image_dark.c

/**
* @file image_dark.c
* @brief C program to darken the image by reducing the pixel values.
* @author Priya Shah
* @version v1
* @date 2018-01-10
*/
#include <stdio.h>
#define THRESHOLD 40

int main()
{
	FILE *fIn = fopen("lena512.bmp","r");					//Input File name
	FILE *fOut = fopen("lena_dark.bmp","w+");		    	//Output File name

	int i;
	unsigned char byte[54],colorTable[1024];
	
	if(fIn==NULL)											// check if the input file has not been opened succesfully.
	{											
		printf("File does not exist.\n");
	}

	for(i=0;i<54;i++)										//read the 54 byte header from fIn
	{									
		byte[i] = getc(fIn);								
	}

	fwrite(byte,sizeof(unsigned char),54,fOut);				//write the header back

	// extract image height, width and bitDepth from imageHeader 
	int height = *(int*)&byte[18];
	int width = *(int*)&byte[22];
	int bitDepth = *(int*)&byte[28];

	printf("width: %d\n",width);
	printf("height: %d\n",height );

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

	if(bitDepth <= 8)										//if ColorTable present, extract it.
	{
		fread(colorTable,sizeof(unsigned char),1024,fIn);
		fwrite(colorTable,sizeof(unsigned char),1024,fOut);
	}

	unsigned char buffer[size];								//to store the image data

	fread(buffer,sizeof(unsigned char),size,fIn);			//read image data

	for(i=0;i<size;i++)										//decreasing pixel values to get image bright
	{
		if(buffer[i] > THRESHOLD)
			buffer[i] = buffer[i] - THRESHOLD;
	}
	
	fwrite(buffer,sizeof(unsigned char),size,fOut);			//write back to the output image
	
	fclose(fIn);
	fclose(fOut);
	
	return 0;
}