Difference between Digibeta and Mini DV?

3 replies [Last post]
ChrisBitz
Offline
Joined: Jun 8 1999

Hi,
I'm just about to film something that may be transmitted on a Cable Channel. I convinced the person commisioning, that many documentaries are filmed in Mini DV and that as long as the master sent to the cable Channel is on Digibeta, it would be ok...

I was told this by a TV Editing suite, but not knowing it for a fact, I just wanted to confirm it with some of the more experienced people out here...

Is there any technique or trick that I can employ whilst filming to ensure that people don't look at the video and say "That's not broadcast quality"

Something like using a couple of Redhead lights or having a larger iris and slower shutter speed or vice versa.... Would anything like that make a significant difference?
I'll be using a TRV900...

Any good ideas?

Thanks,

Chris.

Alan Roberts at work
Offline
Joined: May 6 1999

The thing that gives away the use of DV, is the colorimetry. Generally pictures tend to be less saturated than with full broadcast cameras. That said, though, you can't put it right by winding up the saturation because the camera gamma is probably wrong.

The more you pay for a camera, the better the pictures. Not just the size of the ccd, quality of the lens, etc, although they play a part. The image processing is different. Lower cost cameras (and I include ALL DV units in that, below about £7k) have lower gamma laws than a broadcast camera should have. The BBC "0.4" law is the standard in the UK (generally) and has a gain at black (black slope) of 5, but the vast majority of consumer cameras rarely approch 4, 3.5 is more usual. This makes the pictures more quiet (less noise because less gain at black), more saturated (I could explain why that is, but it would take too long) so they wind the saturation down (thereby reducing chroma noise as well), and black crushed.

Add to that, the 3x3 colour correction matrix and the shaping of the ccd responsivities in a broadcast camera are optimised to get the best colour performance, there are scientific methods for this, too complex to go into here. Consumer cameras may not have a matrix at all, and may have the reponsivity curves tailored to maximum signal efficiency (so high sensitivity with low noise) rathe than good colour performance.

Plus, DV has lower chroma resolution than broadcast formats. DV in "PAL" is sampled 4:2:0, so there is only one chroma sample per pair of luma samples, and only in one axis per scan line. Digibeta samples at 4:2:2, giving one sample of each of Pr and Pb per pair of luma samples. This difference is very visible if you try doing any keying operations.

Aperture correction is usually better conroled in Digibeta as well.

Although you're right that some programmes are shot in DV, there's always a good reason for it, usually cost or convenience. Either way, the customer (the broadcaster) has agreed that beforehand.

I wouldn't like to try to pull the wool over the eyes of a customer.

------------------
alan@mugswellvillage.freeserve.co.uk. Delete village for a spam-free diet.

[This message has been edited by Alan Roberts at work (edited 10 November 2000).]

ChrisBitz
Offline
Joined: Jun 8 1999

Thanks for the reply Alan, I knew I could count on you for a decent sized reply!

Maybe my choice of words could have been better, but I hate the thought that I'm "pulling the wool over a client's eyes" filming with a TRV900 is saving them over £1000 and I also gave them a quote using digibeta too.

The reason for my concern, is that the hugely successful "Trigger Happy TV" on Ch4 was filmed entirely on Mini DV, and at no point did I wonder about the "quality" of the images... (Theres a new series on tonight BTW)

Additionally, I believe digital channels are lower quality than Analog because of the compression - have you noticed the white lines on a football pitch on Sky?

Should I go back to the client and tell them that the picture quality categorically won't be good enough, or are you just scaring me? :)

For an additional question, does a Digibeta camera have a firewire output, or should I get an RS422 adapter or whatever it uses?

Thanks again,

Chris.

Alan Roberts at work
Offline
Joined: May 6 1999

Chris, I wasn't implying that you were trying to cheat or anything, only that you shouldn't conceal anything. If the broadcaster has said "I won't accept DV", you have to ask yourself (or him) whether that means "won't accept delivery on DV" or "won't accept any material that has been through DV". There's a difference, and it might be visible. I was trying to advise you to get a clear statement from the customer as to what is acceptable.

DV is being use increasingly in broadcast tv, but always when the customer is willing to accept it as such. The mini-series "Losr In France", during the World Cup, was entirely DV (but it was DVCam, not ordinary DV), and it showed, contrast handling wasn't very good, there were aliases visible due to excessive AK, chroma resolution was a little low etc. I don't need to tell you how to spot the differences.

there's nothing wrong with using DV as long as the chap buying it knows what he's getting.

On the other subject of digits vs analogue in broadcast, yes I'm aware of the problems. I have a pair of recordings of the Great North Run, one on DV from an OnDigital settop decoder with Rec.601 output via a MADRAS into a Sonh DHR1000, and the other on DV from the S-Video output of an SVHS VCR tuned to BBC analogue. The OnDigital picture looks appreciably worse all through the programme, but there are MPEG arefacts on the analogue signal because some of the cameras were MPEG coded to the studio centre, and the live mix was MPEG coded back to the network centre. At some points there were two, unrelated, PAL codings and two MPEG codings, before the signal got to Crystal Palace for analogue transmission, let alone the OnDigital MPEG. And, before you ask how I know all this, it's just by looking at the pictures and analysing what I see. I can identify the artefacts from each point in that chain just from the pictures. Of course, I also have spies......

------------------
alan@mugswellvillage.freeserve.co.uk. Delete village for a spam-free diet.