// $nchunks = sqrt(min($xlim - $xoff, $ylim - $yoff) / 2.5);
// $nchunks = max(2,min(8,(int)$nchunks));
$nchunks = min( 7, $xlim - $xoff, $ylim - $yoff ) + 1;
// $nchunks = sqrt(min($xlim - $xoff, $ylim - $yoff) / 2.5);
// $nchunks = max(2,min(8,(int)$nchunks));
$nchunks = min( 7, $xlim - $xoff, $ylim - $yoff ) + 1;