Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1998-05-28
2001-03-13
Le, N. (Department: 2863)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S251000, C347S131000
Reexamination Certificate
active
06201560
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to a printer architecture. More particularly, this invention relates to a hyperacuity printer architecture. Specifically, this invention relates to a method and system for driving a printing element in a hyperacuity laser printer.
2. Description of Related Art
According to human visual research, the frequency response or resolution of a printing system need only exceed the resolving power of the human visual system. Such resolving power is known as visual acuity. However, there are human visual considerations that require the placement of edges 10-60 times more accurately than that indicated by frequency resolution considerations. These requirements are based on hyperacuity, or the visual system's ability to differentiate locally misaligned edges to a much greater extent than the inter-receptor spacing of the eye. In this case, it is not the frequency response (resolution) of the visual system that is most important, but the ability to reckon edges with high precision. Therefore, placing edges or transitions in images in both a fast scan direction and a process, or slow scan, direction with precision greater than that of the actual printer resolution is necessary. “Hyperacuity Laser Imager” by Douglas N. Curry, Journal of Electronic Imaging, April, 1993, vol. 2(2), pgs. 138-146, herein incorporated by reference in its entirety, provides a detailed description of the relationship between the human visual system and printer resolution.
Two contrasting techniques have evolved over the last two decades to provide high image quality in laser printing, one based on resolution and the other on phase. High resolution platemakers and prepress printers use spot sizes that are the reciprocal of their binary resolutions to produce excellent image quality. These printers are expensive and slow. However, the resolutions of these printers can approach a pleasing 3,000 to 4,000 dots or spots per inch. Desktop laser printers, on the other hand, are more cost constrained and therefore use lower resolution spot sizes and scan frequencies, such as 600 dots per inch. These printers impart high quality to their images by using phase information from the source image to simulate higher resolution. These printers do not improve true image resolution beyond the physical limit of spot size and scan frequency. Rather, these printers obtain high quality through the precise positioning of edges.
There are several conventional techniques for driving printing elements. The template matching technique provides one or more templates, and looks for particular image portions that match one of the templates. Based on the matched template, an edge position is estimated. This information is then output to render edge information, which is used to drive a print element. The template matching technique is further described in U.S. Pat. No. 5,329,599 to Douglas N. Curry, which is incorporated herein by reference in its entirety.
Another technique for driving a printing element involves postscript decomposers, which use stored image information. A postscript image is rendered or converted to a bytemap image. The rendered bytemapped image is output to the printer to drive the print element.
SUMMARY OF THE INVENTION
Conventional techniques for driving a printing element do not keep track of edges. Rather these techniques instead turn bits on and off in a resolution grid. Thus, a device that uses edges as source information, and is thus capable of high printing accuracy without using higher resolutions, is needed.
Conventional techniques are also unable to use grayscale data to precisely locate edges and to convert the grayscale data into a bytemap usable to drive a print element. Thus, a method and apparatus for driving print elements that use grayscale data source information are also needed.
Accordingly, this invention provides a method and a system for using text and line art information generated from a sampled input image to drive printing elements.
The invention also provides a halftoning technique usable to locate edges.
Sampled grayscale pixel data is used to precisely locate edges. A thresholding technique uses two-dimensional slope and interpolated intensity data to locate edges. The edge placement data may be stored in various formats, including polar values, a linear format or as numerically sampled grayscale values.
A modulator drive device uses the edge placement values derived from the slope thresholder or halftoner and incorporates device-dependent characteristics, such as xerographic development and spot size, to precisely position the edges using a modulator drive function. A spline-based edge reproduction curve (ERC) compensates for slow scan phase errors and a temporal bias compensates for fast scan spot size. The modulator drive device determines intensity values that are used to drive the printer scan. The modulator drive device can drive many types of digital-to-analog converters, such as, for example, electronic digital-to-analog converters, pulse-width modulators or shift registers.
The method and apparatus according to this invention allow a hyperacuity data channel to drive a set of adjacent laser diodes to form a set of adjacent scan lines extending across a recording medium, where the adjacent scan lines are pitched much finer than that of the hyperacuity channel. A modulation drive device converts position coordinates to drive values for each laser diode used to form a scan line within the span, or channel pitch, of that hyperacuity channel. This provides a decompression method for generating data at higher clock speeds for the laser diodes, and increases the number of scan lines per inch in the process direction, while not adversely impacting the rasterized input data for the hyperacuity channel. This results in a practical method of implementing a high speed 2,400 dpi by 2,400 dpi or 4,800 dpi by 4,800 dpi color printer.
These and other objects of the invention will be described in or be apparent from the following description of preferred embodiments.
REFERENCES:
patent: 5485289 (1996-01-01), Curry
patent: 5574832 (1996-11-01), Towery et al.
patent: 5617132 (1997-04-01), Fisli
patent: 5617133 (1997-04-01), Fisli
patent: 5638110 (1997-06-01), Curry et al.
patent: 5648810 (1997-07-01), Tanuma et al.
patent: 5691760 (1997-11-01), Hosier et al.
patent: 5696604 (1997-12-01), Curry
patent: 5805304 (1998-09-01), Sekine
Le N.
Nguyen Lamson D.
Oliff & Berridg,e PLC
Xerox Corporation
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