knowing Sim City, I thought that grayscale images is all that is compatible... the same was when Sim City 3000 load terrain cheat would create land from image... i noticed there is a RGB image import option in SC4mapper... how does that work? and what I mean when I ask how does it work, is both 'how good does it work' & 'the technicalities behind what it does'
Moganite suggested me to make the RGB image mode available because not everyone could generate 16bit png pictures ( only photoshop could write 16bit png by the time I made SC4TF and SC4Mapper ).
So someone with even mspaint ( and a colour table reference ) can achieve a map with the same quality as a 16bit png
Now to be honest, it is hard to draw such a map because the formula to get the height from RGB is the following:
height = (R*256+G*16+B)/10
Hope it helps