Compression and Colorspace for EXR and DPX

(this thread is an extension from this topic…OpenEXR Color Management Question - #7 by PlaceYourBetts)

Yes @ChrisKasten We use EXR (piz) files for our rec.709 graded material.

The file format needs to be thought of a suitcase. You can put anything you want in that suitcase. It might be more appropriate to put a linen suit in an EXR suitcase but I have been putting a Hawaiian shirt and Jandles.

Until recently, when @finnjaeger was talking about the distribution of data making it effectively 10-bit, I was blissfully unaware of any artefacts. In my very narrow test I found no obvious difference in quality between 10-bit DPX and 16-bit half piz compressed EXR graded footage. Except that i found the EXR had added headroom (less clipping) and the reduced file size was more appealing.

I should now open the floor to people wishing to berate me and tell me that my workflow is flawed but I would just like to say in advance. My workflow IS flawed. My clients still expect me to work on small dynamic range, graded material.

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Not only your clients :wink:
It’s quite a challenge to stick to a technical correct workflow. Especially in commercials.

TBH: The artifacts with non-linear EXRs are surely subtitle, but they appear.
And I like to work with dpx more, because performance feels overall better. EXR needs some performance to unpack. Like to go with ZIP1 for performance reasons although PIZ is the more efficient and accurate one. Therefore I also accept some difference in quality.

Keeping EXRs linear do have the advantage, that e.g. a Nuke artist doesn’t need to be too familiar with color management since exrs are flagged linear by default in Nuke. Some headaches less :smiley:

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Would you be using 12-16bit DPX @ChrisKasten?

I love to be contrary to myself but DPX for me have always been 10-bit log (and I do think of rec.709 as a type of log) I am aware that DPX can now go higher but have never used the format. Not since walking away from a facility with a telecine machine.

For Rec709 we traditionally stick with 10-bit DPX. On one side you don’t need the extra bits for Rec709 material and on the other site not every software can handle 12-bit or 16-bit DPX.

If I should deliver ungraded material in a log flavor I’d normally go with 12-bit DPX. But since clients can’t deal with DPX too often it will end up with a ProRes4444.

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The headroom part is a head scratcher, You want to limit your grade to values between 0-1 in grading as your monitor cant display more than that, which DPX can hold just fine. If you go higher than 1 on graded material you will just cut that stuff off on final output to lets say a prores or whatever, or you need to softclip it in flame but that just sounds a bit horrible.

The difference to 10bit DPX is not great yes but compared to 12bit dpx , it is.

The industry is missing wide support for losless
compressed DPX files… thats what we all need for things like that, until then why not stay linear as long as you can? If you have the colorist under control just output aces-AP0 EXRs and bobs your uncle. I personally am fine with just acesCCT Prores4444XQ after grading and for
archival. especially for commercials

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Possible in Europe, damn near impossible in Los Angeles… unless you grade in house.

And that’s not to say that fundamentally you’re incorrect—you’re not. But the simplicity of your statement misses the complexity of the dynamic of commercial color as an industry in a large swath of the post community here.

Not even nearly possible in Europe, too.
That technical ideal workflow is a dream we try at least to live/enforce in-house. But when dealing with vendors/clients that are not so sufficient in post tech that deep, we also need to switch back to good old display referred QuickTime/DPX.
Mainly speaking for commercial world.
But you’ll never give up hope :smiley:

haha yea Its more of a big IF , so yea as @ChrisKasten said its more for in-house things. But then again I try to condition producers to never ever ever ever plan final grading before the comp deadline and that seems to work reasonably well even if I have to provide Pre-Comps for a first grading pass.

Grading before comp needs to die the whole concept is flawed. and for Finishing, colorists are usually fine when I just tell them to export DPX, I then I ingest them to whatever I see fit, add titles and whatever but I try to stay as far away as possible from running graded anything through a comp, not even screenreplacements or beauty work.

In the remote/wfh world where we are at times being sent massive file transfers in DPX I think EXRs w/piz(or ZIPS), are muuuch better.
The times I’ve asked a producer to ask the Colorist to send 16bit(or half float as some colorist will call it), EXRs in scene linear sRGB/rec709 with PIZ compression I’ve ran into no issues or pushback, just saying :slight_smile:
Maybe in New York it’s not a big deal for the color houses?
Now I definitly don’t always ask because I’m not trying to be, “that guy”! Lol
For the most part I ask when a producer ask what type of file I would like to be sent. Or if it’s early on in the game and I’m the lead.
Personally I think it’s actually better with the advantages of smaller files and keeping things linear prior to export.
The times I bring DPX into flame at 16bit with the Framestore set to Uncompressed(which will result in them being stored as EXR’s w/piz compression), as opposed to the Uncompressed/RAW option. I’ve not come across any sort of artifacting issue, at least that I’ve realized. I do leave my batch set to 32bits and my timelines are always 16bit. So maybe that helps?
As far as performance overhead, yeah this can be a thing for sure. But not so sure for an HD timeline.

The positives in my opinion; getting EXR’s in PIZ compression will reduce the size of the file transfer to you by 50% at the Very least. If you are getting Mattes then the file size will be like roughly 90%ish smaller, it’s something crazy like that.

  • Is it just me or is Aspera mad slow lately?

For the most part you retain a little more wiggle room and for me it can make some aspects of comping easier and better looking without the baked in gamma.
PIZ compression for EXR’s was basically designed and meant for shot footage and so ideal for Flame. There’s some old(hopefully not archived), info on ILM’s website about the different EXR compressions they developed.
It/piz, is actually the default compression used in the Framestore it seems.

The sort of caveat, ACES would be ideal/better compared to scene-linear Rec709.

A caveat is that when frames sizes get really big it is definitely using some overhead on the graphics card decompressing the EXRs. So yeah, performance can be impacted I think.

  • For example on my new Mac Pro in which I haven’t upgraded the Graphics card yet, if I bring a 6.5k arriraw into the framestore as Uncompressed so that it becomes EXRpiz frames I’m can’t play it down.
    But, if I bring it in as Uncompressed/RAW then I can play it down.

Well basically(after this super long post LOL), for me, I like working in scene-linear better and at home I also like the space savings and time savings(not waiting forever to get the grade), aspects.

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you can also run zip compression on DPX fil;es its not the fancy wavelet PIZ but still pretty good.

but yes usually 709 inside a EXR is “fine” , its just not “16bit” :smiley: its at least better than puttin log in therebut you still have like roughly only 10bit of precision :slight_smile: but thats usually enough anyhow. whats wrong with ProRes4444XQ if you want to save space? way enough quality for most things.

Getting Linear/709 EXRs is easy on Baselight but requires some manual setup from resolve so thats might be the difference? on baselight (I believe) you wouls just use the “linear” DRT while most people on resolve dont use colormanagement at all. at least in my experience. Wondering if that still bakes in some kind of tonemapping so that it looks the same in flame as we dont have all the fancy T-Cam DRTs? hmm

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@finnjaeger btw: You can actually have T-CAM DRTs.
Filmlight is offering their own „ACES-Variant“ Truelight as an OCIO config for most applications as well as a Color Policy for Flame for free.

Edit: I think, I’ve done a feature request to natively implement truelight color policy into flame. I’ll look it up and post it here .

Edit 02: Here is the feature request: FI-02441
And the link to Truelight OCIO and Color Policy: Filmlight Truelight Colour Spaces Scroll to end of page :wink:

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I think I may have originally requested that 15 years ago as to not have to spend another 20k Euro on a another FilmLight Truelight Hardware box.

…still waiting.

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Hey Finn, I actually haven’t properly tried ProRes4444XQ yet. I seem to always without fail end up keying colors when comping and I did in the past test ProRes4444 in this regard and thought it better as EXR before the ProRes compression. But yeah, haven’t taken a serious look at 4444XQ yet.

oh thats crazy I didnt know they had this public, thank you! when I asked them about it like a year? ago I got no response :face_with_hand_over_mouth:

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Key after grading? you should always have the original camera files for stuff like that ready to go , but maybe I am missing something?

I would say 70%-75% of the jobs I’m on start with conforming the graded plates.

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thats interesting, i havent conformed graded plates in about … 3 years . so thats still normal practice to do VFX on graded plates?

@finnjaeger unfortunately this is still a common thing. In most cases grading will be delivered by external vendors, which often don’t give you more than the graded image sequences without any setups. And more often there is no possibility to push VFX to those vendors to get them back graded.
So far for all my experience in German commercial world.

A scene referred workflow can only be achieved when all disciplines take place in our own facility (or if you plan really good with all involved vendors/clients).

I can think of, that it is different in tv shows or feature… at least, that is what people telling me.

oh wow yea i have been out of the commercial world for a bit now, and we do such heavy VFX that even on commercials we refuse to work on graded as its not even a option for the scope of stuff we do (heavy CG stuff) .

Thats very interesting I just kind of assumed that whole thing died, why do production companies still shedule grading before vfx? like whats the advantage ?

For any TV/Feature stuff I have done Ive never received anyhting graded most was burned in shotgrade into a dnxhd36 some luts and CDLs to match for our dailies but thats about it, always source plates or mostly now ACES-2065-1 EXR pulls.

Quick and kind of ironic answer: people don’t think anymore and stick to their routine.

As far as I’m aware, DOPs and directors doesn’t have much time after shooting because they have new jobs straight away. To make it possible that they join the grading sessions, those will be planned right after editorial.
In nowadays remote world that reason should be vanished but it’s kinda hard to break routines.

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