- F/A/VAn undesirable distortion component that can arise in any digitally encoded information (sound or picture).————————A&VDistortion in the video signal which may manifest itself in different ways, depending on the type of aliasing:• Spectral aliasing is caused by interference between two frequencies, such as the luminance and chrominance frequencies or thechrominance and field scanning frequencies. It appears as moire or herringbone patterns, straight lines that become wavy, or rainbow colors.• Spatial aliasing is distortion that occurs because of limitations in physical resolution of the scanning process. It appears, for example, as straight diagonal lines that become stairstepped or jagged.• Temporal aliasing is distortion resulting from information lost between line or field scans. It appears, for example, when a video camera is focused on a computer screen; the video output shows a flickering bar on the computer screen because of the lack of scan synchronization of the camera and the computer.————————HDDefects or distortion in a television picture due to sampling limitations. Defects are commonly seen as jagged edges on diagonal lines and twinkling or brightening (beating) in picture detail.————————WikiVSomething other than what it appears to be. Stairsteps on what should be a smooth diagonal line are an example of spatial alias. Wagon wheels appearing to move backwards are an example of temporal alias. Aliases are cause by sampling and can be reduced or eliminated by pre-filtering, which can appear to be a blurring effect. Defects in the picture typically caused by insufficient sampling (violation of the Nyquist sampling rate) in the analog to digital conversion process or poor filtering of digital video. Defects are typically seen as jaggies on diagonal lines and twinkling or brightening in picture detail. Examples are: Temporal Aliasing — such as rotating wagon wheel spokes appearing to rotate in the reverse direction. Raster Scan Aliasing — such as sparkling or pulsing effects in sharp horizontal lines. Stair-Stepping — stepped or jagged edges in diagonal lines or the diagonal parts of a letter.
Audio and video glossary. 2014.