[ptx] Enblend and mask editing, revisited

[Rik Littlefield]

Some time ago, there was discussion on the Panorama Tools forum about 
somehow extending Enblend to allow mask editing like with Photoshop stacks.

I have been thinking some more about this, and I have a 
question/proposal to float past this group.

Currently, Enblend uses the mask embedded in the .tiff files to indicate 
valid pixels, and Enblend computes its own seam locations from overlap 
in the valid-pixel masks..

My proposal is to add command-line option to Enblend, to do this instead:
 1. infer valid pixels as the union of (.tiff mask set or RGB value not 
zero).
 2. treat incoming .tiff masks as if they were visibility masks in a 
Photoshop stack -- visible pixels in "higher" images hide pixels in 
"lower" ones.
 3. compute seam locations at the edges of the regions implied by (2).
 4. run remainder of Enblend algorithm as usual.

My thought is that this scheme would allow precise manual placement of 
seams using Photoshop, but requires no extensions to file formats and 
only very modest extensions to Enblend.

But I am not an Enblend expert, so there may be basic flaws in this scheme.

What do you think -- would this work?  Would it break?

Thanks,
--Rik