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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):
* 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
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
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;
}