Keying and the HVX200 on DVCPRO HD

[Oliver Ojeil]

We have 5 TVCs which will be all shot on green/blue screen. It is basically a presenter speaking with a background to be added later in post. The agency proposed to shoot on DigiBeta but they are nagging too much on the budget. Would shooting on the HVX 200 deliver the same keying capabilities in post, especially that they both share the same sampling ratio of 4:2:2?

 

Thanks for the advice guys

[Michael Most]

We have 5 TVCs which will be all shot on green/blue screen. It is basically a presenter speaking with a background to be added later in post. The agency proposed to shoot on DigiBeta but they are nagging too much on the budget. Would shooting on the HVX 200 deliver the same keying capabilities in post, especially that they both share the same sampling ratio of 4:2:2?

 

Yes and no.

 

The camera and the recorder are two different things. If you record the HVX material using DVCPro50, you're getting roughly the same performance as the DigiBeta recorder. However, DigiBeta cameras (in general) have far better sensors, far better glass, and considerably less noise, so the image is arguably superior, which sometimes helps in terms of matte extractions. Bottom line: You get what you pay for, even with the most modern technology. A $75,000 camera and recorder will produce a superior product when compared to a $5000 camera and recorder, even when you're only shooting effects elements.

[Walter Graff]

For the most part you can key fine with the HVX. In other words based on what you say you are shooting, it will not matter, but Mike is absolutely correct, you get what you pay for and a camera with a far better MTF and processing will record a far better picture. While we have accepted the HVX200 as a professional based on marketing, it suffers quite a bit compared to a camera with a dedicated body with more electronics and a real lens. But it will accomplish what you need perfectly well.

[Oliver Ojeil]

Yes and no.

 

The camera and the recorder are two different things. If you record the HVX material using DVCPro50, you're getting roughly the same performance as the DigiBeta recorder. However, DigiBeta cameras (in general) have far better sensors, far better glass, and considerably less noise, so the image is arguably superior, which sometimes helps in terms of matte extractions. Bottom line: You get what you pay for, even with the most modern technology. A $75,000 camera and recorder will produce a superior product when compared to a $5000 camera and recorder, even when you're only shooting effects elements.

 

I will be shooting on DVCPRO HD and P2 cards, not DVCPRO 50 or lower. So is it too much of a difference? I mean is the difference in quality as big as the difference in price? Because if it is not, then I would go for the HVX

[David Mullen ASC]

This is beyond my level of expertise, but some cleverer people here were once talking about being able to do better chroma keys in standard def by shooting in consumer HD but converting the individual channels to get full chroma resolution for each channel in standard def, since all you need is 720 x 480 pixels for each color in NTSC standard def resolution.

 

So you could take 4:2:2 DVCPRO HD, or even 4:1:1 HDV, and basically create "4:4:4" in standard def, do the chroma keying, and then convert to whatever standard def codec you need to deliver in. This method only works if you are finishing in standard def video.

 

But like I said, this is outside my level of expertise.

 

In terms of 4:2:2 being the same for standard def versus HD, that's true, but DVCPRO-HD has more compression than Digital Betacam (note that DVCPRO-HD is 100 Mb/sec and I think Digital Betacam is around 80 Mb/sec?)

[Walter Graff]

This is beyond my level of expertise, but some cleverer people here were once talking about being able to do better chroma keys in standard def by shooting in consumer HD but converting the individual channels to get full chroma resolution for each channel in standard def, since all you need is 720 x 480 pixels for each color in NTSC standard def resolution.

 

So you could take 4:2:2 DVCPRO HD, or even 4:1:1 HDV, and basically create "4:4:4" in standard def, do the chroma keying, and then convert to whatever standard def codec you need to deliver in. This method only works if you are finishing in standard def video.

 

But like I said, this is outside my level of expertise.

 

In terms of 4:2:2 being the same for standard def versus HD, that's true, but DVCPRO-HD has more compression than Digital Betacam (note that DVCPRO-HD is 100 Mb/sec and I think Digital Betacam is around 80 Mb/sec?)

 

I think this is all fine but for what he is doing, he will probably not need anything this special.

[David Mullen ASC]

Yes, he shouldn't have problems doing chroma keys with 4:2:2 anything. This unique solution was more in regards to trying to do chroma keys with consumer 4:1:1 DV25 versus consumer 4:1:1 HDV.

[Walter Graff]

While I know you mentioned it's not an area of expertise for you, I'll offer some options. First of there are plug-ins in software that allow you to soften the edges of 4:1:1 color space. You could also trans code 4:1:1 color space to 4:2:2. DV25 is much more trouble to deal with on the prosumer cameras than it is on the more robust pro style cameras. Bottom line most anything can be keyed these days. Some keyers such as the one available in After Effects is Hollywood quality and can deal with most nay situation. In my experience there are three combinations that make up a good key. One, the equipment. Regardless of the color space, a dedicated lens, larger imager, and more robust camera electronics is better to deal with. Second, is the method you use to key. Some of todays keying softwares allow you incredibly accurate keying. Three talent. As I said in an earlier post somewhere on this board, good keying is earned not acquired. Learning the aspects beyond the production side are invaluable to learning how chroma key works.

 

I should also add that a direct comparison of two formats compression schemes often doesn't tell you enough to matter.

Edited April 12, 2007 by WALTER GRAFF

[Ken Minehan]

Mr. Mullen Can you help explain how you get 4:4:4 from footage shot at 4:2:2 DVCPro HD?

I didn't quite understand.

 

Thanks

Ken Minehan

[David Mullen ASC]

Mr. Mullen Can you help explain how you get 4:4:4 from footage shot at 4:2:2 DVCPro HD?

I didn't quite understand.

 

Thanks

Ken Minehan

 

Like I said, this was someone else's idea, so don't ask me for the technical details. Basically the digital frame in standard def NTSC is 720 x 480 pixels.

 

In theory, 4:2:2 HD footage, if you had shot 1920 x 1080 HD for example, would be 1920 x 1080 pixels for the luminence/green information, and 960 x 540 separately for red and blue information.

 

So if in standard def, all you need is 720 x 480 for each color for a theoretical "4:4:4" (even though I don't think there is such a thing in standard def videotape) then you could derive this from 4:2:2 1920 x 1080 HD, or even 1280 x 720 HD, though the red and blue channels would be slightly less than 720 x 480 and would need uprezzing. You'd basically be separating the color channels in HD and converting them individually to 720 x 480, doing the chroma key composite, and then converting the composite to whatever standard def codec you need.

 

Someone here last year was playing around with this concept for doing chroma keys in standard def. Maybe Phil Rhodes remembers this conversation -- it was a bit over my head.

 

But like I was saying, you shouldn't have problems doing chroma keys with 4:2:2 material anyway, so this isn't really necessary.

[Ken Minehan]

Ok, thanks for the reply. It is still a little hard to grasp, but i kind of think i know what you mean. Kind of. As for shooting Green Screen with the HVX200, you wont have any trouble at all. I have done several green shoots with this camera and all have turned out fine.

 

Regards and thanks

Ken Minehan

[Jaan Shenberger]

i just skimmed the other responses, so i apologize if this is redundant...

 

as long as your footage is properly lit and shot/"exposed", then the DV100 4:2:2 (aka. DVCPRO HD) will key just fine with any half-decent keying software/plugin.

 

do your keying/matte extraction in HD and your downrez to SD is going to look very nice (the key will look better than keyed digibeta footage in my opinion-- the 4x pixels trump the qualitative advantages of digibeta). hope this helps and best of luck.