HVX Pan vs. HDV 1080i vs. HDV 720p for Chroma Key

[Matthew Romanis]

Hi John,
Due to HDV’s highly compressed nature, keys that are near perfect will key well. Any format that has a high degree of compression will present some problems when keyed.
I have recently seen a Sony Z1, DVCAM 450, and a Panasonic DVX 100 performing green and blue screen keys. All cameras and formats performed well when conditions and chroma separation were optimal. When we pushed chroma separation together the Sony Z1 lost out real quick, also when there was any degree of quick movement in frame. The 450 was the clear winner in all tests we performed followed closely by the DVX 100. Interestingly though was when we used the uncompressed output on the Z1 and recorded straight to disk. The results were brilliant. My advice would be to never think of doing a key from tape with the Z1 unless you absolutely have to.
I have been doing keys for years now with PRO 50 camcorders and recently with the Varicam and the HD 100 codec, though I prefer to to use an uncompressed codec when space and time allow. Both codecs offer excellent results, though I would have to say that PRO 50 probably is less time consuming and easier to get great results with.
Hope this helps.

[Barry Green]

In theory the DVCPRO50 and DVCPROHD codecs should provide a significant advantage for chroma-key work, because they sample color at 4:2:2 rather than at 4:2:0. In actual practice this results in about 78% more color samples for DVCPRO-HD 1080i vs. HDV 1080i, and 50% more chroma for DVCPRO-HD 720p vs. HDV 720p. As for standard-def, DVCPRO50 has 100% more color information than DV.

Now, that’s “in theory”. In practice, we haven’t had a chance to compare real-world results. It seems like the Panasonic should have a significant edge, but we have to see what happens to the image when it goes through the lens to the CCDs to the sampling circuitry to the DSP, and eventually to the compression engine.

—————–
Get the most from your DVX camera. The DVX Book and DVX DVD are now available at https://www.dvxuser.com/articles/dvxbook/ and at Amazon (https://tinyurl.com/54u4a)

[Martin]

matthew
Can you help me out here, If I use the uncompressed output on the sony z1 and record straight to disk What sample rate do I get….4.2.2…4.4.4?…If its uncompressed then it would be 4.4.4 right?
When you use the uncompressed output to disk, what speed do the hard drive, disk need to be to capture the footage….7200RPM…or higher?
If the Sony z1 can do the above why are we waiting for the new panasonic p2 cams?
When the most important element of the camera was it’s ability to sample 4.2.2….
Martin

[Graeme Nattress]

It’s nominally 4:2:2, but I don’t know of anyone who’s done a test to confirm that. Uncompressed HD is 1920×1080, and the Z1 doesn’t really have enough definition for it’s 1440×1080, and some of that is down to the lens and some down to how it’s 960×1080 chips are working, and some is the interlace factor, so although the signal coming out could well represent a 1920×1080 image, it will not have the precise definition of a 1920×1080 image that comes uncompressed off the SDI outputs of a CineAlta. However, it should be a lot better for keying than the signal from the HDV compression. Even HDCAM is not easy to key with…..

Graeme

– http://www.nattress.com – Film Effects and Standards Conversion for FCP

[Carlos]

In my experience I got better keys with the SDX900 (DVCPRO50)coming out uncompressed SDI at 10 bits than with HD, in HDCAM or DVCPRO100 codec. Uncompressed HD in the other hand…..but I think is an overkill unless you plan to finish in HD. I even think Digibeta keys better than HD.
If you care for resolution, always try to plan in using an HD Lens with any of these cameras.
Carlos

[Noah Kadner]

I’ve good luck with SDX900 DVCPRO50 keying as well. Bottom line is that it and Digibeta have a very low relative amount of compression- 3.3:1 compared to DV, most compressed HD formats, etc.

Noah

[Toke]

Actually digibeta’s video bitrate is 90 Mbps so its compression rate is more like 2.3.

[Matthew Romanis]

Hi Martin.
The colour space sample rate is 4:2:2 off the CCD block using HD component out. I needed to use a converter to take the HD RGB signal and make it HDSI for capture through a BM card into my G5. So you can see that this rig is not exactly portable in comparisson to the HVX 200 and what it is offering to do. The test we carried out is not a simple nor inexpensive way to go, but does offer a different approach to capturing key material.

[Steve Freebairn]

If all you plan on doing is in a studio setting and you have an uncompressed capture setup, then it would be better to go with the Canon camera, because it has built in SDI out and will output uncompressed from the camera without the need for a analog-digital converter. The reason why the HVX200 is so sweet, is because it is portable and has variable framerates with highquality DVCPRO color.

[Matthew Romanis]

Couldn’t agree more, though has anyone sampled the canon yet. Is it 4:2:2 off the head?
Having had a Varicam now for 2 years and banging my head against the 720 vs 1080 wall more times than I care to think about, it’s going to be nice to have a camera that can do both that will appeal to some of our clients who are in this marketplace.
Now it’s just a matter of getting one to go south of the Equator in PAL guise when it’s released.