This article orginally appeared in the Summer 2019 issue of Professional Lighting & Production magazine.
By Andrew King
We brought you our first video primer five years ago, and in the context of a fluid and fast-evolving technological discipline like video for live events, that’s basically an eternity.
Then, like now, video was becoming increasingly integral to designs for concerts, theatrical productions, and a myriad of other applications, making close and seamless collaboration between visual disciplines vital to success.
What’s more, the trend of technology enabling productions to do more with increasingly shrinking resources has often resulted in lighting professionals being tasked with the design, management, and operation of video systems of varying degrees of complexity.
In light of these ongoing trends, we present our updated glossary of video terms and concepts to facilitate your interactions and collaborations with these technologies and technicians, all with the goal of delivering better shows for everyone in front of, on, and behind the stage.
Here are some basic video terms relevant to virtually any live production, regardless of whether you’re using projection, video panels, or smaller displays.
The American National Standards Institute oversees the use of many guidelines and measurements related to video.
Denotes the shape and dimensions of your image. Generally speaking, there are two traditional and widely used ratios: 4:3 (standard TV) and 16:9 (widescreen TV).
Overall light output from an image. While a brightness control can make an image brighter, it is best used to better define the black level of the image.
The ratio of the luminance of the brightest colour (white) and darkest colour (black) that a system is capable of producing. The larger the contrast ratio, the greater the ability of a video device to show subtle colour details and tolerate ambient room light. There are two generally- accepted standards in the industry to measure contrast ratio:
• Full On/Off Contrast measures the ratio of the light output of an all-white image (full on) and the light output of an all-black image (full off).
• ANSI Contrast is measured with a pattern of 16 alternating black and white rectangles. The average light output from the white rectangles is divided by the average light output of the black rectangles to determine the ANSI contrast ratio.
Tip: When comparing the contrast ratio of different video devices, be sure that you’re comparing the same type of contrast. Full On/Off contrast will always be a larger figure than ANSI contrast for the same device.
A piece of equipment that allows for a camera to roll or slide smoothly when it’s recording.
Refers to the type of video you are shooting as expressed by vertical pixels and frame rate, usually in terms pertaining to resolution such as: 1080/60i or 720/24p. It may also be more generally referred to as standard definition (SD) or high definition (HD) as determined by the lines of vertical resolution. See also: Resolution.
A single frame is one complete video image. When all of the lines comprising the video image are delivered sequentially, it is called progressive video. When the odd lines and even lines are delivered as separate fields, it is called interlace video.
Short for imagine magnification. Frequently used for live concerts, comedy, spoken word, or conferences and conventions, a camera video output relays a live image of the event taking place to a display device in real time.
The small red, green, and blue microdots that make up the image on any type of display. The more pixels there are, the sharper and clearer the picture will be.
Identifies the number of times that an image is “refreshed” every second. The higer the rate, the smoother and more seamless the images.
The size of any given image in pixels. When it comes to video equipment specs, resolution is generally defined as the number of horizontal pixels x vertical pixels. Here are some widely used resolutions:
• Standard Definition (SD) has always been a 4:3 aspect ratio with a pixel resolution of 640 × 480 pixels
• High Definition (HD) video has a higher resolution and quality than standard-
definition. While there is no standardized meaning for high definition, in general, any video image with considerably more than 480 horizontal lines is considered high-definition in North America. Most often, an HD display is one with 720 or 1080 vertical pixels.
• XGA is a display resolution measuring 1,024 pixels horizontally and 768 pixels vertically, giving a total display resolution of 786,432 individual pixels. XGA has a 4:3 aspect ratio.
• SXGA is a display resolution measuring 1,280 pixels horizontally by 1024 pixels vertically, giving a total display resolution of 1,310,720 individual pixels. SXGA has a 5:4 aspect ratio.
• WXGA defines a class of XGA displays with a width resolution sufficient to create an aspect ratio of 16:9. A WXGA display has 1,280 to 1,366 pixels horizontally and 720 to 768 pixels vertically.
• WSXGA defines a class of SXGA displays with a width resolution sufficient to create an aspect ratio of 16:9. A WSXGA display has 1,600 to 1,920 pixels horizontally and 900 to 1,080 pixels vertically.
• UXGA is a display resolution measuring 1,600 pixels horizontally and 1,200 pixels vertically, giving a total display resolution of 1,920,000 individual pixels. UXGA has an aspect ratio of 4:3.
• 2K resolution is a generic term for display devices or content having horizontal resolution on the order of 2,000 pixels.
• 4K resolution refers to a display device or content having horizontal resolution on the order of 4,000 pixels.
• 8K resolution, which is still fairly nascent, refers to a display device or content having horizontal resolution on the order of 8,000 pixels.
Saturation is a measure of colour intensity. In the absence of saturation, the colour hue is a shade of grey. A highly saturated hue has a vivid, intense colour, while a less saturated hue appears greyer and more muted.
Undesirable static, dots, and graininess in a video picture. Noise is a common result of shooting in low light or with the camera’s gained turned up.
• Signal-to-Noise Ratio is that of a desired signal to an unwanted signal, such as static or noise.
Put simply, a projector is a device that integrates a light source, an optics system, electronics, and display(s) for the purpose of projecting an image onto a surface for large image viewing. Here are some terms that pertain specifically to projection.
A common three-colour system for projecting images via LCD (liquid crystal display). It uses dichroic mirrors to separate the RGB components of white light coming from a projection lamp. Each colour is fed to separate LCD panels that control the amount of coloured light that passes through them. The light from each LCD is then recombined using a dichroic prism before going out the lens and on to the surface.
ANSI lumens is the widely accepted measurement of the overall brightness of a projector, specifically in North America. Because the centre of a projected image is brighter than the outer corners, ANSI lumens is the most accurate representation of the image brightness. ANSI lumens are calculated by dividing a square-metre image into nine equal rectangles, measuring the lux (or brightness) reading at the centre of each rectangle and then finding the average of the nine points.
Digital Light Processing is a commercial name for a display technology first developed by Texas Instruments. The technology inside can also be referred to as DMD (Digital Micro-Mirrors). It consists of an array of mirrors where each mirror represents a pixel element. For example, a high-definition DLP projector or rear projector with 1,920 x 1,080-pixel resolution would have over 2 million tiny mirrors (as that resolution would have a total of 2,073,600 pixels). Each mirror is attached to an electronically driven hinge that controls the amount of coloured light that is reflected from the mirror into the projection lens and onto a surface. Projection systems using DLP technology use one to three DMD devices, or chips.
The minimum and maximum distances from the projector to display that will provide a sharp picture.
Keystoning is an effect that occurs when a projector is not exactly perpendicular to the display surface, thereby creating an image that is not rectangular. There are several solutions available to prevent keystoning.
Liquid Crystal Display is a display device for generating colour images using a matrix of LCD pixel elements. Each pixel element consists of three sub-pixels and an RGB colour filter of red (R), green (G), and blue (B). By controlling the voltage to each sub-pixel, each cluster of RGB pixels can create a full spectrum of coloured light. In addition to projectors, LCDs are used in flatscreen displays, cameras, laptops, and other display devices.
Rear-screen projection displays, where the projector is located behind the screen and thus not in the front-of-house area, allow for greater control of ambient lighting. This ultimately means better picture brightness and contrast ratios, and less eye fatigue for operators.
Throw distance is the measurement from the projector’s lens to the screen. A projector with a zoom lens will have a range of throw distances for any given image size, while a projector without a zoom lens will only be able to project one image size at a given distance from the display surface.
The width of the image (W) relative to the throw distance (D) is known as the throw ratio (D/W). For example, one of the more common projector throw ratios is 2.0. This means that for each foot or metre of image width, the projector needs to be two feet or metres away (D/W = 2/1 = 2.0).
LAVISH VISUALS FOR THE CHEMICAL BROTHERS
PL&P Winter 2018 Issue
The Chemical Brothers were busy through the summer of 2018, performing on the main stage of a number of major summer festivals before some high-profile European headlining shows of their own. In both cases, the experience was driven by lavish visuals that ran the gamut from abstract video content to spectacular light and laser displays to, of course, a pair of dancing 5-m-tall tin robots.
Marcus Lyall – one half of @smithandlyall, the creative force behind the design of those shows – told PL&P about delivering a fresh, one-of-a-kind experience that would live up to the duo’s impressive legacy.
“The central mandate from the band is, ‘Put the biggest screen you can fit on the stage behind us.’ We then work out how to make the lighting and other elements work around that.”
The screen for this run of outings was 20 m wide by 11 m high and comprised of GLux 10 mm transparent LED modules, and played host to some very imaginative cinematic imagery throughout the performances.
An LED display is a flat panel display that uses an array of light-emitting diodes (LEDs) as pixels for a video display. Their brightness makes them ideally suited to outdoor or high brightness applications. Also, LED displays are capable of providing general illumination and light effects in addition to visual display, as is being increasingly seen in stage lighting and other more decorative applications (as opposed to informational applications).
There are two types of LED panels:
• Conventional, which uses discrete LEDs
• Surface-Mounted Device (SMD) panels.
Outdoor screens have traditionally been built around discrete LEDs, also known as individually-mounted LEDs. A cluster of red, green, and blue diodes is driven together to form a full-colour pixel, usually square in shape. These pixels are spaced evenly apart and are measured from centre to centre to calculate pixel resolution.
Most indoor screens on the market are built using SMD technology, though this trend has been extending to the outdoor market lately. An SMD pixel consists of red, green, and blue diodes mounted in a single package, which is then mounted on the driver PC board. The individual diodes are smaller than a pinhead and are set very close together.
Is a specification for a pixel-based device that describes the distance between dots (sub-pixels) on a display.
The nit is a comparatively small unit of brightness that measures light emitted from any device. A typical active-matrix LCD panel has an output between 200 and 300 nits. For example, in order for an outdoor LED sign to be visible, it must generate a minimum of 5,000 nits, being that the sun emits approximately 4,000 nits during daylight.
In the case of an RGB colour display, the derived unit of pixel pitch is a measure of the size of a triad plus the distance between triads.
In display technology parlance, viewing angle is the maximum (or widest) angle from the centre of the display at which a display can be viewed with acceptable visual performance. Usually, that means the angle at which the brightness of the display is equal to 50 per cent of the frontal luminosity.
A FUTURISTIC SPECTACLE ON A HISTORIC STRUCTURE
PL&P Fall 2018
Constructed between 1884 and 1887, the Old Post Office in Cambridge, ON, is an elegant two-and-a-half-storey stone building featuring symmetrical twin facades and a striking clock tower all finished with local limestone.
To celebrate its $14.9-million renovation and reopening as the latest Idea Exchange location – a “digital library” and collaborative hub – Toronto’s Westbury National developed a projection-mapped multimedia show displayed on the building’s one-of-a-kind façade with the goal of driving residents and tourists into the library and downtown core over the summer of 2018 and beyond.
The 20-minute show, anchored by four Christie Boxer 2K30 3-DLP projectors, takes viewers on a trip through time, exploring the history and legacy of the building, the city, and the country. Key moments that showcase the technology’s capabilities include the building becoming a digital EQ meter that moves in perfect synchronization with the soundtrack, or a library scene where the spines of the books on a shelf become digitized in commemoration of the new digital library.
VIDEO WALLS – BASIC TO ADVANCED
When assembling or installing multi-panel video walls, the degree of flexibility pertaining to how content can be displayed will vary based on your budget and intended use. This pertains more to the capabilities of your processor or software (see Processing & Control) than your panels.
A basic monitor wall offers a 1:1 ratio of screens to content windows, where the size of the content is limited to the size of the display.
An intermediate multi-window video wall offers more than a 1:1 ratio of screens to content windows; however, the content window size is typically limited to the individual screen boundaries, thus offering window resizing limited to screen boundaries (e.g. 2x2 to 3x3, etc.).
An advanced multiwindow video wall allows content to be freely moved and resized anywhere on the screen, with no limits on window size or screen boundaries.
While projection and video panels/walls are the most common means of deploying video in live productions, there are many other displays – from typical TV screens or computer monitors to more advanced surfaces that employ DLP projection and/or LED technology.
PROCESSING & CONTROL
Outside of the technology that actually brings the video content to the viewer, here are some common devices in the signal chain that store, manage, or process the video signal and optimize it for viewing, plus related concepts.
An image processor, also referred to as an image processing engine or media processor, is a specialized digital signal processor (DSP) used for image processing in digital cameras, mobile phones, or other devices. General tasks include noise reduction, image sharpening, and more.
Simply put, a media server is a device that stores and shares any type of media; however, the increasing popularity of video and motion graphics in live productions such as concerts, theatre, and corporate events has led to the development of media servers designed specifically for such events. These machines are often high-spec computers with increased RAM or hard drive technologies such as RAID arrays or solid-state drives.
These are often bolstered with software that allows for the control and manipulation of video content. One of the primary functions of these machines is to allow current show control technologies to control the playback of video content. That means that, in live production, a media server system may include inputs for DMX512-A, MIDI, or other widespread control protocols.
Streaming is video (or audio) content sent continuously in compressed form over the Internet or other network and played in real time.
A video scaler is a system which converts video signals from one display resolution to another; typically, scalers are used to convert a signal from a lower resolution (such as 480p standard definition) to a higher resolution (such as 1080i high definition), a process known as “upconversion” or “upscaling.” (By contrast, converting from high to low resolution is known as “downconversion” or “downscaling.”)
Also called a video mixer, vision mixer, or production switcher, a video switcher is a device used to select between several different video sources and, in some cases, mix video sources together to create special effects. These can often be used in live production to switch between existing content and live IMAG content.
A VIRTUAL SET FOR PANIC! AT THE DISCO
PL&P Summer 2017
Panic! at the Disco’s 2017 Death of a Bachelor tour was the band’s most elaborate and dynamic to date thanks in large part to a set design that favoured LED video walls instead of physical set pieces.
Playing off of Panic!’s twisted cabaret image, the visuals were delivered through 130 ROE MC7 7.5-mm LED video panels and 52 ACASS-Systems Modlock 7 interlocking LED panels, arranged into tall left, centre, and right columns on the upstage wall, plus curved screens atop five “video chandeliers.” The content was controlled via a pair of Hippotizer Boreal media servers with Barco E2 Jr Event Master processors.
Lüz Studio’s Matthieu Larivée notes the main reason they opted for LED panels across the board in lieu of projection was the scalability required for this tour.
Andrew King is the Editor-in-Chief of Professional Lighting & Production.