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Editing - Color Correction Environment

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dopocc
Editing - Color Correction Environment
on Jun 26, 2006 at 11:49:00 pm

Hi, I am in the process of constructing and designing a new room of 12m2 within our facility for HD editing/color correction applications.Are there any recommendations on any construction-design tips one should have in mind?

To address this question more clearly:

a) Is 6500 Kelvin light temperature ideal?
b) What about CRI (Color Rendering Index) numbers? Is CRI>90 ok?
c) 32-64 Lux for color correction like ISO standards for digital photo darkrooms?
d) would it be recommended to install and use different light fixtures when editing?
e) if yes what would be more ideal just for editing? Halogen or fluorescent and at what lux numbers?
f) we already have in stock enough m2 of neutral grey carpet. Could it be used to cover the walls instead of painting them neutral grey, since the carpet is already lying around and free to use?
g) any other tips would be truly appreciated

Please keep in mind that we are located in Greece, so a) my excuses for the metric system, b) any specialized lighting equipment that is hard to find or US patented will be difficult for us to order and will be custom taxed in the EU, so it would be really preferred to use more "universal" equipment.

Many thanks

Bill Belegris
Cinematographer
Renegade Arts Inc.
HD Cinematography, Audio Production
and Digital Content Creation Studio Services
Thissio, Athens, Greece


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Mark Suszko
Re: Editing - Color Correction Environment
on Jun 27, 2006 at 2:20:20 pm

"Kali-mera, Philos!" (sorry, except for swear words, that's about the limit of my Greek vocabulary:-)

Your list seems fairly comprehensive already. The carpet on the walls will also help quiet the room.

Will the computer and drives be isolated somehow to keep their noise low? Have you figured adequate cooling and ventilation, as well as a technically clean power distribution source? (UPS battery and filter systems).


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dopocc
Re: Editing - Color Correction Environment
on Jun 28, 2006 at 6:34:31 am

Hi!

Yes, computer noise, ventilation and clean power distribution have already been taken into account, but what about kelvin light temperature, CRI and lux numbers?

thanks again


Bill Belegris
Cinematographer
Renegade Arts Inc.
HD Cinematography, Audio Production
and Digital Content Creation Studio Services
Thissio, Athens, Greece


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glenn chan
Re: Editing - Color Correction Environment
on Jun 29, 2006 at 10:12:10 pm

The ideal/standard (i.e. SMPTE) color temperature of the light is D65, not 6500K. The D scheme is for daylight illuminant series, the Kelvin scheme is for black body radiators (or things that behave like them). There's a subtle difference between D65 and 6500K, which is unfortunately confused most of the time (heck, I have a Sony monitor which reads 6500K). There are some sources on the internet which gives the correct chromaticity co-ordinates for D65 and 6500K... one of them:

http://www.etconsult.com/papers/whitepoint.pdf

The practical thing to do is to make sure the white points of lighting sources in your suite matches. It'll be ok if you're slightly off from D65 (your eyes will "white balance" itself regardless). It's only when you're way off from D65 that it's a problem (i.e. using consumer CRTs, which oversaturate reds to compensate for their higher/blue-ish color temperature). Do try to match your computer's white point to your monitor, or vice versa. If the white points are different, your eyes will white balance to one source. When you look at the other, the white balance is off and this affects color appearance.

2- Fluorescent lights (most of em) tend to be a bit green-ish... since they naturally output more light that way. Higher CRI lights tend to be less green. The CRI figure is for how closely the light resembles that of a black body radiator.

Black body radiator: If you heat up an object, it will emit light (i.e. like a stove element). The particular color of light emitted is linked to how hot the object is (which Kelvins is a measure of).

3- SMPTE RP162 defines recommended viewing practices. One of the things it recommends is a particular luminance for the surround... I believe this is 3.5fL (10% of the monitor's luminance when it displays a white field). Or it's 15%, I can't remember.

The thing about RP162 is that many facilities (high-end, mid-end, low-end) do not follow it.
-Monitor brightness: The largest Sony BVM monitor cannot hit 35fL without problems, so you'll have Sony equipment that runs at 20fL. There is also confusion about whether 30fL or 35fL is the correct brightness. In practice, you also have facilities using a whole bunch of other numbers for monitor brightness.
-Surround size: All over the place.
-Monitor distance: For monitoring, it's generally useful to put the monitor a lot closer than what the standards call for.
-Black level: Setting this via PLUGE is inexact, subjective, and depends on how much ambient illumination is hitting the monitor. Ambient illumination hitting the monitor should likely be as low as possible... you can achieve this by positioning some lights behind the monitor (to light the surround), and flagging others.

The TIG mailing list archives (tig.colorist.org) has some discussion on these issues.

e) if yes what would be more ideal just for editing? Halogen or fluorescent and at what lux numbers?
It doesn't matter much. A fluorescent with fairly high CRI or daylight-balanced incandescent should be fine. Getting close to D65 would be good. Matching your computer monitors' white points to the broadcast monitor's would also be important.

If you need to do color matching (for print work), then the metamerism index of the lighting will matter. But that's not the case here.

d) would it be recommended to install and use different light fixtures when editing?
You can edit with the same light. Some people prefer a brighter environment, since too dark causes eye strain.


Unfortunately, there's not that much information on this subject. I don't claim to have all the answers. In practice, I have seen many facilities (with expensive equipment) where the viewing environment is poor. Heck... I've seen a video from a manufacturer of video test equipment where you can see the light fixtures reflecting off their monitor (obviously these reflections will cause color inaccuracy where the reflections land). It doesn't seem like people notice... this may be because our color memory is poor, and because what we see is not very color accurate (because of varying lighting conditions and things like metamerism).

From a technical perspective, knowing about the issues and knowing what to look for (i.e. artifacts, what incorrect levels look like) can be a big help in accurate monitoring. Also testing your monitor is important... I don't think that much attention is paid to this. A simple and good test is to display a black and white image on your monitor (de-saturate it 100% to doublecheck that it's B&W). Look at your computer monitor fro 10 seconds, then look at your broadcast monitor. Is the image completely black and white? This tests the monitor's grayscale tracking and the white point differences between your monitors.
You might want to throw the system out of whack so you know what to look for.

Another issue to be aware of is that your eyes' "white balance" is constantly adapting itself, and that your brain tends to filter out this adaptation so you don't notice it. i.e. everyday you experience dramatic differences in illumination, but you don't notice this. If you are looking at a broadcast monitor, you can be susceptible to white balance drift. This effect is stronger with a darker surround (i.e. what RP166 dictates is darker than people watching TV with the lights on, with white walls). This would be something to keep in mind.

f) we already have in stock enough m2 of neutral grey carpet. Could it be used to cover the walls instead of painting them neutral grey, since the carpet is already lying around and free to use?
The walls do not have to be a neutral grey (not according to RP166 anyways).

g) any other tips would be truly appreciated
From a practical viewpoint, you should also consider how the suite looks like to the client. This can be more important than the technical aspects.


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dopocc
Re: Editing - Color Correction Environment
on Jun 29, 2006 at 10:58:28 pm

Extremely informative stuff, thanks so much, now you certainly got me thinking and I desperately feel like I need to do some more research..

best regards


-billy


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