HP 5961-0509 manual Seed Row, 15-22Raster Graphics

As mentioned, the offset is contained in the lower five bits of the command byte allows for offset values from 0 to 31. Compression mode allows offsets larger than 31 bytes as follows:

zAn offset value of 0-30 indicates that the replacement bytes are offset from the 1st byte to the 31st byte.

zA value of 31 indicates that the next byte following the command byte is an additional offset byte which adds to the first (32) offset value. This allows offset values larger than 31. Also, if this second offset byte is set to 255 (all ones), additional offset bytes follow until the required offset value is obtained. When the formatter detects an offset byte less than 255, it is assumed to be the last offset value and the offset bytes are then totaled (added). The following example shows an offset larger than 31:

Figure 15-10

The total offset 414, which is the sum of the three offset values: 31 + 255 + 128.

Seed Row

The seed row is basically the current raster data row; the row being printed. It is maintained by the printer for use by delta row compression. The delta compression replacement bytes are applied to the seed row to create the new row. This new data row is printed and becomes the new seed row.

The seed row is updated by every raster graphic transfer, regardless of the compression method. This allows delta compression method to be mixed with other methods to achieve better compression performance.

15-22Raster Graphics EN