histogram.c

/*
Author: Himol Shah
Description: Histogram
*/

//  Header files
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <malloc.h>
#include <fcntl.h>

//  Void Function
void main()
{
    //  Declaration of variables
	unsigned char *image;
	int *image_out;
	char output_file[100], input_file[100];
	int pix, npix, scan, nscan, *fp1, npix_out, nscan_out;
	float x,y,r;

	FILE *fp2;  //  creating a file

    //  accepting size of input files
	printf("Enter npix nscan of the image: \n");
	scanf("%d %d",&npix,&nscan);

	image = (unsigned char *)calloc(npix,sizeof(unsigned char));    //  allocating memory to the image array

    //  accepting names of input and output files
	printf("Enter name of the input file: \n");
	scanf("%s", input_file);
	printf("Enter name of the output file: \n");
	scanf("%s",output_file);

    //  setting dimensions
	npix_out = npix;
	nscan_out = nscan;

	image_out = (int *)calloc(256,sizeof(int)); //  allocating memory to output image array

	memset(image_out,0,256*sizeof(int));    //  setting 0

	fp1 = open(input_file,O_RDONLY);    //  opening input image

	if(fp1<0)   //  checking for errors while opening the file
	{
		printf("Error in opening the input file. \n");
		exit(1);
	}

	fp2 = fopen(output_file,"w");   //  creating an output file with writing permissions

	if(fp2 < 0) //  checking for errors while creating the output file
	{
		printf("Error in creating the output file. \n");
		exit(1);
	}

	for(scan = 0; scan < nscan; scan++)
	{
		read(fp1, &image[0], npix*sizeof(unsigned char));   //  reading from input file

		for(pix = 0; pix < npix; pix++)
		{
			image_out[(int)image[pix]]++;   //  incrementing frequency
		}

	}

	for(scan = 0; scan < 256; scan++)
	{
		fprintf(fp2,"%d %d\n",scan,image_out[scan]);    //  printing frequencies with their respective intensities in output file
	}

    free(image);    //  freeing memory
	close(fp1); //  closing file
	close(fp2); //  closing file
}