Colour Management

[Trevor Meier]

Can someone inside RED take us through how colour is mapped from the native sensor colourspace, via RedCine, into available video & data formats and out to the display?

I'm interested in both how to maintain a calibrated preview in RedCine, and ideas on how to maintain a calibrated display throughout post (barring an ultra-expensive solution like TrueLight - though beautiful, mucho $$). Any recommendations for ensuring accurate colour rendition all the way through the pipeline? (monitor profiling, calibration LUTs, getting around Quicktime & FCP's limitations, etc.)


Some side notes:

Currently there's some notoriously frustrating bugs in Quicktime that make gamma rendition inconsistent between inside Final Cut, direct output from the timeline, output via Compressor, and taking files inside of other apps such as After Effects. My particular situation is using Final Cut with two attached Cinema Displays. One example: will doing a calibration of the displays (with one of the various available probes) and using 'Digital Cinema Preview' from inside Final Cut give me accurate colour rendition?

In the canvas window, FCP does gamma compensation based on an assumed 1.8 display gamma and 2.2 output gamma... anyone know if is this true when using 'Digital Cinema Preview'? Any methods for getting around this 'feature'? If anyone has more info on how FCP handles colour mapping on attached displays (i.e. not attached to a video output a la AJA) I'd be very interested to know.

[Graeme Nattress]

Native RED sensor RGB space is transformed to XYZ, and then from XYZ to the selected RGB space, say, REC709. Then, the REC709 gamma curve, say, is precisely added to the linear data, giving a correct REC709 image. Once we pass that image over to the operating system, it's out of our hands though.

We know about the Quicktime gamma nasties and are working to ensure that our codec does not cause issues with this.

Hope that helps,

Graeme

[Corrado Silveri]

One example: will doing a calibration of the displays (with one of the various available probes) and using 'Digital Cinema Preview' from inside Final Cut give me accurate colour rendition?

At this time, no way. FCP via Digital Cinema Preview is NOT an accurate color rendition. The only way is preview your images via Aja/BMD-DVI.

A Graeme article on the subject (using an Apple LCD 23' as a monitoring device via Blackmagic HDLink):

http://www.lafcpug.org/reviews/review_decklink.html

Graeme, is that still valid?

[Graeme Nattress]

For HD, that's correct. The DC Preview is not accurate. I think video has to, for colour calibration, move towards the approach adopted by ICC colour profiles. We can't do that alone, but we do have the science to make our camera work within such a model.

Graeme

[Corrado Silveri]

For HD, that's correct. The DC Preview is not accurate. I think video has to, for colour calibration, move towards the approach adopted by ICC colour profiles. We can't do that alone, but we do have the science to make our camera work within such a model.

Graeme

I'm thinking about this ICC working group:

http://www.color.org/groups.html#digital2

It is a "working" group or not?

[Trevor Meier]

Built-in profiling tools are a big gap in this industry right now... With so many potential colour spaces it's no longer safe to trust the rendition of a particular piece of hardware or software. Digital pre-press went there a long time ago... we need profiling for all things moving digital image.

Slightly OT: Is previewing on a profiled display (using DC preview, or a rendered QT file) going to give an accurate colour rendering for computer-based delivery platforms? (i.e. Quicktime via the web... assuming, and this is a big if, the end-user has a roughly dialed-in display) In other words, does Quicktime obey display ICC profiles & gamma setup (2.2/1.8 etc.)?

OT Side Notes:
* Using adaptive scaling + antialiasing inside compressor can produce some surprisingly good results at 800kbps... though it takes hours to render.
* I've noticed all of the trailers on apple.com are encoded with black at something like 7-10% grey. Is this Apple's way of working around their own bug (gamma issues)?

[Trevor Meier]

Been thinking about this a bit... in digital photography I've got a couple good options as a 'working space' for my shots... Adobe RGB and ProPhoto RGB.

Here's my big wish: Since most of my motion picture material will go out to a variety of final colour spaces (DVD, Digibeta, HDCAM, film, etc), it'd be great if NLE's supported a 'working colour space' that maintained as much colour and dynamic range as is in the image. The NLE would need to obey the system display's ICC profile for converting images from the working space to the colour space of the display. It would need options for 'soft proofing' the video - applying LUTs for sample output spaces: NTSC, sRGB, Rec709, various IP & camera films stocks, etc. On output, it could either convert to (bake in) the colour space, or support any of the upcoming colour metadata standards along with an attached 'working space' profile.

Anyone know if I'm just dreaming?

[GlennChan]

Color management for video is fairly uncomplicated.
A- Most consumer sets have wacky colors, so you can get away with a lot.
Side note: QC reports generally tend not to mention color inaccuracies (i.e. because they tend to stick to objective, asinine stuff), so people aren't getting dinged for inaccurate color.
B- There is only one target gamut. So for monitoring, just get a broadcast monitor and you are done. With HD, this is a lot more difficult as we are moving away from CRT (and CRT's native transfer function) and good HD monitors are very expensive (or not that great quality). But basically this problem is solved with a good HD monitor.

2- There is a movement towards wide gamut / xvYCC for the home theatre/video market, and this will require the monitor to perform color management. IMO, I don't think that xvYCC is a good approach for better image quality and I hope that it will not achieve significant deployment/usage. However, I haven't seen a wide gamut system in practice (other than film projection and slide film, which exceeds video gamuts in some areas).

3- The DI market is already served, albeit many of the solutions don't work with other vendor's products. *Not too sure yet.

4- The DCI / digital projection market doesn't exist yet.

In all the cases above, I don't think working space is really an issue. Your output format has to be a particular colorspace- Rec. 601 / EBU, Rec. 601 / SMPTE C, Rec. 709, DCI (XYZ color space, P3 white point, 2.6 gamma), or a particular film stock. You're only targeting a particular colorspace. (Or did I miss your point?)

[Graeme Nattress]

But 709 is a smaller colour gamut than, say, RED can produce. Therefore by targetting 709 for accurate monitoring, you're throwing away some gamut.

Now, if you kept the image in camera RGB space, and just transformed it to 709 for viewing, you'd not loose anything if you later on wanted to output to XYZ for DCI, or Adobe1998 for print work etc.

We could, like DCI, perhaps, just go from camera RGB to XYZ, (and use a viewing transform to see it as 709 for monitoring, or through to a projector that knows XYZ) but what image processing tools understand XYZ?

Graeme

[Antoine Baumann]

Hello Graeme,

I read your article about the BMD HDLink and Apple 23'' cinema display. I do not want to argue with you, as I do not have a tenth of your knowledge, but you wrote (on that article) that CRT monitor "don't show the full 1920x1080 pixel resolution of HD (due to the physical limits of CRT technology)" and I was sure the Sony BVMA series has 1920x1080 native resolution.
I mention these monitors because some people here in switzerland and france still like to grade on them, and are not trusting the LCD and Plasma monitors. I am not saying they are right, just their experience.

What do you think of product like cine-tal
http://www.cine-tal.com/
or e-cinema?
http://www.ecinemasys.com/products/d...3_features.htm

Thanks,
antoine