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HVX200 in keying - which format is best?


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#1 Olivier Egli

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Posted 10 March 2008 - 06:02 AM

Dear all

I will use the HVX200 in 2 weeks for a musicvideo shooting that involves some keying.
I am very proficient with lithing and also shooting in various formats, however the HVX
is relatively new to me and therefore a question occurs to me:
since it is a 100mbit/s format at 1080 as well as at 720 it must be that since this 1080 has 4times the resolution of sd and sd DV has 25mbit/s the color space or the compression must be similar to DV when shooting 1080p with this camera...right? so wouldnt it be the better guess to shoot 720P maybe even at 50 frames/sec (i am in europe) to get a sharper image and to spare the datarate and benefit from less compression on a smaller frame? my output will be sd anyway, but i want to have more than sd resolution in post to be able to pan and scan the picture without losing resolution. i know that otherwise DVCpro50 would be a good guess, but i need the extra pixels.
so 720p50 or what do you think?

another thing:
since the comp shots from the greenscreen will be put in fron of white and the studio has a decent white background wouldnt it be more sensible to match dark costumes and makeup and hair and shoot in front of white and then luma key the whole thing? the reason is that i want to shoot all the actors separately to have more flexibility in post...
any ideas?

cheers
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#2 Walter Graff

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Posted 10 March 2008 - 07:53 AM

Both Standerd def and high def will key equally well.

But more importantly if you have a cyc, you'll get such a better look than keying them over white. Also please change your name to your real name as is required in this forum.
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#3 Olivier Egli

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Posted 10 March 2008 - 08:58 AM

Both Standerd def and high def will key equally well.

But more importantly if you have a cyc, you'll get such a better look than keying them over white. Also please change your name to your real name as is required in this forum.


i just tried to change my name, but to be hones i dont know how to do this :)
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#4 Adrian Sierkowski

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Posted 10 March 2008 - 09:00 AM

Chick on My Controls, then on the left hand side, at the bottom, "Change Display Name"
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#5 Olivier Egli

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Posted 10 March 2008 - 09:30 AM

okay so i did it, happy?
and now let's get back to topic...still need help
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#6 Olivier Egli

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Posted 10 March 2008 - 09:39 AM

I meant "please help me", thank you
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#7 Walter Graff

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Posted 10 March 2008 - 09:57 AM

okay so i did it, happy?
and now let's get back to topic...still need help



As I said:

Both Standard def and high def will key equally well.

720 will do you fine too as will 1080. There is barely a noticeable difference in the two with this camera.
Luma keying can cause you more trouble than chroma. Chroma key uses the color to assign a luma key to. Luma key only works with levels of light vs dark and means you'll have less room for error corection. Unless everything is black and dark talent wise. I'd say do a simple test of one person in similar get up and see which keys better for you. I did a series of composties for amjor phrmecutical company involving three on camera talents . We shot over four months so I had to later make all their moves and framing match p. I shot them, over a big green screen. Worked out great.

As for shooting HD, it is smarter in that as you say it offers what you said which is the ability to manipulate the picture easier in an SD frame.

In the three sample shots, I had to have them both walk on and end up next to each other. And in between a big logo. So I shot them full screen walking and talking individually and then later matched them up. Notice in third frame is the composite and I had to take the logo out forlegal reasons to show it here so the bottom area looks uneven as a result.

But the idea was to shoot everyone seperate and compostie them together. worked great.

t1.jpg
t2.jpg
t3.jpg
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#8 Olivier Egli

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Posted 10 March 2008 - 10:41 AM

yes, i see what you mean.
i was just trying to get around the problem that my greenscreen is only
18 feet wide but the white studio wall is something around 40 feet.
and since the cameras luma/ color sampling is 4:2:2 in favor of luminance
and the actors will be dressed in black and have very dark make up and hair
i though boosting the background (in that case not equal light levels on the back
ground but probably 1 1/2 stops over) and have the actors at key...
this should give me the contrast needed to pull a matte...or am i deadly wrong?
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#9 Walter Graff

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Posted 10 March 2008 - 10:44 AM

All cameras favor luminece so 4:2:2 has little to do with it. If your actors are all in black and black makeup and you dont have any instuments or anything that can refelct white then a luminence key can work fine.
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#10 Olivier Egli

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Posted 10 March 2008 - 05:22 PM

it would be great to see an example of a scene that has been luma keyed using the DVCproHD codec.
for some reason i think art direction will be more challenged...spill would be deadly on faces and edges.
what tool do you recommend for post....how about ultimatte or primatte for luma keys?
me and my compositing artist we both work mainly in after effects.
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#11 Jim Simon

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Posted 16 March 2008 - 11:39 AM

I'd like to add a little twist to the discussion.

It's my understanding that the DVCPro HD codec uses a fixed data rate of 100 Mbps, when shooting at 1080P. That means each frame has so much data associated with it. That data/frame is fixed. Dropping frame rate does not up the data/frame, it simply drops the overall data rate to less than the total available 100Mbps.

It's the data rate per frame that is fixed, not the overall data rate. Fewer frames per second equals lower overall data rate, not a fixed overall rate with more data per frame.
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#12 Jim Simon

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Posted 16 March 2008 - 11:39 AM

Mispost. Sorry.

Edited by Jim Simon, 16 March 2008 - 11:40 AM.

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