Now, let’s make it looks better.
Rule 1: The More cells we have, the better quality we get.
If the whole mosaic size is limited (fixed), we can try decrease the cell size, by doing so, we can place more cells in same space. and this give us a more detialed result.
Rule 2: Larger photomosaic has better quality than smaller one.
A larger mosaic contains can provide additional space for more cells (keep same cell size), This would persents more detail information of the main image.

