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General HD (720 / 1080) Acquisition
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Old June 24th, 2007, 03:19 PM   #31
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Originally Posted by Thomas Smet View Post
Good keying also comes down to the software you use. The best way to key footage is to interpolate the chroma samples back in.
Yes good software can help a lot. The Cineform products AspectHD/ProspectHD ect.. do an automatic intelligent chroma upsample on conversion, which is a highly under rated feature of the software IMO. This helps a lot when you use your keying software.
I am dropping a link below because it is really hard to find it on their site.

http://www.cineform.com/technology/H...ysis051011.htm
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Last edited by Ken Hodson; June 24th, 2007 at 11:09 PM.
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Old June 24th, 2007, 05:35 PM   #32
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IMO Cineform's chroma upsampling looks non-standard as it disobeys interstitial chroma siting- the center of the chroma is shifted/moved upwards in the Cineform scheme. A better scheme would blur without shifting the chroma center... i.e. chroma blur 1.0 vertically in Vegas (*not sure if Vegas' filter uses the right luma co-efficients for 709/HD; I doubt it).

(This assumes that the MPEG-2 standard calls for co-sited chroma horizontally, and interstitial chroma vertically. I've never read the MPEG-2 spec, but this is what it calls for according to Poynton's book.. which is likely correct [see poynton.com].)
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Old June 24th, 2007, 10:52 PM   #33
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Originally Posted by Jack Jenkins View Post
Is there really a perceptual difference between 4:4:4 color and 4:2:2/4:2:0?
Well you tell me by looking at the image I posted. Can you see any difference between the 4:2:2 and the 4:4:4? I'm not talking about the blown up window but the real image itself.

You also need to remember there is a huge difference between computer graphics and what a video camera can do. A video camera will never ever be as sharp and detailed as a computer image. Most cameras including every single HDV camera in the world only process 4:2:2 in the DSP. This means no matter what you do you will never ever get 4:4:4 out of your camera. The only cameras that process 4:4:4 in the DSP are the SONY F950 Cinealta cameras. I'm not even sure if the F900 will. The only way above that to get 4:4:4 is to use a camera such as Red but then a single chip bayer sensor has it's own color interpolation issues which means you will never have true perfect 4:4:4 source for less then $100,000.00 on a camera.

While the samples on the Onerivermedia website are a good example of what the different codecs do, at the same time they are not really fair of realworld footage. Again no camera in a decent price range will ever resolve perfect single pixel lines.

Current HDV cameras have so many other limitations such as chip size and optics that the difference between 4:4:4 and 4:2:2 is really insane to think about. Even if you had a super clean source which is something you can only get with computer generated images 4:2:2 will be so hard to notice that you would have to be a super geek to even worry about it.
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Old June 24th, 2007, 11:17 PM   #34
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Originally Posted by Glenn Chan View Post
IMO Cineform's chroma upsampling looks non-standard as it disobeys interstitial chroma siting- the center of the chroma is shifted/moved upwards in the Cineform scheme. A better scheme would blur without shifting the chroma center... i.e. chroma blur 1.0 vertically in Vegas (*not sure if Vegas' filter uses the right luma co-efficients for 709/HD; I doubt it).

(This assumes that the MPEG-2 standard calls for co-sited chroma horizontally, and interstitial chroma vertically. I've never read the MPEG-2 spec, but this is what it calls for according to Poynton's book.. which is likely correct [see poynton.com].)
That sample shot is taken from an interlaced HDV source. Sony FX1 I believe. I have only ever used it on progressive HDV footage and it works very well, especially considering it does it automatically.
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Old June 24th, 2007, 11:30 PM   #35
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I suspect it may slightly degrade quality if you were to author a DVD off it.

For chroma key, you're slightly better off doing a vertical blur that does not move the chroma center.

But those are likely really small technical details. For speed/workflow, it may be nice if you're doing lots of chroma key.

Quote:
While the samples on the Onerivermedia website are a good example of what the different codecs do, at the same time they are not really fair of realworld footage. Again no camera in a decent price range will ever resolve perfect single pixel lines.
Probably the most likely case where something like that would happen is if you're pan&scanning still photos, or down-converting CG generated imagery.

You can also have problem with real-world imagery if panning across any color edges.

But then again, extremely subtle artifacts (you kind of have to be looking for them). And there are much bigger issues to worry about than tiny details like that.
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Old June 25th, 2007, 04:16 AM   #36
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I tried the following:

1) Keying HDV (4:2:0) and resize output to SD
2) Resize HDV to SD DVCPro50 (4:2:2) and pull keys from SD

Keying 4:2:0 HDV results in cleaner SD images.
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