GIMP Version: 2.8.14
Operating System: Mac OS
GIMP Experience: New User

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Hi, am at the beginning of a learning curve and tutorial videos could not explain what this problem is or how to solve it, am hoping for some wise feedbacks :-)

First, I am on Mac from 2022 with GIMP 3.0, which i even re-installed tonight. I have a collection of Jpegs that i worked on in gimp & turned into xcf files, and now want to place 4 per page, all the same size, and learned much of that today. Then as advised to bring multiple layers into a new canvas, I selected from the File Menu "new" and "create layers" and then imported all my xcf's, and all of that went wrong! The images were now all different sizes, though my other editing work had saved, and now matter how many times I save them, they keep going to the new size in the new file I started

I know about difference between the canvas & printing size, so was careful to set those up correctly (that took some trial & error with the pop up box, but I was able to get my canvas to 8.5 / 11 inches). Thing is, none of my xcf's conform to the size i keep resetting, again & again & again. Do I need some plug in?? it does not "lock"

Please = after processing individual jpegs into xcf files, how can i keep their size locked when importing them into a new file as a layer?

Help??? What am i doing wrong?

Gimp is a bitmap (raster) editor and works in pixel units. You might have several images ostensibly the same size - say 4" x 6" but with different pixels-per-inch (ppi) values, which means they have different pixel sizes.

If you make a new canvas, especially if using a Gimp template, the USLetter size uses 300 ppi.

Open-as layers is the correct way to go but when the imported images have different ppi then you see the relative size difference. Nothing has changed about your imported images, they are still the same pixel size.



If you want matching sizes then you need to scale the images accordingly.
For example a 4" x 6" @ 72 ppi = 288 x 432 pixels and 4" x 6" @ 300 ppi = 1200 x 1800 pixels
You need to scale the 288x432 up to -> 1200x1800 to fit a 8.5" x 11" @ 300 ppi background

Part 2 It is not very obvious in the Image -> Scale Image dialogue how to get from one ppi to the corresponding background layer ppi.



There is information as to pixel size in Gimp (1) By default values are linked (2) leave it like that
Gimp will do the arithmetic for you (3). Apply the ratio to the width - example is times 300 ppi divided by 180 ppi - *300 /180
Then change the resolution to suit (4) , and do use one of the better interpolation methods.

Confused this a one minute animation of that: https://i.imgur.com/bCOdTpD.mp4
...and checking sizes with Image -> Print Size before and after.

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Part 3 - If you want to work on imported layers - much the same as before except use Layer -> Scale Layer and you do need to know the original ppi.

Goes like this: https://i.imgur.com/R1kkByi.mp4