ProRes 422 HD?

[Lonnie Bell]

Mitchell,
there was talk about AJA making a battery powered accessory for the IOHD, but I can't find any research on it. Did the literature that came with your IOHD allude to anything that a brick may be attached to in the field. The AC current restriction is a deal breaker for me - I'd rather spend almost twice as much and go the Flash XDR route to be more "mobile"...

Thanks in advance,
Lonnie

[Mitchell Lewis]

No, nothing. I think the Flash XDR would be a better route for field use.

We only plan to use the ProRes for studio (chroma key) work. We'll just run a long HD-SDI cable.

[Alister Chapman]

I recently did a whole bunch of Chroma Key tests with my EX3. I recorded 35Mbps HQ, ProRes HQ (via Decklink/HDSDi) and uncompressed. The test were all done with Progressive material as I really don't like the way interlace keys.

I could see very little difference between the 35Mbps EX footage and the ProRes HQ material and the resulting keyed material looked pretty much the same. The uncompressed material on the other hand was far cleaner with less noise and this gave a much better key. Overall I was surprised at how noisy the ProRes material was. It is far from loss-less.

[Mitchell Lewis]

Were you shooting 1080 or 720? So how did you capture uncompressed HD? Does the Decklink hardware allow you to do that?

I thought it was difficult to capture ProRes HQ. I can't imagine how difficult it is to capture Uncompressed HD.

Thanks for passing on your results. Great information.

[Mitchell Lewis]

Here's an old thread that compares the difference between ProRes 422 HQ and XDCAM-EX codec.

EX-1 (or EX-3) for Chroma Key? - DVXuser.com -- The online community for filmmaking

[Lonnie Bell]

Alister,
Thank you very much for sharing your tests and info as you always do. However a follow up I think that would be invaluable would be:

When comparing a scene shot with Exdcam HQ vs the same scene captured via HDSDI to ProResHQ is how well do they "clean up" or can they be pushed in post. Because ProResHQ is 4:2:2 10 bit, are you able to manipulate and push the image in post in such a manner that the Xdcam HQ couldn't because it is 4:2:0 8bit?

And if it was NOT a keyed scene but, rather a narrative shot, could you more easily do a difficult color correction in post, with less/no noticeable degradation in quality (such as day for night, or removing the artifacts in the shadows by manipulating the blacks, noise removal)?

Although intuitively 4:2:2 10bit would seem to be the way to go - if real world results are not enough of an advantage gain over the additional HDSDI field tethering - this would be important info.

Would love to hear your thoughts or results on this...

Thanks,
Lonnie

[Lonnie Bell]

Mitchell,
The Decklink gives your Desktop the In/Outs to connect your camera (HD-SDI) to. To capture uncompressed you would normally need a raid set up, because the data stream is way to large for a normal harddrive setup in your computer to capture without missing frames. This isn't a big deal for studio setup, but for the field as you can guess is an additional chore...

Lonnie

[Lonnie Bell]

Mitchell,
thanks for the link above - I would have missed that. The codecs look indistinguishable to my untrained eye - I don't key much. And I can't tell if there might be more noticeable textures in the red pullover on the Uncompressed side or if the textures are just more noticeable because the keylight on this side seems to be less hot...

Great post from Jim Arthurs though!

[Terje Rian]

Alister,
It´s interesting to hear that you didn´t experiencing any difference between 35Mbps HQ and ProRes HQ. Having done quite a few chroma key sessions shooting 35Mbps HQ myself, I´m not surprised you managed to pull a decent key from this codec. But from my experience when shooting 35Mbps HQ you need to be really careful when you light your object and green screen. I guess that the ProRes HQ will turn out more flexible in a less than perfect shooting situation? And as Mr. Bell mentions, in post I believe that a 4:2:2 color space would hold up better.

When it comes to chroma keying it´s usually done on a location (besides where a specialized chroma key studio is available). Even if uncompressed delivers the cleanest result, uncompressed recordings in the field is a challenge (if you don´t have the budget and the resources available). Alister, do you have any experiences to share when it comes to chroma key shooting on location? I guess Convergent Design´s products are the most practical solution so far? And in just a few weeks Panasonic will start shipping the HPG-20, which will record AVC-Intra 10-bit... Time will show how this solution will compare to uncompressed. At least it´ll be a very mobile solution. Until then I´ll stick to
35Mbps HQ codec for (simple) chroma keying.

Best,
-terje

[Alister Chapman]

The Decklink card gives me HDSDi input on my MacPro. I have a very fast 2Tb raid array so I can easily capture uncompressed, but this is very much a studio setup. The decklink card will also convert the HDSDi stream to ProRes on the fly.

In terms of both keying and grading in the first instance I don't find that there is much difference in working from the native XDCAM EX material or ProRes. Although ProRes is 10 bit the material you are starting out with is still 8 bit as the camera outputs 8 bits (in a 10 bit stream) over the HDSDi.

It all depends on your workflow and how you intend to output your project. For the vast majority of my projects I edit the native EX footage and do any grading in the timeline (FCP). Then I export to my final output codec. I always try to keep the project to one single pass of editing/grading/encoding. Many of my projects are being saved out as either EX (cuts only) or XDCAM HD 4:2:2 @ 50Mbps. For these there is nothing to be gained by using ProRes and I set the timeline to render to EX or XDCAM 50Mbps. Projects that are going to be output to HDCAM I set the timeline to render to uncompressed as there is less noise than ProRes, but these projects eat disk space! For projects where I am unsure of where they will end up I encode to ProRes HQ as they take up less disk space but can be re-edited if needed with little loss.

I find that with my single pass workflow I get the best results editing from the native EX material. Converting to ProRes before editing adds an extra encoding pass and although you are encoding to a 10 bit codec, unless you grade or otherwise manipulate the image during the encode you will still only have 256 levels of gray.

Now, if you are going to put your material through more than a single pass then encoding to ProRes makes much more sense as over multiple generations ProRes is much more robust. But you do need to remember that when you capture over HDSDi as the camera output is 8 bit you will still only start off with 8 bits of information in the 10 bit ProRes data. You will however have a colour space advantage but if you are shooting progressive the colour space difference is minimal. See the attached frame grabs, the left image is EX the right is uncompressed 10 bit 4:2:2.

If you then process your 8 bit data by grading etc and re-render to ProRes you will then start to use the extra data bits and at this stage start to gain some advantage.

I find that HDSDi captured uncompressed is cleaner and as a result grades and keys better than ProRes. ProRes and EX have similar amounts of noise and progressive material keys about the same. The mosquito noise in ProRes isn't bad, but it's there.

The secret to good chroma key with any format is good lighting, ProRes or uncompressed won't make up for bad lighting.

I am going to get a Convergent Nano Flash as this will give me a very flexible yet compact way of getting even better quality from my EX's. Although I'm not really expecting a huge difference just a small improvement as I have done tests at 35Mbps, 50Mbps and 100Mbps and the differences are often hard to see.

[Lonnie Bell]

Originally Posted by Alister Chapman

Projects that are going to be output to HDCAM I set the timeline to render to uncompressed as there is less noise than ProRes, but these projects eat disk space!

Alister - thanks for the details and your time. If you would clarify this quote for me please...

If your output is intended for HDCAM - is your FCP timeline sequence set to XDCAM EX and then under sequence settings you put the render codec to uncompressed? or is the timeline sequence and render codec, both set to uncompressed?

Thanks again my friend,
Lonnie

[Barry J. Anwender]

Originally Posted by Alister Chapman

... Although ProRes is 10 bit the material you are starting out with is still 8 bit as the camera outputs 8 bits (in a 10 bit stream) over the HDSDi.

... But you do need to remember that when you capture over HDSDi as the camera output is 8 bit you will still only start off with 8 bits of information in the 10 bit ProRes data.

Alister, are you certain about the SDI bit depth on the EX1/3?

As you know, the topic has been vigorously debated several times in these forums. Cheers and Happy New Year!

[Terje Rian]

Alister, I´m a bit puzzled by your statement: "Although ProRes is 10 bit the material you are starting out with is still 8 bit as the camera outputs 8 bits (in a 10 bit stream) over the HDSDi."

This issue has been dealt with in other threads on this forum, but are you suggesting that the EX-3/EX-1 only outputs 8-bit (disguissed as 10-bit) over it´s HD-SDI? Or do I misunderstand your wording? Technical discussions in a foreign language (for me) can be challenging sometimes.

FYI Mick Schell of Convergent Design writes in one of the threads:
"I can absolutely confirm that the EX1/EX3 HD-SDI output has a full 10-bit resolution, not just 8-bit with the lower 2-bits forced to zeroes. We tested the output of the EX1/EX3 on our $25K Tektronix WFM-700 HD-SDI monitor. It is unquestionably 10-bit resolution. All HD-SDI sources are 10-bit 4:2:2, but often it's only 8-bit effective, with the lower 2-bits set to zero. The EX1/EX3 is a full 10-bits, which is really amazing given the price of this camera."

And Juan Martinez (Senior Manager Technology) of Sony states:
"We added PsF to the EX3 and EX1 HDSDI EE output due to user requests.
This feature enables capturing the EX's clean, live camera10-bit 4:2:2 progressive signal directly by NLE. The NLE's capture utility recognizes the PsF payload as a true signal and stores it as such. PsF frees the user from having to apply reverse telecine such as Adobe After-Effects or Cinema Tools in post to remove pull down."

Do you have any other information that contradicts these statements? Thank you for your time and help.

Best,
-terje

[Mitchell Lewis]

http://www.dvinfo.net/conf/sony-xdca...pull-down.html

[Alister Chapman]

I'm not going to argue with Mike Schell, if he says it's 10 bit then I stand corrected. But no-one from Sony has ever claimed all 10 bits to be active and I would have thought that if this was the case they would be shouting it out loud. Many far more expensive cameras with 10 bit HDSDi outputs only have 8 active bits.