Your quick guide to the lingo of projection systems, screens and visual displays
Talking about screens and visual displays
Aspect ratio is the width to height dimensions of a projection screen. The earlier tube type televisions have a ratio of 4:3, the common DVD today is 16:9 (1.77:1) otherwise known as wide screen. 16:9 is the standard for most flat panel TVs today. The cinema business is a different story with a number of different aspect ratios used. The most common today is 1.85:1 and 2.39:1.
The screen gain is the brightness factor compared to white. So a neutral white screen will have a gain of 1.0. The higher the screen gain number the brighter the image. This is measured at the centre. The number will normally decrease when measured away from the centre. This is called the Viewing Angle and is measured in degrees.
Contrast ratio simply put is the ratio of white to black. The higher the number the better, or as the industry says, blacker blacks! Better blacks gives a better viewing experience or a better picture.
NPA and OD
NPA stands for Net Picture Area which is the white area of the screen product. OD is Overall Dimension of the complete screen product. The difference typically relates to the black border and the construction of the actual screen product. The distance between the ground and the bottom of the white screen area is known as the skirt.
ALR Ambient Light Rejection
The projection screen has been specially configured to reject annoying ambient light and accept the light source from a video projector. The projection is typically angled up or down towards the screen for optimum results. A good quality ALR screen can be as bright as a LED screen, if mounted correctly. This is a very simplistic explanation with more detailed information found here.
Talking about projectors and visual display parametres
Brightness and Lumens
Every projector has a brightness factor similar to a car with horse power. The video industry measures its brightness in lumens. The standard for the industry is set by the American National Standards Institute otherwise known as ANSI lumens. Not all manufacturers use the ANSI standard and may well use their own measurement in lumens! The higher the number the brighter the picture, just like watts with audio!
High Definition Multimedia Interface is the standard for connectivity with devices such as projectors, games consoles and Blu-Ray players. HDMI carries both compressed and non-compressed data, video and audio signals.
Talking about projectors and screens
This is the distance between the projector lens and the projection screen.
The projector manufacturer will publish a number in the technical specifications. This number is the width of the screen multiplied by the published ratio. As an example if the screen width is 3 metres wide and the throw ratio is 1,5, then the throw distance will be 4.5 metres.
Front and Rear Projection
With front projection one places the projector at the front of the screen, and with rear projection it is at the rear of the screen. Front projection normally uses a white surface or a variation to the white whilst rear typically uses a dark grey screen surface. The dark grey assists with defusing the brilliance of the projector lamp. Theatrical quality stretch lycra screen surfaces are translucent white. As as result, you can use them both for front and rear projection. With this surface you need to place the projector below the screen surface to avoid projector lamp interference with the audience.
Display Resolution is the number of the total pixels or individual dots that a one frame of a video or a single photo is created with. When this number becomes higher, quality of the video becomes high and it creates a very sharp picture. So all the terms like 4K, UHD, QFHD are assigned for different number of total pixels or resolutions. Usually these resolutions are written in a format of multiplication of the number of horizontal pixels and Vertical pixels (Horizontal pixels x Vertical pixels). To get the actual number of pixels you need to multiply those two numbers.
Standard Visual Display Resolutions:
- 8K (7680×4320) Ultra High Definition (UHD)
- 4K (4096 x 2160) Ultra High Definition (UHD)
- 4K (3840 x 2160) Quad Full High Definition (QFHD) (also known as UHDTV/UHD-1, resolution of Ultra High Definition TV)
- 2K (2048 x 1080)
- 1080p (1920 x 1080) Full High Definition (FHD)
- 720p (1280 x 720) High Definition (HD)
- 480p (720 x 480) Standard Definition (SD) (resolution of DVD video)
- 480p (640 x 480) Standard Definition (SD)
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