Atomos recorders upscale from 8 bit to 10 bit - anybody found this to be a problem

[DevonChris]

I'm seriously thinking about buying a Ninja Assassin, but may be using it with a Nikon which outputs an 8 bit data stream over HDMI.

I've been searching to see how their recorders handle an 8 bit input and eventually found this Atomos brochure, but it's from February 2014 :

http://www.atomos.com/downloads/ninja-blade/manual/Ninja-Blade-Brochure-PDS-Feb-2014.pdf

The important bit is this :

The Ninja Blade always records in 10-bit, even from an 8-bit source. We add color registries for incorporating higher bit-depth graphics from CG, animation and special effects. This avoids banding and makes editing and grading, in fact any precision effect, more accurate.

I assume that all their recorders work like this and that this has not changed recently.

So their recorders are adding data to create a 10 bit recording. Does this cause any issues with recording quality - colour accuracy? noise?

Has anybody found any issues with 8 bit recording with Atomos recorders?

Thanks

Chris

S

 

[dhessel]

It is fine, I won't hurt anything. Really the only negative is that the file size will be larger that it would need to be if it were only 8bit. 

[Kristoferman]

I thought it was only placing the video in a 10-bit container but not actually adding any information?

[dhessel]

It just converts the 8bit values to 10bit values. There is nothing added or lost so there is no increase or decrease in quality. For all practical purposes an 8bit file and a 8bit file converted to 10bit are identical, material captured at 10bit v 8bit is a different story.

[DevonChris]

I'm starting to understand it a bit more now.

Prores is a 10 bit 4:2:2 Codec, which is why an 8 bit stream needs to be upscaled to 10 bits before the Prores encoding process, however I still can't see how the colour quality isn't being affected.

By upscaling from 4:2:0 to 4:2:2 the system has to make up colour data that isn't in the original stream

https://en.wikipedia.org/wiki/Apple_ProRes

[bunk]

I still can't see how the colour quality isn't being affected.

By upscaling from 4:2:0 to 4:2:2 the system has to make up colour data that isn't in the original stream

Each and every color that lives in the 8 bit file lives in the 10 bit file as well.

If you create a tiff file with a white background and two red pixels in 8 bit. Why would the 10 bit turn them into some shade of green or blue or even red? Those two pixels stay the exact same color red in 10 bit just as the background stays pure white.

[DevonChris]

Thanks for the comments and thoughts so far.

It looks to be more an issue of the 4:2:0 to 4:2:2 interpolation that the recorders do, rather than converting the data from 8 bit to 10 bit.

Heres a good explanation of Chroma sampling comparing 4:2:2 to 4:2:0 and the use of interpolation to create a 4:2:2 file from a 4:2:0 source using CineScene.

He concludes that there is no benefit in interpolating from 4:2:0 to 4:2:2, but hopefully there are no disadvantages too.

There does seem to be an advantage in using an intermediate Codec such as Prores and at higher bit rates, even if it is from an 8 bit 4:2:0 stream