Haar Feature-based Cascade Classifier XML file argument

asked 2015-01-20 06:12:35 -0600

I'm working with face detection of Haar Feature-based Cascade Classifier. I have searched a lots but I still haven't found the exactly answer for the left_val and right_val in XML file (like this)

  <_>
        <!-- root node -->
        <feature>
            <rects>
                <_>3 7 14 4 -1.</_>
                <_>3 9 14 2 2.</_></rects>
            <tilted>0</tilted></feature>
        <threshold> 4.0141958743333817e-003 </threshold>
        <left_val> 0.0337941907346249 </left_val>
        <right_val> 0.8378106951713562 </right_val></_></_>
  <_>

The left_val and right_val are the return value of a feature ( alpha(i) * h(i) in Viola-jones paper), is it true. And if so, because h(i) is -1 or 1 so we must have left_val = - right_val but in face it isn't true. Can you guys give me some explanation to understand that? Thank you for your help! Sorry my English is not so good

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I think this guy explains it pretty well, and this answer even better. Basically it is the value that is used to calculate the final stage score.

StevenPuttemans ( 2015-01-20 06:49:06 -0600 )edit

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answered 2015-06-02 05:22:20 -0600

chris_x
1

Hi Steven, Can you please tell also what exactly is alpha value? Is it included in the Haar Classifier XML arguments? Thanks Chris

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I am sorry, I moved to using the LBP based features quite some time ago. Also the newer haar features based models trained by traincascade do not got this alpha value anymore. So can you please explain where you found that value?

StevenPuttemans ( 2015-06-02 08:14:45 -0600 )edit

I have found it in an Haar-like implementation included in HLS Video Library, provided with Xilinx Vivado HLS to help accelerate computer vision/image processing applications on FPGA Sadly no documentation is provided for that certain implementtion but i suspect that is based on opencv and an older type of Haar Feature-based Cascade Classifier XML, with a bit different structure [additional "alpha" argument]. Are you familiar of that kind of structure?

chris_x ( 2015-06-06 00:49:21 -0600 )edit

No I am not and this forum only focusses on actual OpenCV implementations. We cannot cover every single software out there which is based on OpenCV. So I guess you will need to find a HLS video library specific forum for that. Also, looking at this page I am afraid that this software is built upon a very old OpenCV implementation which is far from supported :)

StevenPuttemans ( 2015-06-06 08:35:46 -0600 )edit

:-) Thanks Steven

chris_x ( 2015-06-06 11:01:43 -0600 )edit

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Haar Feature-based Cascade Classifier XML file argument

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