Segmented data image types

[mathiasroesler]

I have been using the mapping tools to create segmented data from my masked images and fitting the data to an organ scaffold. However, my masks created with png images do not work but my masks created with jpg images do. It would be great if png images worked the same as jpg images.

[hsorby]

This issue is a problem for a dependency, work on this will be communicated here: cmlibs/zinc#285