Dot Gain

[fredfish]

Hi

I run a Komori L28 4color press.
I have a question about Dot Gain / ISO since I've heard different opinions from prepress tech-guys and teachers in printing.

Let's say dot gain on Cyan 50% is 10%, so that it actually looks 60 % when sheet is printed.
My guess is that we should make a curve in prepress so that when the designer wants 50%, it should turn out to be 50 % right? That's what I've heard from a teacher, but a technician says that the Dot Gain should be set according to the ICC profile, and that the press shouldn't "print correct".

Help me out please..

 

[Lukas Engqvist]

Fred if you look at the ISO papers if you have 50% in application, that means a "theoretical" 50% on a FOGRA plate… wich means on a coated paper you should have ink coverage of 64% (for Cyan, Magenta and Yellow) on coated paper and about 70% on uncoated. For Black 50% you should have 67% on coated and 74% for uncoated.

It does sound strange, but it is because traditionally 50% in application was 50% on film/plate. Dotgain of 10% @50% on printed sheet will looked washed out in midtones compared with an ISO proof.

 

[gordo]

Let's say dot gain on Cyan 50% is 10%, so that it actually looks 60 % when sheet is printed.
My guess is that we should make a curve in prepress so that when the designer wants 50%, it should turn out to be 50 % right? That's what I've heard from a teacher, but a technician says that the Dot Gain should be set according to the ICC profile, and that the press shouldn't "print correct".

Maybe think of it a different way.
You have a choice of target tone reproduction for your presswork. You can either target an industry standard or you can create your own standard.
If you want to create your own standard for tone response in your presswork then you can certainly set your process up so that 50% in the file prints as 50% in the final presswork.

However if your target is an industry standard then you have to align to that.
That tone response is embodied in an ISO or other industry certified proof.

In both cases, the dot gain is not the target.
The target is the final tone response on press. The method is creating a tone reproduction that gives you whatever dot gain (or loss) needed to hit the desired tone reproduction target.

The press is printing "correct" when it is delivering the tone reproduction that you have targeted.

best, gordon p

 

[fredfish]

Yes, thanks both of you.

I want to get closer to the ISO Coated/Fogra 39 and uncoated Fogra29.
So I guess my press should be increasing the mid-tones, and not the other way.

Now we don't have a standard on the two different presses we use. They print quite different results.

Question: I use ISO-certified ink. Would you recommend compensating with curves in prepress so that 50% on plate prints 63% on CMY and 67% on Black (Coated), or is this stupid without measuring Lab-values? Remember, only I intend to get CLOSER to the standard, and not necessarily 100% match.

Thanks again

 

[Lukas Engqvist]

I think it sounds ok, but you may find you need to re-do it after you measure Lab values. Why not just measure Lab values and get your SID first, it will get you better results.

 

[Tech]

I have a different question but it's also related to dot gain...our vendor recommended that we adjust our grayscale images so highlight area falls around 2-3%. They claimed our images with highlights in 13-18% will print muddy on their wet press...even after we opened up mid-tone so we have lighter and contrast photos.

Now 2-3% is nearly white and it's usually considered clipped. Which doesn't make much sense to me why we need to go that far to prevent grayscale images from dot gain plug up. It sounds more like they want an easy way out so they aren't responsible for poor finished products. I may well be wrong but can someone enlighten me?

 

[Bloodsaler]

Actually your press conditon is ok not need a special compensation,but you may adjust a little according the gray balance result.

 

[lyzan]

@fredfish
So why not follow the process. Find out your best solid ink densities first, and then measure your dot gains. Then decide if you need to compensate them in the prepress. You may need to do this per paper type you used.

 

[Lukas Engqvist]

@Tech
What process of printing? I personally think white should be white and clipping of highlights to be a method to compensate for the many steps in film based workflows. I think a smooth transition from 10-0% is necessary to give a good appearance of any graphics that will fade to background, soft shadows etc. 15-18% is way higher than I would ever go for a "watermark" effect. To attain the CMYK mixes in the Pantone bridge you will need to be able to have a reliable 1% dot