How to capture hair wisp structure from an image? - opencv

Question

I want to draw a cue from a specified point along its gradient direction to capture structure of hair wisp. Like Figure2. and Figure3. from an ACM paper, I linked here: Single-View Hair Modeling for Portrait Manipulation. Now I draw an orientation map by gradients, but the results look very chaotic.
This is my code:
#include <opencv2\highgui\highgui.hpp>
#include <opencv2\imgproc\imgproc.hpp>
#include <iostream>
using namespace cv;
using namespace std;
int main(int argv, char* argc[])
{
Mat image = imread("wavy.jpg", 0);
if(!image.data)
return -1;
Mat sobelX1;
Sobel(image, sobelX1, CV_8U, 1, 0, 3);
//imshow("X direction", sobelX);
Mat sobelY1;
Sobel(image, sobelY1, CV_8U, 1, 0, 3);
//imshow("Y direction", sobelY);
Mat sobelX, sobelY;
sobelX1.convertTo(sobelX, CV_32F, 1./255);
sobelY1.convertTo(sobelY, CV_32F, 1./255);
double l_max = -10;
for (int y = 0; y < image.rows; y+=3) // First iteration, to compute the maximum l (longest flow)
{
for (int x = 0; x < image.cols; x+=3)
{
double dx = sobelX.at<float>(y, x); // Gets X component of the flow
double dy = sobelY.at<float>(y, x); // Gets Y component of the flow
CvPoint p = cvPoint(y, x);
double l = sqrt(dx*dx + dy*dy); // This function sets a basic threshold for drawing on the image
if(l>l_max) l_max = l;
}
}
for (int y = 0; y < image.rows; y+=3)
{
for (int x = 0; x < image.cols; x+=3)
{
double dx = sobelX.at<float>(y, x); // Gets X component of the flow
double dy = sobelY.at<float>(y, x); // Gets Y component of the flow
CvPoint p = cvPoint(x, y);
double l = sqrt(dx*dx + dy*dy); // This function sets a basic threshold for drawing on the image
if (l > 0)
{
double spinSize = 5.0 * l/l_max; // Factor to normalise the size of the spin depending on the length of the arrow
CvPoint p2 = cvPoint(p.x + (int)(dx), p.y + (int)(dy));
line(image, p, p2, CV_RGB(0,255,0), 1, CV_AA);
double angle; // Draws the spin of the arrow
angle = atan2( (double) p.y - p2.y, (double) p.x - p2.x);
p.x = (int) (p2.x + spinSize * cos(angle + 3.1416 / 4));
p.y = (int) (p2.y + spinSize * sin(angle + 3.1416 / 4));
line(image, p, p2, CV_RGB(0,255,0), 1, CV_AA, 0 );
}
}
}
imshow("Orientation Map", image);
waitKey(0);
return 0;
}
Can any one give me some hints?

Answer 1

Your Sobels are the same while they supposed to have different code for x and y. 0, 1 and 1, 0.on top of that you loose resolution and sign by specifying cv8U as depth inSobel and only then converting to float. Also please provide input resolution and your outcome image.