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Re: [help-GIFT] Feature Extraction - Range breakdown

From: Henning Müller
Subject: Re: [help-GIFT] Feature Extraction - Range breakdown
Date: Tue, 20 Dec 2011 11:42:30 +0100
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GIFT does not do any feature selection. Many features are binary and thus either present or absent. The different number results from some images containing for example fewer colors than other images and from the fact that not all images have all direction/scale/strength combinations of the Gabor filter responses. For the Gabor filters that default configuration does not use the lowest energy band, meaning the images with many flat regions have fewer features. This is an option in the source code and can be changed.

There is a feature description file in the index directory that has the feature number and feature group (on of the four Gabor histogram, Gabor block, color histogram, color blocks). I do not remember the exact details but it should be described in the early papers on the system such as:

The Gabor blocks are indeed 16x16 blocks, where as the color blocks should be blocks at four scales, so first dividing the image into 4, then 16, 64, 256 blocks, so 340 blocks if I am not wrong.

Kind regards, Henning

On 12/19/11 12:44 PM, Xavier Clements wrote:

I have two questions, the first having two parts.

1. How does GIFT select features for extraction given that I read in one
of these discussions that the range of features extracted for any one
image is between 341 to 3686? Is this upper limit arbitrary in nature
and able to be altered in the code?

2. Is the following breakdown of the ranges for each of the four
extracted feature types correct (taken from a previous post)?

"1. color blocks

- 1st 256 times 16x16 color blocks, where each has 166 possible values
(i.e. features 0..42 495, where 0..165 are from the first block etc.)

- 2nd 64  32x32 blocks,
  (10 624 more feats, i.e.42 496 .. 53 119  <tel:42%20496%20..%2053%20119>)

- 3rd 16  64x64 blocks,
  (2 656 more, i.e.53 120 .. 55 775  <tel:53%20120%20..%2055%20775>)

- 4th 4  128x128 blocks
  (664 more, i.e. 55 776 .. 56 439)

2. color histogram
166 features
(feats 56 440 .. 56 606)

3. gabor blocks
- 256 times 16x16 blocks, each block containing 120 possible Gabor features
(features 56 607 .. 87 325 so that in 56 607..56 726 are the Gabors calculated

from the first block and in 56 726..56 845 <tel:56%20726..56%20845> are
from the second etc.)

4. gabor histogram
last 120 features ( 87 326 .. 87445 )"

Forgive this newcomer for potentially asking questions that have been
previously answered (I looked through a number of the forum's

Thanks in advance,


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Henning Müller, PhD, Prof.
HES-SO Valais
TechnoArk 3, 3960 Sierre, Switzerland
Tel. +41 27 606 9036

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