Image analysis – Image transformation or preprocessing – Changing the image coordinates
Reexamination Certificate
2000-03-31
2003-11-18
Patel, Jayanti K. (Department: 2625)
Image analysis
Image transformation or preprocessing
Changing the image coordinates
C345S426000
Reexamination Certificate
active
06650793
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method and system for producing from an initial resolution input pixel image data an increased resolution output image having smoothed edges on output devices such as inkjet or laser printers. More particularly, this invention relates to such a method and system that accommodates input pixel images that are gray scaled, which method and system preserve in the higher resolution output image the gray scale of the input image.
BACKGROUND
There is a large installed base of inkjet and laser printers having substantially equal vertical and horizontal resolutions of 300 dots per inch (dpi). Recently, higher resolution printers are providing superior print quality due to their ability to produce 600 dpi or higher resolution images. It would unduly burden the host computer that drives the higher resolution printers to require that it create 600 dpi pixel or higher resolution output data from 300 dpi documents, applications or image databases produced thereby. Not only would this require large amounts of memory in the host, but it also would reduce 600 dpi printer throughput or increase host processing time. It is desirable to take advantage of the advent of higher resolution printers in many print applications without paying a significant throughput penalty.
In order to preserve compatibility with lower resolution applications and databases, to take advantage of the higher resolution printers, and to maintain high throughput, it is desirable to perform any needed pixel image data processing at the destination printer rather than at the source computer. Thus, smart printer controllers that are capable of receiving 300 dpi image data from the computer may be used to drive either 300 dpi resolution printers (without conversion overhead) or 600 dpi (or higher) resolution printers (with minimal conversion overhead) to produce respectively lower and higher quality print results. Although a brute-force increase in the fundamental grid resolution does improve print quality, the improvement is not realized in a cost effective manner. Additionally, simply scaling the image resolution, e.g., from 300 dpi to 600 dpi, leaves undesirable jagged edges on text. These jagged edges are particularly objectionable in black-only print applications and in a black image datapath of a multicolor, e.g., cyan-magenta-black-yellow-black (CMYK), print application.
A method of pattern matching of a lower resolution image to generate a higher resolution image is described in U.S. Pat. No. 3,573,789, by Sharp et al., issued Apr. 6, 1971. U.S. Pat. No. 4,437,122 by Walsh, issued Mar. 13, 1984, describes a software implementation. U.S. Pat. No. 5,650,858 by Lund, issued Jul. 22, 1997, incorporated herein by reference in its entirety, describes hardware implementation systems that preserve gray scaled graphic images. These implementations are referred to collectively herein as TES, an acronym for “Thermal Inkjet Edge Smoothing.”
As described in Lund, cited above, TES is performed, e.g., in printer hardware, firmware, or software, by mapping m×n dot matrix input data into m′×n′ dot matrix output data (where m′ is an integer multiple of m, where n′ is an integer multiple of n, and where at least one of m′ and n′ is greater than one) and processing the output data to effect edge smoothing via stored smoothing criteria, both the mapping and the processing being accomplished without affecting any gray scale patterns
As an example, assume m and n×300 dots per inch (defining a 300 dpi by 300 dpi input pixel image), and it is desired to print a 600 dpi by 600 dpi output pixel image. The method and system are applicable generally where m and n may be the same or different and where the integer resolution multipliers may be any positive integers (at least one of which is greater than one, in order to accomplish resolution multiplication).
The 300 dpi source data is converted to 600 dpi and enhanced. Lund's TES system consists of a logic circuit performing rule logic equations. These equations define how individual 600 dpi dots are changed, if appropriate, from the 300 dpi source image. More specifically, for every dot in the 300 dpi source image, a window is created to look at its surrounding 80 neighbors in a 9×9 cell. Each input dot is replaced by a 2×2 dot pattern, effectively generating a 600 dpi image. Based on the binary signals defining the dot pattern, the logic circuit modifies the 2×2 superpixel to remove jagged edges. Lund, cited above, describes algorithms for the implementation of TES formulated as boolean logic equations, flow diagrams, graphic templates, and hardware circuits.
Lund's TES works by scaling image input data, smoothing by adding and deleting dots, then outputting to a printing device. Scaling is typically performed by special hardware in the printer just before printing. No extra resolution is required in the application, data communications, or printer input buffer, but better quality output is produced. TES adjusts only dot placement, but not dot size. It can move dots on a grid finer than the input pixel resolution, and can add or remove dots as required. TES smoothes edges by reducing the step size and increasing the number of steps of ragged line edges. It preserves stroke weights of text and causes minimal changes to dithered halftone images.
Halftone images are created, in one example, by using a variable size pixel at a lower resolution. Importantly, TES does not change the density of these halftone dots. If it is determined that the target pixel is part of a halftoned image, the corresponding superpixel produced at the output for printing preserves the gray scale within the original lower resolution input pixel image without smoothing.
MultiLevel Printing (hereinafter designated as MLP) is a technology that improves color print quality not by increasing dots-per-inch but by reducing the ink drop size to place more dots in a {fraction (1/300)}th inch pixel. This increases the number of color levels per pixel, yielding better color print quality without the data overhead of moving to a higher printer resolution. Whereas a binary pixel has two density levels ON or OFF only, a MLP pixel has more than two levels, for example four density levels (two bits) such as OFF, LIGHT, MEDIUM, DARK. This reduces the time needed to print the document and the need for more powerful and costly hardware. It basically halves the ink drop volume, requiring two passes of a print head to fully saturate a given {fraction (1/300)}th inch pixel. Typically this does not result in a throughput penalty, since normal color printing modes typically already require two passes. The basic principles underlying MLP are described in U.S. Pat. No. 4,672,432 by Sakurada et al., issued Jun. 9, 1987, incorporated herein by reference in its entirety.
MLP provides better color matching, more uniform area fills, lighter secondary colors, better dithering in half-tones, more flexibility in ink dye balance, and a smaller amount of input data when compared to binary data. Using half the ink drop volume enables a printer to deliver 0-3 drops of each ink color per pixel in a normal paper mode, allowing 64 three-color shades per pixel, compared to 8 color shades for binary three-color printing. This enables the printer to halftone with approximately 64 shades instead of 8.
300 dpi MLP input data are typically used in instances where throughput is more important than achieving maximum print quality. The smaller drop volume provides similar detail with less granularity than binary 600 dpi. Even higher resolution detail is supported through 600 dpi MLP data.
In inkjet printing, conventional print heads deliver black ink drops having a weight of, for example, approximately 32 ng (nanograms). This drop size is appropriate to fill a single 600×600 dpi dot. However, at a 1200×600 dpi drop density, 32 ng ink drops apply twice as much ink as is required for a dot. It is desirable, therefore, to reduce the a
Lund Mark D.
Pritchard Thomas B.
Azarian Seyed
Hewlett-Packard Development Company LP.
Patel Jayanti K.
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