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

[Henning Müller]

Hi,

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: http://publications.hevs.ch/index.php/publications/show/189

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:
> Greetings,
>
> 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
> archives...honest).
>
> Thanks in advance,
>
> Xavier
>
>
> _______________________________________________
> help-GIFT mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/help-gift

--
Henning Müller, PhD, Prof.
HES-SO Valais
TechnoArk 3, 3960 Sierre, Switzerland
Tel. +41 27 606 9036
http://medgift.hevs.ch/