GIMP Version: 2.8.10
Operating System: Linux
GIMP Experience: Intermediate Level

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This is a question that's been on my mind lately, but even with research about what PPI (Pixels Per Inch.) is, I'm not sure how it's relevant to editing in GIMP. I'm currently working on a canvas at 300 ppi that isn't much bigger in memory than one at 72 ppi.

It's obviously useful for printing, (So it knows how many pixels are to be printed in each inch of paper.) but doesn't seem to make a difference in what you're editing on the screen itself, visually, from what I can tell. Is the PPI setting in templates, so GIMP has a default value for the printer to go on, or does it actually need more memory at a higher PPI setting?

Might seem like a beginner question to some of you, but I feel like I could use clarification from someone more familiar with these things than I am.

Have a look at, Image | Image Properties.

The resolution setting (as appears in "Image->Print Size") is just a scaling factor and has no effect upon how many pixels are in the image or on the memory used by the image. The resolution setting, in conjunction with the Units setting, is used for determining markings on the rulers, for values displayed in status messages, and for inputting size parameters.

Thanks, saulgoode! That's the simplest description I've heard for PPI. A scaling factor for size references makes sense. It's good to know that it doesn't affect the actual canvas itself in any way.

I think I'll be converting my 72 ppi templates in GIMP and Krita to 300 ppi confidently now, since that might be more favorable for printing than 72 ppi.

Yes but keep in mind that for the same physical print size you need more pixels at 300PPI than at 72PPI

A 720x720pixels image prints as 10"x10" at 72PPI, but only 2.4"x2.4" at 300PPI. Because there is the ironclad elations ship between pixels, definition, and print size:

Looking at your previous posts and all the replies, maybe back to the beginning.




Two identical images, pixel size which is all Gimp uses both 603x521 pixels. One is set to 100dpi and the other to 200 dpi.

On a default Gimp set-up both will display exactly the same. They are exactly the same, although saved in different formats (hence different file size). Both have the same size in memory, again same RGBA + number of pixels, same MB.

However, If you turn off View -> Dot for Dot you see the relative size for printing.

The 200 dpi is twice the height and width of the 100 dpi. Again both the same size in pixels, both the same size in memory changing the dpi does not change the effective size of the image.

That's what I've been needing to confirm. I ran out of memory and crashed Ubuntu once while trying to use a 300ppi canvas at 5000x3000, but that was with GIMP 2.8.2, and I'm not having the same problem occur here with 2.8.10. It could have been a memory leak, looking back on that now.



I'll keep that in mind, thanks! I should try to organize variants of PPI sizes, based on what sizes I want on the canvas, and a print.

This definitely puts PPI to scale for me. If I need a print to be more detailed, and smaller, I go higher. If I need it to be larger, and don't have to worry about details as much, I should go lower.

Thanks for making sense of this, everyone! I can't believe I've been using GIMP for art, and some printing, for over two years without knowing what PPI actually is.