Just doing a little testing with the sub-pixel option in the color mapping controls.
After a few tests I found that although the sub-pixel off option did indeed produce a much more realistic image it comes with some problematic artifacts.
It seems to also be more prominent using Vray sun/sky [is it due to the very bright values producing extremely varied pixel brightness??]
All options are off in the color mapping [except Affect background]
Only option that was changed between the 2 images is sub-pixel mapping.
Note! when you compare the tree in the two images they look very different. It seems to make a big difference on small details such as leaves
Is there a best solution to deal with the artifacts??? as the sub-pixel off seems so much more realistic.
After a bit more reading & thinking & testing yesterday I finally came to understand what is happening [well partly anyway??]
I always understood vray sun was very very bright…as it is in real life… but until I took the time to measure the pixel values in the render I didn’t understand just how extreme it makes the pixel values.
I got got measurements as low as .01 for heavy shadow areas and around 3.0 to 6.0 in areas of full direct sunlight, & the vray sky pixels were reading 20.0.
Obviously the renderer has to struggle to smooth out such massive differences in pixel values. [What’s the best way to deal with this???]
As the only thing I found that seems to help this is higher AA subdivisions then I guess that the issues would also become less obvious rendering at a higher resolution [which is all the AA filter is doing anyway??]
In the images below I did another sub-pixel test on a interior scene. You can see an even greater difference with sub-pixel on/off than the exterior scene. I was really surprised at how big a difference it turned out to be. The more you learn the more you realise the less you know!!
The first two images are rendered at min1 --max24 AA Filter & the final one is using min1 --max100 AA
The sub-pixel ON has a lot less artifacts & much cleaner edges although it has nowhere near the same lighting & colour.
Final image still has random white dots around the scene.
These effects are unfortunate but its nearly impossible to avoid these problems. You either clamp each sample which causes dimming or suffer from bad anti-aliasing caused by over bright samples.
It might be possible to include some intelligent algorithm to compare results of clamped and non-clamped output and tune the result to get non-clamped look with proper antialiasing. Unfortunately this isn’t something easy and fast to “fix”.
