gpu said:
the precomputed method now met banding artifact:(

Then you loose precision at some point. Mayebe that's related to the other PNG problem.
Ofc. there should be zero difference from using precomputed data vs. calculating the same data every frame. So you need to investigate…

gpu said:
do you hav…

OpenGL procedural terrain.
Here is a smalll list of some of the techniques I used here:
. tessellation shaders
. trilinear texture mapping
. 2D billboards
. displacement mapping
. wind animation using noise texture
. HDR
. advanced bloom via downsampling
 

Improved bloom + experiments with adaptive exposure.

Bloom is heavily inspired by the method described by Jorge Jimenez in his great slides here: http://www.iryoku.com/next-generation-post-processing-in-call-of-duty-advanced-warfare (starts from slide 144)

It depends on what you want from the ore distribution, but I can't think of any particular reason why you can't use a noise map for ores given that you are using one for terrain.