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LW_Will
06-14-2003, 09:11 AM
Okay... PC guy showing his ignorance here...

Why is DC50... which transfers the data twice as fast (okay, I get that) of a higher quality? Is there twice the data for the 50 over 25 rate through the FW800 cable?

Also, why is the chromakey better as well? Seems to me I read that the reason is that the chorma info is in 4bit... 4-1-1... it is a little clunky for the keying.

Also, isn't Panasonics top-line prosumer 30/24 frame camera supposed to take this format? I think those cameras are about $5-10k...

Will

ps. And what does this have to do with an HDRI renderer anyway? ;-)

mlinde
06-14-2003, 11:50 AM
Hey, it has nothing to do with Mac/PC.

From Macworld July 2003:
"FireWire 400's potential has never been fully tapped. The DV format, for example, uses only around 16% of FW 400's theoretical maximum bandwidth of 400 Mbps."

The DC 50, which is digital betacam, is a different format, and probably has better usage of the FW bandwidth.

Chromakey problems have to do with the capture resolution. You have to work VERY hard to get a clean key with the DV format because most lower-end cameras are not very forgiving. Also, the smaller CCDs will have more difficulty with things like hair because it (hair) is usually finer than the pixels in the CCD, so you have ...(looking for a phrase)... washout issues with color overlap (sounds like what I mean).

The Panasonic camera that does 30/24 is a MiniDV camera, and will probably be subject to the issues of DV discussed in the other thread (HDRI/FCP 4).

All of this has to do with HDRI format support, which LW has, and now FCP 4 has, but affordable DV cameras don't have. So, great, you can render HDRI from LW, and tweak your renders, but unless you own (or rent) a high-end camera, it doesn't do you any good when working with captured footage.

<revelation>
I wonder if HDRI is really useful to the masses. I know it's usefulness for the big bucks crowd, since they are often in the unenviable position of having to match some crazy setups for feature films, but as an independent animator, who does very little compositing with multi-million dollar projects, HDRI is another word for "set it up loose and fix it in post" instead of setting it up right the first time
</revelation>

Of course, that's my opinion, and 99% of the world usually disagrees with me (even though I'm right)-- :)

Beamtracer
06-14-2003, 05:08 PM
Unfortunately, there aren't any 32bpc (HDRI) video cameras in existence. Most high-end broadcast cameras are 10bpc.

Also, note the difference between RGB and Y-UV. The computer monitor that you are looking at now is an 8bpc RGB monitor. Most images you see on your computer are RGB.

Professional video equipment tends to use a different colorspace called Y-UV. When you convert something from RGB to Y-UV you lose some quality. That's why many people work in 16bpc RGB to create graphics, then transfer it to 10bpc Y-UV video.

So, the discussion about various video formats has nothing to do with HDRI, but was just highlighting FCP4's features.

There are various 25MB/sec DV formats: miniDV, DVC-Pro 25, DV-CAM. There's virtually no quality difference between them. The latter two formats have a guard band between each video track to enable machine-to-machine editing. This is why DV-CAM uses tape at a higher speed.

These cameras are fine for the home video maker or the prosumer, who never do chroma-keys and never colorgrade their images.

The main 50MB/sec video formats are the professional DVC-Pro 50, and Sony's proprietry Digital Betacam, which you'll only find in broadcast production facilities.

The 50MB/sec tape formats are still compressed, but not compressed as much as miniDV or DV-CAM. It's the compression artifacts that make chroma-keying difficult, so the less compression the better your key.

I may be wrong on this, but I believe that mini-DV uses most of the bandwidth of FireWire 400. DVC-Pro 50 cannot use Firewire 400. It requires Firewire 800.

Some of the confusion may be due to the difference between bits and bytes. There's also the issue of sustained output vs peak output. For example, Intel's inferior USB2 interface claims a peak data rate that is a bit higher than Firewire 400. However, Firewire 400 is better for video because it's sustained data rate is greater than USB2. Firewire 800 is more than twice as fast as USB2.

PS... This thread would have been better titled "video formats" or "Firewire" or something like that. While you and I are interested in video talk, not everyone is, but everyone will have to click on the thread "wait a minute" to see what it's about. :)

riki
06-14-2003, 07:47 PM
This thread would have been better titled "video formats" or "Firewire" or something like that

My guess is that Will hit 'New Thread' rather than 'Post Reply'. But I agree the thread title is not very helpful.

js33
06-15-2003, 05:23 AM
Originally posted by Beamtracer
The 50MB/sec tape formats are still compressed, but not compressed as much as miniDV or DV-CAM. It's the compression artifacts that make chroma-keying difficult, so the less compression the better your key.



Actually it is not the compression that makes chroma-keying difficult it is the fact that mini-DV, DVCAM, DVC-25 all have a 4.1.1 colorsampling as opposed to 4.2.2 that BetaSP, DigiBeta and DVC-50 have. Also the figures are all referenced as MegaBits not bytes.
25Mb/sec is about 3.6 MegaBytes/sec. Also Firewire 400 and 800 are in megabits. So 400 Mb/sec is 50 MB/sec and 800 Mb/sec is 100 MB/sec. Mfgs started using MegaBits, rather than the MegaBytes that were used previously, in the mid to late eighties so everything sounds bigger and faster than it really is.
A 1.5 Mbit/sec cable modem is about 187.5KB/sec.
Just divide any speed or size setting you see or hear by 8 to get the real speed or size.

Cheers,
JS

mlinde
06-15-2003, 05:42 PM
Originally posted by Beamtracer
I may be wrong on this, but I believe that mini-DV uses most of the bandwidth of FireWire 400. DVC-Pro 50 cannot use Firewire 400. It requires Firewire 800.

Hey beam, just wanted to clarify: I was quoting directly from the latest macworld, because they were discussing a new AJA video product that "routes uncompressed video, 8 channels of audio, DV50, and machine control over a single FireWire (400) port. Traditional FireWire is a 400Mbps spec. The highest-quality, uncompressed D1 video signal runs 270 Mbps." This is a quote from Ted Schilowitz of AJA Video Systems.

As far as monitors, I know that there are monitors that can display YUV signals (mine would if I had the appropriate video card/connection and cables) -or- RGB.