Opencv Edge extraction

Question

Hi all!

I have an image and I want to create an adge histogram. I divide the image into 1100 image-blocks and try to find edge and its direction (horisontal, vertical, 45° diagonal, 135° diagonal or nondirectional) in each block.

How I can extract that information about edges? Do you have any ideas?

Regards!

Answer 1

I found the answer in this paper: Efficient Use of MPEG-7 Edge Histogram Descriptor by Won.

My goal was to find following edges: picasaweb.google.de/lh/photo/_SpWAe-q3_kBXq27srqQLQ?feat=directlink

Won divide each Image Block into to parts, calculate the average gray level in each of them and use the following coefficients: picasaweb.google.de/lh/photo/CRjAKNXcMQY65YRm1HLYDA?feat=directlink

We use this coefficients as follows and get 5 values: picasaweb.google.de/lh/photo/S_Equ83Peczj3mEZk7Zanw?feat=directlink

Using thresholding we astimate each type of the edge:

program SetEdgeType(max, m_nd, m_h, m_v, m_d_45, m_d_135)
{
if (max < TEdge) then EdgeHisto(0)++
else
{
 if (m_nd > T0)    then EdgeHisto(1)++
 if (m_h > T1)     then EdgeHisto(2)++
 if (m_v > T1)     then EdgeHisto(3)++
 if (m_d_45 > T2)  then EdgeHisto(4)++
 if (m_d_135 > T2) then EdgeHisto(5)++
}
endif
return(EdgeHisto)
}

Threshold values were selected by Savvas A. Chatzichristofis to be: TEdge=14, T0=0.68, T1=T2=0.98.

Sorry for links, I am not allowed to post Images because I am a new user!