US 6,002,847 A · High capacity compressed document image storage for digital color printers

Abstract

A high capacity compressed document image storage apparatus for color printing systems. The compressed document storage system is highly suited for use with high speed color pagewidth print heads. However, the document storage apparatus can also be used with other printing systems, such as color electrophotographic and other systems. The compressed document storage system is composed of the following major components: 1) an image creation system which can operate on a band by band basis. 2) an input memory which stores at least one band of the uncompressed page image. Two bands are preferred to allow double buffering, so that the RIP and compression stages can proceed simultaneously. 3) a page image compression system which can operate on a band by band basis. A new page image compression scheme which achieves high compression ratio and preserves high image quality is disclosed. 4) a mass storage device for storing compressed page images. 5) a real-time page image expansion system which expands the compressed page images at the rate required by the print engine. 6) an output memory which stores at least one band of the expanded page image. The recommended minimum is the number of lines from the first line of the print engine to the last line of the print engine, plus two bands. 7) an interface which reads data from the output memory and provides it at the correct timing to the print engine. The page image compression scheme can achieve a typical compression ratio in excess of 80:1 when compared to a CC'MM'YK 800 dpi bitmap, and in excess of 420:1 when compared to an 800 dpi CMYK contone image. The high compression ratio allows the storage of more than 1,000 A4 800 dpi full color page images on a low cost 1 GByte disk drive. The compression scheme reduces the compressed data rate required for high speed (120 A4 ppm) printing to that which can be achieved using commonly available magnetic hard disk drives. An improvement to JPEG image compression when used with text or graphics overlays is also disclosed.

Claims64

Dependent claims

A high capacity compressed document image storage apparatus which is incorporated in a printing system having a print head comprising:

(a) a plurality of drop-emitter nozzles;
(b) a body of ink associated with said nozzles;
(c) pressure means for subjecting ink in said body of ink to a pressure of at least 2% above ambient pressure, at least during drop selection and separation;
(d) drop selection means for selecting predetermined nozzles and generating a difference in meniscus position between ink in selected and non-selected nozzles;
and
drop separating means for causing ink from selected nozzles to separate as drops from the body of ink, while allowing ink to be retained in non-selected nozzles;
said image storage apparatus comprising:
(1) an image creation system which can operate on a band by band basis;
(2) an input memory which stores at least one band of the uncompressed page image, but less than 50% of said uncompressed page image;
(3) a page image compression system which can operate on a band by band basis;
(4) a mass storage device able to store a plurality of compressed page images;
(5) a page image expansion system which expands compressed page image data to form an expanded page image at a rate which is within 20% of the page printing rate when measured over the duration of the page printing time;
(6) an output memory which stores at least one band of said expanded page image, but less than 50% of said expanded page image;
and
(7) an apparatus which provides page image data from said output memory to a printing device wherein the time taken to provide a band of image data to the printing device does not vary by more than .+-.50% of the mean time to provide a band of image data to the printing device.

12 more elements

A method of page image compression said method including the following steps:

(a) dividing said page image into an array of cells of pixels;
(b) encoding said cells containing only white pixels to a specific code;
(c) encoding said cells containing only black and white pixels to a different specific code, and supplementing said code with information encoding the pattern of black and white pixels in said cell;
and
(d) encoding said cells containing a plurality of colors to a mutually different code, and supplementing said code with information encoding the colors of the pixels in said cell.

2 more elements

An expansion apparatus for expanding compressed page image data in real-time as the page is being printed, said apparatus including:

(a) a mass storage unit for storage of the compressed page images;
(b) a JPEG decoder which expands the JPEG encoded portions of the compressed page image into contone image data;
(c) a contone band memory which temporarily holds at least one band of said contone image data;
(d) an expander circuit which expands compressed black and white text and graphics bitmaps and combines said bitmaps with said contone image data read from said contone band memory.

1 more element

A method of compressing an image said method including the steps of:

(a) dividing the image into a plurality of cells;
(b) detecting which of the pixels in each cell are of a specific color;
(c) compressing information specifying the location of said pixels;
(d) replacing said specific color in said pixels with a different color;
and
(e) compressing said cells by JPEG compression.

3 more elements

A compressed image expansion apparatus comprising:

(a) a JPEG decoder which converts first compressed image data to contone pixel data at a first resolution;
(b) a resolution conversion device which converts said first contone pixel data to a second contone pixel data of a second resolution, said second resolution being different from said first resolution;
(c) a compressed bitmap decoder which converts second compressed image data to bitmap image data at said second resolution;
(d) creation means to create a third contone pixel data at said second resolution, based upon the pattern of true and false entries in said bitmap image data;
and
(e) a combination means which combines said second contone pixel data with said third contone pixel data to produce a fourth contone pixel data.

3 more elements

Dependencies are inferred from the claim text.

High capacity compressed document image storage for digital color printers

Life of this patent

High capacity compressed document image storage for digital color printers

Life of this patent

Abstract

Claims64