Tips on Digital Cinema Theatre DCP test screenings

Here are some questions you could ask the Cinema before you do a DCP test screening:

Does the cinema follow the DCI specifications?

The DCI specification was agreed upon by the big Hollywood studios in 2005 and has been updated regularly.

The current DCI specification tells us to follow SMPTE standards like 431-2:2011 when screening a DCP.

The archived DCI specification 1.2  had these standards as part of the specification. The standards have changed a little since then as errors have been corrected and equipment has improved.

Some important DCI DCP/cinema specifications:

  1. DCI DCPs uses these ST 428-1:2019 example aspect ratios:
    4K Scope 2.39:1 4096 1716
    4K Flat 1.85:1 3996 2160
    2K Scope 2.39:1 2048 858
    2K Flat 1.85:1 1998 1080
  2. ST 431-1:2006 tells us to use 14 fL/48 cd/m2 screen brightness with a DCI white test image, (16 fL with a projector white test image.) If the screen brightness is much lower or higher when screening the DCP, the colors, contrast and details will look different.
  3. The minimum pixel count in RP 431-2:2011 is at least 2048×1080 in length or height. A DCI cinema uses a zoom lens to switch between Flat and Scope. If the zoom lens is fixed at Scope in a common height cinema, a Flat film (1998×1080) is screened in 1525×858, and this is not allowed.
  4. RP 431-2:2011 says to use physical masking for both Flat and Scope.

Is the projector 2K or 4K?

If the DCP is 4K and you watch it in a 2K cinema, only the 2K portion of the DCP is shown. It is best to do a Quality Control test screening of a 4K DCP in a 4K cinema.

If you watch a 2K DCP in a 4K cinema, it will be upscaled to 4K. It will look better close to the screen than in a 2K cinema.

Is the zoom lens working?

It is important that the lens zooms in and out for Flat and Scope, otherwise the picture could be downscaled in Flat.

How much are the Scope and Flat presets cropped? Does the cinema have side masking for flat and scope?

Cinemas may crop some of the picture to mask the fact that the projector is tilted or off-axis. This hides the fact that the shape of the picture has a trapezoid shape and is curved.

Curved screens are often cropped more in the bottom center to mask the curve of the screen and the curve of the picture. You can see how much the picture is cropped if you display the built-in projector test image for Flat and Scope or use a test image DCP. Digital cinema projectors are not allowed to use digital scaling/keystone but can use lens shift to correct some of the effects of a tilted projector.

For a test screening of a DCP, you could ask for a Flat or Scope preset on the projector without cropping, this way you can see if there is something wrong at the edges of the picture. The perceived contrast will be worse if the side and bottom masking does not fit, so using the standard preset could be preferable if you have already have checked the film on a TV/computer.
Movie theatres may have more or less cropping than the cinema you are using, so you need to use around 8 percent safe zones on subtitles and titles.

Different aspect ratios than the standard flat 1.85 and scope 2.39 like 1.78 (1920×1080) could reveal that the projector is tilted and the picture has a trapezoid shape. Also letterboxed 2:1 inside Flat does not have bottom and top masking and could show that the picture has a curve. Some cinemas have presets with masking for 1.78:1, 2:1, and 2.2:1, but many cinemas have only Flat and Scope presets.

Is the peak white luminance 14 fL on the screen?

A projector white test image should measure 16 fL which equals 14 fL on a DCI white test image DCP. Cinemas may have higher or lower luminance, the contrast ratio will be off if it is too low or high.

How is the luminance uniformity?

Old 3D screens can have bad uniformity. Ligh falloff could be 50 percent on the sides of the picture. For DCP test screenings it is best to use a cinema with a matte white screen.

Is the sound level correct?

Is 0 the reference level?
Some cinemas have set their reference fader level 0 to something else like -5 or -10.
With the fader at reference level 0 (7 on Dolby), a -20 RMS pink noise signal played in the center channel is measured to 85 dbC in the center 2/3 from the screen.
With a -20 RMS pink noise DCP and decibel app on a phone, it is possible to check that the reference level is correct.
If you need to set the fader to +10 to achieve 85 dBc in the decibel app you know the reference level is actually +10.

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