Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1998-11-18
2001-05-29
Le, N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S253000
Reexamination Certificate
active
06239829
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to methods and apparatuses for adjusting the maximum, or saturation, laser or LED power in a printing apparatus. More specifically, this invention is directed to methods for controlling the exposure level based on the type of image object currently being exposed.
2. Related Art
Prior to the advent of high quality computer generated page images, page images such as those found in newspapers, newsletters, magazines and the like were formed by graphic artists composing the page images by hand. Thus, each different type of image object on a page image, including text, photographs, constant color areas or graphs such as pie charts, and sampled or continuously changing images such as sweeps, was optimally formed, independently of any other type of image object.
Because these page images, comprising one or more of these types of image objects, were composed by hand, each type of image object was inherently treated independently of the other image objects. Thus, the optimal halftone screen design for photographs, which differs from the optimal halftone screen designs for constant color areas and text could be optimally selected and the screen arranged to an optimal angle. Likewise, such optimal treatment of each type of object could be obtained.
With the advent of digital color workstations, copiers and printers, creators of page images who had previously relied on graphic artists to compose and print page images could instead create, compose and print the page images on their own using a computer connected to the digital color copier/printer.
However, such prior art digital systems for creating a page image, for decomposing the page image into print engine instructions and for controlling the print engine treated a page image as a single, unitary image. Thus, in a page image optimized for text and/or lineart, when a high frequency halftone screen is used, the text portion of the page image will be quite sharp. However, a constant color portion of the page image will contain an obvious mottling from printer noise. In addition, the sampled color portion and the sweep portion of the page image will have obvious contouring due to the lack of sufficient gray levels available with the high frequency screen.
In a page image optimized for a large constant color portion, a halftone screen specifically designed to hide printer instabilities will produce a high-quality, text-free and artifact-free constant color area. However, sharpness of text will decrease and the gray values for each tint will not be well-related, so sampled color portions and sweep portions would be unacceptable. The gray levels will not step smoothly from one to the next because each dot level is designed separately without relation to the other levels.
In a page image optimized for sampled color and sweep portions, the sweep portion and the sampled color portion will have a higher quality because a low frequency halftone screen is used with more gray levels available. However, text will be low in quality and constant color portions will have an obvious texturing.
SUMMARY OF THE INVENTION
Accordingly, in the prior art systems, which treated each page image as a single bitmap or bytemap image, optimizing the image for any one type of object required the image quality of the other types of objects to be compromised. Accordingly, there is a need in the art for a digital color copier/printer and method for creating, decomposing and outputting a page image to a print engine which allows for the printing characteristics of individual objects to be optimized, as in the hand-composing graphic arts field, while simultaneously retaining the benefits and efficiencies available when creating a page image using a microcomputer.
Such page images are created using Page Description Languages (PDLs) such as PostScript™, Interpress™, Graphical Display Interfaces (GDIs), such as the one used with Windows™, Printer Command Languages (PCLs) for controlling a print engine, such as the Hewlett-Packard Printer Command Language (PCL-5)™, or the like.
It is also well known that commercial laser printer products use an unusually strong laser power to expose “write black” images. This is done because the boost in contrast between the write black images and the surrounding regions resulting from this overexposure is aesthetically pleasing to the viewer. The boosted laser power is provided to all regions of the image.
However, this elevated contrast has an accompanying inability to produce narrow lines. Additionally, although over-exposure of text and/or lineart is aesthetically pleasing, overexposure of halftone images is disadvantageous because increased laser power overexposes the halftone cell. Overexposing the halftone cell decreases the control over the total dynamic range. This occurs because an increase in laser power affects the transitions of the shape function through the total dynamic range of a print engine. Specifically, if the laser power is increased, a shape function saturates too quickly and is unable to transition during the high end of the dynamic range.
This invention provides printer controller apparatuses and methods that use print data and printer control commands such that the laser power used to form each type of object in a page image defined using a PDL or the like is optimally controlled or selected. The print data and printer control commands are converted from the page image defined using a PDL or may be provided by any other mechanism known in the art.
This invention separately provides object-optimized printer control devices and methods that generate “metabit” information, i.e., information about how best to render each byte of image data, that includes laser power information, based on the object type of the various objects forming the page image and passes the metabit data to the image output terminal (IOT).
This invention separately provides object-optimized printer control devices and methods that automatically determine the laser power based on the object type for each independent object of the page image.
This invention separately provides object-optimized printer control systems and methods that allow a creator of a page image, using a PDL, to explicitly override or adjust the automatically determined laser power for each independent object of the page image.
This invention separately provides intermediate format file structures that contain information including the laser power information for each object on the page that may be stored for later editing, transmission and printing by an object-optimized printer control device and method.
This invention separately provides different intermediate format files that contain a plurality of data channels and a metabit information channel which each have been optimally compressed, that can be decompressed and printed in real time by an object-optimized printer device such that each type of object in the page image is printed using an optimal laser power for that object.
This invention also provides for the ability to use special hardware and software modules to provide different object-optimized rendering and compression techniques, with each resource module controlled by metabit information controlling the selection of the rendering or compression method, and with the resource modules either distributed through the printing system or concentrated in a single location. The rendering modules can include, but are not limited to, modules which perform object-optimized laser power selection and/or control, object-optimized color space transformations, object-optimized spatial filtering, object-optimized tone reproduction curves, object-optimized choking or spreading, object-optimized halftoning, object optimized thresholding, and object-optimized engine artifact suppression.
As an example of the equipment and method steps to be used in conjunction with the invention a page image which is described using a PDL and stored as a series of PDL commands is input to an object optimizing electronic subsy
Le N.
Nguyen Lamson
Oliff & Berridg,e PLC
Xerox Corporation
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