Step by Step solution about How to resolve the algorithm Percentage difference between images step by step in the C programming language

The provided C program calculates the difference between two images in terms of pixel color values. It takes two image files as input and computes the average color difference between corresponding pixels. Here's a detailed breakdown:

1. Header Files:

   • The program includes the necessary header files:
     • <stdio.h> for input and output operations.
     • <stdlib.h> for memory management functions.
     • <math.h> for mathematical functions like fabs.

2. Pixel Color Constants:

   • RED_C: Constant representing the red color channel index (0).
   • GREEN_C: Constant representing the green color channel index (1).
   • BLUE_C: Constant representing the blue color channel index (2).

3. Image Structure:

   • An image structure is defined but not shown in the code snippet. This structure likely represents an image and may contain fields like width, height, and a buffer buf to store pixel values.

4. Main Function:

   • The program's entry point is the main function.

5. Image Input:

   • It reads two image files specified by the command-line arguments argv[1] and argv[2] using the read_image function (assumed to be implemented elsewhere).

6. Image Size Check:

   • The program checks if the widths and heights of the two images match. If not, it prints an error message and exits.

7. Image Comparison Loop:

   • If the image sizes match, the program enters a nested loop that iterates over each pixel in both images.
   • For each pixel, it calculates the absolute difference in each color channel (red, green, blue) and accumulates the total difference.

8. Average Color Difference Calculation:

   • After iterating through all the pixels, the program calculates the average color difference by dividing the total difference by the total number of pixels in the images.

9. Result Output:

   • It prints the average color difference as a percentage.

10. Image Cleanup:

• Finally, it frees the memory allocated for both images using the free_img function (assumed to be implemented elsewhere).

In summary, this program compares two images pixel-by-pixel, calculates the average color difference between them, and prints the result as a percentage.

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
/* #include "imglib.h" */

#define RED_C 0
#define GREEN_C 1
#define BLUE_C 2
#define GET_PIXEL(IMG, X, Y) ((IMG)->buf[ (Y) * (IMG)->width + (X) ])

int main(int argc, char **argv)
{
   image im1, im2;
   double totalDiff = 0.0;
   unsigned int x, y;
   
   if ( argc < 3 )
   {
      fprintf(stderr, "usage:\n%s FILE1 FILE2\n", argv[0]);
      exit(1);
   }
   im1 = read_image(argv[1]);
   if ( im1 == NULL ) exit(1);
   im2 = read_image(argv[2]);
   if ( im2 == NULL ) { free_img(im1); exit(1); }
   if ( (im1->width != im2->width) || (im1->height != im2->height) )
   {
      fprintf(stderr, "width/height of the images must match!\n");
   } else {
   /* BODY: the "real" part! */
      for(x=0; x < im1->width; x++)
      {
         for(y=0; y < im1->width; y++)
         {
           totalDiff += fabs( GET_PIXEL(im1, x, y)[RED_C] - GET_PIXEL(im2, x, y)[RED_C] ) / 255.0;
           totalDiff += fabs( GET_PIXEL(im1, x, y)[GREEN_C] - GET_PIXEL(im2, x, y)[GREEN_C] ) / 255.0;
           totalDiff += fabs( GET_PIXEL(im1, x, y)[BLUE_C] - GET_PIXEL(im2, x, y)[BLUE_C] ) / 255.0;
         }
      }
      printf("%lf\n", 100.0 * totalDiff / (double)(im1->width * im1->height * 3) );
   /* BODY ends */
   }
   free_img(im1);
   free_img(im2);
}