Reproduction of details
Seeking the reproduction of some details may lead to failed work. A mosaic is ... a mosaic. Neither a photo nor a painting.


The human eye is a detail that usually you want to include in the mosaic of a photo.

The first thing to understand is that when you need to reproduce a detail is necessary to have adequate size tiles less than the detail. (see tiles on the right figure)

The second thing to know is that you must have library of tiles large enough to make statistically likeable to find tiles whose combination is addecuate to achieve certain details. This is particulary important for some subtle details like the eyelashes.

The image above right is a cut of a face that, properly printed in a poster, would have 70-80 inches width (with 1-inch tiles)..

The theme of the tiles
Another consideration needed in the reproduction of detail is the theme of the tiles. Stay away from the screen and observe the two mosaics from below:


Tile's theme: roses. Contain nearly circulars shapes


Tile's theme: fauna stamps. Contain irregular shapes

In the first mosaic the "roses" theme - with basically circular shapes - makes you lose the eyelashes detail, which is not the case when the tile subject is fauna stamps (with irregular shapes). It's possible to achieve the reproduction of subtle details with regular tiles, but that requires huge mosaic prints.
Conclusion: For regular size posters, if you use tiles with regular figures, mix them with irregular tiles.
The tiles size
I previously said that it was desirable to reproduce details using tiles with irregular shapes. This is necessary but not enough: we must also have in our library images with formats other than the square ones.
With: 40 tiles. Height: 40 tiles Tile format: 3x2  With: 40 tiles. Height: 26 tiles Tile format: 1x1 
You can see that in the left mosaic above the girl eyes detail is best achieved. Below, the zone's description for each mosaic:
Of course, always it's possible to increase the resolution of the mosaic always using more tiles, vertically and horizontally. Below, the same painting with different tile densities, though same 3x2 format::
Above left: 400 tiles. Poor definition of the details.
Above right: 900 tiles. Acceptable definition of the details.
Below left: 1600 tiles. Good definition of the details.
Below right: 10,000 tiles. Definition like pointillism. See a Signac paint