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Old December 29th, 2006, 10:09 PM   #1
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HDV Canon Vs. HDMI Sony For Chromakey!

If you had to choose... imagine you're shooting a project ENTIRELY on greenscreen.

You've got a LIMITED budget for only two choices. (HD-SDI and Sony V1U are out) Either an excellent camera image-the Canon A1-but it's compressed HDV 8bit 4:2:0. Not so desirable for pulling keys.

Or you could go the other way and put your money into an expensive RAID and Black Magic Infinity card and pickup a more consumer oriented but less expensive camera-Sony HDR-HC3 or HDR-SR1, but both of which will spit out pure uncompressed 8bit 4:2:2. A lot more desirable for pulling keys.

From a technical hypothesis and FORGETTING about keyer software, lighting etc.-which would you choose for this greenscreen only project and why?

*I have private noncommercial server space and can host greenscreen clips taken with any of the Canon or Sony cameras for the community. PM me if you'd like to share. Thanks.
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Old December 30th, 2006, 10:47 PM   #2
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Hi Derek!

I have not tried any of the following so please use them only as a guide for further research. With that being said, here are some ideas for your problem:

1) A project entirely on green screen! Man, you would need a LOT of keying! How many minutes would that project be? If it is long, I would try to get 4:4:4 colour sampling to avoid hours of correcting the keys. How? Do you REALLY NEED a final export in HD? I have read in a lot of different occasions that HD downsampled to SD gives a full 4:4:4 colour space. Try to find out some more about this because I might be wrong. You may also check http://www.dvinfo.net/conf/showthrea...ight=chromakey, the post by Matt Daviss. He seems to have experience on this issue. Also, don't forget you may uprez your final product in the end (not same as working with HD all the way of course but still a potential workaround if HD is definitely needed for delivery - in what medium, by the way?)

2) How much camera control are you willing to give up? Keep in mind that the small SONY cameras that you mentioned do not have control over shutter and gain. Lack of control on shutter makes a filmout impossible (if that's what you are after). They also do not shoot progressive. Keying progressive frames is supposed to be easier than keying interlaced. You may of' course convert interlaced signal into progressive in post (with all the subsequend loses) but it also means extra post time.

3) Why do you need an expensive RAID to capture through HDMI? You only need that if you want to capture the original HDMI signal. As far as I know, if you use the blackmagic card and capture mjpeg avi files with Premiere, you need normal hard disks. You may need more than one of them depending on the size of your project (around 40GB per hour for the mjpeg codec) but how many hours do you plan to capture? If you already have a good computer it may well be the case that the only thing you need to buy is the Intensity card for 250$. You may want to research some of the posts of Thomas Smet regarding his experiments with the card and the quality of the mjpeg codec for keying. See also his posts on http://www.dvinfo.net/conf/showthrea...magic+software and http://www.dvinfo.net/conf/showthrea...ighlight=mjpeg . If you already have the pc and premiere or Apple and FCP and the only thing you will need to buy is the intensity card then maybe the FX7 may be the best (simplest) solution for your project. The only potential drawback could be that it is not progressive (how are you recording your sound by the way? No XLRs on the FX7).

4) XH-A1 may not have HDMI but it does have component out. Check out GEFEN's converter from component to HDMI. You may also feed audio to it and it embeds it to the HDMI signal. All these for only 180$. Couple it with an Intensity HDMI card and you have a possible solution. I have never heard of anyone using this setup though with an A1 (or any other camera for that matter) so you need to do some research on this as well. How is the conversion done? What is the quality of the final HDMI output? Does it work with Canon's signal? The product is made for Home theatre systems. Will it be good enough for what you need? You may also try writing an email to GEFEN and see what they say. Also, keep in mind that HDMI does not transport 24f (same goes for 24p). This means that you will have to extract the pulldown in post in case you shoot progressive. More work needed...

5) Since you are on a budget, if the Gefen solution works, you may also want to consider SONY's A1. You get XLRs and control on shutter but still no control on gain... Are you interested in 24p? If yes and you are not in pal-land, maybe a good idea would be to also consider buying a pal version of the Sony's A1, so that you can take advandage of the 25F cinema mode. Sony's 25F is supposed to be much better than 24F (is this exported from the component though? I would think yes, but don't take my word for it!). If 24p is not an issue, the NTSC version with it's 30F should do exactly the same job in terms of quality. But not the 24F, as far as I know. Of course you may capture 60i and convert to 24p or 30p in post (do you have the software?). One way or another, going progressive (either with Canon or Sony) will increase the workload in post (either extracting pulldown or converting i to p).

6) Last but not least, there are some people on this board that have extended experience in keying. Try to come in contact with Thomas Smet for example. I have found his posts to be very knowledgeable and helpful.

To summarize, there seem to be two categories of questions that need to be answered:

I) Project related questions:
a) Should the final product be delivered in HD?
b) Should the final product be delivered in progressive, interlaced or it does not matter?

II) Technical questions:
c) HD downrezed to SD gives 4.4.4 colour space, 4.2.2 or what? With what workflow?
d) Does the Gefen (or another?) product encode component to HDMI without loss? Does it work seamlesly with Canon's signal?
e) How much better is it to key progressive frames vs interlaced? Is it worth the hastle?

Hopefuly, some more experienced members will jump on this thread and help out!

Good luck and don't forget to let us know how it worked out for you!

Thanasis
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Old December 31st, 2006, 06:49 PM   #3
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or a 3rd camera that fits your budget ..

IMO shooting a whole project green screen = you get the BEST image for green screening and that would be a image that has 4:4:4 color space ...
based on your budget the camera would be a modified DVX = outputs 1540x990 images plus i think you can go 10bit images

http://www.reel-stream.com/andromeda.php
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Old January 1st, 2007, 10:02 AM   #4
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I know you've said "forgetting keying software", but there is one piece of keying software that can change your workflow. If you're on a Mac you can get very good keys from DV and HDV (in real time) using dvMatteBlast (for Apple Motion) from dvGarage for $99.

It uses a combination of the chroma and luma channels to pull very nice keys out of 4:1:1, 4:2:0, or 4:2:2 footage.

I've used it with HDV from a Sony FX1 in cineframe30 (faux progressive) and a Canon A1 in 25F to pull a exceptionally clean keys.

I'm very pleased with the way they look - although I have to add that I've only been using them on SD products (we film HD for SD output).
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Old January 2nd, 2007, 01:22 AM   #5
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Hi everyone, thanks for taking the time to respond, I really enjoyed the different perspectives you have shared.

Thanasis Grigoropoulos wrote:
"Do you REALLY NEED a final export in HD?"

Yes, it needs to be HD for release in HD DVD/Blu Ray and to be future proofed as much as possible, but thanks for the link. It would be an interesting possibility to shoot HDV and downscale if only releasing in SD.

"How much camera control are you willing to give up?"

Obviously, as little as possible... but as long as I have a clean
image of the talent that's all that really matters since the backdrops will be either cgi or high quality stills. The thing that bothers me about the little single chip cameras is they don't handle highlights that well from what I've seen.

"Why do you need an expensive RAID to capture through HDMI?"

If you're capturing uncompressed you would need at least a 5 disk raid from what I've read. I'll admit, I have zero experience with raids so I could be mistaken about this. I would be using a PC, not a mac and I haven't tried the mjpeg codec yet. If I was happy with it's quality perhaps that could be an option.

"how are you recording your sound by the way?"

Depends what camera I end up with. Main ingest is through a Creative Audigy4 since it has balance inputs and captures at 24-bit/96khz which leads to a terrific sound.

"Check out GEFEN's converter from component to HDMI"

It would be interesting to see what kind of image degradation there was.

"This means that you will have to extract the pulldown in post in case you shoot progressive"

I do this already for SD DV and am OK with it.

"you may also want to consider SONY's A1."

I considered the A1 but the for the $, you don't get any better image then the HC3 IMO. I'm all about image over features. 24p is OK, but not a must.

Thank you for all your suggestions Thanasis!

Don Donatello wrote:
"based on your budget the camera would be a modified DVX"

I seen that reel-stream a long time ago and it is an interesting idea. Overall I didn't think the samples looked anything like HD but if you could get 4:4:4 10bit out of it...it would be a great solution for keying, especially if you only need to frame talent. Hmmmm...I will have to search for a greenscreen sample. Thanks for the suggestion Don.

Alex Leith wrote:
"I know you've said "forgetting keying software""

Well, the project is scheduled to be keyed on a PC based studio setup which has Keylight or Primatte. Both are pretty sweet on SD DV footage. But 4:1:1, no matter how great it looks keyed, always, in my eyes, has that amatuer look I would like to avoid.
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Old January 2nd, 2007, 01:57 PM   #6
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Derek,

I understand your desire to get as clean a key as possible. You have to take into consideration the following factors:

Internal processing in the camera takes place at full resolution in a 4:2:2 color space, which through HD-SDI or HDMI can be captured live @ 1.485 Gbps, if the camera allows that. After the internal processing, the signal is compressed and stored on tape (or external HD) in a 4:2:0 colorspace @ 25 Mbps. So heavily compressed.

AFAIK the HDMI connectors on the Sony cameras allow for digital transfer of the recorded data from tape, not live, so in essence they only allow 4:2:0 @ 25 Mbps streams and not a 4:2:2 stream @ 1.485 Gbps. The HD-SDI version from Canon, the H1 or G1, do allow live capturing at that level.

To capture a stream @ 1.485 Gbps you need a sustained write speed on your disk system of close to 200 MB/s, hence the large disk array.

With the indicated budget restraints, I think you just have to accept you can only work with HDV recorded material, 4:2:0 @ 25 Mbps.
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Old January 2nd, 2007, 03:14 PM   #7
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Quote:
Originally Posted by Harm Millaard
AFAIK the HDMI connectors on the Sony cameras allow for digital transfer of the recorded data from tape, not live, so in essence they only allow 4:2:0 @ 25 Mbps streams and not a 4:2:2 stream @ 1.485 Gbps. The HD-SDI version from Canon, the H1 or G1, do allow live capturing at that level.
Hi Harm!

This is definitely some news for me! So, all Sony cameras output HDMI signal AFTER HDV (or AVCHD) compression and NOT live uncompressed? The blackmagic site claims the opposite (although indirectly: There is a picture of HC3 but no mention in the text - http://www.blackmagic-design.com/products/intensity/). Is this also the case for the component of the XH A1? Or the component of HC1 or Sony's A1?

I have read a lot of other posts claiming that HDMI and component can be captured live before compression, at full 4.2.2. AFAIK, this is the consensus at DVinfo at the moment. But it's true that I never came across any sample footage captured live from HDMI or XHA1 component...

Is there someone who tried this already and can enlighten us?

Happy new year to everybody!

Thanasis
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Old January 3rd, 2007, 07:43 AM   #8
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Quote:
Originally Posted by Thanasis Grigoropoulos

This is definitely some news for me!

I have read a lot of other posts claiming that HDMI and component can be captured live before compression, at full 4.2.2. AFAIK, this is the consensus at DVinfo at the moment. But it's true that I never came across any sample footage captured live from HDMI or XHA1 component...
This would be news to me too. It simply can't be true. The whole point of a HDMI output is to have an uncompressed signal for monitoring...there would just be no point if it was compressed and you couldn't see the true shot you were getting...

Quote:
Originally Posted by Harm Millaard

With the indicated budget restraints, I think you just have to accept you can only work with HDV recorded material, 4:2:0 @ 25 Mbps.
That would be true if I was restricted to HD-SDI. But a raid $3000, and an HC3 $1500 is about the same cost as a Canon A1 so it's completely within reason.

It's really going to come down to one of those 2 choices for me. My main point in starting this thread was to solicit opinions on which would provide a better key for greenscreen:
Canon A1 or HC3 using HDMI out.
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Old January 3rd, 2007, 08:40 AM   #9
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Keep in mind that HDMI is just one part of the entire pipeline.
Consider that a DV image from a palm-sized ZR10 doesn't look the same as a DV image from a new XL2. DV and HDMI are delivery technologies, but the lens, imager, internal processors, user configurable settings, etc. that the image passes through in the camera BEFORE the signal gets to them are every bit as important.

You have a great question, there are many great opinions here in reply.

Ultimately, shooting tests using both tools, with a lighting setup comparable to your production situation to compare the results of the pipelines is the best way to compare the options. Looking primarily at the theoretical specs of HDMI capture vs HDV is a very limited (and perhaps meaningless) scope.

My personal impression (I have no experience with any of these cameras) is that a G1 or H1 with SDI capture would be your best bet. A1 next, due to my instinct (could be wrong) that 3CCDs fed by the A1 lens would perform better than a hand-cam using a single CMOS.

A soft, over sharpened image through HDMI is generally not going to be as useful for keying as a sharp clean image compressed to 4:2:0.

Also, if you control your subject and screen selection to use either a dark subject (Dark hair, dark clothes, dark skin) in front of a green screen ... or use a bright subject (blond hair, fair skin, white clothing) in front of a blue screen .... you can basically avoid color compression based artifacts in your composits altogether and the 4:2:2 vs 4:2:0 concern becomes a non-issue.
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Old January 3rd, 2007, 09:33 AM   #10
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In my earlier post I said:

"Internal processing in the camera takes place at full resolution in a 4:2:2 color space, which through HD-SDI or HDMI can be captured live @ 1.485 Gbps, if the camera allows that."

The reason I made the second remark:

"AFAIK the HDMI connectors on the Sony cameras allow for digital transfer of the recorded data from tape, not live, so in essence they only allow 4:2:0 @ 25 Mbps streams and not a 4:2:2 stream @ 1.485 Gbps."

is based on one fact and one supposition. The fact is that the Sony Operating guide does not mention the capability of live HDMI output @ 1.485 Gbps and let's be realistic, this would be a HUGE selling point. See for instance pages 58 and 61 of the V1 operating guide. The HDMI connector is shown as an alternative to fire wire, because there are few TV's with fire wire connectors, but rather a lot with HDMI.

Secondly, and this is the assumption I made, is the HUGE price difference between cameras with or without HD-SDI. Example Canon A1 vs. G1, around $ 3K. Given the pricing structure of Sony, example the XDCAM-HD 330 vs. the 350, is seems utterly inconceivable to add a live HDMI capability on a less than $ 2K camera and even on the V1 it is unrealistic.

It would be nice if Chris Hurd, DSE or other experts could confirm or deny my statements.
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Old January 3rd, 2007, 10:19 AM   #11
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HDMI lacks timecode and the means to make it work with pro equipment. It's original intent is for HDCP and protecting copyright. I don't think Sony is worried about 4:2:2 HDMI hurting their upper end. There are other factors that effect the signal, such as the lens as already mentioned, and how well you light your scene.

I can understand the difference in cost between a G1 (or used H1) and a Sony HC3. Including a system capable of working with 4:2:2 10bit. But after all that work of setting up your scene and the human effort involved, why make the most important tool in your pipeline the weakest link? Can't you just rent what you need?
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Old January 3rd, 2007, 02:35 PM   #12
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HDMI Out supports "Never Compressed"

Interesting discussion! For clarification, as a manufacturer of an HDMI to HD-SDI converter (HD-Connect MI), I can absolutely assure you that the "live" output from the Sony camcorders has never seen any compression whatsoever. The uncompressed video is 1920x1080i 4:2:2, while the audio is 48Khz stereo, 16-bit uncompressed. Additionally, it is possible, using our converter box to get 720p or 480i out of the Sony camcorder (or M25U deck) in either live mode or while playing back from a tape.

The HD-Connect MI also supports deck control via RS422 to 1394 command translation. You can find more info on our web site as well as a recent technical paper on HDMI technology ("HDMI in HDV and AVCHD camcorders").

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Old January 3rd, 2007, 03:49 PM   #13
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HDMI works just as component output in terms of it being uncompressed. That is the whole point to it.

HDMI is first just a connection to your TV so you only need a single cable to view your material in high quality with very little effort. It is only Blackmagic design who came up with a way to treat this port as a capturing device and I'm sure other people will follow as well.


With that said if live capturing is not an option true progressive 4:2:0 actually isn't all that bad. The Canon F modes and any video from the JVC HDV cameras uses true progressive 4:2:0 encoding which means clean 2x2 blocks of chroma. It may not be as detailed as 4:2:2 but it is clean. If you have decent software that can upconvert or smooth the chroma channels you will get very good results.

The SONY cameras only use interlaced HDV encoding which alternates chroma samples every other line so you really kind of end up with 2x4 blocks of chroma samples which is not very clean. This only happens this way if you deinterlace the video. If you have a progressive frame sitting inside of a 1080i stream then you end up with chroma jaggies because the chroma samples may not line up exactly with the luma samples because they alternate every other line. If you need to shoot interlaced then this isn't an issue because thats the way interlaced 4:2:0 has to be. If you plan on shooting progressive however and need to shoot to tape first then the Canon and JVC cameras will give you a cleaner image with less artifacts. If you will be able to capture the live output from the camera then I'm not yet sure which camera will be better. While HDMI sounds very nice it still has not been used by anybody on this forum that I know of so we do not yet know exactly what it will look like. In theory it should look as good as 8 bit over SDI but I have not seen anything to show this as of yet. The Intensity cards are now starting to ship so perhaps we will see some examples soon.
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Old January 3rd, 2007, 05:28 PM   #14
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Hi Thomas-
The HDMI ouput will be exactly the same image as the 8-bit over SDI. The The same data stream would be used to drive either type of output as well as the analog component encoder.

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Old January 4th, 2007, 07:55 AM   #15
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Quote:
Originally Posted by Mike Schell
Interesting discussion! For clarification, as a manufacturer of an HDMI to HD-SDI converter (HD-Connect MI), I can absolutely assure you that the "live" output from the Sony camcorders has never seen any compression whatsoever. The uncompressed video is 1920x1080i 4:2:2, while the audio is 48Khz stereo, 16-bit uncompressed. Additionally, it is possible, using our converter box to get 720p or 480i out of the Sony camcorder (or M25U deck) in either live mode or while playing back from a tape.

The HD-Connect MI also supports deck control via RS422 to 1394 command translation. You can find more info on our web site as well as a recent technical paper on HDMI technology ("HDMI in HDV and AVCHD camcorders").

Mike Schell
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Mike,

It is interesting indeed, since if your statements are indeed accurate, Sony would have an incredibly attractive deal with all HDMI cameras, blowing all competition to h*ll. Strange however that Sony, who is very, very marketing oriented and always the first to show their strength's in comparison to the competition, would play this MAJOR advantage so low key, no even FORGET about mentioning it.

I posed this question to Sony, asking whether the signal out of the V1 through HDMI was a compressed 25 Mbps signal or a 1.485 Gbps signal and they will investigate further, but the initial reaction was, since it is a TV compatible signal, that it is only 25 Mbps and thus compressed.

There is no possibility to change the signal in the menus from one to another and it definitely is compatible with TV's, this leads me to the conclusion you are possibly wrong in your statement. Once I have heard from Sony, I'll keep you posted.
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