Gamma Shift Upon Rendering?

[Margus Voll]

Some have sayed that video apps use yuv and cgi apps use rgb.

Go wonder.

Pretty similar discussion is going on in reduser forums.
Seems like apple “fault”.

—

Margus

https://iconstudios.eu

[Vladimir Kucherov]

Hmm never knew that but I’ve always tried to stay away from 4444 – in Color there was always a gamma shift when grading DPX and I gave up trying to figure out why.

The other problem is, looking at picture in Quicktime is a total crapshoot – there seems to be no rhyme or reason as to how it displays things and why.

[Nate Weaver]

As i understand it, there are image display parameters that can be embedded in the headers of QuickTime files. I always chalked these differences up to some programs heeding them, some programs ignoring them. Add RGB to YUV conversion issues and sometimes not knowing if a program is writing RGB or YUV to that 444 container, it gets messy indeed.

I just deal with it. ProRes 444 to me is a great thing. Not everything can be uncompressed at the rates they’re paying us these days 🙂

Nate Weaver
Director/D.P., Los Angeles
https://www.nateweaver.net

[Vladimir Kucherov]

Yes, actually even more frustrating when different browsers display Quicktimes differently, even h264.

I agree that not everything can be uncompressed, time and space issues and all but I’m still looking for that perfect special effects round trip workflow and format – and I’m usually too scared to go with ProRes444.

[Alexis Hurkman]

There’s only one ProRes 4444 codec, but it has flexibility in terms of the color space used to encode the data, similar to other media formats. For example, DPX files can be encoded as Y’CbCr, RGB, or XYZ. While RGB is most common, the other colorspaces are possible even though you’re still using the DPX format.

My understanding is that, while ProRes 4444 is capable of either RGB or Y’CrCb encoding, the way the data is encoded depends on the application doing the encoding. Thus, the data you get is not unpredictable, it simply depends on which application you’re writing the files with.

For example, Final Cut Pro renders or outputs ProRes 4444 files that are Y’CbCr encoded because that’s the color space that FCP “likes” best. Apple Color, on the other hand, will render ProRes 4444 files that are RGB-encoded, because that’s Color’s color space. I’m relatively positive that After Effects creates ProRes 4444 files that are RGB-encoded as well.

I have been told by those who know well that colorspace transformations done between the two color spaces are of high enough quality to not introduce artifacts, but I also suspect this has a lot to do with the color science employed by your application of choice.

Gamma handling is entirely up to the application you’re working in (one reason I always loved Shake, it made absolutely no gamma assumptions whatsoever). I cannot speak to gamma issues folks have been having with DPX media as I don’t have DPX-using clients. However, my current understanding is that ProRes 4444 to ProRes 4444 workflows (inputting 4×4 media and outputting 4×4 media) have no untoward gamma processing issues, unlike for example the pain experienced when using the Animation codec in FCP. However, it’s been a while since I’ve done extensive testing on this topic, so I’d be curious to hear back from anyone who’s having ProRes 4444 to ProRes 4444 problems.

http://www.alexisvanhurkman.com | http://www.correctionforcolor.com

[Jay Lee]

That’s interesting Alex thank you.
We outputted our source material in this case via After Effects assuming that retaining the original codec of the source material was most prudent however perhaps not.
Resolve may simply not be handling the RGB ProRes444 very well since we are experiencing the luma shift exporting to other codecs as well.
Is there a way I wonder to see under the hood of a ProRes444 file to determine it’s color space?

Frustrating……no combination of curves in a node attempting to compensate for this shift is remotely close enough to be acceptable.

cheers,

j

[Vladimir Kucherov]

Is there a program that can simply read any and all metadata embedded in a quicktime file and display it out as text? There’s obviously more there than most applications will show – it would be useful to simply have an overview and check what is going on.

[Sascha Haber]

Could we get an official statement from BM regarding the ProRes 4444 luma shift, aka color space handling , please ?

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