Methods and apparatus for efficient sheetside bitmap processing using meta-data information

Apparatus for generating compressed bitmaps in a printing environment, the apparatus comprising:

• a bitmap memory for representing a sheetside image;
• a table containing a plurality of meta-data structures wherein each meta-data structure is associated with a corresponding portion of the bitmap memory and wherein each meta-data structure includes a type of data field and a data indicator field;
• a data object processor adapted to process data objects representing a sheetside image wherein each data object, if written to the bitmap, would cause data to be written in affected portions of the bitmap memory,
• wherein the data object processor is adapted to update the type of data field of each meta-data structure corresponding to each affected portion of the bitmap memory to indicate either a “compact” or a “non-compact” type of data that would be written to the corresponding portion of the bitmap memory by processing of a data object,
• wherein the data object processor, responsive to updating the type of data field to indicate a “compact” type of data, is further adapted to update the data indicator field of each meta-data structure corresponding to each affected portion of the bitmap memory to represent the data object, and
• wherein the data object processor is adapted to write information from processing of the data object to said affected portions of the bitmap memory for each meta-data structure updated to indicate “non-compact” type of data;
• and
• a bitmap compressor adapted to generate a compressed bitmap representation of the sheetside image from the meta-data structures and the bitmap memory
• wherein the bitmap compressor is adapted to generate compressed data based on the data indicator field for each meta-data structure indicating a “compact” type of data, and
• wherein the bitmap compressor is adapted to generate compressed data from the bitmap memory for each meta-data structure indicating a “non-compact” type of data.

A method for generating a compressed bitmap representation of an uncompressed bitmap memory generated from a plurality of data objects, the method comprising:

• defining a plurality of rectangular portions in an uncompressed bitmap memory;
• associating a different meta-data structure with each portion of the uncompressed bitmap memory;
• processing the plurality of data objects wherein the processing of each data object includes:
• determining which portions of the uncompressed bitmap memory the data object may affect;
• and
• for each affected portion:
• determining from information currently in the corresponding meta-data structure whether the affect of the data object on the portion can be represented by information in the corresponding meta-data structure without writing to the portion;
• responsive to determining that the portion can be represented without writing to the portion, updating information in the meta-data structure to represent the portion as affected by the data object;
• and
• responsive to determining that the portion cannot be represented without writing to the portion, updating information in the meta-data structure to indicate that the meta-data does not represent the portion and writing data derived from the data object to the portion;
• generating a compressed bitmap based on the meta-data structures corresponding to the plurality of portions and using the bitmap memory for any of the portions for which the corresponding meta-data structure indicates that the portion is not represented by the meta-data structure;
• and
• outputting the compressed bitmap for presentation to user.