HOG descriptor for Matlab

Image descriptor based on Histogram of Oriented Gradients for gray-level images

Description

This code is simple and commented, what enables the adjust of the HOG parameters. This code was developed for the work: O. Ludwig, D. Delgado, V. Goncalves, and U. Nunes, 'Trainable Classifier-Fusion Schemes: An Application To Pedestrian Detection,' In: 12th International IEEE Conference On Intelligent Transportation Systems, 2009, St. Louis, 2009. V. 1. P. 432-437. In case of publication with this code, please cite the paper above.

• MATLAB release: MATLAB 7 (R14)

[Chris McCormick]

I noticed a bug in the histogram computation. Gradient vectors whose angle is equal to pi are being omitted from the histogram because you check for angle < angle_lim instead of angle <= angle_lim.

I also re-wrote the histogram computation to optimize it in a way similar to what was suggested in an earlier comment.

% Compute the bin index for every angle.
binIndeces = ceil((v_angles + pi) / binSize);

% For each bin
for (bin = 1:B)
% Get the magnitudes for all the pixels that belong in 'bin'.
magnitudes = v_magnit(binIndeces == bin);

% Add all of the magnitudes to 'bin'.
H2(bin) = H2(bin) + sum(magnitudes);
end

[tamanna]

@Oswaldo Ludwig sir, may i have your full paper coding ''Trainable Classifier-Fusion Schemes: An Application To Pedestrian Detection''

[Oswaldo Ludwig]

Could you explain why it was adopted blockwise normalization? From the best of my knowledge, there is no mathematical foundation behind HOG descriptors, only good sense. This is my version, which was made available to be evaluated by the community. Go ahead, you should make the comparison with other algorithms in your case study (Science is not religion, feel free to doubt and inovate).

[Lukas Tencer]

Also you are doing normalization of the final vector, originally it supposed to be blockwise normalization, did you try that version? Why you decided for normalization only of final histogram.

[Lukas Tencer]

Should not be contribution of individual points to the histogram weighted according to gaussian centred in the middle of each cell?

[Algorithms Analyst]

Can anyone help I am runiing this code but finding error?
Thanks inadvance

??? Input argument "Im" is undefined.

Error in ==> HOG at 11
[L,C]=size(Im); % L num of lines ; C num of columns

[PRAVEENKUMAR]

sir,i run your code,i am getting the error

??? Input argument "Im" is undefined.

Error in ==> HOG at 11
[L,C]=size(Im); % L num of lines ; C num of columns

please help me to correct this.

[Raul]

 

[Alsam]

 

[saif]

Can we use this code for object NOT human?

If I want to classify objects such as coca-cola and ketchup, can I do this directly with this code, I mean to use these features?

[Oswaldo Ludwig]

Raul, the number of features depends on the number of cells and histograms bins, see Section II-A of this paper: http://www2.isr.uc.pt/~urbano/PDFs_PUB/Conferencias_Internacionais/2009/[113]2009ITSC09-129-FI.pdf

[Raul]

I would like to know why the size of the HOG vector is the same for each image with different sizes.

[Prabhu]

 

[Aaron]

replace lines 42-47 with code below for 20x speed-up

idx = find(v_angles<ang_lim);
v_angles(idx) = 100;
H2(bin) = H2(bin) + sum(v_magnit(idx));

[Stathis Fotiadis]

 

[Oswaldo Ludwig]

An application for human detection (Windows only) can be found in http://webmail.isr.uc.pt/~oludwig/
The program is based on HOG descriptors for Matlab arranged in SRM-cascade, according to the methodology described in: O. Ludwig; “ Study on Non-parametric Methods for Fast Pattern Recognition with Emphasis on Neural Networks and Cascade Classifiers;” PhD Thesis, University of Coimbra, Coimbra, 2012. New images can be included in the folder "images" with the name "ped_XX". The algorithm was trained by using 18x36 gray-scale images from the Daimler Pedestrian Classification dataset. Double-click in detector_pkg.exe to install the program, then it is possible to run detector.exe.

[Swan]

Hi,what is this section for?
if C==1
Im=im_recover(Im,m,2*m);
L=2*m;
C=m;
end
in what case, C==1?

[Caelyn Low]

 

[Aeris]

Hi, do you have any example showing how the descriptor is applied to an 640x480 image?
And i don't really understand how does 2*pi/B = 360/9 => 20 degrees per bin? As i see it is equal to 40 degrees.
"ang_lim=-pi+2*pi/B:2*pi/B:pi"

Please correct me if i were wrong, thanks.

[Tom]

Hello. Why in this case is use y filter hy=-hx' and not hy=hx'?

Thank you for your answer in advance.

Tom

[David Lewis]

 

[Oswaldo Ludwig]

Dear Luis, you're right, a revised version was submitted.

[Luis Alejandro Fonseca Rodriguez]

Hello, I have found a error in your HOG descriptor program, the magnitude is calculated wrong. You multiply when you should sum.

[Oswaldo Ludwig]

We have achieved good result in object detection, regarding detection speed and accuracy, by combining this descriptor with NN trained by MMGDX, see:

http://www.mathworks.com/matlabcentral/fileexchange/28749-new-version-of-mmgdx-a-maximum-margin-training-method-for-neural-networks