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Re: [help-GIFT] Asymmetric Similarity Matrix

From: Juan C. Caicedo
Subject: Re: [help-GIFT] Asymmetric Similarity Matrix
Date: Thu, 16 Apr 2009 10:59:03 -0500

We were working on analysing both, papers and code. We wonder if the similarity s(x,y) between two images x and y should be the same as s(y,x). And of course it is. We found that the asymmetry is a normalisation effect, in which the results list is scaled by the score of the query applied on itself. So, when we obtained the scores normalised using the auto-score of the image x, they are slightly different to the scores normalised using the auto-score of the image y.

We just modify the source file to avoid this normalization, and now we obtain a symmetric similarity matrix.

Thank you very much for your response.

Juan C. Caicedo

On Thu, Apr 16, 2009 at 4:48 AM, Henning Müller <address@hidden> wrote:
Indeed, the paper:
Tversky, A. (1977). Features of similarity. Psychological Review, 84(4), 327-352.
shows through epxeriments that our visual similarity percetion does not at all correspond to a metric.

Cheers, Henning

Wolfgang Müller a écrit :
I think the Squire et al. papers from 1999 accessible from the Viper site in Geneva cite a paper of Tversky's which justifies asymmetric similarity matrices: What you are looking for influences your notion of similarity.

On Thu, Apr 16, 2009 at 8:14 AM, Henning Müller <address@hidden <mailto:address@hidden>> wrote:

   Dear Juan,

   this is normal as the similarity measure of GIFT is not a metric as
   it is based on a tf/idf weighting form text retrieval.
   Image similarity is calculated in the space spanned by the features
   present in the query, only. Each image has around 1500 features out
   of 87000 possible (most of them binary features), so each image
   potentially spans a different sub-space in which similarity is

   Cheers, Henning

   Juan C. Caicedo a écrit :

       Hello everybody,

       We are building a similarity matrix of an image collection using
       GIFT. However, we notice that this matrix is not a symmetric one.
       Could anybody tells us what is the reason of this behaviour and
       some hints to obtain a symmetric similarity matrix?

       Thanks in advance to all you.

       Juan C. Caicedo


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