Re: SIFT image descriptor patch

[Etienne Grossmann]

On Tue, Feb 14, 2006 at 01:07:08PM +0100, Søren Hauberg wrote:
# tir, 14 02 2006 kl. 05:56 -0500, skrev Etienne Grossmann:
# >   Are the rsults ugly?
# Before my hack I don't get any result shown, but after my hack 
# I get some result that look just fine.

Then your patch is "clean" enough to go to production :-), I'll put it
in asap. Thx for your fix.

  For antialiasing, patches are welcome. Imglines() may be of interest
to the octave-forge users too. Opinions anyone, judging on the help
text below?

## im2 = imglines (im, [r1,c1,r2,c2], col) - Plot line segments on a bitmap
##
## im       : R x C : Greylevel image
## r1c1r2c2 : N x 4 : Enpoint coordinates of segments
## col      : N x 1 : Color (default: lightest color of image, or
##                    lightest+1, if image is uniform)
##
## im2      : R x C : Output image
##
## TODO: Clip segments that stick out of image.
##       Do color images too.

  Cheers,

  Etienne


   

# The lines could use some anti-aliasing, but I can live with that.
# 
# Did that answer the question?
# 
# /Søren
# 
# > On Mon, Feb 13, 2006 at 09:36:33PM +0100, Søren Hauberg wrote:
# > # Etienne,
# > # Thanks for doing this, it's nice to have SIFT in Octave.
# > # I get the following error on some images:
# > # 
# > # error: linspace: npoints is 1, but x1 != x2
# > # error: evaluating argument list element number 1
# > # error: evaluating argument list element number 2
# > # error: evaluating assignment expression near line 28, column 6
# > # error: evaluating for command near line 22, column 1
# > # error: called from `imglines' in file `/home/sh/Dokumenter/Robot
# > # projekt/Octave siftDemo/imglines.m'
# > # error: evaluating assignment expression near line 42, column 9
# > # error: evaluating if command near line 14, column 1
# > # error: called from `showkeys' in file `/home/sh/Dokumenter/Robot
# > # projekt/Octave siftDemo/showkeys.m'
# > # 
# > # I fixed this by a very dirty hack. That is, 
# > # if (len <= 1) len = 2; endif
# > # in imglines.m
# > # 
# > # Thanks,
# > # Søren
# > # 
# > # tir, 27 12 2005 kl. 11:32 -0500, skrev Etienne Grossmann:
# > # >   Hi All,
# > # > 
# > # > this patch could be of interest to octave users who do image
# > # > processing.  You can apply it to the matlab code in siftDemoV4 [1] to
# > # > allow octave to extract SIFT image features [2] with David Lowe's
# > # > package.
# > # > 
# > # >   The SIFT image detector identifies interest points, somewhat like a
# > # > corner detector does, and gives them a local descriptor. The
# > # > descriptor can then be used for matching purposes (another way to
# > # > perform matching could be correlation of a small window around the
# > # > feature). Wrt to corners + local window correlation, SIFT features are
# > # > more robust to changes in illumination and viewpoint [3] and they are
# > # > increasingly used in computer vision.
# > # > 
# > # >   The siftDemo has functions to find sift features and to perform
# > # > matching. I've tested the patch under octave+linux, matlab+linux (it
# > # > works) and octave+win (it fails, probs w/ imagemagick + double).
# > # > 
# > # >   Hth,
# > # > 
# > # >   Etienne
# > # > 
# > # > 
# > # > 
# > # > [1] http://www.cs.ubc.ca/spider/lowe/keypoints/siftDemoV4.zip
# > # > 
# > # >   Synopsis: 
# > # > 
# > # >     unzip siftDemoV4.zip;
# > # >     cd siftDemoV4; 
# > # >     patch -p1 < mySift.patch
# > # >   
# > # >     In octave, make sure sift.m is in your path, then
# > # > 
# > # >     >> [image, descriptors, locs] = 
sift("/home/etienne/prog/various/siftDemoV4/book.pgm");
# > # >    >> showkeys(image, locs)
# > # > 
# > # >    See also 'help match'
# > # > 
# > # > [2] http://www.cs.ubc.ca/~lowe/keypoints/
# > # > 
# > # >   David G. Lowe, Öbject recognition from local scale-invariant
# > # >   features," International Conference on Computer Vision, Corfu,
# > # >   Greece (September 1999), pp. 1150-1157.
# > # > 
# > # > [3] A performance evaluation of local descriptors Krystian
# > # >     Mikolajczyk, Cordelia Schmid International Conference on Computer
# > # >     Vision & Pattern Recognition - June 2003
# > # > 
# > # >     http://lear.inrialpes.fr/pubs/2003/MS03/mikolajczyk_cvpr2003.pdf
# > # > 
# > # > 
# > 

-- 
Etienne Grossmann ------ http://www.cs.uky.edu/~etienne



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