visible benefits of more than 8bit processing:
I've some screenshots to demonstrate that higher than 8bit processing does help in specific situations, but the screenshots are too big to include them in this post, so I'll just post links instead. Please open the 3 links in different tabs of your browser and then switch between them. Please make sure that your browser does not rescale the images, so that there are no additional artifacts added by the browser scaling.
The following screenshots were made with images produced by the "madTestPatternSource" YCbCr test pattern generator. More details about that in this thread:
Now the comparison images:
ATI - VMR9 - colors.png
ffdshow 2867 - colors.png
Haali Renderer - colors.png
madVR 0.1 - colors.png
This test pattern consists of colored rectangles which form a smooth full screen color gradiant. Properly displayed you should be able to see the rectangle borders, but you shouldn't see any visible patterns in the color gradiants.
Now if you look at the ATI VMR9 and Haali Renderer result, you do see some kind of pattern. It doesn't look that bad on the screenshot, but in motion it's really ugly, because the pattern changes with every frame. The ffdshow result is even worse. The madVR result is exactly how the test pattern is supposed to look. It also stays stable in motion. The patterns in the color gradiants are caused either by too low processing bitdepth or by rounding or truncating the final processing result down to 8bit. The madVR output is only that smooth because it uses proper dithering.
If you like these kind of comparisons, I'd suggest to try "madTestPatternSource" yourself. It's contained in the madVR archive. Use it to compare image quality yourself with the renderer you're usually using.
ATI - VMR9 - smallramp.png
ffdshow 2867 - smallramp.png
Haali Renderer - smallramp.png
madVR 0.4 - smallramp.png
On a first check these 3 images might not look all that different. But if you look closer you should see two things: (1) The gradiants in the ATI VMR, Haali Renderer and madVR screenshots are smooth from left to right, while there are some unexpected bright bars standing out in the ffdshow gradiant. (2) In the ATI VMR, Haali Renderer and ffdshow screenshots the whole gradiant is covered by very small and faint vertical bars. In contrast the madVR screenshot doesn't show any such bars.
This test pattern works very well to test whether the processing queue beginning with upscaling and ending with final output somewhere somewhen ends up in rounded or truncated 8bit. If it does, you will see those faint vertical bars. The only way to produce a really smooth output with this test pattern is to do scaling and all the processing steps afterwards with more than 8bit. Also the final result must not be rounded or truncated down to 8bit. Instead only proper dithering preserves the smoothness.