//License: Public Domain
//Written by Nasca Octavian PAUL, Tg. Mures, Romania
//in 20060901
/
*
Steps to obtain the illusion image:
1) Compile this program and run it
2) Convert the .pgm images to .png images with the bash script:
>>>>>cut<<<<<
for file in 
*.pgm
do
    echo $file
    pnmtopng $file > "$file.png"
    rm -f $file
done
>>>>>cut<<<<<
3) Convert png images to "output.avi"
mencoder "mf://
*.png" -mf fps=20:type=png -ovc lavc -oac copy -o output.avi
4) Convert "output.avi" to ogg theora with:
ffmpeg2theora output.avi
5) Run the animation (full screen) and look and stare in the center of it
After 1 minute, look away and you'll see a very interesting illusion (looks like objects/faces/etc changes their shapes) which last few seconds.
*/
#include 
#include 
static const int sizex=640;
static const int sizey=480;
static const float freq=80;
static unsigned char data();
static unsigned char f(float x,float y,float phase)
static void make_frame(float t)
}
static void save_frame(char 
*filename) 
int main(void)