negative_image.c

#include<stdio.h>
#include<stdlib.h>
#include<time.h>

int main()
{
	clock_t start, stop; 
	start=clock();
	FILE* fp = fopen("images/lena512.bmp", "rb");   //read the file//

	unsigned char *imageData; // to store the image information
	unsigned char *newimageData; // to store the new image information, i.e. the negative image
        unsigned char imageHeader[54]; // to get the image header
        unsigned char colorTable[1024]; // to get the colortable

	int i,j; // loop counter variables

	fread(imageHeader, sizeof(unsigned char), 54, fp); // read the 54-byte from fp to imageHeader
	      
	  
	// extract image height and width from imageHeader      
        int width = *(int*)&imageHeader[18];
        int height = *(int*)&imageHeader[22];
	int bitDepth = *(int*)&imageHeader[28];

        int imgDataSize = width * height; // calculate image size

        imageData = (unsigned char*)malloc (imgDataSize * sizeof(unsigned char)); // allocate the block of memory as big as the image size
        newimageData = (unsigned char*)malloc (imgDataSize * sizeof(unsigned char));
	
	if(bitDepth <= 8)	// COLOR TABLE Present
		fread(colorTable, sizeof(unsigned char), 1024, fp); // read the 1024-byte from fp to colorTable
		
	
	fread( imageData, sizeof(unsigned char), imgDataSize, fp);
	   
		
	//Calculate the mean of the image
	for(i = 0; i < height; i++){
	      for(j = 0; j < width; j++){                   
		     newimageData[i*width + j] = 255 - imageData[i*width + j]; 
		 }   
	}

	FILE *fo = fopen("images/lena_negative.bmp", "wb");

        fwrite(imageHeader, sizeof(unsigned char), 54, fo); // write the header back.

	if(bitDepth <= 8)	// COLOR TABLE Present
        	fwrite(colorTable, sizeof(unsigned char), 1024, fo); // write the color table back
	
        fwrite( newimageData, sizeof(unsigned char), imgDataSize, fo); // write the values of the negative image.

        fclose(fo);
	fclose(fp);
        stop = clock(); 
	double d = (double)(stop - start) * 1000.0 / CLOCKS_PER_SEC;                                                   
        printf("%lf\n",d);

}
// header=imageHeader, data=imageData,