, machine and provider. You can compare in this list of a print service the TAC of a few profiles: https://www.printall.ee/for-designer/color-profiles/

Unfortunately I don't know a simply (1-click) way to determine the total ink of an entire Affinity document. Though APhoto offers in its Develop mode to visually mark clipped highlights, shadows and tones this option requires RGB (to enable Develop mode) and therefore wouldn't help to inspect a CMYK document, e.g. it would convert your 99% K spot (1) into a mixture of R+G+B.

An external alternative could be e.g. Acrobat which marks the total ink of an entire image (or document's page with various objects) as preview for a certain profile + a custom TAC. For your screenshot (RGB) it gives, with Fogra39 selected, values which don't correspond to your Affinity document (CMYK), for instance its 99 % K spot shows a mix of RGB. So these two screenshots show the principle only but don't correspond with your Affinity document:

 

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[thomaso]

8 hours ago, Lagarto said:

You can use total ink picker of the Info panel in Photo (...) This way you can ensure that there are no areas with more ink than recommended

Lagarto, the screenshot linked in the OP's initial post illustrates their awareness of this picker info feature.

The point seems to be that manually picking is required to detect possible culprit areas. So, to really ensure the required TAC, currently AP doesn't offer an accordingly automatic function, self-checking the entire image area + informing the user about its result.

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[aymanzone]

 

hi @thomaso

Are you using a special tool in Adobe to get this information? And why is total ink for entire document useful? I thought it's for for pixel, to make sure there is no blotting.

 

hi @Lagarto

5 hours ago, Lagarto said:

As the OPs profile is Coated Fogra 39 they really just need to pay attention to very dark areas.

So I don't have to worry about total ink causing blotting unless it's black color?

 

I seem to be asking too many questions. Sorry guys. I thought I discovered something unique. kk. Thank you.

[thomaso]

1 hour ago, aymanzone said:

Are you using a special tool in Adobe to get this information? And why is total ink for entire document useful? I thought it's for for pixel, to make sure there is no blotting.

In my screenshots the window aside the document is a feature of the Pro version, nothing really special but possibly not included in the free Reader version.

The total ink measured above for the entire document just makes it easier to check the TAC because you don't need to place the pickers at various single spots to detect the max. color. Above the exceeding TAC is shown (~reported) with the pink colored areas. Note in this sample have set the limit for the TAC manually to 280 %, though FOGRA39 allows 330 %.

The TAC in offset printing isn't meant to avoid 'blotting' but rather to prevent increased drying time for the printed sheet + to prevent wet ink * from sticking on the next sheet which gets placed by the machine on the recent, fresh print. Also exceeding the TAC may cause that the ink isn't stable fixed on the paper and can stick that way on a reader's fingers.
* Ink for offset print isn't liquid but has rather the consistency of butter at room temperature.
(sorry, my English must sound quite cumbersome because of a lack of correct terms)

When you assign (or convert to) a profile than its TAC gets applied. So, if you know the TAC of the profile you also know it for the document. In case of your used FOGRA39 the TAC is 330%. That doesn't neither mean the darkest colors nor any other color has 330 %, it just says that there is no spot above this value, because the TAC names a maximum only.

The absolute possible maximum is 400 %, made of 100 % for each of the 4 print channels (the inks C + M + Y + K). You can create a very dark gray either with CMY + a little K (black) or with 100 % K and no or a little of CMY. That way your blue picker spot can show a higher TAC than your gray spot: While the blue possibly got defined as 100 % C + some K it can result in a TAC above 100, whereas your gray spot may be defined with 98 % K only (–> TAC = 98). Because C, M, Y and K have different brightness their visual appearance may give you the impression that a bright, vivid 100 % Yellow for instance would have a TAC smaller than a gray made of 80 % K – but in fact the yellow prints more ink, though it appears lighter than the gray.

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[aymanzone]

hi @thomaso

I wasn't aware that TAC does all of this, I was just thinking of blotting. This is quite informative and helps in imagining the process. Thank you, I feel more wiser now. 

[aymanzone]

hi @Lagarto

Thanks for the tip on using the histogram. Tried the histogram with the Marque option and it did help a bit. I modified the CMYK image. Whenever possible, it's more safer to try to get away with modifying the  RGB image pre-conversion instead of modifying the converted CMYK image. Your diagrams were quit insightul.

There are other competitors for Adobe tool that @thomaso used that can do same thing for preflight but they cost more. Or les, depending if you want to do a one time purchase

https://www.enfocus.com/en/pitstop-pro

and

https://markzware.com/products/flightcheck/

are few that stood out.

I was never as aware of TAC as I should be, before conversation

Thank you @thomaso and @Lagarto

 

 

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[aymanzone]

Nice, thank you @Lagarto