suggestion for lens distorsion : cropping to visible area and alpha channel

[pierrelabreche]

When lens distorsion is applied, the output image contains invisible pixels (out of the image area black pixels).
It would be useful to have an automatic cropping option, creating a rectangular image which contains only visible pixels.

Another feature could be to permit he resulting image be saved as a png with an alpha channel corresponding to the visible pixels.
This could be useful, for example, when assembling panoramas from distorsion-corrected images.

[jsachs]

Picture Window does not support alpha channels for images so there is no way to make part of the image transparent.

[pierrelabreche]

Another way to accomplish this goal would be to automatically create an output mask in the lens distortion transform, and to export to png with the mask as an alpha channel in a second transform.