Flat land not rendering properly

[Tsokoa 9]

Hi,

I'm making a map using a greyscale image I've made with Photoshop. The map has little relief so it's basically a flat unicolor piece of land with a few hills. But my problem is that the land that is supposed to be flat since it's the same color (7D7D7D) on my map is not perfectly flat in-game after I render it with SC4Terraformer.

Would anyone know what is causing this and what I should do ?

Thanks.

[Tsokoa 9]

I've solved my problem by using 16bits png instead of 8bit jpg but it's weird since I didn't have this problem with many maps I used from the Stex that were 8bit jpg.