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HDCAM to 35mm blow-up issues...


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#1 Noam D

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Posted 10 March 2009 - 03:54 PM

Hi all,

I'm gonna get some footage from a feature shot in HDCAM 25p (Sony F900), and will have to key out some green screens and switch their background to high-res still images on After Effects.

The feature is going to the lab to get blown-up to 35mm, and I've been told that the edges of the keyed out green screen will be more grainy, on the 35mm - or something like that.

Is this a known problem when doing chroma-key on HDCAM later to be blown-up ? Do I need to take some special actions or handle the keying different than usual?


Another issue- how can I prevent the footage from flickering when blown-up to 35mm?



Oh- the final master tape sent to blow-up, will be HDCAM 25p as well.

Thanks!
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#2 Steve Shaw

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Posted 20 March 2009 - 06:07 AM

If the keying is done well there is no reason for the edges to look any different in the final print that to the rest of the image.

However, HDcam is 4:2:2, so has less colour detail which may cause the keying to be less than ideal, although I've done a lot of HDcam keying work with no problems - depends on the kit you use.

Actually, HDcam is a lot less than 4:2:2 due to the nature of the recording format... see the info on my website (linky below)

As for flickering - that's down to the way film is projected, and the 'shutter angle' used on the camera when capturing (but that's 'strobing' rather than flickering). There is very little you can do to stop this.

Steve
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#3 Nigel Smith

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Posted 24 March 2009 - 03:44 PM

If the keying is done well there is no reason for the edges to look any different in the final print that to the rest of the image.

However, HDcam is 4:2:2, so has less colour detail which may cause the keying to be less than ideal, although I've done a lot of HDcam keying work with no problems - depends on the kit you use.

Actually, HDcam is a lot less than 4:2:2 due to the nature of the recording format... see the info on my website (linky below)

As for flickering - that's down to the way film is projected, and the 'shutter angle' used on the camera when capturing (but that's 'strobing' rather than flickering). There is very little you can do to stop this.

Steve


Would the fact that HDCAM is 8 bit be another limitation in chroma keying work?

Edited by Nigel Smith, 24 March 2009 - 03:47 PM.

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#4 Steve Shaw

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Posted 25 March 2009 - 03:25 AM

Would the fact that HDCAM is 8 bit be another limitation in chroma keying work?


The answer is yes, but to be honest the compression and chroma reduction used is a bigger problem than 8 bits. With an 8 bit image with no compression and a 4:4:4 signal it would be virtually impossible to see any difference to a 10 bit image...
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#5 Evangelos Achillopoulos

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Posted 28 March 2009 - 05:15 PM

The answer is yes, but to be honest the compression and chroma reduction used is a bigger problem than 8 bits. With an 8 bit image with no compression and a 4:4:4 signal it would be virtually impossible to see any difference to a 10 bit image...


HDCAM is, 3:1:1, 1440 x 1080, 8 bits.

http://en.wikipedia.org/wiki/HDCAM

The 3.1.1 is the limitation to keying...

HDCAM-SR is 4:2:2 and 4:4:4, 1920 x 1080, 10 bits.
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