Physics Talk

Roger Breton · Guest

I took my faithful Minolta CS-100 along tonight to see a movie at the local
Famous Player theater and I was shocked to find luminances no higher than 20
cd/m2 in the brightest part of the projected movie.

The cinema manager told me once they are using powerful Xenon lamps in their
projector which cost them an arm and leg.

But I was expecting much higher luminances than what I measured tonight.

I suspected my CS-100 calibration could be completely off. But I don't see
how it could be so off.

In comparison, my 30" Samsung CRT TV set produces 115 cd/m2.

My Eizo CG21 LCD measures 100 cd/2 (I calibrate it that way).

I can't believe that Holywood movies are viewed in so little luminance in
commercial theaters.

I wonder if Hunt writes about luminance in movie theaters in Color
Reproduction?

Roger Breton

ImageAnalyst · Guest

On Apr 26, 9:46 pm, Roger Breton <gr...@videotron.ca> wrote:

Gernot Hoffmann · Guest

arahne schrieb:

arahne · Guest

Roger Breton wrote:

ImageAnalyst · Guest

On Apr 27, 2:08 pm, Roger Breton <gr...@videotron.ca> wrote:

Roger Breton · Guest

Gernot, Du¹an,

I since found that SMPTE requires around 55 cd/m2 radiating from the screen
in commercial movie theaters. But that value is *without* any film, just the
bare luminance off the projector. My measurement were made *with* film in
the projection path, which must absorb some amount of the light emitted. But
even if I subtract a few candelas to take into account absorbtion by the
film base, I suspect the luminance would still not go down so low as to
reach only 20 cd/m2 in the brightest part of the image, as I measured last
night.

Thank's for the link Gernot. I better understand how to convert Lumen to
Luminance now.

I'll continue taking measurements in my next outing to see Indiana Jones or
some other popular movie with my family.

MfG / Roger

Roger Breton · Guest

Gernot,

Dieter Michel · Guest

Hi Roger & Gernot,

Roger Breton · Guest

Only 91 cents? You're kidding me. You know, it's a shame the price they
charge for popcorn -- I'm appalled when I have to pay 5$ for a bag of
popcorn which does not even cost them 5 cents :(

Thank's for the reply,

Roger

Roger Breton · Guest

Dieter,

There was not more than 40 peoples in the theater. Maybe that's why no one
from the cinema staff came up to check on who was doing what in the room.
But it made my son nervous that I kept pointing my CS-100 to the screen all
the time. I was not too sure how I would react if the manager showed up and
ask me to explain what I was doing.

I'm pretty sure 20 cd/m2 corresponded to the whitest white off the screen
because that corresponded to light sources in the movie.

I am anxious to compare other theaters now to see whether their luminance is
actually higher or lower.

My hypothesis is that the lamp in the projector had lost some of its power
but the cinema decide not to replace the lamp right away, to try to stretch
their dollar.

Still, I am puzzled how our visual system can adapt so well to such a low
range of luminance and still have a powerful cinematic experience. I
measured the face of actors typically in the 9 cd/m2, good close-up of actor
faces. Only 9 cd/m2, I thought? And that is still provide a lot of detail
for the visual system to watch and explore -- wow!

I wonder how they gamma correct Hollywood movies?

Such an extremely dim environment must decrease perceive contrast.

MfG / Roger

grADE · Guest

The SMPTE spec for an open gate theatre projector is 16 Foot Lamberts,
which equates to 54 cd/m2.
With a clear 'white' piece of film running through the gate this drops
to 48 cd/m2.

This is what a decent theatre would aim to keep their projectors
running at. Of course there are those who try to get more
life out of their lamps and run them at lower power. This will also
effect the white point of the lamp which is another question all
together.

You are right about the percieved contrast in such a dark theatre.
Even turning on the house lamps to dim will wash out the image.

Adrian Hauser
Digital Intermediate Colorist
Cutting Edge
Sydney Australia

DougD · Guest

In article <C43A395C.25450%graxx@videotron.ca>, Roger Breton <graxx@videotron.ca> wrote:

PTKen · Guest

According to this web site <http://www.practical-home-theater-
guide.com/projector-screens.html>:

"In standard 196M, the SMPTE determined that sufficient brightness for
showing motion pictures in a darkened room using a unity gain matte
white projector screen, as 12 - 22 foot-Lamberts. In practice, the
luminance target level is set to about 16 foot-Lamberts, while the
average bright scene brightness level in a movie theater is typically
60% to 75% of this target value."

So, according to this 60% of 16 foot-Lamberts is approximately 33 cd/
m^2 for an average bright scene. Even at the lowest recommendation of
12 foot-Lamberts (~ 41 cd/m^2), 60% of that is about 25 cd/m^2. So
even for the worst case it looks like your measurements are a little
low.

Ken

Gernot Hoffmann · Guest

Roger Breton schrieb:

Dieter Michel · Guest

Hi Roger,