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Getting high color space for keying

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Phil RadelatGetting high color space for keying
by on Apr 8, 2011 at 4:30:52 am

Hi folks, is there an interface that allows you to extract a signal from a videocam or DSLR to get higher color for keying than you'll get from the h.264 encoding the camera will record in? For instance, if using a DSLR, can you tap full color from the HDMI port? If there is such a thing, can it record directly to, say, a TGA sequence files?

Thanks.


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Tudor "Ted" JelescuRe: Getting high color space for keying
by on Apr 8, 2011 at 8:41:18 am

"To ensure baseline interoperability between different HDMI-sources and displays, all HDMI compliant devices are required to support sRGB video 4:4:4, at 8 bits per component. Support for YCbCr color-space and higher color-depths ("deep color") are optional. HDMI permits xvYCC 4:4:4 (8–16 bits per component), YCbCr 4:4:4 (8–16 bits per component), or YCbCr 4:2:2 (8–12 bits per component).The color spaces that can be used by HDMI are ITU-R BT.601, ITU-R BT.709-5 and IEC 61966-2-4."
http://en.wikipedia.org/wiki/HDMI
So yes, HDMI supports 4:4:4.
The problem comes in with the output signal from all the dslr cameras that shoot HD video (up to this date at least). What you will get is a compressed signal 1920x1080 with 1.0 pixel ratio and 4:2:2 color space.
This thread may help:
http://www.hv20.com/showthread.php?7008-Recording-1080p-via-HDMI-cable

Tudor "Ted" Jelescu
Senior VFX Artist


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Phil RadelatRe: Getting high color space for keying
by on Apr 8, 2011 at 12:20:35 pm

So essentially the answer is no. That's too bad. Your second link is now three years old. I don't know if there have been improvements to the available ports on newer cameras or not.

However there are essentially two problems. The first is the signal quality (or lack thereof) of the port output, and the second is the lack of available capture hardware to grab a 4:4:4 signal and write it out uncompressed.


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Tudor "Ted" JelescuRe: Getting high color space for keying
by on Apr 8, 2011 at 1:03:29 pm

For capture you will be able to buy this pretty soon:
http://nanoflash.net/gemini_444

The short answer is no though. here's a link to an article that explains things in more detail:
http://dslrhd.com/?p=1442

Tudor "Ted" Jelescu
Senior VFX Artist


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Phil RadelatRe: Getting high color space for keying
by on Apr 8, 2011 at 11:23:07 pm

The Nano flash is cool as a portable unit, if you can either afford it or are able to rent one when needed. The Decklink is a more down-to-earth (or at least pizza-budget :-D) approach, but it still begs the question of where will you get the full-color source signal.

It's unfortunate that DSLRs, even of present-day ilk, don't have full-color ports. Of course, probably no one's really tested recent units, but it's probably safe to say they don't. I don't know if anyone's tested recent Nikons, which will be my camera of choice. Considering Nikon doesn't sell a videocam like Sony, Pana and Canon, it makes you wonder. Hope springs eternal. :-)

Videocams that may supply full-color ports will typically not have the depth-of-filed capabilities of even DX DSLRs. I know there are a few new toys out there that do, but they're pretty expensive for occasional key work. Of course, if they become available on the rental market, that will certainly make them a little more attractive, but I still won't be able to shoot a scene with them using, say, my beloved 135mm f2 Nikkor. :-)


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Walter SoykaRe: Getting high color space for keying
by on Apr 11, 2011 at 9:10:26 pm

[Phil Radelat] "Videocams that may supply full-color ports will typically not have the depth-of-filed capabilities of even DX DSLRs. I know there are a few new toys out there that do, but they're pretty expensive for occasional key work. Of course, if they become available on the rental market, that will certainly make them a little more attractive, but I still won't be able to shoot a scene with them using, say, my beloved 135mm f2 Nikkor. :-)"

Why would you want shallow DoF on a chroma key shoot? Soft edges won't key well.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events


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Walter SoykaRe: Getting high color space for keying
by on Apr 12, 2011 at 1:19:04 am

Replying to my own post, of course using DoF to blur out the green screen will improve your key -- I immediately jumped to super-shallow DoF, which may not have been a correct assumption.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events


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Phil RadelatRe: Getting high color space for keying
by on Apr 12, 2011 at 2:00:15 am

Actually my shallow DoF reference wasn't really about keying, it was really about having the best of all worlds if you could adequately key off a DSLR and also have it's filmic shooting capabilities with optics such as my 135mm f2 Nikkor.

That is an interesting point about smoothing a screen with shallow DoF, but you could only really get away with that with a static subject. If there were any dynamics in the scene you couldn't take advantage of that.


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Joey ForemanRe: Getting high color space for keying
by on Apr 8, 2011 at 1:04:38 pm

There's about to be a second best option (4:2:2), but it will be expensive.

http://www.fcp.co/hardware-and-software/pro/292-the-sidekick-hd-another-pro...

Joey Foreman
Editor/Compositor/VFX Artist


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Phil RadelatRe: Getting high color space for keying
by on Apr 8, 2011 at 11:24:21 pm

Well, that appears to be a Mac-centric device, so it useless to me.


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