Chroma Key with Z1 in SD mode

[Augusto Manuel]

In the past I have tried to do some chroma keying with DV cameras but I have not been as successful as when doing it with DigiBeta and bigger cameras. I think that the size of the chips and resolution of the bigger cameras allow for much better chroma keying capabilities.

But has anyone attempted to do some chroma keying with the Z1 in Standard mode (not HDV because I think CK will definitely be better in HDV). But I am interested if any of you have done chroma key with Z1 in SD, and how much effort did it involved compared to other bigger cameras?

(By the way I am quite knowledgeable shooting chroma key backgrounds, so I am not asking how to do chroma keying in production or post but just your experience with the Z1 in these situations).

[Nick Jushchyshyn]

Many of the "bigger" (DigiBeta, DVCPRO50) cameras shoot with 4:2:2 color sampling, which is much easier to color key with than the 4:1:1 (NTSC) or 4:2:0 (PAL) color sampling of DV. In short, the issue is not so much about CCD resolution or size, but more an issue of the DV data spec.

If you shoot to DV with a Z1, the resulting file will likely be as challanging to key as the same shot from something like a PD150. Shooting to HDV will generally provide a better source image to work with since, in addition to extra resolution, I believe HDV uses 4:2:2 color sampling.

[Meryem Ersoz]

i was just listening to an experienced DP talk about this last night who recommended shooting the key in HD, then downconverting out of the camera into SD. i haven't tried this myself, but according to this guy, shooting the chroma key in HDV is much easier and cleaner, and it translates to the SD downconvert. it seemed like a good idea.

[Ben De Rydt]

You should record in HDV mode, capture in HDV mode and downconvert the footage to SD in your NLE. The reason for this is stated here: http://www.dvinfo.net/conf/showthread.php?t=59514

Downconverting in the camera won't gain you anything: you still end up with 4:1:1 DV.

[Augusto Manuel]

The reason I stated that this is in SD, it is because it has to be in SD, no HDV, because the customer will take the tape (s) and the end of the shoot and he does not have HDV equipment. Otherwise, I know that HDV will be the way to go. I have no choice. I may have to go back to my old Betacam SP camcorder which works great for chroma key.

Originally Posted by Ben De Rydt

You should record in HDV mode, capture in HDV mode and downconvert the footage to SD in your NLE. The reason for this is stated here: http://www.dvinfo.net/conf/showthread.php?t=59514

Downconverting in the camera won't gain you anything: you still end up with 4:1:1 DV.

[Augusto Manuel]

Well, this is not quite true. The resolution and size of the CCD and the electronics and image processing in the camera head seem to matter. I have no problem doing chroma key when I shoot using a D50 with a DVcam back or a Betacam SP back. The DVcam recording using a D50 camera head has the same color sampling as a typical small 3 chip camcorder like the PD150, yet it keys much better than the PD150.

Also, I never had any problems with the D50 coupled with a Betacam SP back. This is considering that the chroma bandwidth of the Betacam SP recording is quite similar to the color sampling of the DV format. So it seems that the camera section does have an effect on the results you get doing chroma key.

And again, HDV is not an option for this shoot. The customer does not have HDV equipment and needs to get the tapes at the end of the shoot.

So I was hoping if any of you had any experience shooting with the Z1 in SD mode since the camera section has better Chroma SNR, Luma SNR and overall better signal processing than other small size DV cameras.

Originally Posted by Nick Jushchyshyn

Many of the "bigger" (DigiBeta, DVCPRO50) cameras shoot with 4:2:2 color sampling, which is much easier to color key with than the 4:1:1 (NTSC) or 4:2:0 (PAL) color sampling of DV. In short, the issue is not so much about CCD resolution or size, but more an issue of the DV data spec.

If you shoot to DV with a Z1, the resulting file will likely be as challanging to key as the same shot from something like a PD150. Shooting to HDV will generally provide a better source image to work with since, in addition to extra resolution, I believe HDV uses 4:2:2 color sampling.

[Nick Jushchyshyn]

I believe that Betacam SP uses 4:2:2 color sampling and the 12bit dynamic range in the DXC-D50 far excede the 8 bit, 4:1:1 DV data spec recorded by the PD150.

Assuming you're shooting NTSC, recording to DV using an onboard tape in the Z1, you will be left with 8 bit 4:1:1 color data at 720x480 pixel resolution and will essentially be no easier to key than something shot on the PD150.
If your client can only accept miniDV, there is no escaping this limitation.

An alternative that may be worth exploring though....
Would be to use the analog out from the Z1 and record that on your BetacamSP deck. Doing this may allow you to exploit the resolution and colorspace supported by the internals of this camera.

[Augusto Manuel]

There is no such thing as color sampling for Betacam SP. Color sampling is a thing of the digital formats. Furthermore, Betacam SP chroma bandwidth (this is the term to use instead of color sampling) is equivalent or quite similar to the 4:1:1 sampling rate of DV.

DV samples luma at 13.5 MHz and chroma at 3.375 MHz. DV-NTSC uses 4:1:1 sampling in which the chroma is sampled once for every four horizontal luminance samples. Let's say typical luma bandwidth of a DVcam recorder such as DSR-85 is approx. 5.0 Mhz while chroma bandwidth is 1.5 Mhz. With Betacam SP decks the chroma bandwidth is quite close and luma bandwidth even lags behind that of DV. That's why Betacam SP may be considered the equivalent of a 3:1:1 digital format. And even recording on Betacam SP using a D50 I get better chroma keying than recording in DVcam sometimes (!!!)

So, Betacam SP bandwidth is definitely quite close to DV. You are confusing Betacam SP with Digital Betacam which has a sampling rate of 4:2:2 same as DVCPro50 and the almost defunct Digital S (Better known as D9). If Betacam SP had an equivalent "translated" sample rate of 4:2:2 then there would be basically no difference in quality between Beta SP and DigiBeta. And this is definitely not the case.

So I still would insist that the camera section plays an important part also on the success of efficient chroma keying. There is a reason to have Power HAD chips.

Giving the analog out from the Z1 to the Betacam SP deck would be a nightmare because then you endup with a compromised analog recording. I would be better off recording directlly with the Betacam SP camera in that case.

Originally Posted by Nick Jushchyshyn

I believe that Betacam SP uses 4:2:2 color sampling and the 12bit dynamic range in the DXC-D50 far excede the 8 bit, 4:1:1 DV data spec recorded by the PD150.

Assuming you're shooting NTSC, recording to DV using an onboard tape in the Z1, you will be left with 8 bit 4:1:1 color data at 720x480 pixel resolution and will essentially be no easier to key than something shot on the PD150.
If your client can only accept miniDV, there is no escaping this limitation.

An alternative that may be worth exploring though....
Would be to use the analog out from the Z1 and record that on your BetacamSP deck. Doing this may allow you to exploit the resolution and colorspace supported by the internals of this camera.

[Jerry Matese]

Originally Posted by Augusto Manuel

There is no such thing as color sampling for Betacam SP. Color sampling is a thing of the digital formats. Furthermore, Betacam SP chroma bandwidth (this is the term to use instead of color sampling) is equivalent or quite similar to the 4:1:1 sampling rate of DV.

DV samples luma at 13.5 MHz and chroma at 3.375 MHz. DV-NTSC uses 4:1:1 sampling in which the chroma is sampled once for every four horizontal luminance samples. Let's say typical luma bandwidth of a DVcam recorder such as DSR-85 is approx. 5.0 Mhz while chroma bandwidth is 1.5 Mhz. With Betacam SP decks the chroma bandwidth is quite close and luma bandwidth even lags behind that of DV. That's why Betacam SP may be considered the equivalent of a 3:1:1 digital format. And even recording on Betacam SP using a D50 I get better chroma keying than recording in DVcam sometimes (!!!)

So, Betacam SP bandwidth is definitely quite close to DV. You are confusing Betacam SP with Digital Betacam which has a sampling rate of 4:2:2 same as DVCPro50 and the almost defunct Digital S (Better known as D9). If Betacam SP had an equivalent "translated" sample rate of 4:2:2 then there would be basically no difference in quality between Beta SP and DigiBeta. And this is definitely not the case.

So I still would insist that the camera section plays an important part also on the success of efficient chroma keying. There is a reason to have Power HAD chips.

Giving the analog out from the Z1 to the Betacam SP deck would be a nightmare because then you endup with a compromised analog recording. I would be better off recording directlly with the Betacam SP camera in that case.

Augusto,

My experience is Beta SP does have significantly better color space than standard DV, that combined with the lack of compression makes a BIG difference in your ability to pull a good key. I have both an older Beta SP setup and a new Z1u and the old Beta SP does a better job for keying verses standard Z1u/DV. Analog from your Z1u would NOT be compressed however I still think the Beta scenario would give you the better results. It you opt to capture in HDV, key it in HDV in something like ULTRA and then down convert to an uncompressed AVI your resulting alpha files would be superior to your native Beta SP workflow. This would take considerably longer though.

Jerry

[Augusto Manuel]

Reread my post, Jerry. It is not really the bandwidth (again there is no color space for Beta SP since Beta SP is not a digital format). It is the camera head that matters quite a bit and those chips. Looks like you did not read all the posts carefully. You even talk HDV and reread my explanation, please. I am not interested in HDV for this particular shoot.

Originally Posted by Jerry Matese

Augusto,

My experience is Beta SP does have significantly better color space than standard DV, that combined with the lack of compression makes a BIG difference in your ability to pull a good key. I have both an older Beta SP setup and a new Z1u and the old Beta SP does a better job for keying verses standard Z1u/DV. Analog from your Z1u would NOT be compressed however I still think the Beta scenario would give you the better results. It you opt to capture in HDV, key it in HDV in something like ULTRA and then down convert to an uncompressed AVI your resulting alpha files would be superior to your native Beta SP workflow. This would take considerably longer though.

Jerry