What Causes Pixelation in HDTV?

By Alex Diaz-Granados

Since its large-scale introduction in the 1990s, digital high-definition television (HDTV) has replaced analog standard-definition (SD) TV as the video broadcast signal of choice in the United States. HDTV has many advantages over SDTV due to its higher resolution and digitally compressed sound. However, for all its improvements on image sharpness and clarity, HDTV can have problems due to pixelation.

HDTV

High-definition television is an audio-visual (mostly video) signal that possesses considerably higher resolution than the older standard-definition (SD or SDTV) signal used in broadcast, cable and satellite television until the early 21st century. HDTV contains up to six times the resolution of analog SDTV; digital HDTV images are comprised of 1 million to 2 million pixels when scanning images at 1,080 lines of resolution, whereas analog SD images only contain 300,000 pixels at scan rates of 480 lines.

Pixels

A pixel, an abbreviation for the term "picture element," is the smallest visual part of a raster image. Pixels are used to create images in print and video in a similar fashion as tiles are used to create mosaics. Pixels have no fixed size, due to the wide array of image resolutions available, but the number of pixels in an image determines how sharp and clear the image is. HDTV images have up to three megapixels.

Pixelation

Pixelation is a common problem in digital imagery; not just in HDTV sets but also in digital photography and computer monitors. It manifests itself when a viewer can see the usually small individual picture elements (usually monochromatic tile-like squares) on a TV screen or a digital photo with the unaided eye. In HDTVs, pixelation occurs on sets with larger screens during scenes with rapid motion because the set can't keep up with the onscreen action.

Causes of Pixelation

Pixelation on HDTVs is not always caused by the set's inability to keep up with the images it receives; television producers often use pixelation to obscure images deliberately to cover up nudity on non-adult programming or to hide someone's face to protect his identity on a news segment or interview.Other causes of pixelation include bad weather; the HDTV set is older or a lower-end model; the HDMI cable is low quality; and faulty or substandard cable boxes.