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Old August 11th, 2008, 04:44 AM   #1
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10-Bit vs 8-Bit Color

I figured I'd post here b/c you guys really take the image apart and probably have best view of subtle color differences.

I'm contemplating capturing out of the HD-SDI port of either a Canon XH-G1 or a Sony EX1. Besides workflow differences and sensor size, a siginificant difference between the cameras is color depth: Canon is 8-bit, Sony is 10-bit.

I would think this should be significant, but I've seen footage comparisons and for the life of me really can't tell where 8-bit was an impediment. The difference just isn't obvious, even though using 256 levels of color instead of 1,024 should be pretty significant.

But I am viewing on a computer monitor w/ untrained eyes, so I leave open the very real possibility that 10 bits is quite an improvement.

FWIW, I'm doing a documentary with mostly sit-down interviews. I hope for a theatrical release, but nothing is certain.

Thanks for any insight!

Last edited by Peter Moretti; August 11th, 2008 at 06:10 AM.
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Old August 11th, 2008, 04:55 AM   #2
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When you start pushing the colours in colour correction or processing the difference can become more apparent.

8 bit can also cause "stepping" in what should be smooth colour gradients. Things like blue skies, clouds, smoke etc.

For most shots, 8 bits copes very well.
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Old August 11th, 2008, 08:52 AM   #3
 
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I think the implications of 8 bit material implies a 4:2:0 color space whereas 10 bit implies a 4:2:2 space. There's a lot more info color info available with 4:2:2, which makes color timing 4:2:2 less full of artifacts.
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Old August 11th, 2008, 09:48 AM   #4
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That isn't always true. There are plenty of 4:2:2 8 bit codecs such as DVCPRO 50 & HD.

The bit depth and chroma resolution are independent.

It is a good point to consider though, is the Canon true 4:2:2 out of the HDSDI or 4:2:0 up converted to 4:2:2?
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Old August 11th, 2008, 10:29 AM   #5
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Peter, I've also done my own comparisons between 8-bit and 10-bit. The difference is there, but I didn't find it to be significant for most uses. But, please don't tell my colorist, as he's likely to throw a fit. Whenever I mention "some of the footage was shot on HDV", he gives me a mournful look, like we just had a big disaster. But I do appreciate the additional things that he can do with real 4:2:2 vs. 4:2:0. On a side note, I'm really excited about Scarlet RAW as it lets you choose the best colorspace and bit depth for the material.
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Old August 11th, 2008, 11:01 AM   #6
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Hi

speaking of 420 n 422, is it a good decision to convert your 420 8bit to 422 10bit (something like cineform) video prior to Color timing, so tht colors remian intact n footage has less artifacts? as i know there is no advantage, anyone has anything to say?

Thanks
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Old August 11th, 2008, 12:46 PM   #7
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The matter is more complex than simply stating 10-bit color is better than 8-bit. Your question is ultimately about quality. And overall quality is composed of different components, visual as well as technical.

If you focus on the technical side you can say that any "higher" spec is better, like better subsampling (4:4:4 > 4:2:2 > 4:2:0), better color quantization (8 vs 10-bit), higher bitrates or better - newer, faster and more efficient - codecs.

Quite often you will find yourself in a 'format' discussion about all combinations of these and the most important parts are left out: the lens, the sensor and the (in-camera) processing pipeline.

Older camera's often have less sophisticated sensors that record less data in the first place. That is information you never get back, whatever you do.

Then there is the processing pipeline; high(er)-end camera's may use 14-bit A/D converters for precision, other may use 10 or 12-bit (it should always be higher than the sensor quantization and the output).

What is "eventually" output for recording may be 8, 10 or 12-bit. And only then does the recorder/encoder come into play.

And even there things are not so clear cut. 50Mb/s of anything is not always the same quality. Newer implementations of (hardware) encoders - using the same codec - are simply able to do a better job than previous generations. New codecs may also be better than older codecs, but possibly not for all applications.

And lets not forget about the lens! This is the first component in the system that affects the image quality. It relates closely to the sensor. In short: it is much more difficult to make a lens with a high resolving power for small sensors. So a smaller sensor generally means a worse lens.

For comparisons you really have to know what you are looking for and then compare 'systems' as to their individual performance. Manufacturers don't publish enough information to make any useful assessment from the technical specs.

The sensor is IMHO the biggest factor. Bigger size and full resolution will give you more information and if it is coupled with a good A/D converter and records using a modern encoder/codec, with a reasonable bitrate, you should have great visual quality results.

Higher bitrates will yield increasingly less visual improvements. 4:2:2 will give you more information but is only really useful if you need serious color correction; the same pretty much goes for 10-bit quantization.

If you (think you) need 4:2:2 over 4:2:0 or 8-bit over 10-bit you really need both. For a feature film shot on different sets/locations and times, 4:2:2 and 10-bit quantization may be requirements to make it easier to bring everything together. For interview and doco footage this may be less so.

For color correcting 8-bit footage you can use a 10-bit codec in post to preserve as much information as possible.

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Old August 11th, 2008, 06:31 PM   #8
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Thanks VERY MUCH for the replies!

BTW, as for 4:2:0 versus 4:2:2, with either camera I'd be capturing out of the HD-SDI port, so would by bypass their respective codecs. And single link HD-SDI is 4:2:2.
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Old August 11th, 2008, 08:04 PM   #9
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If you plan to drag uncompressed footage from the EX1 you best have a super fast computer and lots and lots and lots of drive space.....

The best way to get that footage from the EX1 is use a XDR recorder... and even at that the footage is still compressed...
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Old August 12th, 2008, 12:09 PM   #10
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Ray,

Thanks for your input. The plan is to use a fast workstation w/ a large RAID array for capture. For the sit-down interview portion, mobility is not an issue.

If this proves unwieldy, then I'd probably use a 10-bit color codec like Cineform. In which case, image degredation due to the compression/decompression will be pretty minimal.
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Old August 12th, 2008, 12:16 PM   #11
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don't forget that most LCD screen are 8 bits, so disply will utimately been done on 8 bits.
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Old August 12th, 2008, 08:23 PM   #12
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Right, which really makes me think that the difference is more significant than I'm seeing.
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Old August 12th, 2008, 09:57 PM   #13
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You might get some ideas over at the Black Magic web site... they have products for capturing uncompressed 10 bit data...

yes, I like Cineform very much... but I think you will need some hardware to go along
with Cineform, to work the way you want..
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Old August 13th, 2008, 01:59 PM   #14
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Quote:
Originally Posted by Giroud Francois View Post
don't forget that most LCD screen are 8 bits, so display will utimately been done on 8 bits.
True, but if you consider printing to film it is worth it. You'd better use a display like the HP DreamColor LP2480zx color-critical (10-bit) display. On the road you can take the released HP EliteBook 8730w with you, which has an integrated 17" DreamColor display (only 8-bit tough).

Quote:
Originally Posted by HP Press Release, August 11, SIGGRAPH 2008
Mobile workstations for the ultimate creative professional

Designed for the most sophisticated graphic-intensive applications, the new HP EliteBook 8730w is the only mobile workstation on the market to offer a 17-inch diagonal HP DreamColor Display, which offers over 16 million colors, a significant improvement to the 260,000 available colors on traditional notebook PCs. The notebook also offers an Intel® quad-core processor, 8 gigabytes (GB) of memory (64-bit OS needed) and NVIDIA’s next generation of Quadro FX cards with up to 1 GB dedicated video memory.
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Old August 13th, 2008, 03:38 PM   #15
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i think HP is making a feature out from nothing with their laptop.
yes, while most PC screens are TN LCD (with 6 bit color) there is a huge quantity of screen
made from VA technology (MVA, PVA, S-PVA) or IPS (and S-IPS) with 8 bit color.
So assuming THEY provide 8 bit while the rest of world is stuck to 6 bit is a bit strong.
Last year , Apple was almost sued by doing the same kind of advertising with their new laptop.
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