Lossy and lossless compression in raster image processor

• US 5,758,042 A
• Filed: 05/09/1996
• Issued: 05/26/1998
• Est. Priority Date: 07/06/1994
• Status: Expired due to Term

• Current Assignee: Agfa-Gevaert Naamloze Vennootschap, Agfa Corporation (Agfa-Gevaert N.V.), Agfa-Gevaert N.V., Xeikon NV (ColourOz TopCo)
• Original Assignee: Agfa-Gevaert N.V.
• Inventors: Deschuytere, Frank Andre
• Primary Examiner(s): Rogers, Scott
• Application Number:
  US08/647,167
• Time in Patent Office: 747 Days
• Field of Search: 395/114, 382/180, 382/234, 382/239, 382/244, 382/250, 382/248, 358/426, 358/432, 358/433, 358/429
• US Class Current: 358/1.15
• CPC Class Codes: H04N 1/3871 the composed originals being of different kinds, e.g. low- and high-resolution originals
• CPC Class Codes: H04N 1/41 Bandwidth or redundancy reduction by scanning H04N1/17 ; methods or arrangements for coding, decoding, compressing or decompressing digital video signals H04N19/00

Abstract

Digital input commands defined in a page description language are separated in two types of instructions: first instructions resulting in solid regions on the printed output and second instructions resulting in halftoned regions. The first instructions generate a binary bitmap indicating a high or low density of the solid regions and a binary bitmask indicating whether recorder elements belong to a solid or screened region. The bitmap and bitmask are preferentially compressed by a lossless compression method. The second type of instructions generate a contone map, representing images having contone levels and graphics having intermediate levels. The contone map is preferentially compressed by a lossy compression method, stored on a storage medium and retrieved once the output device must render the rasterized image. The rasterized image is constructed on the fly from the compressed bitmap, bitmask and contone map, which is halftoned before combination with the bitmap. A serious amount of memory can be saved, while keeping up with the speed of the rendering process in the output devise and without deteriorating the quality of the reproduction.

Claims

1. A method for generating regions of a rasterized image, described by digital input commands including:

first instructions to fill a first said region with a solid pattern, and

second instructions to fill a second said region with a halftone screen pattern;

said method comprising the following steps;

converting said first instructions to a first internal representation by a first conversion;

converting said second instructions to a second internal representation by a second conversion;

storing said first and second internal representations;

retrieving said first and second stored internal representations;

combining said first and second retrieved internal representations for generating said regions.