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Turn .PIC image file upside down (flip vertical), DeSmet C

For saving images in a semi-portable device-independent bitmap-like format on the Heathkit H-100 computer, I created a graphic format that I called .PIC.

This short DeSmet C program reads the scan line data from one .PIC file and writes the lines in reverse order to a second file, turning the image upside down.

/*	upsidown.c	11/23/93
	Copyright (C)1993 Steven Whitney.
	Initially published by http://25yearsofprogramming.com.
	Published under GNU GPL (General Public License) Version 3, with ABSOLUTELY NO WARRANTY.

	REWRITES LINES FROM A .PIC FILE IN REVERSE ORDER TO A NEW FILE. 
	LINE 225 BECOMES LINE 1 IN THE NEW FILE, ETC.,
	SO THE IMAGE IS TURNED UPSIDE DOWN.

*/
#include "stdio.h"
main(argc,argv)
int argc;
char **argv;
{
FILE *infile, *outfile;
char buf[640];
unsigned i, j;
int fline;

if(argc != 2)
	abort("Usage: UPSIDOWN source      (output is UPSIDOWN.PIC)\n");

if(!(infile = fopen(argv[1],"r")))
	abort("Input file not found.\n");

outfile = fopen("upsidown.pic","w");

j = 0;
fseek(infile,0L,2);						/* find end of file */
for(fline = 0 ; fline < 225 ; fline++)
{
	fseek(infile,-640L,1);				/* back up 640 bytes */
	fread(buf,1,640,infile);			/* read the bytes */
	fseek(infile,-640L,1);				/* back up to where we were */
	printf("Line %d of 225\n",++j);
	fwrite(buf,1,640,outfile);	
}
closeall();
exit(0);
}