Re: enblend algorithm

Tago -

On Jun 12, 10:06 am, tago <liquidt...@...> wrote:
> Why zero?

        If you are on the border, i.e. at the
red or green lines then the distance to the
respective border is zero.


> If I start the line in the middle of the overlap wouldn't
> the horizontal distance between red and green borders exactly half of
> the overlap width ?

        What is the middle?  How would you
define it?  Does your definition also hold if
you turn the the example 90 degrees?

As I said before the problem is manifestly
two-dimensional.  Just looking at one border is
not enough.  We must look at _all_ borders at
the same time to find out what is the minimum
distance to any of them.


> Is the line generation based on something like the grassfire
> transform ?

        I'm sorry, but I cannot tell you what
Enblend's original algorithm is based upon,
because I never understood it.  8-|

The new algorithm employed in the "staging"
branch uses two nearest neighbor transforms
(NNT) of the differences between the mask files
A and B.  It constructs the seam mask by
assigning zeros to pixels closer to the borders
of A-B and ones to pixels closer to the borders
of B-A.  The boundary between the zeros and the
ones makes up the initial seam line.

You see that neither the computationally
expensive Grassfire-, nor Watershed-
transformations are necessary.  The final
assignment step is a point-wise operation and
thus of linear complexity in the image size.  It
parallelizes trivially.

Latest revisions of "staging" do compute both
NNTs in parallel threads, too, given the project
has been configured with "--disable-image-cache
--enable-openmp" and the compiler supports
OpenMP.


> Are there details on how optimization works ?

        I guess there are lots of them!  It is
just that I have not looked at the seam-line
optimization close enough to tell you what is
going on there.  What about you inspecting it
and teaching me?


> I guess one needs to
> find a line that does not pass thru mismatches (i.e. parallax or
> moving objects).

        As far as I understand, this is the way
Enblend works.  It would explain why SmartBlend
sometimes produces superior output.

I have an idea of how to improve on the
optimization, though.  Hopefully, it will take
us on a par with SmartBlend.  (Kornel will love
to hear this;)


HTH,
        Chris

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups "hugin and other free panoramic software" group.
A list of frequently asked questions is available at: http://wiki.panotools.org/Hugin_FAQ
To post to this group, send email to hugin-ptx@...
To unsubscribe from this group, send email to hugin-ptx-unsubscribe@...
For more options, visit this group at http://groups.google.com/group/hugin-ptx
-~----------~----~----~----~------~----~------~--~---