Green Screen and the HVX200

Steven White · May 27th, 2005, 08:09 AM

Down-converting 1080p DVCPRO-HD to SD will yield 4:4:4 SD and excellent keying. (essentially 100 Mbps 4:4:4 SD - uncompressed SD is 238 Mbps).

DVCPRO-50 will offer 4:2:2 SD at 50 Mbps, and will be inferior to 1080p DVCPRO-HD for SD keying.

At HD resolutions, on a per-pixel basis, DVCPRO-HD is just as compressed as miniDV, but offers increased colour information (4:2:2 over 4:1:1) and introduces more spatial compression. I would expect that at native 1080p resolution DVCPRO-HD will key about as well as miniDV, however, I do not have an appreciation for how large an effect mosquito noise has on a good key, in comparison with colour space. Does anyone know which is more important for good keys?

-Steve

Thomas Smet · May 27th, 2005, 01:22 PM

In order to try and get down converted HD close to a 4:4:4 SD the resolution would have to be half. The sad thing about DVCpro HD 1080 is that it is only 1280 pixels wide. This means in order to get a good 4:4:4 down convert you will end up with 640x540. This would then need to be scaled up and interpolated either to 720x480, 853x480, or 960x540.

Even though 4:2:0 HDV can offer problems in trying to get a good 4:4:4 at least it is 1440x1080. This means we can get a natural 720x540 image in 4:4:4 which can then be scaled down to a anamorphic 720x480 for DV or DVD. Of course these numbers only work great for NTSC. PAL would need to be scaled up to match it's resolution.

If you do not use a 1/2 scale ratio your luma and chroma pixels will not match pefectly so it wouldn't be a real 4:4:4 but an interpolated result.

At one point I heard a rumor that the Europe DVCpro HD specs were going to allow 1440x1080 since there is a lower framerate there is extra bandwidth to play with. I'm not sure if that is true or not but it would be nice.

Dean Harrington · May 27th, 2005, 03:01 PM

I appreciate your responces. I'll run some tests via the software trials.
Will be using a switcher. Any recommendations on a good one?

May 27th, 2005, 03:01 PM	#18
Dean Harrington Major Player Join Date: Nov 2002 Location: Tokyo Posts: 898	thanks...... I appreciate your responces. I'll run some tests via the software trials. Will be using a switcher. Any recommendations on a good one?

May 27th, 2005, 08:09 AM	#16
Steven White Major Player Join Date: Nov 2004 Location: Canada Posts: 547	Down-converting 1080p DVCPRO-HD to SD will yield 4:4:4 SD and excellent keying. (essentially 100 Mbps 4:4:4 SD - uncompressed SD is 238 Mbps). DVCPRO-50 will offer 4:2:2 SD at 50 Mbps, and will be inferior to 1080p DVCPRO-HD for SD keying. At HD resolutions, on a per-pixel basis, DVCPRO-HD is just as compressed as miniDV, but offers increased colour information (4:2:2 over 4:1:1) and introduces more spatial compression. I would expect that at native 1080p resolution DVCPRO-HD will key about as well as miniDV, however, I do not have an appreciation for how large an effect mosquito noise has on a good key, in comparison with colour space. Does anyone know which is more important for good keys? -Steve

May 27th, 2005, 01:22 PM	#17
Thomas Smet Trustee Join Date: Mar 2004 Location: Milwaukee, WI Posts: 1,719	In order to try and get down converted HD close to a 4:4:4 SD the resolution would have to be half. The sad thing about DVCpro HD 1080 is that it is only 1280 pixels wide. This means in order to get a good 4:4:4 down convert you will end up with 640x540. This would then need to be scaled up and interpolated either to 720x480, 853x480, or 960x540. Even though 4:2:0 HDV can offer problems in trying to get a good 4:4:4 at least it is 1440x1080. This means we can get a natural 720x540 image in 4:4:4 which can then be scaled down to a anamorphic 720x480 for DV or DVD. Of course these numbers only work great for NTSC. PAL would need to be scaled up to match it's resolution. If you do not use a 1/2 scale ratio your luma and chroma pixels will not match pefectly so it wouldn't be a real 4:4:4 but an interpolated result. At one point I heard a rumor that the Europe DVCpro HD specs were going to allow 1440x1080 since there is a lower framerate there is extra bandwidth to play with. I'm not sure if that is true or not but it would be nice.