conveylive.com

Working Principle of MPEG Player

Derek Thompson
Derek Thompson
Sep 28, 2009
0 Comments | 2346 Views | 1 Hits


 

Working Principle of MPEG Player
 
The job of MPEG is to take analogue or digital video signals and convert them to packets of digital data that are more efficiently transported over a network. Being digital it has the following advantages :
  1. Signal does not degrade
  2. Picture does not get fuzzy
  3. Signal-to-Noise ratio goes down slowly
MPEG is derived from the original work by the Joint Pictures Expert Group (JPEG). The JPEG standard is for still images and is a lossy technique.
 
It takes advantage of the nature of the human eye and removes redundant information that we just do not see.
 
In a motion picture two adjacent frame sequences are usually very nearly identical. Most of the times, the only difference is that some parts of the picture have shifted slightly between the frames. MPEG compression takes advantage of this temporal redundancy by carving each new frame into convenient pieces and searching the previous frame to determine where each piece came from. If the content of the current frame was mostly sent in the previous frame, then the entire frame is not sent all over again. Just send the instructions for shifting pieces of the previous frame to their new positions in the current frame are sent.
 
Within a single frame many patches, such as regions of sky or walls are almost entirely the same color. MPEG compression exploits this spatial redundancy by carving images into convenient pieces and reducing such patches to a single color. If several pixel points in the same area are all very nearly the same color, those colors are not sent over and over again. Just the color for the whole area is sent once. MPEG compression also eliminates non- essential color detail that the human eye tends to gloss over anyway.
 
Input
Image 1
This image represents an image that has been carved up into about 300 squares to perform the compressions by MPEG algorithm. The gray patches represent areas that were found in the previous frame and shifted to new positions to form this frame. A uniform gray patch indicates an exactly matching area was found. Mottled gray patches indicate a near match. This operation is performed to compress temporal redundancy.
 
Output:
Image2

The final compression step consists of reducing the number of shades used to represent the fine picture detail. This corresponds to reducing even further the intensity of the light areas representing fine picture detail (the areas not in the single color corners.) In addition to applying more reduction to fine detail within a single square, MPEG provides separate weight for each whole square. Squares containing more fine detail are compressed relatively more. Image 4 shows the relative amounts that each square patch is reduced.
Author's note: MPEG_Player
Keywords: MPEG_Player



Please Signup to comment on this article