washerboard( FILE *image, int nrows, int ncols, int nripples ) { int r, c, gray ; /* write out the pixel data */ for ( r=0; r<nrows; r++ ) { for ( c=0; c<ncols; c++ ) { gray = 127 + 127*cos( 2*M_PI*nripples*r/nrows ); fputc( gray, image ); } } }