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(Completely rewritten version.)

I'm a writer doing a book for an overseas publisher. My deliverables for them are .doc files for the text and .png files for the graphics. I have no control over print production processes.

The publisher tells me that my .png files are "too light" and will cause problems during printing. (I've been told this doesn't make sense; nothing I can do about that.) They've asked me to do darker versions. Since these are screen captures of web applications, the only way to make them darker is to edit the files. I've tried editing them using the Brightness/Contrast tool in GIMP, but this introduces weird color distortions. There's presumably some simple adjustment that will make these images look darker, but I lack the expertise to find it.

Simple example:

it's too light!!!

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I voted to close because this isn't anything you're doing. It should print, thats what printers do. If its not printing then its an issue on the vendors end and this question won't help anyone else because of that. I'd also add that their "production person" should be able to darken it if they so require it to be darker and help you with that. –  Ryan Jun 13 '13 at 2:11
2  
Can you define (or have production define) what "bleed on printing" means? As it is, it makes no sense. –  Scott Jun 13 '13 at 2:42
    
@Ryan Can you take another look at my rewritten question? Please note that I'm dealing with a publisher not a printer. –  Isaac Rabinovitch Jun 13 '13 at 5:08
    
I have to disagree with the close vote. This is an issue I have seen before. Basically, not enough color is applied. While there usually is a maximum of color (300%), they seem to have a minimum. But this is determined by the printer, not the publisher. And it is something you have control over to change. –  KMSTR Jun 13 '13 at 6:17

2 Answers 2

If it's not high quality printing, text in a gray color can become very hard to read. To create gray, they have to screen back black into a halftone, and on coarser line screens, that can turn out hard to read.

So maybe that is their concern. I don't know. I'd definitely ask them what they specifically mean by 'too light'.

As for making them darker, I don't really see why you should have to do that. But if you must, I'd consider using the LEVELS or CURVES tools in your photo editing app to see if you can boost the grays to be a bit darker.

Another option might work depending on your images is to place the image into your photo editing app, duplicate the layer, and set the top layer to 'MULTIPLY'. Here's an example of the result of that technique:

enter image description here

If you start seeing weird artifacts like you are doing, that typically means you're working with a JPG image. You definitely don't want to edit the JPG. Make sure your screen shot software is capturing in a better format for this such as PNG.

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Note the your multiply-by-itself trick is basically equivalent to applying gamma expansion with a gamma value of 2.0. –  Ilmari Karonen Jun 14 '13 at 19:43

So it might be true that it can't be printed due to little color application. But that is a print production issue, your publisher might just be speaking out of experience, warning you.

You can check for yourself in Acrobat Pro in the Output Preview to get an idea.

enter image description here

Based on that you can correct your screens and re-test them in Acrobat.

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One more time: I'm only dealing with graphic files, not PDFs. –  Isaac Rabinovitch Jun 13 '13 at 17:36
    
You are missing what he is showing you. You have NO black and your image has a grey scale. –  Matt Jun 13 '13 at 20:44
    
I merely opened your file in Acrobat to show the colors used and that they in fact might be too light. –  KMSTR Jun 14 '13 at 14:27
    
Be that as it may, an example in an image editing tool would be more useful. This is an involved process for finding out if I got it right -- and you'ven't told me how to get it right. –  Isaac Rabinovitch Jun 16 '13 at 0:13
    
It will depend on the images you use. There is no one-size-fits all. Others have suggested how to do this and I agree with them. What I showed you is how to make the result measurable. Otherwise you'd be flying blind. –  KMSTR Jun 16 '13 at 7:33

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