[ptx] Band Blending [was: Hugin wishlist, RFC]

[Andrew C Mihal]

>1. Band blending (or some other intelligent blending)
> 
>   Even with setting every capture parameter at my camera to some fixed
>value, I still end up having differently exposed images that hardly match
>up, even with large feathering. Adjusting brightness kills the blue sky
>in most images, adjust color paints them pink. Adjusting both does both.

Hi,
    I spent a couple hours this weekend researching this. The fundamental 
paper from Burt & Adelson is here:

http://citeseer.nj.nec.com/burt83multiresolution.html

I even managed to find an implementation in the (old) Utah Raster Toolkit.

http://www.cs.utah.edu/gdc/projects/urt/help/man1/pyrmask.html

I had to do some hacking to get this tool to run because there seems to 
be a malloc/free bug. I didn't fully fix it - I'm just letting it leak 
memory, it's good enough to test it out. I had to do some ridiculous 
tiff->pnm->rle conversions to try it but the results were promising.
I stitched two images with autopano-sift and hugin and ran the result
through pyrmask. There is no noticable seam in the sky and no noticable
ghosting in the foreground. I think it's better than what I can do by hand 
in gimp.

One downside is that you have to give the pyramid blender a mask to 
identify the transition zone. This paper talks about calculating the mask 
automatically:

http://www.worldserver.com/turk/computergraphics/pstitcher.pdf

But the authors there don't exactly address the question of how to set the 
mask values at points outside the intersection of the two images. This 
caused some problems that I can elaborate on if anyone is interested.

Is anyone working on this? I think it would be straightforward to update 
pyrmask to work on tiffs directly - the tiff->pnm->rle->pnm chain seems to 
lose the alpha channel. I haven't fully looked into the automatic mask 
creation algorithm yet.

Also, has anyone thought of doing some wavelet processing to improve 
sharpness in the overlap region? This is usually on the edge of a frame 
where the focus is not so good. There are some astrophotography image 
stacking programs that do something like this.

Andrew

---------------------------------
Andrew Mihal
www-cad.eecs.berkeley.edu/~mihal
mihal at eecs.berkeley.edu