Film-Tech Forum ARCHIVE: Color Temp of Screen?

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Posted by Eliza Plumlee (Member # 4242) on 03-12-2009, 11:33 PM:

Hi,
I am projecting some film tests for a DP who wants to know what the color temperature of the screen should be when the lamp of the projector is on and no film is running through it.

he is not asking the color temp of the lamp, but the temp of the screen with the light on it. i'm not sure how you would even measure this..... I am not aware of any reflective color temperature meters.

I know, kind of weird, but do any of you know the answer to this?

thanks for your thoughts.
E

Posted by Sam D. Chavez (Member # 1841) on 03-13-2009, 12:27 AM:

If I understand the issue,

There are only two measurements generally used in setting up cinemas. Absolute light output in Foot Lambert, and color temperature. Both are reflective measurements off the screen.

The reflected color measurement is the net result of the bulb, reflector, lens glass, port glass, and the screen surface.

In the film world, there is very little you can do to change the color temperature even if you have an appropriate color meter to measure and document it, except to change the bulb, reflector, lens, port glass (more or less in that order)and of course the screen. Mostly, the director learns to live with the existing condition at hand or moves to a screen he/she like better

[ 03-13-2009, 10:55 AM: Message edited by: Sam D. Chavez ]

Posted by Eliza Plumlee (Member # 4242) on 03-13-2009, 03:13 AM:

thank you! any idea what that ideal color temp. measurement is? even if we could not correct the issue it would be helpful to know if it were off.

Posted by Pete Naples (Member # 761) on 03-13-2009, 03:30 AM:

Osram quote the colour temperature of their cinema xenon lamps as being approx 6000K, prints are timed and graded with that in mind, so it should be somewhere around there, without taking into account all the factors Sam mnentioned.

The only way to accurately answer his question is to use a colorimeter, any tech setting up DLPs should have one at their disposal.

Osram Info

Posted by Steve Guttag (Member # 268) on 03-13-2009, 06:57 AM:

The official Color Temp for Film cinema is D55 or 5500K on the Daylight curve. However, xenon lamps can not hit on the daylight curve like Carbon Arcs could.

As Sam mentioned, everything the light starts with though what the light uses affects color temp.

Since one is not on the Daylight curve, today, most color is specified as a pair of coordinates (x,y) on the CIE 1939 chart.

Using a Chromaticity meter, that translates to x=.332, y=.347.

The biggest factor in the equipment is going to be the reflector, particularly if you are trying to match between two machines. Other things to note...some lenses due to their coatings, tend to alter the native color of the system. Schneider lenses will tend to add about 200K, ISCO will tend to be neutral or even subtract as much as 100K.

One should note, the tolerence, as specified by SMPTE 196M is 5400K +600/-200, so there is a bit of a range...but when matching projectors, they should be within 200K.

Schneider does make color matching filters called Accucolor.

Schneider Web Page

They are not cheap but they will allow one to satisfy a color temp or matching a pair of projectors.

Strong also is pretty good about marking their reflectors with a three-letter code which signifies its color temp. If I recall correctly, BDH is a 5400 reflector.

Steve

Posted by Mark Gulbrandsen (Member # 72) on 03-13-2009, 09:37 AM:

I think your DP is off his rocker. They don't pay very strict attention to absolute color temp in dailies!! He may be trying to cover his ass in some way shape or form... this is very common. Critical color timming is never done in dailies but always done after the final edit and in a very critical film or video evaluation room propose built and normally at some lab. If you're using your movie theater to let them run dailies then LET THEM DO THE MEASUREMENTS AND MAKE THE ADJUSTMENTS SO THE DP IS HAPPY!!! Then he can't argue or blame your equipment if his own people made the adjustments! However if your an equipment renter as I was years ago doing many location dailies jobs then you'd best have your equipment at least up to SMPTE specs, preferably even better in both picture and sound. When the adjustments are finished and you're set to run have the DP come in and view the results. HAve him view a piece of footage he is familiar with and let him take light and color measurements, etc so he can tell where the system's at before they start shooting.

Also, learn set ettiquite(Sp?)before you hang around them much!

Mark

Posted by Scott Norwood (Member # 30) on 03-13-2009, 12:14 PM:

Stupid question: why is film 5500k and video (at least for monitors...not sure about projected video) 6500k? Is the 5500k measured with or without blank film in the gate? If it is with clear film, should it be B&W or color stock (assuming that it makes a difference)?

Suppose you have a changeover booth where the projectors don't (subjectively) match with respect to color temperature (bulbs are same type/hours, etc.). What's the fix? Replace reflectors? Gels taped to port glass? The Schneider filters (the price of which would make most theatre owners faint)? Install a platter (sorry, Steve)?

Posted by Gordon McLeod (Member # 33) on 03-13-2009, 04:25 PM:

In labs often two prints are projected simulatniously side by side to compare colour and so they use matched reflectors and lamps

Posted by Paul Mayer (Member # 355) on 03-13-2009, 10:25 PM:

Old old but still useful thread on this topic

Posted by Eliza Plumlee (Member # 4242) on 03-14-2009, 12:57 AM:

Thanks guys! my DP was very pleased with the information. (except for the bit about being off his rocker, Mark!)

Posted by Steve Guttag (Member # 268) on 03-14-2009, 08:37 AM:

Scott, D5500 comes from natural Daylight and Carbon Arc also naturally settled around there, hence that is where film has historically targeted.

It has been understood that bluer images tend to "look" brighter. Monitors have also had 9000K settings as well.

I believe, however 6500K, not on the daylight curve, has been CRTs more natural color though.

Also, xenon lamps are not on the daylight curve and don't natively hit 5500K either. In order for one to hit 5500K with xenon, the image tends to have a bit of a green shift.

With DCinema, I think the 6500K or more precisely the x=.314/y=.351 comes from a color that the system could easily hit with minimal filtration (loss of light). You can make a DCinema projector hit 5500K, but you will loose light doing so. It isn't native for the system.

There is discussion of moving the film spec up to similar coordinates in a gradual manner. I have been more in favor of a wholesale change rather than stepping it in. It isn't like the film systems are on the daylight curve anymore either. All studies of actual theatre conditions have come back with a "scatter plot" so changing the spec isn't going to cause most people to change anything. Odds are though, since most of the systems installed today are over 6000K, they will be closer to the spec. Hence making films that way makes sense. It WILL affect labs and review rooms that are currently at 5500K as they would need to change out their reflectors. But clinging to 5500K when you really can't achieve light on the daylight curve anymore seems a bit silly.

Steve

Posted by Jonathan Wood (Member # 4614) on 03-24-2009, 05:38 AM:

I agree with Mark, I think you have a fussy DP , I can say that because I am a DP!! My experience with col temp tells me that there are so many variables throughout the chain that although its very useful to know the conditions in which you are screening, any col temp concerns/issues should really have been addressed before a frame of film was exposed. A colour temp meter should read the col temp of the light bouncing off the screen, I suppose he wants a reading off the screen incase your screen is off white?! [Smile]

Posted by Gordon McLeod (Member # 33) on 03-24-2009, 08:14 AM:

I have an issue with a standard being modified to suite basically one manufacturer
Up here strong the predominate american manufacturer installed has been typically 5400K systems +/-200K
Xebex of which there are a lot are also in that range and all the orc and cinemecanicas with rhodnium or nickel reflectors usually fall close to that as well
I really don't think that the theatres that paid the cost and made the effort to due it right should be required then to replace there reflectors
Also I spoke to the majority of colour timers at two labs and they said they would not work with the higher colour temp as they complain of too much eye fatigue

Posted by Mark Gulbrandsen (Member # 72) on 03-24-2009, 08:15 AM:

Believe me Eliza... there are many that are very definately living in another world!!! I might ad that I had always wanted to become a DP... work my way up through the ranks and so on, that is until I had to work with some of these guys... There are also many who are definately real world and really nice/professional people.

Mark

[ 03-24-2009, 10:28 AM: Message edited by: Mark Gulbrandsen ]

Posted by Steve Guttag (Member # 268) on 03-24-2009, 05:20 PM:

Gord, the reality is nothing would change but the spec. However, as new rooms come on line, the odds that the screening room color matches theatre color would be higher.

It is also bull that people are at 5400K...that is, they are not on the daylight curve...they have a skewed color space to have the coordinates translate into a desired number.

The change in the color temp spec would NOT be to satisfy a particular company but to attempt to change the standard to one that all COULD meet if they wanted to.

Steve

Posted by Charles Greenlee (Member # 3856) on 03-24-2009, 05:38 PM:

This thread does tend to remind me of a question I had when I first joined about the color capability of carbon arc vs. xenon. The answer I got then, and the info I see here now both indicate that carbon arc is somewhat superior as far as color rendering. It's interesting that there haven't been any innovations in trying to make a longer burning carbon arc. Sure, a single rod can't ever hope to keep up with the thousands of hours a xenon can take, but at least make one that can run for a whole feature, if not for more than 1 feature. Anyhow, just a little near-topic flashback.

Posted by Steve Guttag (Member # 268) on 03-24-2009, 06:40 PM:

"Clean Carbon?" An interesting concept.

I don't think anyone has ever claimed that xenon was a superior light source to carbon. Its spectral distribution certainly does not match sunlight as well as carbon.

This is a case of practicality, I think. However, yes Carbon is a superior light source to xenon for color.

Steve