[ptx] Questions on Lowe's SIFT algorithm

[Sebastian Nowozin]

Hi Fang Xianyong,


On Sat, May 15, 2004 at 10:24:20PM +0800, Xianyong Fang wrote:

> I find that the SIFT algorithm of Lowe's paper is not robust to scale
> transform. When I try to register two images with different scales, there are
> few (or not so many correct) matches existing. To images with rotation and
> different scales, it works even worse.  But when I apply the sift algorithm
> to images with simple shift or small rotation, it works fine and almost all
> the returned matches are correct.  Does anyone have the same experience with
> me?

I have not tested in detail, but only some small tests with scale-different
pictures. It always worked fine. Can you upload a testcase somewhere? And,
which implementation do you use?

If it really is not scale-invariant as much as it should be, I still think for
panorama images it is no problem at all.


> I also find that in Lowe's IJCV paper "Distinctive Image Features from Scale
> Invariant Features" the testing images showed almost have the same scale. I
> can't help thinking that maybe his algorithm is hard to copy with images of
> different scales.

While the paper is good in general and I used it exclusively for my SIFT
implementation it has some shortcomings for practical implementation purposes
(some small but important steps must have been ommited in the paper, though I
do not know why or if my conclusions are wrong at some points).


> In addition, I also try to intergrate "PCA-SIFT: A More Distinctive
> Representation for Local Image Descriptors" into the matching process and
> find the same problem. 
 
Sounds interesting, URL to that paper?


> Xianyong

ciao,
Sebastian

PS: I finished adding RANSAC and some image model to my autopano-sift toolbox,
and would like to have your and the other people's opinion on the image align
model I use. I will upload a small sketch and the new version tomorrow or on
Monday and post to the list then.

-- 
nowozin at cs.tu-berlin.de --- http://user.cs.tu-berlin.de/~nowozin/