The Buyer's Guide to HDTV Terminology

The Buyer's Guide to HDTV Terminology

Jason Yang
Jun 1, 2011

Walk into any Best Buy or similar electronics store and you'll face a giant wall of television sets, slim and shiny and new, and all vying for your hard earned money. Each new set shouts out its features, trying to convince you that it's the TV of your dreams. 65!" 240 Hz! 1,000,000:1 contrast ratio! We provide an in-depth guide to the technical terms and specifications used with modern TVs.

Screen size
Understanding a TV's screen size sounds like a no-brainer, but there are just enough curveballs to make it interesting. Traditionally, a television's size is reported as the diagonal measurement of the screen. Most of us can remember when TVs weren't always the current 16x9 aspect ratio and 4x3 was the standard (or 5x4 for previous generation computer monitors before they started trying to integrate the two). A little algebra and the Pythagorean Theorem can help you determine the actual physical dimensions of the screen, and it's important to note that the TV itself has larger dimensions due to the bezel and stand.

The marketing wizards working to sell us brand new shiny TVs have also begun to throw around the term "class" in advertising a TV set's screen size. A 50" class TV might actually be 49-9/10", but that's just not quite as marketable a number.

Refresh Rate (Hz) and Frame Rate (Fps)

A TV's refresh rate refers to the number of times per second an image is drawn onto the screen. The higher the refresh rate, calculated in Hertz (Hz), the "smoother" the picture. The frame rate is the number of unique images per second produced by a video source such as DVD, Blu-ray, or your TV signal.

Because the refresh rate is generally much higher than the frame rate, individual frames are often shown multiple times. Depending on the source, your TV goes through an internal calculation to translate how to fit the number of frames per second into the refresh rate. Ideally the TV would have a refresh rate as a multiple of the frame rate, but since source material is often quite different, a bit of magic known as 3:2 pulldown helps make everything run smoothly.


Flat panel TVs have a fixed number of pixels used to display images on screen. The resolution you hear (generally 1080p or 720p) indicates the number of vertical pixels that the TV has. Recall that TVs have an aspect ratio of 16x9, so 1080p TVs have an overall resolution of 1920x1080 and 720p TVs are 1280x720. Ideally, the source material resolution matches the TV resolution. This is when the pixels from the source map 1:1 to the TV itself, but when that's not the case, your TV does some more magic known as scaling to mathematically compress or enlarge the image to match your screen resolution, with loss of quality as the compromise.

Contrast Ratio

Contrast is the difference between the luminence of white and dark as displayed on screen, displayed as a ratio. The higher the contrast ratio, the better your TV is supposed to be at displaying the details and depth of a picture. Unfortunately a big problem, as highlighted by cnet, is that you can never take the reported number at face value. There is no standard method of measurement for contrast, and manufacturers use and abuse this at their marketing whim.

Energy Star

Energy Star is a designation for TV sets designed to use less electricity and save you money. Most Energy Star TVs use about 30 to 40% less energy than comparable models without sacrificing features.

Connectivity: HDMI, DVI, Component, S-Video, Composite

HDMI is a standardized cable that carries both digital audio and video between your source (DVD, Bluray, etc.) and your TV. Just note, all HDMI cables are pretty much the same (correction: except in the case of 3D HDTV sets, which are optimized for use with "high speed HDMI" rated cables), so there us no need to purchase brand name cables at premium prices.

DVI is a video-only signal commonly used for computers that many TVs provide inputs for to allow easy computer hookup to your TV. Keep in mind in order to play copy-protected video content from your computer to your TV via DVI your video card and TV must support HDCP, a form of copy protection that's embedded into the video signal. Component, s-Video, and composite are all older forms of cables that carry analog video signals and are mostly out-dated and kept on TVs for legacy equipment.

(Images: Flickr members Jerry W. Lewis and AleGrnholm, licensed for use under Creative Commons)

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