From help-request at octave dot org Tue Feb 14 05:01:26 2006
Subject: Re: SIFT image descriptor patch
From: Etienne Grossmann <etienne at cs dot uky dot edu>
To: =?iso-8859-1?Q?S=F8ren?= Hauberg <soren at hauberg dot org>
Cc: etienne at cs dot uky dot edu, etienne@isr.ist.utl.pt, etienne.grossmann@laposte.net,         Octave Help <help@octave.org>, etienne@cs.uky.edu
Date: Tue, 14 Feb 2006 05:56:37 -0500


  Are the rsults ugly?

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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