A still image is a spatial distribution of intensity that is constant with respect to time. Video, on the other hand, is a spatial intensity pattern that changes with time. Another common term for video is image sequence, since video can be represented by a time sequence of still images. Video is simply a sequence of digitized picture. Video can also be referred to as moving picture. The terms “frame” and “pictures” ar e also used interchangeably in relation to video.
The term video (“video” meaning “I see”, from the Latin verb “videre”) commonly refers to several storage formats for moving pictures: digital video formats, including Blu-ray Disc, DVD, QuickTime, and MPEG-4; and analogue videotapes, including VHS and Betamax. Video can be recorded and transmitted in various physical media: in magnetic tape when recorded as PAL or NTSC electric signals by video cameras, or in MPEG-4 or DV digital media when recorded by digital cameras. Quality of video essentially depends on the capturing method and storage used. Digital television (DTV) is a relatively recent format with higher quality than earlier television formats and has become a standard for television video.
The size of a video image is measured in pixels for digital video, or horizontal scan lines and vertical lines of resolution for analogue video. In the digital domain (e.g. DVD) standard-definition television (SDTV) is specified as 720/704/640×480i60 for NTSC and
768/720×576i50 for PAL or SECAM resolution. However in the analogue domain, the number of visible scan lines remains constant (486 NTSC/576 PAL) while the horizontal measurement varies with the quality of the signal: approximately 320 pixels per scan line for VCR quality, 400 pixels for TV broadcasts, and 720 pixels for DVD sources. Aspect ratio is preserved because of non-square “pixels”.
New high-definition televisions (HDTV) are capable of resolutions up to 1920×1080p60 , i.e. 1920 pixels per scan line by 1080 scan lines, progressive, at 60 frames per second.
Video resolution for 3D-video is measured in voxels (volume picture element, representing a value in three dimensional spaces). For example 512×512×512 voxels resolution, now used for simple 3D-video, can be displayed even on some PDAs.
Pixels on computer monitors are usually square, but pixels used in digital video often have non-square aspect ratios, such as those used in the PAL and NTSC variants of the CCIR 601 digital video standard, and the corresponding anamorphic widescreen formats. Therefore, an NTSC DV image which is 720 pixels by 480 pixels is displayed with the aspect ratio of 4:3 (which is the traditional television standard) if the pixels are thin and displayed with the aspect ratio of 16:9 (which is the anamorphic widescreen format) if the pixels are fat.
SELF ASSESSMENT EXERCISE
Explain the principles of Video
We have introduced to you that a Video is simply sequence of digitized picture.
In summary, this unit looked at the basic information about the video as an element of a multimedia system. You can now attempt the questions below.
6.0 TUTOR MARKED ASSIGNMENT
1). State 2 reasons for video in the Multimedia System
2). Explain the features of a Video