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Tech Terms Demystified: HDMI upconversion and HDMI conversion

Ralph Graves is one of Crutchfield's blog editors, and part of the company's social media team. He writes about home audio/video gear, specializing in Apple-related and wireless technologies. Ralph holds a master's degree in music composition, and his works have been released on various labels. He's served as product manager for an independent classical and world music label, produced several recordings, and worked extensively in public broadcasting. Since 1984 he's hosted a weekly classical music program on WTJU, and is also active as a blogger and podcaster.

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HDMI is a bit of a mystery for most people - especially HDMI video upconversion. Part of the problem is that the term "upconversion" is used interchangeably with "scaling" and "upscaling". And it's often confused with HDMI conversion - which is actually part of the video upconversion process. And both terms are sometimes interposed with HDMI switching.

Puzzled? You're not alone. Let's try to untangle this Gordian Knot.

HDMI video conversion
A receiver with HDMI conversion just translates incoming an analog video signal into a digital one of the same resolution so it can be sent through a High Definition Multimedia Interface cable to a TV. If, for example, the incoming analog signal had a resolution of 480i, it would be converted to 480p digital signal to be sent through the HDMI cable.

That resolution may or may not be the best one for your TV, which can result in a less-than-ideal viewing experience. You may see the image broken into little square blocks (especially when there's fast motion), random pixels (called digital artifacts), and distinct color bands rather than one hue blending naturally into another. That's where upconversion comes in.

HDMI video upconversion
A receiver with HDMI upconversion looks at the resolution of incoming analog video signals and then adjusts them to better match the picture resolution of the high-definition TV it's connected to.

If the incoming signals are already digital, most receivers will simply pass them through unaltered, regardless of resolution. A few high end receivers, however, have the ability to scale an incoming HDMI video signal to a higher resolution if necessary.

Take, for example, a TV with screen resolution is 720p and a source video signal with a resolution of 480p. The receiver's scaling circuitry detects that the signal's resolution is low compared to the TV's. So it fills in additional picture information to increase (or upscale) the resolution of the video signal to 720p before sending it on.

It's sort of like connecting the dots to make a line. Upconversion adds information that isn't there to begin with by looking at what is there and making logical guesses about what should go between the spaces.

The result is that the TV in our example displays a 720p image on its 720p resolution screen. This minimizes pixilation and digital artifacts, so the image looks as good as it can. HDMI upconversion doesn't turn a low-resolution image into a high-definition one. A worn-out videotape will still look pretty grainy on a digital TV screen. Upconversion simply optimizes the image to the display.

Think of it this way: HDMI conversion is like exchanging currency - the resolution of the image, like the buying power of your money, remains about the same. HDMI upconversion is like taking that exchanged currency and making the best possible purchase you can.

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