Allow to fill image width or height to crop area aspect ratio

The question is how to fit a vertical image in an horizontal crop area, without loosing information (sometimes important, like logos, posters, etc).
Its the same question to fit a horizontal image in a vertical crop area.

I think, the best solution will be allowing toolbox to select an area bigger than image, and filling this area with transparent or white color.
Now, in some conditions, jscrop fills this area, but with black color.

I give you an example of this filling with black color.
http://test.donostiarrak.com/es/content/imagejscrop-test-black-image-fil...

Many thanks, merci beaucoup, muchas gracias,
for your help and for this great module.

Josean.