92
DIS-1/S and DIS-1/L
Dallmeier electronic GmbH & Co.KG
A 4
What is MPEG?
This section provides a brief introduction to the compression method called
MPEG. We have intentionally kept the explanations simple and refrained
from considering complex algorithms.
Picture compression
Anyone who has saved pictures on his or her computer will know the
various types of file in use and their corresponding sizes. When a picture
is saved as a bitmap file, for example, all the pixels in the picture are saved.
The volume of data involved is accordingly large. For instance, the following
picture with the dimensions 140 x 90 mm and a resolution of 150 dpi (dots
per inch) would require approximately 3 MB of memory. Various com-
pression methods are used to reduce the volume of data. To obtain a
general idea of how this works let’s consider the JPEG method.
Picture saved as a bitmap file without compression.
JPEG compression
Probably the best known compression technique is JPEG (Joint Picture
Expert Group). With JPEG the entire picture is evaluated and redundant (i.e.
similar and interchangeable) pixels are grouped in blocks. The higher the
degree of compression, the more pixels are grouped in a block. At a high
level of compression the creation of blocks has a negative effect on picture
quality, with the blocks (artifacts) becoming clearly visible in the picture.
JPEG compression always entails a loss of data, hence it is impossible to
restore the picture to its original condition.
