[ptx] Re: [PanoTools-devel] PTmender, and update

[Daniel M. German]

 Pablo> Daniel M. German <dmgerman at uvic.ca> wrote:
 >> Pablo d'Angelo twisted the bytes to say:
 >> 
 >> 
 >> Thanks Pablo. One thing I have not done yet is the feathering. I'll
 >> take a look at nona to see how it is being performed.

 Pablo> Nona doesn't do any feathering, but I think the algorithm could be modified to
 Pablo> do some.

 Pablo> Also, enblend 2.5 contains an optimized version of the seam creation
 Pablo> algorithm, so it would be good to look there.

The algorithm in PTstitcher for seam calculation is really bad, and
creates seems in very strange locations (it is already implemented, by
the way. Feathering will also help "ease" the transitions.

I would prefer a seam that is computed in the following manner:

* For each photograph, choose a pixel that is closest to its center
  (center as before the panorama transformation).

My assumption is that the "best" pixels tend to be closer to the
center of a given photograph. Of course there is no way to avoid
ghosting this way.

My main problem in Panoramas has been vignetting. Vignetting will be
removed by doing this (I haven't tested the vignetting feature in
Hugin yet).

I also read a paper that tried to automatically blend photos taking
"ghosts" into account by creating the seams around them:

  Eliminating Ghosting and Exposure Artifacts in Image Mosaics, IEEE
  Computer Society Conference on Computer Vision and Pattern
  Recognition (CVPR Dec. 2001), M. Uyttendaele, A. Eden, and
  R. Szeliski, (pdf)

 Pablo> But actually, it would be desirable to have a much more sophisticated seam
 Pablo> generation mechanism, like
 Pablo> http://grail.cs.washington.edu/projects/photomontage/ available as opensource.
 Pablo> Right now smartblend does something remotely similar (although not as foolprove
 Pablo> and nice as in the paper above).

I'll have to check it out. 

 Pablo> The code for the photomontage system is available, as well as a standalone
 Pablo> program to blend images.
 Pablo> http://thread.gmane.org/gmane.comp.misc.ptx/3560/focus=3560

 Pablo> Unfortunately it relies on the graph cut optimisation routines which are not
 Pablo> released under the GPL. One would have to reimplement these, or look for an
 Pablo> alternative implementation. Additionally it is a bit slow, and the gradient
 Pablo> domain blending used by it has created some artifacts in the example I have
 Pablo> tried.

 >> Today I finished TIFF flattening and JPEG/PNG generation. I'll upload
 >> the changes tomorrow.

 Pablo> How do you create the boundary between the images. I don't know the algorithm
 Pablo> used by PTStitcher for that.


This is a broad overview of the algorithm.

Each photograph is scanned from left to right, then from right to
left, top to bottom and bottom to top.

The result of this scan is, each pixel, a counter keeps its minimal
distance (in pixels) from the edge of the photo (remember this
distance is either horizontal or vertical, not optimal).

A final scan is done (line by line) where for each position, the pixel
with the maximal distance is chosen.

This is why the seams created by PTstitcher are usually created of
straight lines. 


 Pablo> Probably nobody uses these ones. I would give these a very low priority.

Indeed.

 >> 16 bit PSD  seems to be out of the question. We need some legal
 >> agreements with Adobe and that complicates matters.

 Pablo> Hmm. well thats bad (not for me, but for all the photoshop users out there...).
 Pablo> Is the agreement required for getting documents about the file format, or has
 Pablo> Adobe patented the file format?

They want agreements, and I am not sure what they would make me
commit to. Jim is probably the one that knows the best what the issues
are.

BTW, I should correct. One layer 16bit PSD _is_ supported. We just
can't generate multilayer PSD. One option is reverse engineering of
the format, but I think we have many other things that can use our
time. One can get around this restriction in photoshop by using
actions.

dmg



 Pablo> ciao
  Pablo

 Pablo> ----------------------------------------------------------------
 Pablo> This message was sent using IMP, the Internet Messaging Program.

--
Daniel M. German                  "A pro photographer is like a tourist
   Lisa to Jeff in the Rear Window. ->in an endless vacation."
http://turingmachine.org/
http://silvernegative.com/
dmg (at) uvic (dot) ca
replace (at) with @ and (dot) with .