4.2.2. versus 4.2.0

[James Huenergardt]

Rats! I was pretty excited.

I think their product would be a good complement to the XDcam EX though, and much more portable than hauling a PC around to shoots.

[Mike Schell]

Originally Posted by Alexander Ibrahim

Well Ben as a fellow indie I am buying into the EX1. I like the HVX, but I really want the 1/2" sensors, focus marks and full raster 1080p image.


Alternatively there is the Convergent Design Flash XDR. That is MSRP $5995. It uses compact flash drives and records a 4:2:2 intraframe codec at 160Mbps. It also offers 50Mbps and 100Mbps 4:2:2 with Long GOP. That might come out a bit cheaper if you have to buy a Mac and external drives for the purpose.

http://www.convergent-design.com/dow...lash%20XDR.pdf

Just a quick note of clarification, the Flash XDR is $4995. Also the Flash XDR offers a much wider range of bitrates (19.7 to 160 Mbps), so you can dial in the rate depending on the job. You can also select between 4:2:0 and 4:2:2 sampling as well as Long-GOP or I-Frame Only. Flash XDR is small enough to snap onto the back of your camcorder for run and gun applications.

Mike Schell
Convergent Design

[Mike Schell]

Originally Posted by James Huenergardt

Alexander,

Quoted from Alexander Ibrahim
"Alternatively there is a Cineform Flash XDR. That is MSRP $5995."

I'm familiar with the Convergent Design product, but didn't know it was Cineform based.

Where did you hear that it was Cineform based? That would be very exciting for me anyway.

Hi James-
Flash XDR is MPEG2 based, either Long-GOP or I-Frame only in 4:2:0 or 4:2:2 recording at up to 160 Mbps. Also the price is $4995.

Mike Schell
Convergent Design

[Alexander Ibrahim]

Originally Posted by Thomas Smet

Kevin I created that image in 3D Studio Max.

...

So it is computer generated but really that means it has a lot more raw detail then what most cameras can do.

Thanks Thomas, I was about to say the same thing. Except I was going to say any camera.

Kevin, you never get a better key than with CG images.

Also, this image has relatively mild JPEG compression.

XDCAM 4:2:0 shoves a 1.4 Gbps stream into 35Mbps of data. That's about 41:1 compression.

Compression is complicated by noise levels. (One place the EX1 should outshine a lot of its competitors due to its 1/2" sensors.) Noise makes compression more difficult and can break a codec rather thoroughly.

Also when considering camera systems, you have to consider the bit depth of your codec. 8 bit or 10 bit or 14 bit. I don't think there are cameras that use float or half, then again 14 bit log is pretty impressive. Most of the formats we use, HDV, DVCPRO, XDCAM are all 8 bit formats.

That makes a 10 bit 4:2:2 HD SDI capture even more appealing.

Alexander, Sure the straight keying looks better with 4:2:2 but your example doesn't show any chroma upsampling or softening.

I wasn't trying to get a great key.

I think you are missing the point. The point isn't to demonstrate advanced keying techniques, but rather to show the difference in the chroma sampling.

In this example I'd normally use Keylight in Shake. That pulls a cleaner key with default settings. I am not a fan of "magic bullet" keying- but in this case Keylight works a wonder.

I picked Primatte, because its included in Motion, which more people have.

In fact, thinking of Keylight and Shake, I think the alpha channel Keylight creates is instructive. I'll attach it here. (its actually just a screen grab of the Shake interface, about 1000x1000)

Its always worth it to see if one of the built in keyers can do an acceptable job, because they will always be faster than a tree/script you devise.

Back to my point.

This Alpha channel represents the default setting of Keylight. Right off the bat I can use the 4:4:4 and 4:2:2 keys... I can even just use the keylight node to lay in the background.

The 4:2:0 keys need a lot more work. I don't work the same way you do, but think of the time needed to key using the technique you describe.

Saving that artist time, and quite a lot more in many real effects situations, is the real advantage of 4:2:2 and 4:4:4.

[Alexander Ibrahim]

Originally Posted by Mike Schell

Just a quick note of clarification, the Flash XDR is $4995. Also the Flash XDR offers a much wider range of bitrates (19.7 to 160 Mbps), so you can dial in the rate depending on the job. You can also select between 4:2:0 and 4:2:2 sampling as well as Long-GOP or I-Frame Only. Flash XDR is small enough to snap onto the back of your camcorder for run and gun applications.

Mike Schell
Convergent Design

Thanks for the info Mike, I corrected my original post. Glad to see you are reading here.

Is there a whitepaper on the codecs used in the Flash XDR?

[Alexander Ibrahim]

Originally Posted by David Heath

I think any confusion might be that I am speaking theoretically, you are speaking here and now, so yes, for present practical purposes I agree.

But for the future, and the ideal progressive only world we all long for, 4:1:1 and 4:2:2 are colour spaces conceived for the interlace world. Their non symmetry matched the non symmetry of interlace. Progressive images are symmetrical, and much better suited in theory by 4:4:4 or 4:2:0.

Well, if I am going to dream about the future... how about mathematically lossless compression of 8K at 16 bits per channel at every pixel in log space? I'd ask for a 16:9 sensor, but I'd like the camera to offer a 2.39:1 cine aspect ratio, where the sensor could increase its frame rate in turn for using lower vertical resolution. Oh, and solid state or holographic recording please with faster than real time transfer to my NLE, which should of course be a mid range Mac laptop.

Actually I expect all of that will eventually happen.

Well except for the part about Apple having a mid range laptop. That's just madness.

[Thomas Smet]

Originally Posted by Alexander Ibrahim

I wasn't trying to get a great key.

I think you are missing the point. The point isn't to demonstrate advanced keying techniques, but rather to show the difference in the chroma sampling.

In this example I'd normally use Keylight in Shake. That pulls a cleaner key with default settings. I am not a fan of "magic bullet" keying- but in this case Keylight works a wonder.

I picked Primatte, because its included in Motion, which more people have.

In fact, thinking of Keylight and Shake, I think the alpha channel Keylight creates is instructive. I'll attach it here. (its actually just a screen grab of the Shake interface, about 1000x1000)

Its always worth it to see if one of the built in keyers can do an acceptable job, because they will always be faster than a tree/script you devise.

Back to my point.

This Alpha channel represents the default setting of Keylight. Right off the bat I can use the 4:4:4 and 4:2:2 keys... I can even just use the keylight node to lay in the background.

The 4:2:0 keys need a lot more work. I don't work the same way you do, but think of the time needed to key using the technique you describe.

Saving that artist time, and quite a lot more in many real effects situations, is the real advantage of 4:2:2 and 4:4:4.

I also wasn't talking about keying ability but the fact that progressive 4:2:0 is not garbage. In it's raw form 4:2:2 is better but with filtering the results are going to be much closer.

I don't know why you say my method takes a lot of time. It doesn't really take that much at all. A filter in FCP takes a second to drop in. In shake it just takes a few quick nodes which you can then save to reuse for the future. There are other tools as well that will process the footage right in your software so it doesn't have to take any time at all. To some people using such tools can mean getting great quality keys out of 4:2:0 material. Hey I agree with you that 4:2:2 is better and that I try to allows convince my clients to go 4:2:2 all the way but I just don't agree with you that 4:2:0 is garbage. Sure it takes some work but some darn good keys can come from progressive 4:2:0 material. I like where you come from but I cannot agree with you that 4:2:0 is garbage. The key you did of my image does of course show 4:2:2 as better but not by all that much. I have done some very high quality keys with good 4:2:0 footage and many other people do as well.

[David Heath]

Originally Posted by Ken Hodson

I am not an expert on this but I was told that PAL's 4:2:0 does not equate to DVD's 4:2:0. Therefor PAL is of no advantage.

I don't think that is true. I also think that by "PAL's 4:2:0" you are referring to "PAL DV 4:2:0", and whilst it is true that there it is defined differently to the MPEG definition, I seem to remember the difference is fundamentally a half line shift in chroma.

Hence, in PAL, DV-MPEG (and therefore DVD) recoding should only result in a slight chroma shift, whilst in NTSC it results in throwing away half the chroma information. Dv25 to DVD should therefore be much better in PAL than NTSC, with the exception of DVCPro, which is the only example (AFAIK) of 4:1:1 in a PAL system.

[Thomas Smet]

Ok here is my chroma example image but this time I upsampled the 4:2:2 and progressive 4:2:0 sections. I didn't do the interlaced 4:2:0 section because I would have had to use some other tools to do it and I was too lazy to do it. Interlaced 4:2:0 really is a pain in the rear.


Edit: You will notice all jagged edges are now gone. I didn't fix the blown up cross section of course just the main image.

The only artifact you now have is a slightly thicker dark border around the subject which is due to the smoothed chroma samples. You now have some of the color bleeding a little bit.

[David Heath]

Originally Posted by Alexander Ibrahim

Well, if I am going to dream about the future... how about mathematically lossless compression of 8K at 16 bits per channel at ...............

Actually I expect all of that will eventually happen.

Hmmm. I think most of that really is dreaming....... :-)

Whereas 4:4:4 seems perfectly feasible within proven technology - just 50% more bits than 4:2:2, keeping all else equal.

Desirable though much of your wishlist may be, I'd expect a general move to wavelet compression (as used by Red and JPEG2000) to be the next big step.

[John Mitchell]

Originally Posted by Alexander Ibrahim

I am not entirely convinced on that unit. It seems promising, and I'd like to be convinced. I am extremely excited by the prospects.

My first concern is that I haven't heard of Convergent Design, which may be my own fault. I have to be convinced about them as an engineering facility. Do they make solid products? For that I can turn to the community- what has been the experience of people here with Convergent Designs products?

Just to calm your fears Convergent Design have been around for some time and are well known for producing some of the better, more robust production gear. I like the fact that they are an innovator with an ear close to the market.

[Mike Schell]

Originally Posted by Alexander Ibrahim

Thanks for the info Mike, I corrected my original post. Glad to see you are reading here.

Is there a whitepaper on the codecs used in the Flash XDR?

Hi Alexander-
Thanks for the correction. We don't have a white paper on the CODEC in Flash XDR, but I can tell you that we use the very same CODEC as the new Sony 4:2:2 camera. (We buy a module directly from Sony). We actually have two MPEG2 CODECs chips on board, so we can support 4:2:2 (a single CODEC will only do 4:2:0).

Since we record to Compact Flash, we can easily adjust the bit rate over a wide range of 19.7 to 160 Mbps. Rates over 100 Mbps will require the higher speed Compact Flash cards, such as the SanDisk Extreme IV.

I really suspect the sweet spot for recording will be the 100 Mbps 4:2:2 in either Long-GOP or I-Frame mode. Then you can use the lower cost Sandisk Extreme III cards (16GB cards are now around $200).

We plan to post comparison video at the various bitrates so everyone can evaluate the quality differences.

Mike Schell

[Kevin Shaw]

Originally Posted by Thomas Smet

So it is computer generated but really that means it has a lot more raw detail then what most cameras can do.

So this wasn't an example of any actual video footage, just a demonstration of the limits of various chroma formats? If so all that tells us is that it pays to edit in a 4:2:2 or 4:4:4 format, which you can do with footage from any HD or SD camera.

To simulate how footage from different cameras might compare, I created a 960x540 image in Photoshop and added a small dot, then resized that to 1920x1080 and added another dot of approximately the same size. I'm not a chroma-keying expert but I have a feeling the dot on the right would be easier to work with...

http://www.videomem.com/temp/two-circles.jpg

[Kevin Shaw]

I really suspect the sweet spot for recording will be the 100 Mbps 4:2:2 in either Long-GOP or I-Frame mode. Then you can use the lower cost Sandisk Extreme III cards (16GB cards are now around $200).

Mike: since the Extreme III cards are supposed to support sustained write speeds of 20 MB/sec or 160 Mbps, can you go beyond 100 Mbps reliably with your device on those cards?

[Thomas Smet]

Originally Posted by Kevin Shaw

So this wasn't an example of any actual video footage, just a demonstration of the limits of various chroma formats? If so all that tells us is that it pays to edit in a 4:2:2 or 4:4:4 format, which you can do with footage from any HD or SD camera.

To simulate how footage from different cameras might compare, I created a 960x540 image in Photoshop and added a small dot, then resized that to 1920x1080 and added another dot of approximately the same size. I'm not a chroma-keying expert but I have a feeling the dot on the right would be easier to work with...

http://www.videomem.com/temp/two-circles.jpg

Yes that is exactly what this image is for. This image shows the perfect example for the best outcome. No video camera can ever be this sharp or detailed. It doesn't matter if you have 4:2:0 from a computer image or 4:2:0 from a video camera they are both still 4:2:0. In fact with a video camera you may not even notice the edges as much because everything has smooth details.

Keying also doesn't matter with how soft an edge is. only in bad keying is this a concern. A good key means the edge looks natural as if it was shot that way with a camera. If you zoom in and look at the edge of any footage you will notice how the edges have gradation and are not pixel sharp. Again no camera shoots perfect pixels. When you do your key you want the edges to look as close as possible to how they looked before you did the key. So in your image the soft dot wouldn't be any harder to key then the sharp dot. They would just have different looking edges. If your camera shoots a little softer then you want to keep everything that way so the key edges have the same look as if you shot that person in that environment. This is why for visual effects a lot of times we turn the electronic sharpness totally off on cameras and key that way. It gives a more natural look to the edge because camera sharpness can create fake looking edges. In fact in terms of chroma subsampling your sharp image would be harder to key because the 4:2:0 would show up even more because of how sharp it is. If the edges were softer the color change would be softer and not a sudden change. This i why shooting 4k is so nice with Red. Red shoots some pretty natural but soft images because it takes the image right from the chip without any edge enhancement. 4k allows people to work with the softer images but they still have a lot of detail because they are so large. the edges are still nice and soft and natural.