In testing techniques to lessen the banding effect on a graduated background I've come across some unexpected results that I hope some of you can explain or comment on…
I created a 16bit Composition in After Effect that adds fractal noise to a radial graduated background. It looks very good in AE on the computer monitor at 100%.
Then I exported the composition to both ProResHQ and AvidDNx175x – both 10 bit codecs. The DNx175x file was 364MB and also looked very good when played back in Quicktime, but the ProResHQ file was only 200MB and definitely showed some banding and color contamination in what was a neutral grey background. I was surprised that the file sizes and results were so different between the 2 codecs.
I then did a fast import of the DNx175x file into Media Composer, put it on a timeline, and did a video mixdown to ProResHQ. Viewing at 10bit on my external FSI monitor I really cannot see a difference toggling between the original imported clip and the mixdown. But when I do a Same As Source export, the resulting ProResHQ file viewed in Quicktime has the same banding I saw in the ProResHQ file that After Effects created. And, this new file is now only 84MB in size! Checking the Avid MediaFiles the mixdown mxf file is also 84MB.
We normally mixdown to ProResHQ and export Same As Source because it has always given consistent, high quality results for encoding to H264 and other deliverables. In this case, the ProResHQ file is being played back directly from a laptop to a big screen movie house system. Everything looks great except for the banding issue I was trying to solve. Now I'm surprised to see what a quality difference there is between the two 10-bit codecs. Why does the Same As Source file have banding I can't detect in the mixdown with my grading monitor? And why does Avid's mixdown create such as small file compared to the ProResHQ that After Effects created (even though they have similar banding)?
Thanks for your comments!
Craig Mikhitarian
ACM Productions, Ltd.
Posted by: CraigACM@aol.com
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