image matching algorithms

[Daniel Fetchinson]

> > Since you seem to know quite a bit about this topic, what is your
> > opinion on the apparently 'generic' algorithm described here:
> > http://grail.cs.washington.edu/projects/query/ ?
> > So far it seems to me that it does what I'm asking for, it does even
> > more because it can take a hand drawn sample image and query the
> > database for similar photos.
> >
> > There is even a python implementation for it here:
> > http://members.tripod.com/~edcjones/pycode.html
> >
> > On the histogram method I agree that it won't work partly because of
> > what you say and partly because it is terribly slow since it's
> > comparing every single pixel.
>
> I'm hardly the expert and can't answer authoritatively, but here's my 2c.
>
> I can't comment as to the actual accuracy of the algorithm, since it
> will depend on your specific data set (set of photos). The algorithm is
> sensitive to spatial and luminance information (because of the YIQ
> colorspace), so there are simple ways in which it will fail.
>
> The histogram method uses only color, but has a lot of numbers to
> compare. You may find the histogram method insensitive to spatial
> relations (a landscape with the mountain on the left and one with the
> mountain on the right) compared to the wavelet approach.
>
> This is a relatively old paper, and I've seen other more recent image
> retrieval research using wavelets (some cases using only the
> high-frequency wavelets for "texture" information instead of the
> low-frequency ones used by this paper for "shape") and other information
> retrieval-related research using lossy compressed data as the features.
> If you have time, you may want to look at other research that cite this
> particular paper.
>
> And just a thought: Instead of merely cutting off at m largest-wavelets,
> why not apply a quantization matrix to all the values?

I'm not at all an expert, just started to look into image matching, so
I'm not quite sure what you mean. What's a quantization matrix in this
context?