What is difference b/w 1080i and 1080p ?
Santosh, this actually needs a very detailed explanation. I am writing an article that I will publish soon. In the meantime, here is a quick explanation.
The 'i' after the 1080 refers to Interlaced, while 'p' refers to Progressive. Both are methods to display an image on a TV display.
The film that you see in a movies hall consists of a reel of still pictures. Each picture is called a frame. Each successive frame differs from the previous frame in small way. For example, if a man is walking, the first frame will display an image of the man in the starting position. The second frame will display the mans image with the legs and hands in a slightly different position. When all these frames are shown quickly one after the other, you eye perceives the still pictures as motion. This method of moving the still frames one after the other is termed as Frames Per Second or fps.
The human eye can perceive motion at 16 fps, but Hollywood, for various historical reasons, had adopted 24 fps as the standard frame rate for all movies.
In a film that you see in a movie hall, each still picture fills the entire frame. This is called progressive source. This means that the frame rate is the number of individual full pictures. In the came of film this is exactly 24,
INTERLACED
In the initial days of TV, there was no way to display a full frame on a Cathode Ray Tube or CRT screen, This is an analogue device. In all CRT monitors, the image is painted on the screen by an electron beam that scans from one side of the display to the other drawing thin lines. This scan is used to display the transitions in color, intensity and pattern, and each complete pass of the electron gun is called a FIELD. A field will consist of 'n' number of scanned lines. Analogue TV uses a process that relies on the brain's ability to integrate gradual transitions in pattern that the eye sees as the image is painted on the screen. Each picture or frame on a television screen is composed of 525 lines, numbered from 1 to 525. During the first phase of screen drawing, even-numbered lines are drawn - 2,4,6,8 and so on. During the next phase, the odd lines are drawn 1,3,5,7 and so on. The eye integrates the two images to create a single image. See picture below. The fields are said to be interleaved together or interlaced. A frame or complete picture consists of two fields. Like with film, each picture is from a different moment in time. Unlike film, the rate of individual pictures, or fields, is twice the frame rate.
Though modern television are not made this way any more, and modern LCD and Plasma TVs can display a full frame, remember the TV production and broadcast systems have been designed around the FIELD concept and is entrenched around the world.
There are two dominant interlaced scan systems used in the world today - NTSC and PAL.
NTSC is based on a 525-line, 60 fields/30 frames-per-second at 60Hz system for transmission and display. . This is an interlaced system in which each frame is scanned in two fields of 262 lines each, which is then combined to display a frame of video with 525 scan lines. NTSC is used in the U.S., Canada, Mexico, some parts of Central and South America, Japan, Taiwan, and Korea.
PAL is based on a 625 line, 50 field/25 frames a second, 50HZ system. The signal is interlaced, like NTSC, into two fields, composed of 312 lines each. PAL is used in the U.K., Germany, Spain, Portugal, Italy, China, India, most of Africa, and the Middle East.
PROGRESSIVE SCANNING
In progressive scan the image is displayed on a screen by scanning each line (or row of pixels) in a sequential order. In other words, in progressive scan, the image lines are scanned in numerical order (1,2,3) down the screen from top to bottom, In NTSC for example, by progressively scanning the image onto a screen every 60th of a second rather than "interlacing" alternate lines every 30th of a second, a smoother, more detailed, image can be produced on the screen,
While film only has progressive frames, and analog video only interlaced fields, digital video may have either or both. In the digital domain, displaying progressively is a property separate from the contents of the frame. Although it's possible to encode and store interlaced video as a stream of fields, most interlaced video is encoded in pairs in the form of frames. As a rule, frame based interlaced encoding is less efficient than progressive encoding. This means that files with comparable bit rates will have lower quality if they contain interlaced video.
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