Should the DCI/SMPTE 431 digital cinema standards be updated for RGB LASER projectors?
Higher contrast ratio
The SMPTE RP 431-2:2011 digital cinema standard document describes the reference projector viewing environments used in DCI digital cinemas.
–SMPTE 431 Review room 14 fL, 100:1 Intra frame contrast, 1500:1 Sequential contrast
–SMPTE 431 Cinema Theatre 14 fL, 100:1 Intra frame contrast, 1200:1 Sequential contrast
Most cinemas will see an improvement of contrast ratio and light levels with an upgrade to RGB Laser projectors.
This improvement will be noticeable on the DCPs used today.
Rec 2020 color space
New digital RGB laser cinema projectors use red, green, and blue lasers as their light sources. They can (almost) reach the REC 2020 color space.
The RGB laser projectors also have a better contrast ratio and can reach higher light levels without ruining the black level.
The DCI-P3 color space and 1200:1 contrast ratio in SMPTE RP 431-2 are based on what you can achieve with a Xenon lamp projector.
REC2020 covers 99.9 percent of pointer’s gamut, while DCI-P3 cover 91.4 percent.
This means that REC 2020 can do all the primary saturated colors, while DCI-P3 is more limited. DCI-P3 lacks the dark Cyan color that was possible with 35 mm film projection.
Cinemas are also limited to colors that can be achieved with 14 fL.
It would be difficult to use an automatic algorithm to map some of these colors to DCI-P3 without changing the artistic expression of the film.
The Alexa SXT camera that is used on many films is compatible with REC2020
Barco White paper “What are ‘better pixels’?”
This Barco white paper from 2016 looks at REC.2020 and a higher contrast ratio in cinemas with RGB laser projectors. They also recommend keeping the optical light path clean.
In practice, it turns out that some effort in reducing the auditorium reflectivity and lens glare (by e.g. keeping the lens and port hole clean of dust) can yield the same or better results than moving to HDR projection.
Dolby Vision and Imax Digital
You can watch RGB laser projection with (almost) REC 2020 color space and higher contrast ratios in Dolby Vision and IMAX Laser cinemas.
These cinemas can reach higher light levels and use bright colors that are not possible in ordinary cinemas.
Read a review of both here.
A LASER IMAX system demonstration used an intra frame contrast checkerboard test image to show the intra frame contrast of their dual LASER projectors. They said in the demonstration that they changed the furnishing and changed the screen to get a better contrast ratio.
Dual inventory of DCPs?
I think you can have two kinds of DCPs until all cinemas get RGB Laser or similar projectors:
RP 431-2:2011 DCPs for Xenon/UHP and Phosphor Laser projectors
RP 431-2:RGBLASER DCPs for RGB Laser projectors.
Dual inventory of DCPs is not a big problem.
DCP delivery services that use fast internet to distribute DCPs to cinemas send the 3D DCP to the 3D cinemas and the 2D DCP to the 2D cinemas. In the future, if a venue has an RGB laser projector, it would be easy to send them the RGB laser DCP instead of the xenon DCP.
RP 431-2:RGB LASER REC 2020 could possibly use:
-REC 2020 color space,
-and higher contrast ratio
inside the 12 bit 2.6 gamma X`Y`Z` JPEG 2000 250 mbit encoding used in today’s DCPs.
Or use the SMPTE ST2084 EOTF standard to be able to use higher light levels.
Upgrading the light path
Changing screen and furnishing to get good intra frame contrast is essential to good projection.
If the intra frame contrast is bad you could try to:
– Clean the port glass and optics.
– Avoid spill light from projection booth.
– Use matte black seats and furnishing.
– Install an iris in the projector.
– Upgrade to a laser projector.
A laser projector will be better at reaching today´s 3D light levels with just one projector and better at reaching today’s standard contrast ratio. 6P Laser projectors can use 3D with matte white screens and one projector.
A new RGB Laser standard could keep today’s light levels and contrast ratios and just add REC2020 color space. Or the standard could go beyond today’s values. RGB Laser projectors could manage higher values. But in a dark viewing environment, higher luminance values can seem very bright.
The higher contrast ratio you could get with a laser projector could be ruined by reflective furnishing in the auditorium and other factors like old silver screens.
There should be a certification that cinemas could get to show that they are RP 431-2:2011(Xenon) or (future) RP 431-2:RGBLASER certified and have the correct intra frame contrast ratio and light levels.
Or they could get a certification that says they reach the correct light levels in 2D and 3D. (The cinemas should be able to reach these levels also when the lamp gets older.)
This way the public would know that kind of cinemas they can choose between.
Projecting video can look good in a cinema if it is done correctly.
Here are some tips on video projection:
-Use a good video processor.
-Use the best audio/video connections.
-Use a cinema technician to calibrate the digital cinema projector.
-2.4 is the recommended gamma for HDTV monitors in a dim environment Link:ITU-R BT-1886. 2.2 – 2.6 can be used.
-A non-digital cinema projector should at least be adjusted with the contrast and brightness controls on the projector. You should not clip the whites or crush the blacks.
-You have to decode Stereo sound with Dolby Prologic or similar. Otherwise, the speech will either sound as it is coming from the right or the left speaker.
-Video Cassettes can be converted to digital files in a visually lossless format like Apple Prores 422 and be played with an HD-SDI device from a computer.
-Alternatively, you can convert video to the DCP format with Fraunhofer Easydcp Creator and play the video from digital cinema servers.
I have done this at several film festivals. Fraunhofer Easydcp Creator does not raise the black levels or crush the white level. It displays the d65 white point correctly. It has a fast jpeg2000 decoder that can convert prores 422 QuickTime files in real-time speed on fast computers. If you only accept SRGB prores 24/25/30 FPS 422 Quicktime files in 1920×1080,1998×1080 and 2048×858 with 5.1 sound as separate 24 bit, 48khz wave files you can convert the films without other software.
The best video scalers:
-have good upscaling algorithms.
-have 10 bit HD-SDI OUT/IN.
-can auto-adjust sound sync.
-detect if the source is interlaced (video) or progressive (film).
-detects the correct cadence.
-detects common video mastering errors.
-can switch between anamorphic 16/9, standard 4/3, letter-boxed 4/3.
-have a good conversion from one frame rate to another.
A modern scaler that have HD-SDI in/out is the Blackmagic Design Teranex 2D Processor..
It might not have the ease of use of a consumer scaler and it lacks HDCP but it has better upscaling/frame rate conversion.
1.Digital component SDI/HD-SDI
The best transmission of audio:
1. 3 digital AES pairs with 5.1 sound (HDCAM SR)
(You might need 75 ohm BNC to 110 ohm XLR adapters)
2. Analog 5.1
3. DOLBY E bitstream 5.1 sound (HDCAM)
(you need a DOLBY DMA-8 plus or similar to decode it.)
4. Digital stereo AES pair
(You need a HD-SDI audio de-embedder on some HDCAM Decks. Need to be decoded with Dolby Pro Logic 1/2)
5. Analog stereo
(Dolby Digital is compatible with a lot of cinema equipment, but the professional videocassette formats do not support it)
Do you need a video scaler?
A proper video scaler makes video projection easier.
But if the only video source is HDCAM/Blu-ray you can manage without a video scaler.
I have used HDCAM directly on a Christie digital cinema projector:
-A Christie digital cinema projector can auto-detect the field type on the HD-SDI input.
-If the auto-detect does not work you can try the different field types until you get the correct picture.
-If the sound needs a delay you can set it in the sound processor.
-You could make different presets on the projector for different aspect ratios.
Converting video to the DCP format
I have converted video material to DCPs at film festivals with the help of After Effects, Pro tools and Fraunhofer Easydcp.
To do this you need to:
-Tell the people who submit films that the films will be converted.
-Have a HD-SDI capture device to capture digibeta and HD-CAM cassettes to prores hq 422 quicktime.
-Have a computer that can capture the video cassettes to Prores 422 Quicktime files. Like a Mac Mini.
-Ask for HD prores quicktime video files with separate 5.1 sound to make the conversions easier.
The video material I work with are mostly 25 fps and I convert them to 25 fps DCPs.
Projecting video with a video scaler and a computer with HD-SDI
Before I started converting all video material to DCPs (2006-2011), I used a computer with an SDI/HD-SDI Card to send the video in its native form to a video scaler. This way it is was the chipset in the video scaler that did all the work.
A video scaler:
-Decides if the source is interlaced or progressive
-Decides how to fix mastering errors
-Guess the cadence
-Decides how to convert frame rates…
-The DVDO scaler I used had buttons for the aspect ratios 4/3, 16/9, and letterbox for standard-definition material.
-For HD material the HD-SDI device can be connected directly to the projector.
The equipment I used then has been replaced with cheaper alternatives:
Here are some current video playback solutions:
A mac and a Blackmagic Design Ultrastudio Monitor
– The mac can play prores files in their native form and send it through the thunderbolt cable to the Blackmagic Design Ultrastudio Monitor that sends it to the scaler/projector in either pure 8 bit HDMI or 10 bit HD-SDI.
If you use Final cut x as the playback software, you can upscale and fix aspect ratio errors and then render in a prores 422 project before playback.
– A scaler that accepts audio on HDMI or HD-SDI can be used.
– If you use an audio de-embedder you could connect the HDMI/DVI or HD-SDI directly to the projector if you are only using 1080p HD video.
Another alternative is The Teranex and a Mac with a thunderbolt port:
-you can use the teranex as a video scaler in standalone mode and play HD-CAM cassettes directly with the HD-SDI IN/OUT connections
-you can capture video with it.
-you can play captured video or master Quicktime files through the thunderbolt connection IN/ HD-SDI OUT connection.
-you do not have to decide if the film is interlaced/progressive or decide how to convert framerates.
-you can play 5.1 sound
-you can upgrade to DCP conversion with Fraunhofer Easydcp Creator later and convert the captured video to DCPs.
Notes on the Teranex:
-It can be used instead of After Effects for upscaling and deinterlacing video that is going to be converted to DCP. But it does not yet have 2K upscaling so you are limited to 1080P DCPs.
-The teranex will automatically do some of the things you do manually in After effects.
In fields and pulldown in interpret footage in After Effects you have to find the right cadence, and decide if the material is no field/upper fields/lower fields (progressive/interlaced).
The Teranex does this automatically and support mixed cadence/progressive/interlaced material.
To convert mixed cadence material in After Effects I have used adjustment layers and the fieldkit deinterlacing plugin
-If you can’t show the SMPTE DCP framerates like 30 FPS and need to convert hard telecined material to 24 FPS, this is the box that does it the best.
It can convert these formats to 1080p24, and record them as prores 422:
-You could make a XLR patch panel that is connected to the digital 5.1 inputs on the cinema sound system, this way you can connect to the terranex using a standard yamaha db-25 to xlr AES cable.
-It does not support HDCP. But if the Terranex is connected to the HD-SDI input on a Doremi IMB, you can switch between DCPs, Terranex and HDMI with HDCP (commercial blu-rays)
DCI/SMPTE 431 compliant
The first versions of the DCI specifications described all aspects of digital cinema projection like the minimum contrast ratio and the white illumination target. The latest version says that cinemas must follow the projector environment described in these two SMPTE 431 documents:
The best cinemas have good acoustics with good acoustic materials on the walls.
The best cinemas are adjusted and calibrated to sound good.
The best cinemas are powerful enough to be able to play content at reference levels.
The best cinemas do not turn down the volume faders to low levels for all features because some are mixed too loud. They check the sound of every film.
Example: In an Uncalibrated cinema with 35 fL and a low contrast ratio:
-The image will be too bright.
-Black will be gray.
-Dark scenes will look brighter.
-Muddy and washed-out picture.
Some projection best common practices in digital cinemas:
-Adjust the white illumination to 14 fL (using a DCI White test image, not a projector white test image which is 15-16 fL)
-Check and adjust the framing with a framing chart,
-Check the sound for 85 dBc per channel and play the movie at reference level (7 on Dolby, 0 on other equipment)
This is how I do the standard tests from the projection guidelines:
1. Check for 14 fL
-Check that the light path is clean.
-Turn the lamp on the projector and wait 10 minutes.
-Auto adjust the lamp.
-Go to the middle of the auditorium
-Point the spot meter on the Sekonic L-758-C-U at the DCI white square inside the test DCP.
-Check for 14 fL.
-Then adjust the power until it is 14 fL. (If the projector is set to auto adjust the power, check that the projector’s auto power adjustment is really 14 fL.)
-Repeat at least once a week.
Another test that should be included is a basic intra frame contrast test.
To read the intra-frame contrast accurately you need the Minolta LS-110 or similar and the correct Intra Frame test image DCP.
But with a Sekonic L-758Cine or L-758-C-U spotmeter and a projector checkerboard test image you could measure the light from the black and white squares and get some idea of what the intra frame contrast is. The intra frame contrast should be 100:1 for Theaters according to SMPTE/DCI. If you get around 0,5 fL in the black squares, the intra frame contrast is around 32:1.
If the intra frame contrast is bad you could try to:
– Clean the port glass and optics.
– Avoid spill light from the projection booth.
– Use matte black seats and furnishing.
– Install an iris in the projector.
– Upgrade to an RGB laser projector.
2. Check the framing chart.
If the movie has a framing chart you can adjust a preset on the projector to fit the framing chart. It is important to avoid cropping 3D movies because it could break the 3D illusion on movies with floating windows.
You can also use the projector framing test images to check the framing.
You could also check if the picture is in focus when checking the framing.
3.Check sound levels
Your theater sound system should be tuned to 85dB (C-weighted) on all screen channels using pink noise. The correct fader setting on Dolby and DTS systems is 7. On SDDS systems, the correct master volume setting is 0.
Use an SPL meter to check the dBC level. If there is a drop in dBC in one channel you should check speakers and amplifiers for faults. You should also play a familiar DCP at the reference level to check if the sound system works OK. Note: A cinema sound system can pass the 85 dbC test without having enough amplifier power headroom. The pink noise signal that is measured to 85 dbC is -20 Dbfs, a cinema system should also be able to play louder material without clipping.
Note: Many films these days (2015) are not meant to be played at reference levels. The dialogue can be mixed at high levels and you need to turn the fader down to a low level. These movies lack dynamics.
Alternatively, you could use a Real-Time Analyzer (RTA) to check dBC level when playing the pink noise.
I’ve tried the umik-1 microphone with 90-degree calibration in REW as an SPL/RTA.
The DCI/SMPTE standards
Some cinemas may need to change port glass, change audio equipment, change screen, laser projectors, and similar actions to meet the DCI/SMPTE standards.
The X-Curve/85 dbc sound standard:
Virtually all cinema playback systems today are aligned using SMPTE 202M or ISO 2969. The two documents are virtually the same and both define the measuring method and the resulting frequency response known as the “X-Curve”. This provides a uniform frequency response adjustment for all theaters throughout the world. Cinema playback is also tuned to a specific level. All standard cinema systems are optimized for 85dB SPL (2/3rds back in the center) from each front channel and 82dB SPL for each of the rear channel arrays. All channels should have 20dB of headroom. The LFE channel is set at 10dB of in band gain; that is, 10dB greater than the screen channels in each 1/3 octave frequency band. SPL ranges from 88dB to 92dB, depending upon the specific bandwidth of the LFE system in use.
The present alignment standards and recommended practices leave some room for degradation of the sound system, by using equalization to mitigate problems which should be solved in more fundamental ways.
– B-Chain Frequency and Temporal Response Analysis of Theatres and Dubbing Stages SMPTE link
Other tips from the report:
-Match the channels. Do not use a different rollercoaster EQ on the left and right surround channel. The phase cancellation from the different speakers in the surround array can not be removed with EQ.
-Do not EQ the subwoofer too much and.
-Use a 120 Hz low pass filter on the subwoofer.
The current concepts of calibration were developed at a time when reasonably good room acoustics and high output, low distortion, wide directivity loudspeaker systems were by no means as easy to find as they are today. Good systems in good rooms should automatically produce good sounds
Loudspeaker and amplifier technology has also moved far ahead of where it was in 1971. Above all, however, there has been a trend towards reduced theatre sizes and drier acoustics, which reveal much more detail in the sound and render much more obvious the effects of inappropriate equalisation.
Many cinemas turn down the fader level because the sound does not sound good at the standard level. The problem with turning down the level is that the sound will be different at lower fader settings:
-The dynamic range of the sound will be less, some sounds may not be audible anymore.
-Different frequencies will sound louder.
-The surround sound could sound lower compared to the main channels.
A better solution would be to get the sound mix to sound good at the standard fader level.
This is difficult.
Applying one calibration level for all cinema rooms has been shown to lead to an unpleasant, overpowering sensation in smaller rooms.
You have to turn down the fader in small auditoriums to get a pleasant sound.
Here are some possible ways to improve the sound:
-The sound X-curve has some +/- tolerances, so the X-Curve EQ could be adjusted by ear to sound better. The X-Curve was made for big rooms, for small rooms you need to use a modified X-Curve.
-“Floor dips cannot, and should not, be equalized.” Newell et. al. Cinema Standardization V.2
-Listen to the material at the standard level and check if the sound system sounds good and can handle it.
-Better acoustics (example: Baffle wall, good acoustic materials on the auditorium walls )
-Modern amplifiers with enough power that are close to the loudspeakers
-Digital transmission of sound to the amplifiers. Digital transmission of the sound from the server to the sound processor.
Intra Frame Tests
“Intra-frame (or ANSI contrast) is measured with the Checkerboard target shown earlier in Figure 5.3. The luminance of each of the white patches and each of the black patches is measured with a spot photometer. Intra-frame contrast is then computed by summing the white patches and dividing by the sum of the black patches. In its operating environment, the intra-frame contrast is reduced by many factors including projection lens flare, portal glass flare, ambient light spilling onto the screen and back reflections from the room itself.”
-Color and Mastering for Digital Cinema
by Glenn Kennel
The Sekonic L-758cine has less accurate fL readings than a Minolta LS-110, but it will give you a good idea of what the intra frame contrast is and gives you an accurate white illumination fL reading. Flicker is not a problem.
The LS-110 gives accurate readings of intra frame contrast and sequential contrast. The sequential contrast should be 1200:1 in a cinema theatre.
– You could use the built-in fL system in the projector and match the fL values the various presets had when they were calibrated.
Lamp best practices
-You should be at the target illumination 14 fL (2D)/ 4,5 fL (3D) when a new lamp is at 65-75 percent power in the Scope preset.
-You should regularly auto adjust the lamp and use the auto-adjustment of lamp power so it is always 14 fL
-At the end of the lamp’s life it should be at 100 percent, not at the start.
All silver screens not in use for 3D should be changed to matte screens to meet DCI/SMPTE 2D standards. If 3D is used upgrade to better modern silver screens like:
3D silver screens/high gain screens can cause some difficulties in conforming to the 2D 14 fL standards.
In a common height cinema, you often have to use a more powerful lamp to get 4.5 fL for 3D, and another less powerful lamp to get 14 fL for 2D. If you use the same lamp for 2D as you did for the 3D feature, you could get too much light in 2D.
Old silver screens have difficulties conforming to the SMPTE 431-1-06 standard that says:
Luminance sides – Theater – 75-90% of center.
-Even with a curved screen, 75 percent luminance on the sides is not likely.
-You are allowed to have 14 fL +/-3 fL in the center so you could use up to 17 fL (or more) in the middle to compensate for the lower total luminance because of the low luminance uniformity.
-The checkerboard test image will give you some idea of the luminance uniformity.