Display definition standards

Several standards of display definition exist, from standard to full high definition. There are three major broadcast techniques, as well as a myriad of displays available with many differing resolutions used across Europe. Most digital displays have all been based upon broadcast standards. Here we look at these standards and how they relate to display technologies.

Scaling is a function of display screens that tries to match the content coming into the display with the actual native resolution of the display itself. For instance, a Plasma (or LCD) display with a resolution of 720 x 480 can display 480 horizontal lines, with each line able to show 720 individual pixels. However, if the content coming into the screen is only 360 x 240, then each line of content will need to be used twice on the display, and each line will need to have each horizontal pixel replicated to ensure a full-size display. This process of increasing the content is called “upscaling.“ The process of losing lines and pixels is called “downscaling.”

Traditionally, all broadcasts have been interlaced, which means each line of the display is refreshed in an alternating pattern. On the first pass, all odd-numbered lines are refreshed, and on the second pass, all even lines are refreshed. A more modern technique is called Progressive Scan, where each line appears in order, and a complete screen refresh happens in only one pass.

There are three main TV broadcast standards available within Europe: NTSC, PAL and SECAM. The American-based NTSC standard defines a resolution of 720 x 480 and runs at 60 Hz. This means there are 60 screen refreshes a second. Both PAL and SECAM have a native resolution of 720 x 576 with a 50 Hz refresh rate.

New semi standards, such as PAL-60, have emerged to increase the quality of the content, which uses a refresh rate of 60 Hz instead of the traditional 50 Hz, that increases the sharpness of the picture and eliminates flicker on fast moving content.

This is where confusion can often enter. There are a lot of displays stating that they are “HD Ready“. Whilst this means they can attain a higher resolution than standard, it does not mean they can display a full high-definition signal. The medium standard definition is defined as 1280 x 720 pixels, and this is the resolution of medium HD content. There are many screens of this format available, but there are a lot more that increase the number of pixels available to 1366 x 768. It is easy to display 1280 x 720 content across a 1366 x 768 display; however, these screens cannot attain the full high-definition resolution of 1920 x 1080.

On a 1280 x 720 display, medium definition content will be displayed pixel for pixel. On a 1366 x 768 display, medium definition content will be upscaled slightly to increase the original pixel count. Other screen resolutions such as 1024 x 768, 1024 x 1024 are used by screen manufacturers, purely to reduce costs on producing the display itself.

This is the latest top-of-the-range standard, defining resolution of 1920 x 1080 pixels, typically using Progressive Scan. This standard is often referred to as 1080p. Original content created using 1920 x 1080 resolution, will be displayed on a pixel-by-pixel basis requiring no scaling hardware or software.

A full high-definition display (1080p) can also display all the standard and medium high-definition modes by using built-in scaling hardware and software. Future standards have been discussed up to 7680 x 4320, and some have been physically demonstrated; however, it will be some time before these systems become available in any form.