Am I better off with DPX?

I need to capture some green screen shots with a Sony EX1 and I want to use a Decklink SDI. It will be edited in FCP and color corrected in Color.

I noticed Media Express allows capturing to DPX.
I had originally planned capturing the 1080p 10 bit 422 from the EX1's SDI to ProRes HQ, but it seems Prores can be noisy and I have heard of people pulling better keys with normal XDCAM footage than ProRes because of the noise.
So I'm wondering if I'm better off capturing to DPX with Media Express?
Are there any issues with that? Any reason why i would be better of with Prores HQ?
Will I need a raid to capture to DPX?
Any issues with DPX inside FCP?
Any issues with Color?

Thanks.

>I need to capture some green screen shots with a Sony EX1 and I want to use a Decklink SDI.

Well, if you can drag it on set and hook it up straight to the camera's SDI feed, and capture in ProRes. Doing so, you bypass the XDCAM EX codec compression. I doubt you're doing that. I'm not sure what noise you mean, because I would rather shoot straight to ProRes than XDCAM EX, but obviously I won't want to hook up a desktop to a camera on set. I'll rather shoot to an AJA KiPro.



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Yes, that's exactly what I'm doing. Hooking up a desktop computer straight to the EX1 HD-SDI feed. Why would you doubt I'm doing that?
I have not made any tests yet. But I read several people mentioning Prores can be noisy, reason I was thinking about going with DPX instead. But I'm afraid the files will be too big and will demand too much of the system to capture DPX. Thanks.

>Why would you doubt I'm doing that?

Because it's very clunky, and very expensive to create a rig to go on set with. If you're doing that, then you would be set to go.

My first assumption was someone trying to hook up the EX 1 to the mac after the shoot, which means the footage has already been compressed to XDCAM EX on the SxS card. My apologies if I am wrong on this one.

The SDI output on the EX1 would not be able to send out a 10 bit 444 log signal. The best you can do is to capture it as Uncompressed 4:2:2 as that is what is being floated across the HD SDI signal. And you'll need a huge RAID config to float that 130 MB/s signal (sustained, not peak).

To capture 4:4:4 RGB, you'll need to go off a substantially more expensive camera that sends either a Dual Link or 3G SDI signal.



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>But I read several people mentioning Prores can be noisy, reason I was thinking about going with DPX instead.

Read where? ProRes isn't noisy. It is FAR LESS noisy than native XDCAM, that's for DARN sure. Especially if you capture direct to ProRes and avoid the XDCAM codec to begin with. I don't know where you read that, but they are wrong.

Look at it for yourself. Or have you? On a PROPER BROADCAST MONITOR...not ANYTHING you see on the computer monitor...not the Viewer, not the Canvas, not full screen on the monitor. ONLY a broadcast monitor.

And what the heck is MEDIA EXPRESS? Final Cut Express? How are you using that with a Decklink card...capturing as ProRes? It doesn't do ProRes.


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DPX and log are not perfect synonyms. DPX files CAN be log, but they can also be gamma. Or even linear, I think.

That said, whoever's telling you ProRes is noisy is full of crap. ProRes was designed to be, and has been demonstrated to many times, perceptually lossless. It's incredibly difficult to spot the difference between an uncompressed source and ProRes 422, even with test gear.

I happen to be looking at some greenscreen footage shot on EX1 just today, coincidentally. The biggest challenge is the focus, or more specifically the lack thereof. Either the operator couldn't pull focus correctly (not unlikely), or the camera's lens stinks (also not unlikely). So every frame is soft, which makes pulling a good key a bit harder. The compression artifacts from XDCAM are minor compared to the overall softness of the image, and the softness would be there even if incompressed 422 had been tapped straight into a recorder on set.

So short answer, no, you definitely don't need anything other than ProRes.

So what you're saying is that DPX would be a waste because my data wouldn't fill it?
It seems DPX would be 190MB/s. I just did a test capture and each frame is 7.9MB. Huge!
Do you have experience with capturing to Prores for green screen work?

How about Cineform? I heard it's better than Prores. How much of a hassle is it to work with Cineform on the Mac? Could it be a good option for this application? It seems Cineform has a workflow with the decklink as well.

About the system being very clunky and expensive to create to go on set with, well, mine is just a MacPro with a decklink. Nothing special. It seats on a desk at the studio and the cable runs from the computer to the camera. Not much of a rig really. I can image this would be a hard rig to create for location work but for studio is not a big deal. Thanks.

>DPX files CAN be log, but they can also be gamma. Or even linear, I think.

Ah. My bad on that.

>So what you're saying is that DPX would be a waste because my data wouldn't fill it?

Yes. Because an SDI signal only contains 4:2:2, which is 1 chroma sample every 2 pixels. To go better, you would capture 4:4:4, usually RGB (not sure if any cameras shoot to 444 Y'CbCr), either off a dual link feed or a 3G SDI feed, and you would need a far superior camera. Then, you're better off shooting R3D, is 4:4:4, but with wavelet compression.

ProRes is far far better than the XDCAM codec, in fact if the charts are to be believed it's even less noisy than D5-HD!



www.strypesinpost.com

Shane Ross Wrote:
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> Read where?

I researched all over and in one of the forums online I read somebody saying he did tests and found that he could pull a cleaner key from XDCAM material than from the Prores SDI captured material from the EX1 or something along these lines. I will see if I can find the thread again but I searched a lot of forums so it may be hard to find it again. If I do I will post the link here, if it's allowed posting links to other forums.

Shane Ross Wrote:
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> Look at it for yourself. Or have you?


No, not yet. I'm set to do that tomorrow.
Just wanted to hear some opinions about other people's experiences too.

Shane Ross Wrote:
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> And what the heck is MEDIA EXPRESS?

It's Blackmagic's stand alone capturing application which comes with the Decklink card. On the Mac it gives you the option of capturing DVCPRO HD, uncompressed, Prores if you have FCP installed and DPX.

Jeff Harrell Wrote:
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> I happen to be looking at some greenscreen footage
> shot on EX1 just today, coincidentally. The
> biggest challenge is the focus, or more
> specifically the lack thereof. Either the operator
> couldn't pull focus correctly (not unlikely), or
> the camera's lens stinks (also not unlikely). So
> every frame is soft, which makes pulling a good
> key a bit harder. The compression artifacts from
> XDCAM are minor compared to the overall softness
> of the image, and the softness would be there even
> if incompressed 422 had been tapped straight into
> a recorder on set.

So what are you saying here? That the problem is that the EX1 is a bad camera or not adequate for green screen?

strypes Wrote:
-------------------------------------------------------
> >DPX files CAN be log, but they can also be gamma.
> Or even linear, I think.
>
> Ah. My bad on that.
>
> >So what you're saying is that DPX would be a
> waste because my data wouldn't fill it?
>
> Yes. Because an SDI signal only contains 4:2:2,
> which is 4 luminance samples and 2 chroma samples
> per pixel. To go better, you would capture 4:4:4,
> usually RGB (not sure if any cameras shoot to 444
> Y'CbCr), either off a dual link feed or a 3G SDI
> feed, and you would need a far superior camera.
> Then, you're better off shooting R3D, is 4:4:4,
> but with wavelet compression.
>
> ProRes is far far better than the XDCAM codec, in
> fact if the charts are to be believed it's even
> less noisy than D5-HD!

I see, thanks.
Any words on Cineform? I was tempted in using it because like R3D it is wavelet. I was just not sure how much of a hassle it would be for FCP and Color.

ONE person? Did you find the other posts from hundreds of others who say that ProRes is better than the GOP XDCAM format for pulling a key? I guess not. Well, it is. Test with the Decklink capture tool, and then test with FCP. And then test with shooting XDCAM. FAR less noise, and no horrid GOP compression, that keying doesn't like.


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>No, not yet. I'm set to do that tomorrow.

Lock the camera, shoot a chip chart and do a difference matte, or zoom in to check how much each codec aliases on the fine lines. Check for banding on gradients.

>Any words on Cineform?

Someone had a render bug on Cineform. But it's pointless. Your signal is a 10 bit 4:2:2 Y'CbCr signal, so you cannot get better than that.



www.strypesinpost.com

strypes Wrote:
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> Lock the camera, shoot a chip chart and do a
> difference matte, or zoom in to check how much
> each codec aliases on the fine lines. Check for
> banding on gradients.

Thanks for the tips. Will do that.

strypes Wrote:
-------------------------------------------------------
> >Any words on Cineform?
>
> Someone had a render bug on Cineform. But it's
> pointless. Your signal is a 10 bit 4:2:2 Y'CbCr
> signal, so you cannot get better than that.

What do you mean? I know I can't get better than uncompressed, which would be the 10 bit 4:2:2 Y'CbCr and not matter what I do I won't get 444. But we are talking bout Prores, a compressed format. Not all compression is the same and wavelet is said to be better than DCT at least in theory. So it's just analyzing which compression to use, reason I don't understand your "it's pointless. Your signal is a 10 bit 4:2:2 Y'CbCr signal, so you cannot get better than that." If Prores is throwing info away and so is Cineform I obviously can do better than both, but I wanted to know about Cineform vs Prores. I'm not wanting to do better than uncompressed, or implying that recording in some flavor of 444 would gain me something, which is the only case where your comment would make sense and it would indeed be pointless. Sorry for the confusion.

A downside to Cineform w/FCP is that Cineform is not a 'blessed' codec by Apple's RT Extreme engine which means anything you do to the footage will result in a red render bar.

On paper, wavelet is better than DCT, but it is also a lot more processor intensive. Between ProRes and Uncompressed, you are likely to see any differences. You can capture to Cineform. You may get slightly better results than ProRes, but then it's more processor intensive, then you may prefer to offline in a more efficient codec, then re-link back to your Cineform master during the online. Then you may prefer working Uncompressed or even shooting straight to a RED One which at 4K, gives you a lot more space to reposition and scale your footage for HD delivery.



www.strypesinpost.com

I understand you don't want to compromise quality in any way but you have to think realistically about this. ProRes HQ is a virtually lossless codec, meaning that it does lose information but anything it loses is imperceptible, nor will it affect any keying you plan to do.

If you want to preserve every last bit of information, go with Uncompressed 422. However, the bandwidth requirements are severe and Cineform, while more reasonable with bandwidth, needs to be rendered in FCP. So ProRes really is your best bet.

P.S. If only one person on the entire internet is reporting problems with ProRes, he's probably doing it wrong. Many people, myself included, are using ProRes successfully.

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Jon Chappell Wrote:
-------------------------------------------------------
> I understand you don't want to compromise quality
> in any way but you have to think realistically
> about this. ProRes HQ is a virtually lossless
> codec, meaning that it does lose information but
> anything it loses is imperceptible, nor will it
> affect any keying you plan to do.
>
> If you want to preserve every last bit of
> information, go with Uncompressed 422. However,
> the bandwidth requirements are severe and
> Cineform, while more reasonable with bandwidth,
> needs to be rendered in FCP. So ProRes really is
> your best bet.
>
> P.S. If only one person on the entire internet is
> reporting problems with ProRes, he's probably
> doing it wrong. Many people, myself included, are
> using ProRes successfully.


What you are saying makes sense Jon.
Prores seems to make a lot of sense in the Apple platform. FCP obviously will handle Pores better than Cineform or any other non Apple codec. But one fact that can't be overlooked is that we are talking about green screen shots here not normal footage, which means before it's ever brought into FCP for editing it will need to be keyed, composited and the shot "finished" in another program like Nuke or Fusion where you shouldn't work in Prores and specially not output in Prores. So by the time the footage actually hits FCP it will be a Tiff or DPX image sequence. Actually it will get converted to that before it's brought in for keying in the compositing software as no compositor likes or should work with video files.
When you consider that, doesn't it cancel the advantages of capturing to an FCP friendly codec ? And doesn't it also cancel the disadvantages of Cineform for FCP editing? Both Prores or Cineform will most likely have to be converted to an image sequence way before FCP. So the processor needs of Cineform won't matter either.
When you consider all that I think the most important thing is to capture to the codec that will conserve as much info as possible. Perfect being uncompressed, but unrealistic.

i don't want to stir the pot so much as to add my observations.

we started cutting a feature about a month ago.
shoot is on 35mm 3perf

someone with experience suggested we DONT capture to ProRes,
due to the noise that would turn up in the blacks.

i tested this and captured to both Prores 1920x1080 and DVCProHD 1080.

the were right: there was noticeable noise in the blacks of the ProRes image compared to the DVCProHD.
i was told this only manifested itself when coming off a film source.
don't ask me how that works.

so this may not be relevant to your project, AClaude,
but it's probably worth pointing out that Prores isn't perfect.


test, test, test.

nick

Since we're just chatting here, I'll have a go at that one.

Film is, obviously, grainy. DVCPRO HD is a very low-resolution format, though, as HD formats go. It's a mere 1280x1080. So what you thought was "noise in the blacks" was actually the train of the film, being preserved by the full-raster 10-bit ProRes and smeared away by the low-resolution 8-bit DVCPRO HD.

I just invented that with my brain. But short of seeing TIFFs or something, it's the best I can do. Seems at least vaguely plausible to me, and consistent with my experience, so maybe that's it.

Hi Jeff.

not quite.
the film wasn't THAT noisy.

but the thinking on this end is that it IS something to do with the film grain.
something about the way ProRes works amplifies it.
perhaps.


nick

Eh, I was just guessing, Nick. It is entirely possible that ProRes did something odd on you, but that would run 180° counter to all my personal experience (for what that's worth) as well as everything I've ever seen written about the codec. It's been tested to destruction and found to be incredibly transparent.

Not saying you're full of crap or anything stupid like that. Just that even if ProRes does fall apart under specific circumstances, those circumstances appear to be extraordinarily rare. Like Bigfoot rare.

That said ? got any stills or sample footage? I'd love to see it for m'self.

yeah, i can post after the Easter break.

if i get a chance to go back into the lab, i'll see if they have a tape version of the test telecine i can compare.


cheers,
nick

Cool, that'd be fun to look at.

sheesh. Geeks!



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