#sobel operator

[wolframcarbide]

[wolframcarbide]

[wolframcarbide]

[bigrichardc]

Edge Detection in Processing Using the Sobel Operator (Code)

Here is a quick run through of the code used to do an edge detection in Processing.  First up I create an array that can contain all of the values of the screen intensities, place an image on the screen and load the image pixels into the system Pixels[] array:

  int[] pixelarray = new int[width*height];   PImage img = loadImage("image.jpg");   image(img,0,0);   loadPixels(); 

Iterating through each individual pixel, I get red, green and blue intensity values for that pixel add them together and depending on the values in the Sobel operator I have multiplied and added them to the overall intensity.  For example the top left pixel in the Sobel matrix:

      px = pixels[((y-1)*width)+(x-1)];       redvalue = red(px);       bluevalue = blue(px);       greenvalue = green(px);       intensity = redvalue + greenvalue + bluevalue;       Gx += -intensity;       Gy += intensity;

Once I have worked out values for all of the surrounding pixels I work out using Pythagoras the overall gradient length.   Then I normalise it so that it can be used as a output value.       //calculate normalised length of gradient       glength = sqrt((Gx*Gx)+(Gy*Gy));       glength = (glength/4328) * 255;     

I load this new information into the array of intensities which is used to create the image of the outline.  I have also used a threshold value to remove the detail from within the picture.

      if (glength > 10)         pixelarray[x+(width*y)] = color(glength);       else         pixelarray[x+(width*y)] = color(0);

Finally I load the array into the system array of pixels which is used to display the new image.    for(int i = 0; i<width*height;i++) {      pixels[i] = pixelarray[i];    }

Full code - https://github.com/bigrichardc/sketchbook/blob/master/sobelImageDetection.pde