REMINDER: Context is key; this information should be taken as broad strokes on a subject that can vary based on creative intent. Please read “2D LED In-Camera VFX Field Guide Overview” for context on where the information presented here comes from and is intended for.
Table Of Contents
Overview
On-Set System Flow
Content Playback Technology
For 2D content playback on LED panel technology, a special piece of playback software is required for a couple reasons: 1) you need to arrange and map your content between panels (pixel mapping), deal with corners, ceiling, etc. and 2) you need to communicate with the LED Image Processing technology. Most of the software comes configured to work with accompanying hardware (i.e. Disguise) and sometimes a specialized playback codec (i.e. 7th Sense servers). Most Content Playback systems available these days rent with the hardware to use it. The hardware is specially configured to do one thing: play content of varying sizes to varying outputs in real-time. Remember that no ordinary computer can easily playback 4K (let alone more) in real-time for extended periods of time.
However, it shouldn’t be just about the compute power! When choosing a playback solution, consider the usability and flexibility of the software. If the software is hard to use, it won't matter how powerful the hardware is.
Playback System Elements
|
ELEMENTS |
IDEAL REQUIREMENT |
REQUIREMENT RANGE |
Details |
Notes |
|---|---|---|---|---|
|
Codec |
ProRes |
≥10 bit, lossless compression, capable of handling high resolutions (≥ UHD) |
There are many other codecs that definitely meet/exceed our requirement range - NotchLC, DNxHR and HapQ being other popular options. |
We are listing ProRes as our ideal requirement because it is widely supported, used, and generally understood. For performance, though, NotchLC is ideal because it’s GPU based and incredibly performant. Note that it is not supported everywhere, but gaining traction. |
|
Color Correction Controls |
OCIO/ACES framework |
Hue/Sat/Exposure/WB |
Most playback systems will have basic color correction functionality - but you can tell a good from great by the effort put into usability and ease of function. Look for:
|
We realize full color management such as ACES via OCIO in a Playback System is a lofty goal. However, we do believe in pushing this forward as it will enable easier workflows for the whole chain - especially when a DIT is involved for on set color. |
|
Framerate |
Same as primary capture |
23.976-120 FPS |
These systems can play almost any framerate their supported codecs can playback. |
Pay special attention to this. It’s incredibly important to play back content at the same rate that it will be captured to avoid issues in motion cadence. |
|
LED Panel Mapping Controls |
Flexible 3D Placement |
2D “grid” - full 3D Environment mapping |
Look for keywords in the software description or manual such as: Flat, curved, half-dome, 3D modeled shape, projection mapping, in-GUI visualization, warp, blend |
There are many different levels of playback software out there. The most important thing is mapping out your requirements beforehand, so you can pick a system that meets those needs. |
|
Playback System Controls |
Either |
Cue or timeline based |
Different software may use "cue" based controls vs. a linear timeline. Either is fine, will depend on your workflow. |
|
|
Memory |
64-96GB |
32-120GB |
As with CPU, the larger your overall LED screen footprint, the more memory it will require to be performant. |
|
|
Resolution (per unit) |
4096x2160 |
2K-8K |
Lower-end models all seem to be HD - either you're paying for the high quality unit or you're getting something much less powerful in every aspect. |
|
Resolution (total surface max) |
16k |
8k-16k |
Different players have different capabilities of genlock synchronization between playback servers to create synced content at large resolutions. The general max on most systems currently available seems to be 4 - so 16k across. |
|
Server Genlock |
Yes |
No range, it's a must have |
All mid- to high- range playback systems have this ability. |
|
|
Storage |
2TB SSD |
1TB-5TB SSD |
This could be pretty flexible, depending on size of screen, length of project and codec choice. |
|
|
Video Outputs |
HDMI 2.0 or DisplayPort 1.2 |
HDMI, SDI, DisplayPort, USB |
Make these decisions in conjunction with your Image Processor Technology. |
Image Processor Technology
The Image Processor is the element of the pipeline that adapts, interprets and translates the video feed coming from the Playback System to the required LED data distributor (commonly a network switcher) which feeds the LED panel the correct data. In other words, the image processor plays the role of the imaging negotiator between the Content Playback System and the LED Panel. The image processor operations can vary to include scaling, color space conversions, synchronization to LED gain, white point temperature control, LED calibration and overall LED power output.
While there is almost always a data distribution switcher between the image processor and the actual panels to handle signal flow, the performance of an LED screen are directly correlated to the ability of the image processor to drive the LED wall. The capabilities of a good image processor can also be limited by the quality of the LED screen and the receiving card. The two things are very much tied together. In a normal computer monitor, the panel and the image processor are designed to work together and built in such a way that the performance will be consistent and determined by the manufacturer. When it comes to LED panels, the user can combine many LED walls with different (compatible) image processors, thereby creating discrepancies or varying performance levels. Like the rest of the technology in this space, the modular nature lends itself to both flexibility and variability.
Important note: each image processor it's only compatible with a specific (or a very limited set of) receiving card which have to be installed on the LED panels. In order to change Image Processor in your pipeline, you must make sure that the LED receiving card installed on your panels will be compatible with the new processor.
Image Processor Elements
| ELEMENTS | IDEAL REQUIREMENT | REQUIREMENT RANGE | DETAILS | NOTES |
|---|---|---|---|---|
| Color Adjustments | Yes | White point Temperature, Gamma, Gamut mapping | Retouch incoming video signals can be done on the playback system, but it could be required to do a final pass on the processor | Nice to have settings: Black Level, Contrast, Hue, Saturation, RGB Shadow and Highlights, RGB Gain, Brightness, White point Temperature, Gamma |
| Data port | 1Gbe Output | 1Gbe/ 10Gbe Copper - 10Gb single mode Fibre | The data port is the connection between the Image Processor and the distribution units and ultimately the LED panels | |
| FrameRate Multiplication | Yes | OFF, x2, x4, x6 | This features allow the image processor to multiply the incoming video frames and get more use of the fast refresh rate of the LED panels in order to achieve the best possible combination of image playback performances and smooth perceivable motion on screen. | |
| Genlock | Sync to source over external source | PTP, SDI, HDMI Ref In | Genlock can be used to lock the processor and LED refresh to a camera’s shutter. This provides a better on-camera performance, by preventing the unsightly rolling black bars seen on video walls using free-running systems. Alternatively, you can use Genlock to lock multiple LED processors together for completely seamless shows with no tearing. The processor can even add extra delay should it need to match with other slower video systems. | |
| Infoframes | Supported, Static | Static, Dynamic | Auxiliary Video Information (Infoframes) that carries over HDMI, DP or SDI statuses such as Color Space, HDR format, Color Primaries, Max CLL Max FALL | Important to handle HDR content correctly |
| HDR Formats | HDR 10 | HDR10, HLG | Processors automatically detect and handle HDR content | Some Image Processors allow to access to HDR mode only after the necessary calibration |
| Input Resolutions | Custom | Minimum UHD | Content can be created at several different resolutions. It is important for the processor to be able to receive custom resolutions. | |
| Internal Test Patterns | Available | Ideally, every processor will be able to display into any LED panel one of the standard test patterns used commonly in Display Calibration (Checkerboard, Gradient, SMPTE Bars, Color bars, Solid colors) | ||
| Latency | none | 1 to 3 frames | Latency is usually referred to in ms (milliseconds) or frames, which represents the response time or traverse time that one device takes to communicate with another. | |
Bit Depth |
10 bit | 10-12bit | Bit depth refers to the bit depth at which video data is encapsulated, packetized and sent to connected LED Panels via Fibre or Copper | The bit depth you use to set up the processor, determines how many pixels of LED panels can be used. |
| Processor Redundancy | 0 frames (Fallover into back up) | Unknown (set up dependent) | A Processor configuration where two outputs can be configured to operate as a redundant pair, Main and Back-Up. This allows the Back-Up to be able to continue the signal path, when the Main’s infrastructure is damaged. |
LED Panel
In-Camera LED Panel Elements
| ELEMENTS | IDEAL REQUIREMENT | REQUIREMENT RANGE | DETAILS | NOTES |
| Pixel Pitch | < 2.6mm | < 3.2mm* |
In the simplest of explanations, pixel pitch is the distance from the center of an LED cluster (or pixel) to the center of the next LED cluster/pixel, measured in millimeters. The smaller the pixel pitch, the higher the density on the LED tile, the higher the resulting picture resolution is. Pixel pitch affects things like moire and optimal viewing distance between the camera and the LED wall. As a rule of thumb, the shorter the viewing distance from the camera is, the smaller pixel pitch is required. |
*Depends on the application, it could go over 3.2mm if the LED wall is only required for non-direct filming (eg ceiling or reflections) |
| Refresh Rate | 1920Hz | 1920-3840Hz+* |
The refresh rate is the number of times in a second that a display updates its buffer. This is distinct from the measure of frame rate which indicates when the display is provided with new data: the refresh rate includes the repeated drawing of identical frames, while frame rate measures how often a video source can feed an entire frame of new data to a display. For example, most movie projectors advance from one frame to the next one 24 times each second. But each frame is illuminated two or three times before the next frame is projected using a shutter in front of its lamp. As a result, the movie projector runs at 24 frames per second, but has a 48 or 72 Hz refresh rate. For LED lighting this happens on a scale 10 times bigger and it’s essential to find a refresh rate that can be synced with the framerate of the camera shooting the LED wall. As a rule of thumb, a refresh rate needs to be a multiple of the shooting frame rate. i.e. 1920Hz/2/2/2/2/2/2=30Hz so it syncs with 30fps. This rule can be bent by altering other factors of the shooting imaging pipeline, such as the camera shutter speed. |
*Depends on the application and on the LED panel multiplexing ratio |
| LED Configuration | RGB linear cluster | RGB or RGB+ either with a triangular cluster or a linear cluster |
In order to reproduce video content with an accurate color representation and brightness, the LED tile should be able to produce a wide range of colors throughout the visible spectrum. Most likely, in order to do so, it is required to have LED pixels capable of emitting light following the Red, Green, Blue additive color model principle, therefore providing a spectral power distribution in the areas of 564–580 nm (for the Red), 534–545 nm (for the Green), and 420–440 nm (for the Blue). This can be checked on the LED panel white sheets.
Furthermore, how these pixels are arranged on the LED tile might affect visual artifacts such as a visible moiré pattern in camera and viewing angle. We refer to this as LED pixel clustering, and in order to obtain better results, it seems that a linear arrangement is preferable.
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|
|
Contrast Ratio
|
8.000:1
|
6.000:1 > 1.000.000:1
|
The contrast ratio is defined as the ratio of the luminance of the brightest shade (white) to that of the darkest shade (black) that the LED system is capable of producing.
|
Note that very few LED panels reach a contrast ratio above 10.000:1 and that both the reflectivity of the LEDs and the mask applied to the panel will affect this parameter considerably. |
|
Reflectivity
|
Very low
|
None to low
|
Some LED screens have matte surfaces, while others are more shiny. The latter can cause your actors, props and lighting to reflect on the screen and cause flares and make your projected content blacks look milky | |
|
Multiplexing Drive
|
≤ 1/8
|
1/1 - 1/16
|
Multiplexing is a technique used to connect multiple LEDs together in a matrix of columns. This manufacturing technique simplifies the hardware due to the reduced number of pins required to connect each LED pixel.
Each column is switched on in sequence to turn on the desired LEDs. To fool the eye into seeing a continuous display, the sequencing is typically done at a fast speed, more than 50 times per second.
Typically this feature is expressed as a fraction that indicates in how many rows the LED tile has been divided. The smaller the fraction, the more are the sections on the tile. A high number of sections can bring to artifacts, mostly visible in camera as a “flicker”, similar to the one generated by an off-synced refresh rate.
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|
LED panels manufacture technology (common cathode vs common anode)
|
Common Cathode
|
Common Cathode, Common Anode
|
The way the LED tiles are manufactured can influence aspects of heat dissipation. There are two techniques: “common cathode” and “common anode”. Common cathode is a more reliable and less heat-producing (higher dissipation) solution which creates less hotspots in the image on the screen. This also creates a larger uniformity and less color differences over time, creating a longer lifespan with higher quality. Common anode tends to produce more heat and have a less efficient heat dissipation, producing hotspots in the panels that are easily being picked up in camera.
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|
|
Brightness
|
≥ 1000 nits
|
600-2000 nits
|
This is the peak brightness produced by a LED tile. There is not a correct value for this, as it really depends on the application and your pipeline. In order to have enough power to balance the scene, the LED wall should try to produce the same, if not higher brightness, of the light sources used on set to light the scene. Please note that, due to multiplexing, if a LED panel is too bright, it might struggle to reproduce dark images without creating artifacts.
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|
|
View Angle V/H
|
≥ 140º
|
≥ 120º
|
The way LED pixels are clustered and arranged on a LED tile determines the optimal viewing angle of the LED tile/wall.
The viewing angle (or viewing cone) defines a number of possible viewing directions in which the LED tile/wall can be viewed with acceptable visual performances. These performances are defined by color consistency, color accuracy, visible blur, tonal contrast, black level, moire patterns, etc. Ideally, the angle should be as close to 180º as possible but typically goes around 140/120º.
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|
|
Bit Depth
|
16
|
10-16+
|
The bit depth defines the precision on which colors can be expressed (shades of Red, Green, Blue) within a color range (gamut coverage). For LED walls, bit depth is mostly expressed as a grayscale value as it represents the LED panel's driver IC capabilities.
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|
|
Gamut Coverage
|
P3
|
r709 - r2020
|
The ability of the LED wall/tile to cover and accurately reproduce the color areas defined as standard color gamuts within a CIE XYZ color system diagram.
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|
|
CRI/TCLI
|
≥ 90
|
≥ 85 - 100
|
Color Rendering Index (CRI) is the quantitative measure defined by the CIE of the ability of a LED light source to reveal the color of various objects faithfully in comparison with an ideal or natural light source.
The index is measured from 0-100, with a perfect 100 indicating that colors under the light source appear the same as they would under natural sunlight.
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TM-30-18 (Rf/Rg)
|
≥ 90/100
|
≥ 90/90-110
|
Similar to the CRI measurement, the TM-30-18 is a new standard of defining color accuracy for light sources.
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Hanging/Stacking
|
20/14
|
16/12-25/25
|
How many panels can be hang and stacked together in a LED wall
|