Video Wall Digital Cinema Glossary of Terms
For anyone paying attention, direct view LED display technology is tracking to replace projection technology within the cinema space with better performing digital alternatives. As the viability of direct view LED within theaters improves, members of the cinema and digital display industries will need to familiarize themselves with the confusing, and expanding, terminology. Consider the following an informal glossary of terms to help readers understand the various acronyms and buzzwords they’ll surely encounter soon.
Digital Cinema Initiatives, LLC (DCI) is a joint venture of major motion picture studios, formed to establish a standard architecture for digital cinema systems.
The organization was formed in March 2002 by Metro-Goldwyn-Mayer, Paramount Pictures, Sony Pictures Entertainment, 20th Century Fox, Universal Studios, The Walt Disney Company and Warner Bros.
The primary purpose of DCI is to establish and document specifications for an open architecture for digital cinema that ensures a uniform and high level of technical performance, reliability, and quality. By establishing a common set of content requirements, distributors, studios, exhibitors, D-cinema manufacturers and vendors can be assured of interoperability and compatibility. Because of the relationship of DCI to many of Hollywood’s key studios, conformance to DCI’s specifications is considered a requirement by software developers or equipment manufacturers targeting the digital cinema market.
DCI-P3, or DCI/P3, is a common red-green-blue (RGB) color space for digital movie projection from the American film industry. See Figure 1.
ITU-R Recommendation BT.2020, more commonly known by the abbreviations Rec. 2020 or BT.2020, defines various aspects of ultra-high-definition television (UHDTV) with standard dynamic range (SDR) and wide color gamut (WCG). It is an expanded color space relative to DCI-P3 and is not yet regularly met by display technologies today. The Rec.2020 color space can reproduce colors that cannot be shown with the Rec. 709 (HDTV) color space or the DCI-P3 color space. See Figure 2.
The bit depth of a digital display is one element of the display’s color representation. It is measured by the number of bits used to process each color. The greater number of bits in a pixel, the better grayscale it can represent.
Most common formats are 8, 10, and 12 bit per color on digital system.
The accuracy of the A/D converter determines how close the actual digital output is to the theoretically expected digital output for a given analog input. In other words, the accuracy of the converter determines how many bits in the digital output code represent useful information about the input signal. For a given ADC (Analog to Digital Converter) resolution the actual accuracy may be much less than the resolution because of internal or external error sources. So for example, a given 16-bit ADC may only provide 12 bits of accuracy. In this case, the 4 LSb’s (Least Significant Bit) represent random noise produced in the ADC.
Frame rate (expressed in frames per second or fps) is the frequency at which consecutive images appear on a display. The term applies equally to film and video cameras, computer graphics, and motion capture systems. Frame rate may also be called the frame frequency, and be expressed in hertz.
The refresh rate (most commonly the “vertical refresh rate”, “vertical scan rate” from cathode ray tubes) is the number of times in a second that a display hardware updates its video buffer. This is distinct from the measure of frame rate. 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.
As a second example, NanoLumens LED architecture can receive video input at 24, 30, or 60 times per second, but its internal logic can repeat the frame multiple times allowing it to run on the LED screen up to 2,400 frames per second.
In computer graphics and digital imaging, image scaling refers to the resizing of a digital image.
When scaling a vector graphic image, the graphic primitives that make up the image can be scaled using geometric transformations, with no loss of image quality. When scaling a raster graphics image, a new image with a higher or lower number of pixels must be generated. In the case of decreasing the pixel number (scaling down) this usually results in a visible quality loss.
Figure 3. SDR and HDR on Video Systems
High-dynamic-range video (HDR video) describes video having a dynamic range greater than that of standard-dynamic-range video (SDR video), which uses a conventional gamma curve. The dynamic range of a display is a measurement of the difference between the brightest and darkest points of an image.
HDR technology attempts to make digital images more true to life by revealing more details in shadowy areas and in blown out bright areas by exposing the images multiple times. In other words, the camera records the same image multiple times at different exposure and brightness levels and then has software blend the images to borrow elements from both. See Figure 3.
HDR10 is an open source digital image formatting technology. HDR10 provides a display with static bright/dark image metadata so the display can set a single contrast level. All HDR devices should be capable of accommodating HDR10.
HDR10+ is an updated version of HDR10 that communicates dynamic rather than static metadata so that displays can more accurately determine appropriate contrast and brightness settings.
Dolby Vision is a proprietary brand name HDR format from Dolby Labs. The two main differences Dolby Vision has over HDR10 is that Dolby Vision has dynamic metadata and allows for 12-bit color depth.
An acronym for the Society of Motion Picture and Television Engineers, SMPTE develops technological standards, practices, and guidelines for the entertainment industry.
In their own language, SMPTE is “a professional membership association of technological geniuses who make it possible for everyone to experience the advancement of entertainment technology.”