Wednesday, January 21, 2015

About Interlaced Video

Interlaced video refers to the technique for doubling the frame rate of a video display without the making use of extra bandwidth. Generally speaking, the interlaced signal consists of two fields of a video frame captured at two different times. Interlaced video are powerful in function as it can enhance motion perception to the viewer and reduce flicker by making use of the phi phenomenon effect.

As a result, compared to non-interlaced footage (for frame rates equal to field rates), interlaced video doubles the time resolution (also known as temporal resolution). At the same time, interlaced video has a lot of requirements which need to be satisfied in order to make it function well. A display capable of showing the individual fields in a sequential order is necessary for interlaced signals. As a result, considering the electronic scanning and apparent fixed-resolution, there are only two kinds of displays are able to display interlaced signals: CRT displays and ALiS plasma displays.

Interlaced scan, along with progressive scan, is one of the two common methods for “painting” a video image on the electronic display screen which is realized by scanning or displaying each line or row of pixels. Under such condition, two fields are utilized to create a frame by this technique. One field contains all odd lines in the image, while the other contains all even lines.

For example, a PAL-based television set display scans 50 fields every second (25 odd and 25 even). A full frame, every 1/25 of a second (or 25 frames per second), is created by the two sets of 25 fields working together. At the same time, a new half frame every 1/50 of a second (or 50 fields per second) is created with interlacing. On the other hand, deinterlacing is applied to the video signal in order to display interlaced video on progressive scan displays in the process of playback.