Resize image numerically, keeping aspect ratio?

Is it possible to resize an image by entering the dimension numerically, so that the aspect ratio does not change?

I know you can drag the image corner with the shift key, but this does not allow you to get an exact measurement. On the other hand, you can enter the dimensions manually, but then changing width does not affect height (and vice versa). What we need is an "Keep aspect ratio" checkbox near the dimension input fields.

Hi,

Thank you for the feature request. It's sounds like a useful feature and I've added it to our to-do list.