For info: - with a default Gimp there are image details top of the image window, typically imagename - colour mode - layers - size in pixels.
A few thoughts about sizes and printing as a flyer.
What is the size, inches/centimetres of the flyer?
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edit: got the calculator up: 1224 x 792 pix @ 72 ppi is 17" x 11"
Did you start off by setting up a canvas using 17" x 11" ?
Gimp is a raster editor, everything is measured in pixels, and you need to start off on that basis.
A canvas size of 5100 x 4200 pix is a better size to produce a quality 17" x 11" print. No good scaling up your small image, you will just be disappointed with the result.
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For quality printing 300 ppi is best although less can be acceptable. For example the Gimp default A5 is 1754 x 2480 so if you used that size (A5) then print size for your background 1224x792 would be around 150 ppi.
Obviously, the greater the size of the flyer in pixels the larger you can make a thumbnail (in pixels) and that leads to better quality.
However, a thumbnail is a thumbnail, and reducing from 2400x1200 pix to say 240x120 pix loses a lot of information, it is not reasonable to expect an exact copy of the original. It might be possible to recreate a simplified version at a tiny size. If possible post the layer you are trying to scale. Text in particular does not scale well.
The other aspect is the actual printing. A flyer? never going to be a work of art although it is possible to get a run on glossy paper.
A few thoughts about sizes and printing as a flyer.
What is the size, inches/centimetres of the flyer?
-----------
edit: got the calculator up: 1224 x 792 pix @ 72 ppi is 17" x 11"
Did you start off by setting up a canvas using 17" x 11" ?
Gimp is a raster editor, everything is measured in pixels, and you need to start off on that basis.
A canvas size of 5100 x 4200 pix is a better size to produce a quality 17" x 11" print. No good scaling up your small image, you will just be disappointed with the result.
-----------
For quality printing 300 ppi is best although less can be acceptable. For example the Gimp default A5 is 1754 x 2480 so if you used that size (A5) then print size for your background 1224x792 would be around 150 ppi.
Obviously, the greater the size of the flyer in pixels the larger you can make a thumbnail (in pixels) and that leads to better quality.
However, a thumbnail is a thumbnail, and reducing from 2400x1200 pix to say 240x120 pix loses a lot of information, it is not reasonable to expect an exact copy of the original. It might be possible to recreate a simplified version at a tiny size. If possible post the layer you are trying to scale. Text in particular does not scale well.
The other aspect is the actual printing. A flyer? never going to be a work of art although it is possible to get a run on glossy paper.