Comparing 10-bit to 8-bit
a) Place your source on the bottom track (in this case your 10-bit data)This results in a completely black image, even though we know a 8-bit TGA doesn't have as much information as a 10-bit Cineon or CineForm AVI. Note: I believe Combustion is doing the same 8-bit processing on the difference matte -- as Atomic VFX found in their own testing.
b) Place your new clip (in this case the TGA sequence) on the second track.
c) Place a Menu bar > Effects > Keying > Difference Matte on the second track
d) Set your Difference Matte options to the following:
View: Matte Only
Difference Layer: (Your 10-bit source image layer)
Matching Tolerance: 0%
Matching Softness: 0%
Blur Before Difference: 0%
The simpliest way to see the difference and advantage of an 10-bit image over an 8-bit image is to boost the contrast 4-5X on an image with gradients, the 8-bit data will show banding and contouring in the gradients that is very annoying. Yet I wanted a test similar to the white count test to the difference between any 10-bit vs 8-bit images (not just the areas in a gradient.)
The test I come up with using the 16-bit mode of After Effect is as follows:
1) Start with your 10-bit source, either a CineForm AVI file or DPX/Cineon sequence.
2) Export that as a 8-bit Targa (TGA) sequence (really only needs to be a few frames worth.)
3) Import the TGA sequence place it in a composite above the 10-bit source.
4) Place a "Levels" filter on both tracks, set them with these parameters.
Input Black: 0.05) On the TGA track set the Blend Mode to "Difference". The composite will now appear black, however moving the mouse over the image to reveal RGB differences between 0-3.
Input White: 32768.0
Output Black: 0.0
Output White: 1024.0 (to normalize to 10-bit precision)
6) Add an Adjustment Layer.
7) Place a "Levels" filter on the adjustment layer a set it with these parameters.
Input Black: 0.0If you want to perform a white count test, simply nest this composite with a clip of solid black and perform the first test listed above (the One River Media test.) You will discover only approximately 2% on the pixels are unchanged by the 10->8bit truncation, mostly a white image will show.
Input White: 1.0 (This will make all differences visible)
Output Black: 0.0
Output White: 32768.0
P.S. I'm planning to create a page to easily explain the advantages of 10-bit for color correction, even using 8-bit sources, as this tests above doesn't explain why the difference between 10-bit and 8-bit matters in post-production.