Jacob

(Just A COntent Based query system for video databases)

Developer

Computer Science & Artificial Intelligence Lab, University of Palermo, Italy.

URL

http://www.csai.unipa.it:80/research/projects/jacob/. A demo is available at site http://www.csai.unipa.it:80/research/projects/jacob/jacob_demos.html.

References

[CA96].

Features

The system makes queries based on color and texture features. Color is represented by means of a histogram in the RGB space. Texture features used are two measures extracted from the grey-level cooccurrence matrix, the maximum probability $max_{m,n}f(m,n,r,\theta)$, and the uniformity $\sum_m \sum_n (f(m,n,r,\theta))^2$. An 8-dimensional vector is obtained by computing the joint probability $f(m,n,r,\theta)$ for distance r=1 and orientation $\theta=-45^{\circ}, 0^{\circ}, 45^{\circ}$, and $90^{\circ}$. Another vector is composed of edge density measures (the fraction of edge pixels in the total number of pixels in the image) along four directions, $-45^{\circ}, 0^{\circ}, 45^{\circ}$, and $90^{\circ}$.

Querying

The queries may be direct or by example. A direct query is made by inserting a few values representing the color histogram and/or the texture features. For a query by example, the user must give an image.

Matching

Two color histograms are compared using the following distance measure: $d(H_1,H_2)=\sum_{y \in S}\sum_{x \in I(y)} \vert H_1(y)-H_2(x)\vert s(y,x)$ where H₁,H₂ are the histograms, S is the reduced RGB space, I(y) is a small interval centered on the point y and s is a color similarity function. The distance measure used for the texture feature vectors is not mentioned. When performing a query, the user choose a value between 0 and 1 to indicate the relative importance of a feature with respect to the other one. As a result the two distances computed are weighted in a global similarity measure.

Result presentation

The system returns the best matching frames in a similarity order. The number of returned frames is chosen by the user.

Applications

The matching of images is used for querying video databases.