This is why it is important to use small tiles. You want to start from an image which is 320 x 240 pixels. That means 320 x 240 tiles. That means 76800 tiles. If each tile is 1cm square then that means that the finished mural is 3.20 meters across.
All tiles are square.
I am not pretending my conversion service makes truly artistic mosaics. It can however convert a truly artistic photograph into a good quality grid mosaic. I am also saying that a conversion utility that uses Colour Blending is a massive improvement on those that do not. If you want any more info, or if you want to tell me what you think of my conversion service, here's where to contact me.