1. Open or create a new file (while writing this, i'm using 4000 by 3000px)
2. Selection Rectangle tool, Fixed ratio (width 6, height 4.5)
3. Select an area and crop to selection
4. Image->Resize (Best Quality, absolute size, maintain aspect ratio; resolution: 200 pixels/inch; print size: width 6 inches)
If the selection is larger than 1200x900 pixels, the result is scaled down properly to 1200x900 (in this example)
If the selection is smaller, the result will be 1200x901. Scaling up results in a rounding error somewhere.
The resize action doesn't need to be completed to see the ef