BMCC: Color quality after debayering?

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Peter J. DeCrescenzo

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BMCC: Color quality after debayering?

PostSun Oct 21, 2012 3:21 pm

The following is from the "Shipping Updates" thread ...
viewtopic.php?p=10583&sid=a27d934b822d7e460bb2710e9fe250d1#p10583

... re-posted here because this topic is something I'd like to learn more about. I suspect I'm not asking the question correctly because I don't yet fully understand the issues involved. Clarification & discussion welcome.

Theodore Prentice wrote:I think you missed what me and Peter were ultimately discussing. The theoretical difference between a larger sensor capturing at 8bit vs a smaller sensor at 10bit both transcoding at the same 10 bits. ...


Hi Theodore: If you're still around ... and as I continue to wrap my head around what I think we were discussing ... :lol:

I vaguely remembered something Barry Green posted on the BMCuser forum, so I did a search and found it. I've copied & pasted it below because we're not allowed to link to other forums.

If I understand what you & Barry are saying, the pixel array size (resolution) of a single-sensor camera, after debayering, can limit the maximum color quality recorded, regardless of the recording method used (10-bit compressed, 12-bit RAW, etc.) if the sensor res isn't high "enough".

I may not have this right, but if I do, is this related to your point, or are you referring to something else?

Cheers.

===========================================
Gabriele Turchi:

Q: Are you saying that the 2.5k bayer pattern of the BMC camera even when loaded into Resolve on a 1080p project have the same chroma latitude and info of a 422 ?

Barry Green:

A: Seems like a simple question, but leads to a complex answer. It depends on what sensor made the 1080p image! But let's assume for the moment that we're talking about a true three-chip 1080p camera, so there's true color info in all of the 4:2:2 decimation, that would give you chroma resolution of 960x1080. Or, per frame, 1,036,800 color samples.

The BMC has 1200x675 chroma samples from its sensor. If you debayered and stored in ProRes 444, you could preserve all that chroma, and would have 810,000 chroma samples. So no, it's not possible to have as much chroma resolution (even with ProRes 444) as a true 4:2:2 camera would deliver.

Now, when shooting ProRes 422, it's a little worse actually, because your 1200x675 will get scaled down to fit into 960x1080, so the net result will be 960x675, for a grand total of 648,000 chroma samples.

The way to preserve the most chroma information is to avoid going to a 4:2:2 codec. Keep it raw, or transcode to a 4:4:4 codec, and you'll have the most chroma the camera can give you. ..."
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Adonis

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Re: BMCC: Color quality after debayering?

PostSat Dec 01, 2012 5:54 am

It’s hard to really explain to some people the advantages of one camera system over another.
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rick.lang

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Re: BMCC: Color quality after debayering?

PostTue Dec 11, 2012 3:01 pm

Adonis wrote:It’s hard to really explain to some people the advantages of one camera system over another.


Following Barry Green's post, it appears even a 4K (3840x1600 at a 2.4:1 aspect ratio) won't give you a true 4:4:4 image at 2K resolution (2048x858) in either horizontal or vertical direction. The lines of resolution fall obviously short. Ergo, perhaps the 5K sensor or certainly the Dragon 6K sensor are better. At least providing true 4:4:4? But realistically, not a serious issue until tackling the most demanding keying and VFX. Less than perfectly true 4:4:4 still works for the movie consumer. Even less than perfectly true 4:2:2 works. I can't see the pursuit of perfection in this regard as worth it for indie filmmakers but once Dragon is available, time will tell who is using it and at what delivered resolutions.

Maybe a 3CCD system wasn't such a bad idea!

Rick Lang
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