Team Gryffindor

Team Gryffindor

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Gryffindor Team Logo
Team Members Chad Nelson - cnel711 Mihir Awatramani - mihir Mengduo Ma - marinama Kuan-Hsing Ho - pm429015

Assignment #2

Description of Sobel's Algorithm - This is a great website teachs us how it works, and it also provide some examples, which help us to implement in C code.

Compiler:

gcc -O -lm sobel.c -o sobel

./sobel

Sobel edge detection algorithm code with C (Since the code is very long, I just show key part of algorithm):

  int sobel(double threshold) {
  unsigned int  x, y, i, v, u;             // for loop counter
  unsigned char R, G, B;         // color of R, G, B
  double val[MASK_N] = {0.0};
  int adjustX, adjustY, xBound, yBound;
  double total;

  for(y = 0; y != height; ++y) {
    for(x = 0; x != width; ++x) { 
      for(i = 0; i != MASK_N; ++i) {
        adjustX = (MASK_X % 2) ? 1 : 0;
                adjustY = (MASK_Y % 2) ? 1 : 0;
                xBound = MASK_X / 2;
                yBound = MASK_Y / 2;
            
        val[i] = 0.0;
        for(v = -yBound; v != yBound + adjustY; ++v) {
                    for (u = -xBound; u != xBound + adjustX; ++u) {
            if (x + u >= 0 && x + u < width && y + v >= 0 && y + v < height) {
              R = *(image_s + byte_per_pixel * (width * (y+v) + (x+u)) + 2);
              G = *(image_s + byte_per_pixel * (width * (y+v) + (x+u)) + 1);
              B = *(image_s + byte_per_pixel * (width * (y+v) + (x+u)) + 0);
              
                  val[i] +=    color_to_int(R, G, B) * mask[i][u + xBound][v + yBound];
            }
                    }
        }
      }

      total = 0.0;
      for (i = 0; i != MASK_N; ++i) {
              total += val[i] * val[i];
      }

          total = sqrt(total);
          
      if (total - threshold >= 0) {
        // black
        *(image_t + byte_per_pixel * (width * y + x) + 2) = BLACK;
        *(image_t + byte_per_pixel * (width * y + x) + 1) = BLACK;
        *(image_t + byte_per_pixel * (width * y + x) + 0) = BLACK;
      }
            else {
              // white
        *(image_t + byte_per_pixel * (width * y + x) + 2) = WHITE;
        *(image_t + byte_per_pixel * (width * y + x) + 1) = WHITE;
        *(image_t + byte_per_pixel * (width * y + x) + 0) = WHITE;
      }
    }
  }
  
  return 0;
}

We use color lena with 24bit bmp file

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Profiling Sobel edge detection algorithm

This command will generate a test file:

gcc -lm -pg sobel.c
./a.out
gprof a.out > test
  

test file:

%      cumulative  self             self     total           
   
80.80      0.15    0.15        1   145.44   175.53  sobel
16.72      0.18    0.03  4706312     0.00     0.00  color_to_int
0.00      0.18     0.00        1     0.00     0.00  read_bmp
0.00      0.18     0.00        1     0.00     0.00  write_bmp

Assignment #2 (New Algorithm)

Compiler:

gcc -O -lm sobel.c -o sobel
./sobel

• files
  • mypgm.h - header file
  • sobel.c - sobel algorithm
  • Lena.pgm - image files

Sobel edge detection algorithm code with C

void sobel_filtering( ) {
    /* Spatial filtering of image data */
    /* Sobel filter (horizontal differentiation */
    /* Input: image1[y][x] ---- Outout: image2[y][x] */
 /* Definition of Sobel filter in horizontal direction */
 int maskx[3][3] = {{-1,0,1},{-2,0,2},{-1,0,1}};
 int masky[3][3] = {{1,2,1},{0,0,0},{-1,-2,-1}};
 double pixel_value_x, pixel_value_y, pixel_value;
 double min, max;
 int x, y, i, j;  /* Loop variable */
 /* Initialization of image2[y][x] */
 x_size2 = x_size1;
 y_size2 = y_size1;
 for (y = 0; y < y_size2; y++) {
   for (x = 0; x < x_size2; x++){
     image2[y][x] = 0;
   }
 }
 /* Generation of image2 after linear transformtion */
  for (y = 1; y < y_size1 - 1; y++) {
    for (x = 1; x < x_size1 - 1; x++) {
      pixel_value_x = 0.0;
      pixel_value_y = 0.0;
       for (j = -1; j <= 1; j++) { 
        for (i = -1; i <= 1; i++) {
              pixel_value_x += image1[y+j][x+i] * maskx[j+1][i+1];// do x-convolution
              pixel_value_y += image1[y+j][x+i] * masky[j+1][i+1];// do y-convolution }      
     pixel_value = (abs(pixel_value_x)+abs(pixel_value_y)); // easier to implement on hardware  
     if (pixel_value >= 255)pixel_value=255;
     if (pixel_value <= 0)pixel_value=0;     
     image2[y][x] = (unsigned char)pixel_value;
    }
   }
  }
}
main( )
{
 load_image_data( );   /* Input of image1 */ 
 sobel_filtering( );   /* Sobel filter is applied to image1 */
 save_image_data( );   /* Output of image2 */
 return 0;
}