C program to implement Optimum Thresholding (binarize image)

/*
 C program to implement Optimum Thresholding to binarize an image
 Sandipan Dey
 BCSE, JU, Kolkata
 2003
*/

//MUST USE MEDIUM MEMORY MODEL
//USE 256 COLOR BITMAP FILE (WIDTH%4=0)
// Input image files: RABBIT.BMP, BIRD.BMP

#include <math.h>
#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
#include <graphics.h>
#include <string.h>
#define DEFAULT "output.bmp"
#define MAX 256
#define PI 3.14159
#define VAL 1

struct Point {
    int x,y;
};

struct SE {
    Point p[4];
};

double ln(double x) {
    return (x>0?log(x):0);
}

void main(int argc,char* argv[]) {

    FILE* fp=NULL,*fo=NULL;
    long int n[MAX]={0};
    double p[MAX]={0};
    int c,type;
    char INPUTFILE[100],OUTPUTFILE[100],s[100];
    long int imgoffset=0;
    double sum=0;
    strcpy(OUTPUTFILE,DEFAULT);
    clrscr();
    if(argc<=1) {
        printf("\nNo Input File!");
        getch();
        exit(0);
    }
    strcpy(INPUTFILE,argv[1]);
    if(argc>2 && strcmp(argv[2],"\0"))
    strcpy(OUTPUTFILE,argv[2]);
    if((fp=fopen(INPUTFILE,"rb"))==NULL) {
        printf("\n File Not Found!");
        fclose(fp);
        getch();
        exit(0);
    }    // File Not Found
    fo=fopen(OUTPUTFILE,"wb");
    if(fgetc(fp)!='B' || fgetc(fp)!='M') {      // Check Signature
        printf("\n Not a valid BMP File!!!");
        fclose(fp);
        fclose(fo);
        getch();
        exit(0);
    }
    fseek(fp,10,0);         // Find Offset of Data
    imgoffset=fgetc(fp)+(fgetc(fp)<<8)+(fgetc(fp)<<16)+(fgetc(fp)<<24);  // Data Offset
    fseek(fp,28,0);         // Find No. of Bits to Represent a Pixel of the Bitmap
    type=fgetc(fp);
    switch(type) {
        case 1:printf("\n A Monochrome (1-Bit) Bitmap!");break;
        case 4:printf("\n A 16-Color (4-Bit) Bitmap!");break;
        case 8:printf("\n A 256-Color (8-Bit) Bitmap");break;
        default:printf("\n Not a 1,4 Or 8-Bit Bitmap!");break;
    }
    if(type!=8){
        fclose(fp);
        printf("\nAn 8-bit Bitmap expected!!!");
        fclose(fo);
        exit(0);
    }
    long int w,h;
    fseek(fp,18,0);
    w=fgetc(fp)+(fgetc(fp)<<8)+(fgetc(fp)<<16)+(fgetc(fp)<<24);
    h=fgetc(fp)+(fgetc(fp)<<8)+(fgetc(fp)<<16)+(fgetc(fp)<<24);
    int threshold=0;
    double minH=1000000.01,q1,q2,m1,m2,v1,v2,H,sumsq=0;
    for(int i=0;i<MAX;++i){n[i]=p[i]=0;}
    int gd=VGA,gm=VGAHI,x=0,y=h;
    struct palettetype pal;
    initgraph(&gd,&gm,"");
    getpalette(&pal);
    for(i=0;i<16;i++)
    setrgbpalette(pal.colors[i],i*4,i*4,i*4);
    fp=fopen(INPUTFILE,"rb");
    fo=fopen(OUTPUTFILE,"wb");
    fseek(fp,0,0);
    while(!feof(fp)) {
        fputc(fgetc(fp),fo);
    }
    fseek(fp,imgoffset,0);
    while(!feof(fp)) {
        c=fgetc(fp);
        putpixel(x,y,c/16);
        x=(x+1)%w;
        if(!x){--y;}
        ++n[c%MAX];
    }
    getch();
    cleardevice();
    for(i=0;i<MAX;++i)sum+=n[i];
    for(i=0;i<MAX;++i)p[i]=n[i]/(sum*1.0);
    threshold=0;
    for(unsigned int t=1;t<MAX-1;++t) {
        q1=sum=0;
        for(i=0;i<t;++i){q1+=p[i];sum+=i*p[i];}
        m1=q1?sum/q1:0;sumsq=0;
        for(i=0;i<t;++i){sumsq+=(i-m1)*(i-m1)*p[i];}
        v1=q1?sumsq/q1:0;
        q2=sum=0;
        for(i=t;i<MAX;++i){q2+=p[i];sum+=i*p[i];}
        m2=q2?sum/q2:0;sumsq=0;
        for(i=t;i<MAX;++i){sumsq+=(i-m2)*(i-m2)*p[i];}
        v2=q2?sumsq/q2:02;
        //printf("%lf %lf %lf %lf\n", q1, q2, v1, v2);
        H=(1+ln(2*PI))/2-q1*ln(q1)-q2*ln(q2)+(q1*ln(v1)+q2*ln(v2))/2;
        if(H<minH){minH=H;threshold=t;}
    }
    int xstart=10,ystart=470;
    line(xstart,ystart,620,ystart);
    line(xstart,ystart-470,xstart,ystart);
    setcolor(14);
    for(i=0;i<MAX;++i)  {
        line(xstart+2*i,ystart-5000*p[i],xstart+2*i,ystart);
        if(!(i%15)){
            setcolor(getmaxcolor());
            line(xstart+2*i,ystart-5,xstart+2*i,ystart+1);
            sprintf(s,"%d",i);
            outtextxy(xstart+2*i-7,ystart+2,s);
            setcolor(14);
        }
    }
    setcolor(4);
    outtextxy(xstart+2*threshold+7,ystart-200,"Threshold");
    line(xstart+2*threshold,ystart,xstart+2*threshold,ystart-470);
    setcolor(14);
    fflush(stdin);
    getch();
    cleardevice();
    sprintf(s,"Threshold=%d",threshold);
    outtextxy(520,421,s);
    outtextxy(520,445,"Sandipan Dey");
    outtextxy(520,455,"BCSE-IV");
    outtextxy(520,465,"Roll-99710");
    fseek(fp,imgoffset,0);
    fseek(fo,imgoffset,0);
    x=0;y=h;
    int c1;
    while(!feof(fp)) {
        c=fgetc(fp);
        c1=(c<threshold)?0:15;
        fputc(c1,fo);
        putpixel(x,y,c1);
        x=(x+1)%w;
        if(!x){--y;}
    }
    fclose(fo);
    fclose(fp);
    getch();
    closegraph();
}