Film-Tech Forum ARCHIVE: Can a picture be too bright?

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Posted by Peter Castle (Member # 1997) on 09-30-2012, 12:51 AM:

We've just updated our projector from an NEC1600 to a 3240, going from 4K to 7K lamps. One of the reasons for this was to improve our 3D brightness. What we didn't account for is the lower limit on the brightness of the lamp (of 70%). While we haven't set up our 3D yet (some problem with the scaling), our 2D image is now very bright: about 19fL for scope and 25fL for flat. The scope looks pretty good, but the flat flares a bit on white - especially subtitles. Now obviously we could drop the lamp to 6K, but we'd then be reducing our 3D brightness again.

Has anyone had any experience using neutral density filters for reducing the brightness of projectors? An ND2 filter would reduce the brightness by 50% - we could then increase the percentage to get 14-16fL for 2D, removing the filter for 3D. (We use shutter glasses.) Not currently having access to the projector, can anyone tell me the diameter of the filter I'd need to cover the lens (an NC50LS18-Z)?

OK, now for the question I asked as the topic. How bright can DCI be cranked up to before being "too bright"? I'd like to know specifically regarding 2D, but I'd also like to know how high 3D can go, considering the 'prints' are colour-balanced for 4.5-6fL.

Posted by Kris Verhanneman (Member # 5562) on 09-30-2012, 03:25 AM:

If a 7K bulb is to much place a smaller one.
You'll get more hours of it and you gain in less power consumption.

But even that isn't perfect.
Bulbs that swap between full power and minimal power don't work that long as bulbs that run more or less around the same current the whole time.

For a 2D feature run a 4K bulb and for 3D a 6K.

Posted by Peter Castle (Member # 1997) on 09-30-2012, 04:23 AM:

Changing lamps is not an option. We run pre-show and trailers in 2D, even with 3D movies, so we have to use the same lamp. Lamp life is also not a worry - we have run for almost 3 years and only used 850 hours of lamp. (We only run once a week.)

Also 4KW is not really sufficient for scope, as our previous projector experience indicated. The idea of a ND filter was to enable us to run the lamp at reasonably consistent amps.

19fL for scope is quite OK - it's the 26fL for flat that is the problem. Are there ND1 filters where more than 50% passes?

Posted by Dave Macaulay (Member # 813) on 09-30-2012, 07:24 AM:

That doesn't sound too bad to me, although obviously "out of spec".
I wonder about "flares a bit on white", a TI light engine won't flare unless it's in serious trouble so that seems like a defective or dirty lens. I have seen 2D images in the 60s (silver screens) without flare so that doesn't seem at all normal. With a too-bright image I see blacks turn to gray - the electronically masked area (when there's no screen masking) is medium gray rather than black. Dark detailed objects look weird and the entire image looks strange, kinda washed out. Very few patrons complain, and I have had theatre management prefer super bright images and ask for the "correct" screens to be made brighter to match.
But with the spec going to 16, I would accept 19/25 unless it's a screening room. As well, with 2D on silver 3D screens it's normal to be too bright in the hot spot so that the rest of the screen is reasonable bright.
ND filters are an option but remember you have serious light energy in the beam from a 7kW projector: it isn't like a camera lens filter that just deals with incident light. An ND filter is absorbing light by definition. Camera filters may just crack from heat stress. The filter may also fade in unexpected ways. There are filters that are made for projection use that cost a bundle, I have seen them used in 35mm timing rooms for changing from full screen to side-by-side projection. Theatrical lighting sheet filter will be fine for the heat but optically it's not designed for image projection, just production/stage lighting.

Posted by Peter Castle (Member # 1997) on 09-30-2012, 08:10 AM:

Thanks Dave.
By flaring, I just mean that white titles on a dark background aren't sharp but glow outwards a little. I'm happy to go with the brighter image. We screen on Wednesday, so I'll seek comment from our audience. BTW our screen is 48' x 20' scope with a 110' throw.
Screen is not silver, but nor is it matt. I see what you mean about the heat that would be absorbed by the filter.

When we set up the 3D, I'll see what the brightness is. Maybe using the smaller iris won't reduce the 3D brightness too much - it's just a waste to lose some of our new-found power.

Posted by Carsten Kurz (Member # 5396) on 09-30-2012, 08:51 AM:

The 'glow' might not be part of the brightness itself, but might indicate issues with dirt or substandard porthole glass. Increased brightness might bring these things into visibility. You should first try to rule out possibilities like this (take out porthole glass temporarily). Screen surface could also cause this, just that you never noticed it before at lower levels.

Even if it wouldn't flare in 2D, I would still consider the increased black level ('greyness') unacceptable for a cinema presentation at increased levels.

It sounds stupid, but the problem of balancing 2D and 3D brightness is actually there, so a suitable, large, heat resistant ND could actually be the easiest way to solve it - although its surface could introduce even more artifacts/reflections. It would also be the easiest to change between presentations compared to all other 'proper' options.

A large ND from optical glass with proper optical coating could be quite expensive.

With one show per week, I personally would actually swap the lamp between 2D and 3D, and live with the issue for the preshow stuff alone, or use the ND only during the preshow.

- Carsten

Posted by Monte L Fullmer (Member # 2797) on 09-30-2012, 06:16 PM:

Be a tech's job using a light meter and a blank white test pattern on the screen, but one can program a macro on the NEC to change rectifier (ballast) output per each picture format on the projector.

Why the 4.5 to 6 fL output is to keep from seeing the double image throrugh the glasses.

Get the image too bright and you'll see ghosting everywhere.

It has to run this dark for the 3D to be fully functionable and presentable.

Sorry, 3D isn't the greatest tasting frosting on the cake to have.

Posted by Peter Castle (Member # 1997) on 09-30-2012, 06:20 PM:

I wasn't aware that ghosting due to brightness was a problem with shutter glasses, only with polarising systems.

Posted by Dave Macaulay (Member # 813) on 09-30-2012, 06:35 PM:

Every 3D system has a certain maximum cancellation to stop the "dark" eye image from being seen. "Shutter" glasses are actually a polarizing filter and a liquid crystal panel that changes polarization when electricity is applied to it... they aren't that much better than a silver screen system except for the screen, which can never be 100% reflective when new and only gets worse from then as it gets dirty. Dolby uses optical comb filters that have crosstalk as well.
If the projector's screen illumination is way too bright you see the ghost image quite plainly; at the spec brightness, with every 3D system the ghosts are still there but much less annoying.

Posted by Peter Castle (Member # 1997) on 09-30-2012, 06:41 PM:

So how did this take place?

In a landmark event, XPAND 3D, the world leader in 3D for the cinema, home and beyond, today announced that an XPAND active 3D system will be used with a Christie’s first laser projector for the screening of Martin Scorsese’s Hugo 3D at the IBC show in Amsterdam on Monday, September 10.

This marks the first feature-length 3D film to be screened using laser projection technology and also the first public screening of a 3D movie shown at full 2D movie specification brightness (14 FL). The screening will be the final event of the IBC Big Screen showcase, which is dedicated to featuring the latest in cinema technology.

The system will include XPAND Infinity 3D glasses, which provide up to 38% transparency and a 3000:1 contrast ratio. The glasses’ lightweight ergonomic designs ensure long-wearing comfort, and their wide 3D viewing angle provides an optimal 3D image across the entire cinema. All new XPAND cinema systems and glasses fully support HFR (High Frame Rate) double and single flash at 96fps, 120fps, 144fps, 192fps, 240fps and even variable fps.

“XPAND firmly believes that laser projection technology represents the future of cinema projection and everyone who attends the IBC Big Screen Monday Night Movie will see why,” said Maria Costeira, CEO of XPAND 3D. “Moreover, the viewers will benefit from wearing our Infinity 3D glasses, which delivers the most immersive and dynamic 3D experience available in the world!”

“Advanced 3D glasses combined with the proper light levels and, in the months to come, high-frame rate content, will increase the enjoyment factor of millions of moviegoers around the world when viewing 3D projections, and we welcome XPAND’s participation in Monday’s groundbreaking event,” said Richard Nye, Cinema Sales Director, Christie EMEA.

The screening will take place at the 1,700-seat Amsterdam RAI Theatre at IBC and will begin at 6:30 PM.

Posted by Chris Slycord (Member # 4239) on 09-30-2012, 07:03 PM:

How did that event happen? Probably by having a version timed for that brightness instead of the normal one? They make specific versions for even the 6 FL installations for real-d...

Posted by Carsten Kurz (Member # 5396) on 09-30-2012, 07:36 PM:

Shutter glasses systems still have a factor of 5-10 better stereo separation than standard RealD. So you should experience less to no ghosting with shutter glasses and Dolby3D even at increased brightness levels. Maybe this better stereo separation was indeed the reason why Christie went with XpanD for the high brightness 3D laser projection demo. Wavelength selection like Dolby 3D/Infitec wouldn't work with laser illuminated projectors - at least not easily.

That said - I recently sat in the front row of a cinema and watched Hugo through XpanD. This was a small screen and I was only about 1.5 m away from the screen.
I noticed quite some ghosting off axis, that is, I could provoke noticeable ghosting by turning my head and fokussing high contrast details though the side parts of my glasses.

Anyway Peter - I wouldn't actually call 19/25 fL 'over spec'. Double it, THAT would be too bright.
Even DCI allows for +3fL tolerances in theatres. Either your numbers are wrong, or this halo/glow is caused by something else.

You mentioned not having set up 3D - I guess you actually mean 19/25fL in 2D, and we are not talking about 3D ghosting?

And if you currently get 25fL from a 7kW lamp in 2D, your XpanD can never be too bright.

- Carsten

Posted by Peter Castle (Member # 1997) on 10-02-2012, 03:29 AM:

Here's another issue.
Many projectors these days are supplied with an iris which can be used to reduce light output. I thought that might be a solution to my problem of excess brightness at the minimum lamp percentage.

Now I see another reason. Documents on the NEC website indicate that the 2000:1 contrast ratio REQUIRES the installation of the iris. What does this mean? Anyone know how much light output is effected by the use of the iris?

Posted by Carsten Kurz (Member # 5396) on 10-02-2012, 04:10 AM:

The iris or aperture plate is nothing you can adjust 'at will' to balance between 2D and 3D brightness. It's a fixed installation option in the light engine for increased contrast on smaller screens, e.g. screening rooms. You need a service technician to install it.

Theoretically you could have a variable Iris within the lens, but as far as I know, there are no lenses for DCI projectors offering that feature. Some consumer projectors have it to increase contrast and lower blacklevel.

With high wattage projectors, lens-internal iris could lead to severe heat problems and lens performance degradation, I guess.

- Carsten

Posted by Peter Castle (Member # 1997) on 10-02-2012, 04:23 AM:

Carsten, I am aware that using the iris would just reduce the brightness constantly. But what I want to know is why the iris increases the contrast, and by how much the brightness will go down.

While such a solution will lower the brightness of both 2D and 3D, it may be enough to get the 2D brightness down without too dramatically losing out on 3D brightness - a compromise.

Posted by John Wilson (Member # 269) on 10-02-2012, 05:23 AM:

Leave the 3D in place when you show Flat 2D. Problem solved.

[Big Grin]

Posted by Peter Castle (Member # 1997) on 10-02-2012, 07:45 AM:

What do you mean, John?
We use shutter glasses. There is nothing in front of the projector to leave there.

Posted by Peter Castle (Member # 1997) on 10-03-2012, 04:21 PM:

The figures are in.
I did not indicate to our audience that there was any change in our presentation for the screening last night.
The only comments were positive ones, so 25fL isn't considered too bright by regular patrons.
I myself certainly noticed the grey areas outside the picture area on flat but our audience didn't.
So we'll go with it as is. It will be interesting to see what brightness we get on 3D.

Posted by Carsten Kurz (Member # 5396) on 10-03-2012, 06:26 PM:

So this the 7kW bulb? At what operating current?

- Carsten

Posted by Peter Castle (Member # 1997) on 10-03-2012, 09:17 PM:

70% - the lowest possible
7kW lamp

Posted by Carsten Kurz (Member # 5396) on 10-04-2012, 10:43 AM:

You should be glad you're not running Dolby 3D.

- Carsten

Posted by Marco Giustini (Member # 4544) on 10-04-2012, 01:11 PM:

I have seen flat 2D pictures at 40fL - guess who: Dolby 3D involved! I personally cannot stand a dark picture. I do love a 18-20fL picture over the standard 14fL. Over that level black level becomes too high and - depending on the movie of course - the picture washes out a bit.

In your setup, I wouldn't be too worried about it. You can set a different light output using different "titles", you can run your lamp at 7K on 3D, and at 3.5K on 2D, even though this is not very good for your lamp. It shouldn't be a problem to run your lamp at 6K in 2D though.

Is the "flare" you're seeing maybe caused by the Silver Screen (assuming you're using a Silver Screen?)

Posted by Peter Castle (Member # 1997) on 10-04-2012, 06:00 PM:

Our 3D is now set up.
We are running both 2D ratios (flat and scope) on setting of 70%, as that's the lowest it can be.
3D scope we have at 100%, 3D flat at 90%.
We couldn't seem to measure the brightness level of the 3D as simply as the 2D, so we just did it by look - it looks great.
So, while the 2D is a little bright, the 3D is the best I've seen.
No silver screen, shutter glasses. Using a Harkness tester.
One side effect is that, in the past, we could mix 2D and 3D trailers together in one playlist, and patrons would leave their glasses off for the 2D. Now the 2D part is way too bright, but looks OK with the glasses on.