rotate.c

/*
Author: Himol Shah
Description: Rotate an image
Details: Please link the mathematical library while compilation
use: "gcc rotate.c -lm"
*/

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

//	Main Function
void main()
{
	//	Declaration of variables
	int pix,npix,scan,nscan, npix_out,nscan_out,*fp1,*fp2,cnt,temp,x,y,a,b,i,x0,y0,xx,yy;
	char input_file[100],output_file[100];
	float theta;
	double radians;
    	
	//	Accepting size and names of input and output files
	printf("Enter npix nscan of the image: \n");
	scanf("%d %d",&npix,&nscan);

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

	//	accepting angle of rotation
	printf("Enter angle of rotation:\n");
	scanf("%f",&theta);

	radians = theta*22/(7*180);	//	computing radians from degrees

	//	computing npix and nscan for new image
	npix_out = ceil(abs(npix*cos(radians))+abs(nscan*sin(radians))) + 1;
	nscan_out = ceil(abs(npix*sin(radians))+abs(nscan*cos(radians))) + 1;

	//	defining x0 and y0
	x0 = nscan/2;
	y0 = npix/2;

	//	declaring and allocating memory for entire image
	unsigned char **image = (unsigned char **)malloc(nscan * sizeof(unsigned char *));
    	for (scan=0; scan<nscan; scan++)
        	image[scan] = (unsigned char *)malloc(npix * sizeof(unsigned char));

    	unsigned char **image_out = (unsigned char **)malloc(nscan_out * sizeof(unsigned char *));
    	for (scan=0; scan<nscan_out; scan++)
        	image_out[scan] = (unsigned char *)malloc(npix_out * sizeof(unsigned char));

	//	initializing image_out for output image
	for(scan = 0; scan < nscan_out; scan++)
	{
		for(pix = 0; pix < npix_out; pix++)
		{
			image_out[scan][pix] = 255;
		}
	}

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

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

	close(fp1);	//	closing the input image file

	fp2 = creat(output_file,0666);	//	creating a new file

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

	for(scan = 0; scan < nscan_out; scan++)
	{
		for(pix = 0; pix < npix_out; pix++)
		{
			//	performing change of coordinates operation
			x = nscan_out/2-scan;
			y = pix - npix_out/2;
			//	using trigonometric identities for changing the coordinates
			xx = (int)(x*cos(-radians) - y*sin(-radians));
			yy = (int)(x*sin(-radians) + y*cos(-radians));

			xx = nscan/2-xx;
			yy = yy+npix/2;

			if(xx < 0 || xx >= nscan || yy < 0 || yy >= npix)
				image_out[scan][pix] = 255;	//	blacking out the unwanted part

			else
				image_out[scan][pix] = image[xx][yy];	//	mapping the exact coordinates of input image to the output image
		}
	}

	for(scan = 0; scan < nscan_out; scan++)
	{
		write(fp2, &image_out[scan][0], npix_out*sizeof(unsigned char));	//	writing into the output file
	}
	close(fp2);	//	closing the file
}