After two days of rendering I was finally strong enough to beat the evil compositor and its render layer army.
[SUP]Final Render, looks way better when you click on it.[/SUP]
The image uses only one texture, a bunch of very simple trees (60,000), some fog, a grand canyon height-map and solid hexagons for cloud shadows.
I had problems with using the z-pass to color the far parts blue, because the volumetric fog seemed to be unsure, what it’s z-depth was, so it came out very noisy every time.
I solved this by creating a second render layer without the fog and using its z-pass for the color in the full render (with fog). It sounds easier than it was, but that’s about what I managed to do since yesterday morning. Very frustrating, until I saw the result.
Then I put a sky in the background and adjusted the colors in Photoshop and now I’m happy again. Serves well as a Desktop wallpaper.