08-25-2019, 10:32 PM
In Gimp (and other bitmap editors), the only thing that matters is pixels. When you see inches, you are just seeing the interpretation of pixels with a given "definition" in pixels per inch (as displayed/st in Image>Print size and in the image creation dialog).
If you save the image as XCF, or export it as JPG and PNG, this definition is saved in the file, so the size in inches when you reload should stay the same. There is no such feature in the GIF format, the image definition is lost.
It is otherwise true that the units in the rulers is a property of the view and not of the image. You set this with the small indicator at the bottom of the image window (marked 7 in the screen shots here). You can do View>New view to have two views on the image, one with the rulers in inches and one with the rulers in pixels. This settings also acts in the displays of the Measure tool.
If you save the image as XCF, or export it as JPG and PNG, this definition is saved in the file, so the size in inches when you reload should stay the same. There is no such feature in the GIF format, the image definition is lost.
It is otherwise true that the units in the rulers is a property of the view and not of the image. You set this with the small indicator at the bottom of the image window (marked 7 in the screen shots here). You can do View>New view to have two views on the image, one with the rulers in inches and one with the rulers in pixels. This settings also acts in the displays of the Measure tool.