Hello Rahul:

> i m a student and interested in gsoc project:Fast Adaptive Resampler
> Tailored For Transformations Which Mostly Downsample

> I have read the requirements properly for this project which also
> includes jacobian transformation,box filtering algorithm and
> bilinear resampling.But i am having some problem in relating all
> these in one algorithm. Please guide me.Also I would like to know
> the status of this project progress.

The >>programming<< for this project has not started. "No progress" is
consequently a fair description.

This would be a brand new way of doing downsampling, so I can't point
you to "one algorithm."

Computing jacobian information (for an arbitrary point transformation)
approximately using finite differences is probably too ambitious. My
current opinion is that this method should only be used when the point
transformation "communicates" this information to the sampler. This
probably means that a point transformation (e.g., scale, rotate) needs
to have this info part of its implementation as an object. I'll need
opinions from people who know better at some point.

You need to understand exact area methods, and in particular, exact
area box filtering (basically, you understand images as being a
piecewise constant surface, with the pieces determined by the set of
points which are closer to a pixel center than any other pixel center,
and you (approximately) integrate this surface over an area associated
with the new pixel centers (determined by the point transformation).

References which may help understand what is going on are

  author =       {N. A. Dodgson},
  title =        {Image resampling},
  institution =  {University of Cambridge Computer Lab.},
  year =         1992,
  number =       {UCAM--CL--TR--261},
  address =      {15 JJ Thomson Avenue, Cambridge CB3 0FD, UK},
  month =        {Aug.}


  author    = {Nicolas Robidoux and
               Adam Turcotte and
               Minglun Gong and
               Annie Tousignant},
  title     = {Fast Exact Area Image Upsampling with Natural Biquadratic
  pages     = {85-96},
  ee        = {http://dx.doi.org/10.1007/978-3-540-69812-8_9},
  bibsource = {DBLP, http://dblp.uni-trier.de},
  crossref  = {DBLP:conf/iciar/2008}

Also, a student and I programmed a C filter (for 8-bit ppm/pgm) which
does exact area box filtering in the very simple case of pure image
resizing. If you're still interested, we'll put this on the web.

The proposed method is none of the above. More precisely, it is a
composite method: It "fits" a new fast but accurate downsampling
method (related to box filtering) and bilinear together so that
Frankenstein is flexible and "smoothly varying."

Note: French is my mother tongue. If you are more comfortable in
French, you can communicate with me---not this list---in
French. Obviously, English is fine too.

Best of luck,

Nicolas Robidoux
Universite Laurentienne

Gimp-developer mailing list

Reply via email to