Conflicting dpi and printing too small

[Alexras]

I've been trying to make something for a while, and ran into some problems that led me needing to take a screenshot of something and then bring the png into GIMP as the starting point for my project. I added some images, then sized and aligned everything to fit the dimensions I need when I print. (The exact dimensions matter as this will be printed on card stock and made into boxes that need to fit in a bigger box.)

I tried printing out test pages, but it came out too small. Part of the problem is that my printer doesn't want to try printing the page size I need (A3), but instead will only print Letter. But this problem led me to looking into dpi, which led me to a different problem.

I click Image > Print Size and see the resolution is 3.78px/mm or 96 dpi.
I click File > Print > Image Settings and see that the resolution is somewhat higher. I try changing the resolution in this dialogue box to see if I can get it to 96 dpi, but it goes to a minimum of 4px/mm or 101.6 dpi, no lower.

My guess is that this disparity between the resolutions is the reason why it's printing too small. Am I right? What can I do about this? How can I get it to print the right size without completely overhauling everything?

Thank you.

Windows 10.0.18362
GIMP 2.10.20 (Revision 1)

[rich2005]

Seems a never ending problem with Windows Gimp (all versions going back years). The common advice is, do not use Gimp for printing, use some other application. XnViewMP or maybe IrfanView are both freeware and should print what you want.

Quote:..Part of the problem is that my printer doesn't want to try printing the page size I need (A3)..

This is assuming that the printer is capable of printing A3. Gimp only takes the settings from the Windows printer driver supplied by the printer manufacturer, so check that first. I have come across similar before, I think it is a bug in the Gimp 2.10 print plugin but since I generally use linux can not be sure.

More generally.
96 ppi (dpi) is a common resolution for computer display, too low for decent printing, photographic printing rule-of-thumb is 300 ppi, printing for packaging? Could be less say 150 - 200 ppi

Gimp works in pixels and comes with A3 templates already set up @ 300 ppi = 3508 x 4960 pixels If your graphic is 1123 x 1587 pix (A3 @ 96 ppi) then beware.

A printer usually imposes margins on full size images. A full A3 (or A4) will shrink. That can be seen in the print dialogue, typically 300 ppi adjusted to 307 ppi. There is a tick box in the print dialogue for ignore printer margins. One trick is to shave a little off the left side of the image (crop the width) then the printer is able to fit the image onto the paper at the correct ppi.

[Alexras]

Rich, thanks for the reply.

My major problem, it seems, is that I am only able to get the basic template of the design I want via screenshot. I don't know of a way to get a screenshot in 300 dpi.

Also, good news! I found suggestions for exporting as png, and then I did a test run at my local Staples. That worked! It came out with the right dimensions. Unfortunately, the image was suboptimal, and there were artifacts introduced that I can't see any sign of in GIMP (weird bits of stuff where there should be only blank white).

Thanks again for the help.

[rich2005]

Quote:My major problem, it seems, is that I am only able to get the basic template of the design I want via screenshot.

When you consider a HD computer display is 1920 x 1280 pixels and the design probably only part of that, the lack of quality becomes understandable.

The best way is take what you have as a template and manually re-draw at a decent size.

[Alexras]

Yeah, I was worried I might have to re-draw manually. But perhaps it won't be as much work as I've been expecting it would.

Thanks.