Film-Tech Forum ARCHIVE: Measuring Screen Brightness (FL) without a meter

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Topic: Measuring Screen Brightness (FL) without a meter

Monte L Fullmer
Film God

Posts: 8367
From: Nampa, Idaho, USA
Registered: Nov 2004

posted 02-08-2019 06:07 PM

I installed a light meter app in my android and it's not too bad.

I took the formula posted and times it by the .291 to get fL and I got close to what I should be getting (14fL) using a white light test pattern.

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Justin Hamaker
Film God

Posts: 2253
From: Lakeport, CA USA
Registered: Jan 2004

posted 02-08-2019 06:12 PM

What app did you install?

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Carsten Kurz
Film God

Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009

posted 02-08-2019 09:01 PM

quote: Justin Hamaker
Although I am very careful to make sure I'm using the correct versions, it would make life easier to not have all the version we can not play. It would be a simple step to help ensure customers are getting a proper presentation.

As they maintain site databases for 5.1, 7.1, 3D, or your specific server certificates, they could just as well maintain an entry for screen brightness for every screen, and issue KDMs only for those that qualify for a specific CPL, be it by sound system or brightness. Locations with different screens may show different features, so, you would want all those features to arrive, but the KDMs would sort out what plays where.

- Carsten

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Marcel Birgelen
Film God

Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012

posted 02-08-2019 09:15 PM

It would be helpful if you could simply check a few boxes defining the stuff you would want to receive.

But then they need to either start to parse DCP container names or even need to maintain some extra metadata per DCP.

Also, for them it's not really a winning situation, as they're broadcasting it via satellite, they need to broadcast every version of the DCP anyway.

And for the client side, they probably happily sell you extra storage. [Wink]

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 02-09-2019 03:22 PM

A potential problem of just shooting a picture of a white screen is where did the white come from?

Was it a white test clip playing through the entire system (use the glasses to verify that it appears white through them and that there are no flickers (indicating sync issues).

It is normally tricky to get a projector to put up a white test pattern at the proper color (.314, .351) and your phone/camera won't help you there. Using the server with a white pattern should get everything right.

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Justin Hamaker
Film God

Posts: 2253
From: Lakeport, CA USA
Registered: Jan 2004

posted 02-09-2019 03:41 PM

quote: Carsten Kurz
they could just as well maintain an entry for screen brightness for every screen, and issue KDMs only for those that qualify for a specific CPL, be it by sound system or brightness. Locations with different screens may show different features, so, you would want all those features to arrive, but the KDMs would sort out what plays where.

As it is we only received KDMs for the ones we can play, at least from most studios. What I'm talking about is only pushing the CPLs which the theatre can use. If I only use the 2D 5.1 and 7.1, and the 4.5fl 3D 5.1 and 7.1, what's the purpose of pushing all the other CPLs. Sometimes we receive nearly 20 different versions of movie.

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Marcel Birgelen
Film God

Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012

posted 02-09-2019 05:15 PM

Since it doesn't cost them any more bandwidth than they're already paying for (it's broadcast), there are two reasonable explainations for this:

- They're lazy.
- They want to sell you extra storage. [Wink]

quote: Steve Guttag
A potential problem of just shooting a picture of a white screen is where did the white come from?

While your argument about the source of the white on screen is still valid, most of those apps don't derive their measurement from the camera itself, but rather the light meter that's in most of modern smartphones. The light meter is usually at the front of the device and used for all kinds of stuff, like auto-brightness adjustment of the display.

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