Team Gryffindor

Team Gryffindor

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

Assignment #2 (New Algorithm)

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):

  * 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;
}

We use color lena with 8bit pgm 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           
   
 100.27    0.04     0.04        1    40.11    40.11  sobel_filtering
 0.00      0.04     0.00        1     0.00     0.00  load_image_data
 0.00      0.04     0.00        1     0.00     0.00  save_image_data