background image
ISO/IEC 10918-1 : 1993(E)
4.1
Elements specified in this Specification
There are three elements specified in this Specification:
a)
An encoder is an embodiment of an encoding process. As shown in Figure 1, an encoder takes as input
digital source image data and table specifications, and by means of a specified set of procedures generates
as output compressed image data.
b)
A decoder is an embodiment of a decoding process. As shown in Figure 2, a decoder takes as input
compressed image data and table specifications, and by means of a specified set of procedures generates as
output digital reconstructed image data.
c)
The interchange format, shown in Figure 3, is a compressed image data representation which includes all
table specifications used in the encoding process. The interchange format is for exchange between
application environments.
TISO0650-93/d001
Encoder
Table
specifications
Source
image data
Compressed
image data
Figure 1 Encoder
FIGURE 1 [D01] 5 cm = 195%
TISO0660-93/d002
Decoder
Table
specifications
Compressed
image data
Reconstructed
image data
Figure 2 Decoder
FIGURE 2 [D02] 6 cm 234%
Figures 1 and 2 illustrate the general case for which the continuous-tone source and reconstructed image data consist of
multiple components. (A colour image consists of multiple components; a grayscale image consists only of a single
component.) A significant portion of this Specification is concerned with how to handle multiple-component images in a
flexible, application-independent way.
CCITT Rec. T.81 (1992 E)
13
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