Bit Depth

I am working with AVCHD video (which I understand is 8bpc) in After Effects. When I change the composition bit depth settings to 16 or 32 bpc what, exactly, is that doing to elements within the composition? Is, all of a sudden, a video that's 8bpc going to magically become 16 or 32 bpc? I do understand that some effects that support 32 bpc will look better, I just don't understand what happens with video or, for example, a jpg image. Thanks for the help.

Jason

putting 8-bit footage into a 16/32-bit comp won't change the footage at all... it's still 8-bit.

what it will do is allow effects that are 16/32-bit to use all those extra bits.

i think this tutorial demonstrates some of that:

http://www.videocopilot.net/tutorials/earthquake_with_32bpc/

i think andrew actually 'fakes' 8-bit to 32-bit footage by using blending modes, but i think it illustrates how you might benefit from using a higher bit depth for compositing.

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW

Um, you've got other problems here that you're not aware of, namely using AVCHD video. Here's a quote from Wikipedia:

"AVCHD utilizes MPEG-4 AVC/H.264 (AVC) video coding and either Dolby AC-3 (Dolby Digital) or uncompressed linear PCM audio coding."

Since you run AE 9, that's a problem and here's why:

Dave's Stock Answer #1:

If the footage you imported into AE is any kind of the following -- footage in an HDV acquisition codec, MPEG1, MPEG2, AVCHD, mp4, mts, m2t, H.261 or H.264 -- you need to convert it to a different codec.

These kinds of footage use temporal, or interframe compression. They have keyframes at regular intervals, containing complete frame information. However, the frames in between do NOT have complete information. Interframe codecs toss out duplicated information.

In order to maintain peak rendering efficiency, AE needs complete information for each and every frame. But because these kinds of footage contain only partial information, AE freaks out, resulting in a wide variety of problems.

I'm a Mac guy, so I like to convert to Quicktime movies in the Animation or PNG codecs; both are lossless. I'll use Apple's Compressor, Adobe Media Encoder or Quicktime Pro to do it.



This has been solved with AE 10, incidentally. By the way, there's a new update to AE 9... no fooling! You should get it!
http://blogs.adobe.com/toddkopriva/2010/10/after-effects-cs4-9-0-3-update.h...

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA

[Jason Schoenfeld] "why would Canon use it? "

The main reason: they're trying to shove ten pounds of shi.... uh, sugar... into a five-pound bag.

It's just like the entire concept HDV; it's just barely good enough to look great to the human eye, but computers see things differently. Ain't no fooling them, especially when trying to do chroma keys -- garbage in, garbage out.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA

[Jason Schoenfeld] "So is AVCHD a lesser quality HD format?"

Yes, sad to say. It comes down to the issue of color resolution.

Think of the TV picture recorded in any given codec as a B&W layer overlaid by a color layer. The best you can get is 4-4-4 color resolution: for every 4 bits on the B&W picture layer, you have 4 bits on the color picture layer. It's a great chroma key. The problem: the cameras capable of recording such color resolution are really expensive.

The next best: 4-2-2 color resolution: for every 4 bits on the B&W picture layer, there are 2 bits on the color picture layer. This is what the vast majority of good, reasonably-priced cameras use, and you can still get a good key, even though there's half the color information as there is B&W information.

Then there's 4-1-1 color resolution and its partner in crime, 4-2-0 color resolution. For every 4 bits on the B&W picture layer, there's just 1 bit on the color picture layer -- 1/4 of the color information. And what do you need for good chroma (aka "color") keying? Accurate color information.
In this bargain basement is where the DV & HDV cameras hang out with a depressingly-large number of of TV cameras, using a confusing number of codecs .

You can't see the nasty-looking color information because you're human: there's enough color info there to fool your eye and make you think everything is great. I wouldn't see it, either; I'd be fooled. But you're not going to fool a computer.


In my shop, we do our chroma key work on a Panasonic HD camera which records in the 4-2-2 DVCPro HD codec onto P2 cards, and does the job nicely for us.
We also shoot on Sony V1U HD cameras, which have a pretty good reputation. We wouldn't touch 'em with a 10-foot-pole for keying because they're 4-1-1 HDV, and that means stinky color resolution.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA

Yes, thanks for all the help and info. I've got a much better feel for what I'm working with - especially understanding the 4-1... color profile stuff, which I've never really understood before. A friend of mine and I were also discussing AVCHD the other day and I really didn't have much information. So, this clears up a lot.

Thanks again,
Jason