1080p 420 8bit is as good as 1080i 422 10bit?

[Cranky]

http://www.ambarella.com/docs/1080p60.pdf

This creates the opportunity to use 1080p 60 4:2:0 60p at 8bits-per-sample as a unifying format for both contribution and distribution. This is the case because down conversion of 1080p60 4:2:0 at 8 bits-per-sample can deliver 4:2:2 with increased dynamic range (almost 10 bits) at both 1080i and 720p resolutions.

I can buy that when scaled to 1080i or 720p, 1080p 420 can produce as much chroma as the target 422 formats, but bit depth? How 8bit depth can be resampled to 10bit depth with actual data, not just my means of interpolation? How added spatial resolution can improve dynamic range? Do I understand it correctly that when downconverted, the tiny specs of 8-bit black and white are averaged to 10-bit gray? (Yes, I know that 8-bit samples are gray too, I tried to make it simple to understand).

 

[Barry_Green]

Sounds like nonsense to me. 1080/60p at 4:2:0 isn't going to have any additional interline chroma to make 4:2:2 with. The difference between 4:2:0 and 4:2:2 is that 4:2:2 has chroma on every line, versus 4:2:0 which averages two lines together. You can't un-scramble an egg once it's been scrambled; 1080/60p @ 4:2:0 isn't going to have any increased chroma samples to create 4:2:2 from.

And scaling 1080p down to 720p doesn't result in 4:2:0 becoming 4:2:2 either. It can result in higher overall color sampling but it won't be doubling.

As for 8-bit becoming 10-bit... there's something to be said for that, I guess... Once you've sampled down to 0-255, you're not going to get back to 0-1023. Now, if it was a true quartering of the image (going from 1080/24p to 480/24p) you could add the four adjacent pixels together and get a "fat" pixel value range of 0-1020... I haven't really thought this through but at first glance it seems like an argument could be made. But you'd have to drop down to SD resolution to really pull it off; I don't think it's practical to argue that 1080/60p 8-bit could be converted to 1080/60i 10-bit!