Applying traps to a printed page specified in a page description language format

A process for electronically trapping a color page including a plurality of color regions, the color page being expressed in a page description language in an input data file, the process comprising the steps of:

• (a) separating the input data file into a plurality of tiles;
• (b) for each tile in the input data file;
• (i) translating the page description language instructions into a format suitable for detection of color edges between color regions;
• (ii) analyzing the tile to identify color edges between color regions;
• (iii) determining whether to create traps for the identified edges;
• (iv) creating, for those edges which are to be trapped as determined in step (iii), a set of trap vectors according to a set of trapping rules;
• (c) converting the trap vectors into the page description language;
• and
• (d) appending the converted trap vectors expressed in the page description language to the input data file to create a trapped color page expressed in the page description language.

A process for electronically trapping a printed color page including a plurality of objects, the process accepting input page data which represents the page in the form of a page description language and producing output data comprising the input page data transformed by a set of trapping rules, the output data also in the page description language, the process comprising the steps of:

• (a) dividing the page into a plurality of sub-portions or tiles, with each tile represented by a clipping window corresponding to the location and size of the tile;
• (b) evaluating, for each tile, the input page data within the clipping window and interpreting the input page data of the tile to produce a bit map representation of the tile;
• (c) converting the bit map representation of each tile into an edge description, the edge description including a list of the locations of object boundary lines and colors adjacent each boundary line within the tile;
• (d) generating a set of trap vectors from the list of edge descriptions, the trap vectors generated in a format compatible with the page description language in which the input page was initially specified;
• and
• (e) merging the set of trap vectors and the input page data to produce the output page data.

Apparatus for electronically trapping a printed color page including a plurality of color regions, the color page being expressed in a page description language format, comprising:

• (a) means for reading an input data file which represents the color page expressed in the page description language format;
• (b) means for translating the page description language instructions comprising the input data file into a format suitable for detection and analysis of color intersections between color regions;
• (c) means for analyzing the translated input data file to identify color intersections between the color regions;
• (d) means for creating, for at least some of the color intersections, a set of trap objects according to a set of trapping rules;
• and
• (e) means for producing a trapped output file containing the trap objects, the trap objects being expressed in the page description language format.