Raster Graphics
2-35
raster data represents a repeating pattern or an uncompressed (unencoded) pattern. It also
determines the number of pattern repetitions or bytes of uncompressed data.
The control byte is a two’s complement value that can be either zero, positive, or nega-
tive. A negative value (-1 to -127) indicates that the following byte represents a repeating
pattern. The number of repetitions of the pattern is determined by the absolute value of
the control byte.
If the control byte is zero or positive (1 to 127), the following byte(s) of data represent an
uncompressed pattern. In this case, the value of the control byte plus one indicates the
number of bytes making up the pattern.
In TIFF encoding, the two’s complement value -128 indicates a non-operative control
byte. The byte following such a byte is handled as a new control byte.
Commands for Printing Raster Data
PRESCRIBE provides a number of commands for printing raster data, including:
• STR (SeT dot Resolution)
• RVRD (ReceiVe Raster Data)
• ENDR (END Raster data)
• RVCD (ReceiVe Compressed raster Data)
• SRO (Set Raster Options)
The principle function of the SRO command is to specify the presentation mode; i.e., the
orientation of the raster image. If the presentation mode is 0 (the default mode), raster
lines print along the width of the physical page, regardless of the current page orienta-
tion. If the presentation mode is 1, raster lines print in the orientation of the logical page.
This is illustrated in the figure that follows.
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