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High Lattitude in Intermediate codecs

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Tim Parsons
High Lattitude in Intermediate codecs
on Jul 9, 2014 at 7:08:24 pm

I need some help in wrapping my brain around something. Please look here and then please tell me what I'm missing.

Everyone says PNG, Animation, DNxHD, etc, are all great intermediate codecs.

Why then can I not get ANY of my high-bit latitude to render out in ANY of these intermediates???

I finally had to render out in an EXR sexuence, which I've never heard of, and finally had latitude to work with.

What gives?


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Dave LaRonde
Re: High Lattitude in Intermediate codecs
on Jul 9, 2014 at 9:18:25 pm
Last Edited By Dave LaRonde on Jul 9, 2014 at 11:34:08 pm

From the look of those two waveforms, it appears you're trying to ressurect some extremely blown-out footage... i.e. WAY overexposed. AE might be able to help a little, but that's about it.

According to that waveform, there aren't any peaks in the levels... just flat lines when the image reaches maximum exposure. It would take a MIRACLE to make that stuff look good!

AE's good at helping a little bit. It can't work miracles. Unless I'm missing something -- something that could be explained by a screen shot of the footage and not Color Finesse -- I'd say a re-shoot is in order.

Dave LaRonde
Promotion Producer
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA


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Conrad Olson
Re: High Lattitude in Intermediate codecs
on Jul 10, 2014 at 12:40:23 am

It seems your question is answered in the other posts. The Avid codec is designed to be used with video that was originated from a video camera. Most video cameras only capture 10 or 12 bits of latitude, so there is no need to store super bright values.

When people say that ProRes or Avid DNxHD are good intermediate codecs, they are usually talking about transcoding camera footage, or rendering out final pieces of work from After Effects (or Nuke etc) to send back to an edit application. In these cases you shouldn't really need the floating point range any more. Your floating point composites or effects should be converted into a 10 bit colour space, like rec709.

Almost all displays and delivery formats are 8 or 10 bit, so you can't deliver anything in float space.

If you are pre-rendering something to continue using in After Effect then you will need to pick a format that supports 32bit floating point values, which realistically is only EXR. TIF files can do it but are much slower to work with.

---

conradolson.com


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Tim Parsons
Re: High Lattitude in Intermediate codecs
on Jul 10, 2014 at 2:08:13 pm

[Conrad Olson] "If you are pre-rendering something to continue using in After Effects"

Yes, I am rendering something (pre-color grading) for continued use in AE. So I need the color space.


[Conrad Olson] "you will need to pick a format that supports 32bit floating point values, which realistically is only EXR"

I have never ever heard this before. In my opinion, it needs to be more prevalent in talk about intermediate codecs.

And just why in the world don't more codecs support high dynamic range?! seems like everyone would need that kind of functionality, since color grading is usually done last.

[Dave LaRonde] "AE's good at helping a little bit. It can't work miracles. Unless I'm missing something -- something that could be explained by a screen shot of the footage and not Color Finesse -- I'd say a re-shoot is in order."

Yeah, I'm afraid you are missing something. The first waveform is the original footage. The highlights are blown out, but the subject is properly exposed. The second waveform is the same footage, rendered out of AE and re-imported. the color space above 100 IRE is completely gone. That's the thing: i'm trying to preserve highlights, not recover them.


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Conrad Olson
Re: High Lattitude in Intermediate codecs
on Jul 10, 2014 at 6:07:44 pm

I have never ever heard this before. In my opinion, it needs to be more prevalent in talk about intermediate codecs.

And just why in the world don't more codecs support high dynamic range?! seems like everyone would need that kind of functionality, since color grading is usually done last.


I think you are misunderstanding the point of these intermediate codecs. They are there to provide a compromise between file size, low CPU utilization, and quality. They are also aimed at people working in edit packages more than people compositing.

Most displays, edit software and final delivery formats don't need floating point colours, as part of the compromise process they limit the bit depth.

In your situation, you cannot compromise on bit depth, so you have to use a different format, but sacrifice file size and realtime playback. Once you have all the your final composite you can afford to clamp your floating values, because no one will see them anyway.

---

conradolson.com


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Tim Parsons
Re: High Lattitude in Intermediate codecs
on Jul 11, 2014 at 1:32:14 pm

[Conrad Olson] "In your situation, you cannot compromise on bit depth, so you have to use a different format, but sacrifice file size and realtime playback."

I understand. I think my confusion came in at "10 bit." I thought 10 bit was a higher dynamic range than 8 bit. So when I used 10 bit codecs and they clamped, I was confused.

I suppose this is not the case?


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Conrad Olson
Re: High Lattitude in Intermediate codecs
on Jul 11, 2014 at 5:02:17 pm

I can see how that could confuse you.

Dynamic range and bit depth are kind of linked, but not really. In the case of the Avid codec the extra bit depth just adds more fidelity within the same range.

Even in After Effects, switching between 8bit and 16bit doesn't add dynamic range to the project, it just adds more steps between black and white. You only get to with with values brighter than white and darker than black (float) when you switch to 32bit.

---

conradolson.com


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Tim Parsons
Re: High Lattitude in Intermediate codecs
on Jul 11, 2014 at 5:11:04 pm

Ok... So how then is an MXF file out of a P2 camera (Panasonic AG HPX250 P) able to have a dynamic range beyond 0 and 100 IRE? Why can an inexpensive camera (compared to big production/film cameras) record highlights and shadows beyond 0 and 100, but a professional editing suite can't encode that without a ridiculously large and relatively unknown format like an EXR sequence?

I'm more than willing to read up on help files and tech journals on the issue, but I don't know where to look, since my concept of related terms and specs just got up-ended. Feel free to link away.

I appreciate your patience as my head continues to spin...


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Conrad Olson
Re: High Lattitude in Intermediate codecs
on Jul 11, 2014 at 5:35:10 pm

I'm afraid I don't know anything about the P2 or MXF format so I can't answer that directly.

A lot of cameras can shoot a higher dynamic range but this range has to be squeezed into the limits of the delivery format somehow. Remember, there aren't really any viewing options that show higher dynamic range images so everything has to be clamped at some point. The idea is not to clamp the values until right at the end of your work.

I work on feature films with Nuke and we work with floating point values all the time but we always view our work through a LUT (look up table) that shows us how the values should look on a projector, or HD display. We send these float images to the grading suite (as EXR or DPX image sequences) so they have the whole range to work with, but then the final movie is clamped once they have everything in the right place.

There are codecs that let you render QuickTimes with floating point values, but they will be equally as big, and rendering image sequences is a much more robust workflow for this kind of situation.

EXR is a very common format when it comes to rendering VFX, and is ideal for the purpose of pre-rendering something to re-use in another After Effects composition. It is completely loss-less so you keep every tiny detail from your original comp. There are some loss-less compression options in the EXR format that help keep file sizes down without losing any detail.

There is a brief description of some of the terms and concepts in this PDF from Steve Wright: http://vfxio.com/PDFs/Nuke_Color_Management_Wright.pdf

His book has a lot more detail about some of the more technical aspects of VFX work and is probably the best description you are going to get about color space. I think you can get a Kindle version.

---

conradolson.com


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Chris Wright
Re: High Lattitude in Intermediate codecs
on Jul 13, 2014 at 2:54:20 pm

"It is completely loss-less so you keep every tiny detail from your original comp."

from my tests, EXR with no compression still gives a single digit change in renders on individual pixels, very, very small but not mathematically perfect.


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Conrad Olson
Re: High Lattitude in Intermediate codecs
on Jul 14, 2014 at 4:38:17 pm

I think this could be due to rounding errors in calculations, and I think is down to the software rendering the files out. I have seen this before. It's usually negligible.

But you're right, not mathematically perfect.

---

conradolson.com


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Dave LaRonde
Re: High Lattitude in Intermediate codecs
on Jul 11, 2014 at 5:43:17 pm

Well, that's because your camera DOESN'T have much of a greater dynamic range. If it did, you wouldn't see a flat line in the waveform at the very top. You'd see peaks and valleys.

Blown-out footage is blown-out footage. Plain and simple.

You want HDR? You have to plan out the shot with multiple exposures so that you retain detail in the bright and dark areas... and then do some very tricky AE work to get those exposures to work in the more limited dynamic range of the delivery codec.

And because it's so tricky to pull off in footage that moves, you rarely see it done.

Dave LaRonde
Promotion Producer
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA


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Conrad Olson
Re: High Lattitude in Intermediate codecs
on Jul 11, 2014 at 5:48:45 pm

Dave, if you look carefully at the two waveforms in his original link you will see that he is definitely loosing some detail in the highlights in the second one. There is detail above 100 in the first one. There is still some clipping in the original image, but not nearly as much as when he rendered it out and re-imported it.

This conversation has been about solutions to that problem, not about his original footage.

---

conradolson.com


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Dave LaRonde
Re: High Lattitude in Intermediate codecs
on Jul 11, 2014 at 6:11:18 pm

Sure, I see the clamping that took place: it looks like what happens with an old-style video proc amp.

My point is that the OP shouldn't have expected to recover much detail from an overexposed shot in the first place, whether he's woking in 8, 16 or 32-bit. If the image information isn't there to begin with, it's gone.

With a properly-exposed shot -- or better lighting -- Then this entire discussion wouldn't have been necessary.

Dave LaRonde
Promotion Producer
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA


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Conrad Olson
Re: High Lattitude in Intermediate codecs
on Jul 11, 2014 at 6:13:40 pm

He isn't trying to recover highlights that aren't there.

He is trying to keep the highlights that he does have while rendering a precomp to use in another comp in After Effects.

---

conradolson.com


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Tim Parsons
Re: High Lattitude in Intermediate codecs
on Jul 11, 2014 at 6:14:01 pm

[Dave LaRonde] "With a properly-exposed shot -- or better lighting -- Then this entire discussion wouldn't have been necessary."

I'm quite certain you're still missing something. The question is not at all about recovering highlights. It's an It's about preserving highlight information above 100 IRE when rendering to intermediate codec.


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