[ptx] Enblend 1.0

[Jim Watters]

The paper "Registration, Calibration and Blending in Creating High 
Quality Panoramas" by Ken Turkowski and Yalin Xiong
http://www.worldserver.com/turk/computergraphics/papers.html
Describe a way of creating a special mask image first that defines where 
the seams should be.  This eliminates any problems with the order that 
images are blended.  See Fig 7 in paper.
Each image is assigned a number 1 to n
Each pixel on the mask is assigned number to represent the source image 
that contributes best.
When determining the seam not only is the edge of the mask considered 
but also any existing seams.
...Best to read the paper.  No algorithm given but the it is described 
in better detail.

I think it was a discussion on Enblend that pointed me to this paper.

 Jim Watters

 Graphic Software Developer
 http://members.rogers.com/jimwatters



Andrew C Mihal wrote:

>I noticed problems like that a couple times during development. It seems 
>that occasionally the greedy assembly heuristic will make bad choices as 
>to which images to blend next. If it picks an image with a long, skinny 
>overlap region, there will not be enough space to use very many pyramid 
>levels. Then there will almost always be a line in the result. Then in the 
>next blending step, it will think that the line is really supposed to be 
>there, and will blend future images against the line. Therefore the line 
>will never totally go away. In cases like this the right thing to do is to 
>blend the images in a different order. Save the image with small overlap 
>for later, when there might be a bigger overlap region to use.
>
>Another option would be to force it to use a specified number of blend 
>levels no matter the size of the overlap region. Then enblend will use 
>extrapolation to guess what happens off the edge of each image. But this 
>can go wrong too. I've seen an example where parts of the image start to 
>turn gray - I think this is because the blending zone exceeds the overlap 
>zone too much.
>
>So there should be a better way to automatically decide what image(s) to 
>blend in next. For now you might try using the -s flag to specify an order 
>manually and see if you can get that line to go away.
>
>Andrew
>
>---------------------------------
>Andrew Mihal
>www-cad.eecs.berkeley.edu/~mihal
>mihal at eecs.berkeley.edu
>
>
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