Stripped renders

Simple question:

My 2.34 seems to render at very low color depth. Images are striped, like a bitmap converted to 256-colour file. It looks like a hipsometric map.
I see no color depth controls in the program. I seeked for the answer in literature, but I found nothing. Moreover, the manual [Blender Manual 2.3, chapter “Your first animation in 30+30 minutes”] says nothing about setting such parameters of the renderer and shows a well-rendered image; when I exactly reproduce the procedure, I get that poor image again.

Any ideas what is it and how to fix it welcome.

Everything is fine here. Maybe your display color depth is too low?

No, Im not such total beginner... I set the value to the maximum and I get good results in several other applications. Im not sure but I think I had good results even in previous versions of Blender…

Hm, in that case I have no clue what could cause such a strange behaviour. Do you use the official version? And what OS? What gfx card and gfx driver? Could it be some OpenGL error that affects the render display? Did you save your image? Does it show the same color stripes when you open it in a paint program? Just try anything you can think of to narrow down possible causes.