Lately I've been using the GIMP a lot to crop images with a specific aspect ratio in mind, often with the intention of resizing the result down to a given resolution.

Examples: * Cropping and scaling a picture down to a LiveJournal userpic. * Cropping a picture down to 5"x7" for professional printing (maintaining the original resolution but scaling the dpi).

I think the pan and zoom interface on the Aladdin Digital Photo Centers (printing kiosks) are much more useful for this sort of thing than the GIMP's crop & resize tool. I think the pan & zoom feature on my camera is even better. The Aladdin displays the entire image, showing a rectangle around what you've selected to crop, with buttons to pan up/down/left/right, and shrink/enlarge the selection box. I think it's better to show only what you've selected to crop, as a sort of preview of the resulting image, similar to the interface on my camera (if only it could do the cropping....).

To do this via the GIMP, currently the best way I've found is, using the crop & resize tool, select an area roughly the size and shape that I want, pick which of the dimensions (X / Y) that I care most about, calculate the appropriate dimension for the other based on the aspect ratio that I need, type that in, re-adjust the position of the selection box, then click crop. Having a button to lock the aspect ratio (like in the scale image tool) would be an improvement, but I really think a pan / zoom / preview type interface would be much better.

I'm currently trying to crop and scale a picture down to 640x480. I really like a particular view of it zoomed in and panned around on my camera, but am having a lot of difficulty getting it just right via the tools I'm aware of in the GIMP.