10 bit 422 vs 8 bit 420

Question

I have been looking around for commentary on this, but have not been successful. So, I hope you folks can point me in the right direction. Hopefully, this is the right forum for this kind of discussion, since there might not be 1 correct answer.

For a while now, I've been using my canon 1D4 for most video production. It's ok for what it does. At times, I supplement with other video sources for multi angle shoots.

This past summer, I did an interview on the back of a truck with a fixed-mount camera (7D w/ 15mm due to tight geometry). Basically it looks great. However, we were going in and out from under trees and the lighting switched from kinda dark to very bright. Since I was also working B camera angle and audio for the interview (very crowded, no room for others) I was distracted and there are some very blown out sections of the video.

I have seen reviews and samples on the bm(p)cc showing how blown out sections can be recovered using ProRes 422, much like raw photos can be recovered. Ditto for underexposed clips. Of course, my video was 420 and had no option to recover from either end of the histogram. What's done is done, much like a jpg image.

So: need to work on resolving this issue. For a single-person 'team', I need equipment that is forgiving. been reading about shooting directly to 422 and getting a very wide exposure latitude. The Black Magic cameras (especially pocket) seem to fit the requirements. However, everyone is raving over the GH4 which, tho it shoots 4k, is 8bit 420 unless you record to outboard via 1080, which seems to defeat the 4k benefits.

Any discussion on this topic would be most welcome.

Answer 1

420 vs 422 only really matters in terms of color accuracy. The significant part is 8 bit vs 10 bit. The reason RAW files give so much recover-ability is that they are typically 12, or in the case of your 1D mark 4, 14 bit files. Every extra bit doubles the total number of possible values that can be stored. Some of this goes in to having more detail within the typical 8 bit range, but some of this also goes in to holding additional headroom above white and below black for a typical 8 bit image.

Even better than shooting 10 bit is to try shooting pure RAW video. You may be able to actually try this with your 1D by using high speed cards and the third party firmware hack Magic Lantern. I've used it on my 5D Mark iii and the results are outstanding. It can record full 1080p resolution with each frame being a 14 bit raw file that has full use of RAW image correction tools.

Alternately, you can help increase recover-ability in 8 bit video by keeping your image away from the black and white points by decreasing contrast. This will result in a more subdued image without color correction after the fact and will result in fewer total colors after expansion, but it will buy you room to deal with blown highlights and shadows since they will still fall within the 8 bit range of values. This technique is often referred to as recording a "flat" image.