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Brightening and sharpening for offset printing

Forum|Forum|3 years ago
August 22, 2022
7 replies
2174 views

Hi,

I prepared a book for offset printing by using Indesign, Acrobat and 'device gray' images.

The 1st run printed out fine. Now I plan to print a 2nd one at a different printery, so I ordered test pages and I asked the printer not to modify anything. I was curious to see how it will look 'by default'.

The test pages turned out not so sharp and also they are too dark. It's not awful, but it's not great either. This is probably due to the dot gain / TVI and the fact that I didn't apply any sharpening. But who knows, maybe it's the different equpment.

I think that the 1st printer modified the images in the doc by brightening and sharpening them. I think I can notice that. I also assume that the 1st printer used an Acrobat plugin for this, but I can also do it in Photoshop.

The question is: what kind of curve should I use now to brighten the images? Is it a rule of thumb for dot gain/TVI curve to be:

Input: 50 (centered)
Output: depends on the dot gain of the printing machine (10%, 20%, 30%...)

I've read somewhere that only the midtones should be affected. Then the material will look a bit 'washed out' and as such it will be printed to a plate (in this case it's a plate that must be processed), but during the printing on paper, this will be compensated and it will become darker - a complimentary curve will be applied by the machine. But how this curve looks in this particular machine, I don't know.

I will consult the printery, but it's small and inexpensive, they do not abide to any standard and they often improvize, they set things 'by eye' and so on (you get the picture).

Some people tell me to just brighten the images by using the ordinary brightness command, but I doubt that it will help. It's kind of weak.

I also don't know how much sharpening should I apply.

The Pitstop plugin in Acrobat offers actions such as: 'Apply -10% @ 50% dot gain curve to all separations' and 'Sharpen images using USM - Standard', so maybe this is what I need, but I'm not sure.

Thanks for your advices

Print

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Correct answer James Gifford—NitroPress

I would say this has more to do with choosing the right export profile than by modifying images that are suitable in the layout. If your printer isn't sophisticated enough to be able to tell you want profile and export characteristics to use (and I've dealt with these old-school "we'll tweak the press while it runs" guys), then you maybe should consider another printer or (here or elsewhere) get some very specific advice on your export settings.

But I wouldn't go in and tweak the images themselves just to sorta-kinda accommodate this printer.

—

S

sd5e8aAuthor

Inspiring

I received a notification in my email that this post has a correct answer, but it was a wrong one. The following answers seem to be correct:

If your printer isn't sophisticated enough to be able to tell you want profile and export characteristics to use (and I've dealt with these old-school "we'll tweak the press while it runs" guys), then you maybe should consider another printer

By @James Gifford—NitroPress

Are you sure the first printer didn't adjust the job on press? That's pretty common.

By @Dave Creamer of IDEAS

I agree that tweaking the images is probably a waste of time if the printer is going to make adjustments on press anyway.

By @Peter Spier

I don‘t think you can know that for sure.

By @rob day

You are all right. I cannot know for sure what the printers were doing, so guessing is futile. If they don't play by any rules and if they set things by the eye, then this is futile.

@rob day, assuming that I can find a more sophisticated printer in my area (and also an affordable one), would you be so kind to tell me how this should be set:

1. If the printer uses the profile "FOGRA XY":

- The color content should be converted to "FOGRA XY":

- The grayscale content should be converted to "Black Ink - FOGRA XY"

- The Output Intent of the PDF/X file should be set to "FOGRA XY"?

Is this correct?

2. I hope that I can do all the necesary conversions in Acrobat (without going back to Indesign), so please tell me:

Should I attach ICC profiles to the images in the PDF and then use the Color Converter to convert them to FOGRA XY?

But if I do this, the grayscales might become 4-color grays, so should I check the options: "Preserve Black," "Promote Gray to CMYK Black" and "Preserve CMYK Primaries"? Will this be the same as "Black Ink - FOGRA XY"?

I know that these questions are a bit offtopic, but in a way they are related to the original topic.

Thank you

S

sd5e8aAuthor

Inspiring

this has more to do with choosing the right export profile
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By @James Gifford—NitroPress

First I wanted to recreate the look of the 1st print by applying a curve, but it tuned out that its simple: I just went to Output Preview, I switched between profiles, the numbers changed and in some cases the images appeared brighter. What I got on my screen was very similar to the 1st print.

To put it simple, it seems that the content should have been treated with profile X, but the 1st printer messed up something and used Y instead. But I also have some more theories (later).

I liked the 1st print for it's brightness, but I liked it for creative reasons, not because its accurate. The 1st print misled me to believe that this kind of brightening is a normal feature of offset printing.

So the 2nd print is more accurate. Now I looked into it more carefuly (under a sunlight) and it seems closer to what I see on my screen. It is a bit dark, but whether this is objective or subjective, I don't know, cause my display is not idealy calibrated. But in any case, this is closer to the original.

I've dealt with these old-school "we'll tweak the press while it runs" guys
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By @James Gifford—NitroPress

Exactly, they do that, which might produce too pale or too dark prints. But the issue that we are discussing now doesn't seem to be related to that.

Hi @sd5e8a , InDesign manages the display of grayscale objects when Overprint Preview is turned on using the document’s CMYK profile—the grayscale is displayed as if it is on the CMYK black plate. Photoshop lets you profile a grayscale image using Black Ink profiles, which typically are more accurate than Dot Gain or Gamma profiles.

By @rob day

When I do that, the images appear brighter. This seems to be the same as if I'm viewing them in Output Preview with a CMYK profile on (which I described previously).

I can also get something like that if I convert from Gray to CMYK (black channel) with the Pitstop plugin for Acrobat (it offers actions such as: Clean up black, Gray to Real Gray or something like that, but I don't fully understand what is it for). Maybe the 1st printer applied something like this? That's another theory.

In any case, it is clear that the 1st printer changed something - by accident or not, I'm not sure, but this wasn't at the press. This led to brightening, which made the 1st print brighter than the 2nd one.

rob day

Community Expert

In any case, it is clear that the 1st printer changed something - by accident or not, I'm not sure, but this wasn't at the press. This led to brightening, which made the 1st print brighter than the 2nd one.

I don‘t think you can know that for sure.

When you place a grayscale in InDesign any embedded profiles are ignored and the Overprint/Separation soft proof preview is handled by the document’s CMYK (black) profile—the grayscale‘s output numbers are not changed, only the preview is affected by the assigned CMYK profile.

So if your document’s assigned CMYK profile is something like Coated FOGRA27, Overprint/Separation Preview will soft proof the gray values as they should print on the black plate of a press running to, or close to the FOGRA27 stndard:

If you send a file with the same gray values to printer B, and that printer’s press is running closer to the US Sheetfed Coated profile, the same gray values are going to print considerably darker in the mid-tones. The only difference here is I have assigned US Sheetfed Coated to the document—the soft proof is darker, but the output values are unchanged. which is what’s going to happen when there is more dot gain on press.

Also note that the Grayscale has an embedded Gray profile—Black Ink ISO Coated v2 300%—InDesign ignores embedded gray profiles and uses the document’s CMYK Black Ink profile instead

rob day

Community Expert

Hi @sd5e8a , InDesign manages the display of grayscale objects when Overprint Preview is turned on using the document’s CMYK profile—the grayscale is displayed as if it is on the CMYK black plate. Photoshop lets you profile a grayscale image using Black Ink profiles, which typically are more accurate than Dot Gain or Gamma profiles. More on setting up Black Ink profiles here:

https://community.adobe.com/t5/indesign-discussions/greyscale-jpegs-or-psd-images-are-going-much-darker-when-dropped-in-on-indesign/m-p/11152264

https://community.adobe.com/t5/indesign-discussions/exporting-rgb-cmyk-and-grayscale-to-print-pdf/m-p/10990825#M179498

Robert at ID-Tasker

Legend

Grayscale pictures should be - to get best results - printed using dedicated Pantone or full CMYK with a bit of CMY - to highlight details and make them deep / rich. Otherwise you'll get old-newspaper quality 😉

Peter Spier

Community Expert

I suspect the reason for going grayscale is the cost ...

And I agree that tweaking the images is probably a waste of time if the printer is going to make adjustments on press anyway.

That said, twenty years ago before we all used a color-managed workflow I learned from the old guys at the newspaper to adjust the midtones on grayscale images so they looked just a little "milky" on screen.

Peter Spier

Community Expert

I should add that now, with a calibrated monitor, I work to a dot gain 20% profile as the default condition and adjust the tones to look good.

Jumpenjax

Community Expert

I agree with James, your printer should be able to tell you the setting that will give you the best quality. Once it is set save the pdf specs under the printer name. So, if you have to print again or make changes, when you go to save as pdf you just have to choose the printer.

Lee- Graphic Designer, Print Specialist, Photographer

Dave Creamer of IDEAS

Community Expert

Are you sure the first printer didn't adjust the job on press? That's pretty common. Maybe the second printer just ran it as is and didn't make any adjustments one would make on a longer run.

David Creamer: Community Expert (ACI and ACE 1995-2023)

James Gifford—NitroPressCorrect answer

Legend

I would say this has more to do with choosing the right export profile than by modifying images that are suitable in the layout. If your printer isn't sophisticated enough to be able to tell you want profile and export characteristics to use (and I've dealt with these old-school "we'll tweak the press while it runs" guys), then you maybe should consider another printer or (here or elsewhere) get some very specific advice on your export settings.

But I wouldn't go in and tweak the images themselves just to sorta-kinda accommodate this printer.

—

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