Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1998-12-28
2002-01-22
Coles, Edward (Department: 2622)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S001140, C382S167000
Reexamination Certificate
active
06341020
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to high-quality digital printing in which objects are intermixedly printed, and more particularly, in which a printing process exhibits characteristic, statistically predictable defects which degrade quality. A system-specific and defect-specific function is applied to the digital signal anamorphically (different in the scan and process directions) to change the color or other attributes as a function of distance from an edge to pre-compensate for a defect and thereby increase quality.
2. Description of the Related Art
Digital color printers form a digital image for each of several separations, such as cyan, magenta, yellow, and black. The digital image instructs the printing mechanism of the printer in the amount of each color ink to deposit and the method of deposition at each addressable point on the page.
A digitally imaged page can consist of graphical objects such as text, lines, fills, pictures, etc, all imaged in ways which can be isolated from each other, can abut one another at one or more points, can partially overlap one another, or can completely overlap one another. The resulting printed page or graphic image is therefore made up of a patchwork of shapes representing the graphic objects, some of which are “clipped” by objects imaged later in the succession.
In practice, every color printing system has characteristic defects which can cause subtle problems that detract from achieving the highest possible quality color printing. For example, ink jet printing must handle excessive ink coverage which can cause bleeding or spreading of colors and paper distortion. Xerographic printing contends with a different set of problems which can detract from print quality. Examples are “haloing”, in which toner in one separation interferes with toner transfer at the same location in another separation, “tenting”, which is toner deletion caused by high toner pile casting a mechanical or electrostatic “shadow” which prevents correct development of abutting toner, trail-edge deletion and starvation, which cause toner deletion at certain edges, or misregistration between two colors. Many of these characteristic problems in printing systems can be traced to undesirable interactions between abutting colors on the page.
Despite known problems, the digital image sent to the printer has in the past assumed a perfect printing mechanism, and provided an ideal image to print. While increasingly sophisticated controls have been added to printing mechanisms to reduce defects and come closer to the perfect printer expected by the digital image, electro-mechanical defects in any printing system are still common and are to be expected at both the low end where system cost restraints preclude use of expensive controls and the high-end where production speeds challenge existing control systems.
Recent work has begun to look at modifying a digital image in advance in order to pre-compensate for expected problems in a printer. The work may be divided into two groupings. A first grouping of prior art does “object-based compensation”, which predicts and pre-compensates for printing problems unique to each object type (text, fill, image, etc.). A second grouping of art does “trapping compensation”, which predicts and pre-compensates for only one printing problem: misregistration between two abutting colors.
The first (object-based) grouping deals with isolated objects only; it does not look at problems caused by interactions or adjacencies between colors or objects on the page. Pre-compensation for printing problems is based purely on individual objects being printed, such as text, fill, or picture, without reference to other adjacent objects. Different object types have different predictable printing problems. For example, large uniform color fills can contain visible mottle in what should be smooth color, because the random noise of the print mechanism causes tiny variations in the amount of color put on the page. Text can show rough or fuzzy edges. Images can show unnatural colors. In order to pre-compensate for each special problem, the type of image processing to be done is changed as each different object type is processed for printing. This object-specific rendering pre-compensates for expected predicted printing problems by using different processing for different image types.
For example, when a large color fill is being prepared for imaging, it is possible to switch to a “quieter” halftone that will not show mottle so much. Similarly, if text is being printed, processing which emphasizes sharp edges to overcome limitations in the printer's resolution is chosen. Graphics such as charts and graphs should have color processing which emphasizes bright, saturated colors even in printers of limited gamut, while pictures should be rendered with halftones that have a greater number of available tone values and color correction that emphasizes natural colors.
U.S. Pat. No. 5,634,089 to Kulbida et. al., provides background information on a digital processing method that differentiates among, for example, sampled images and text, and uses tags to process them differently so that sharp edges may be preserved in text while a fuller set of tone values is preserved in pictures.
U.S. Pat. No. 5,704,021 to Smith et. al., describes another system which automatically detects certain object types and changes the image processing accordingly so as to produce a better printed image.
U.S. patent Ser. No. 09/012,651 to Rumph, et. al., describes a more complete system called Object Optimized Rendering which can include hardware-assist for speed and compression, object tags that can be specified by the user or generated automatically and carried throughout the software and hardware image processing system, and even includes object-based measurement feedback to dynamically adjust color correction on an object type basis. This system, in addition to looking at object types as a guide to optimized rendering, also looks at object parameters such as the size of a fill in determining the types of rendering to do.
The second (trapping) grouping of prior art is more limited in scope in that it attempts only to pre-compensate for a single printer defect caused by adjacent colors: misregistration. If a printer misregisters between separations, an thin unwanted white or color line occurs when certain adjoining colors don't abut perfectly. This second group of inventions doesn't care about individual object types or a large range of printer defects as the first (object-based) grouping does. Instead, this group of prior art simply looks at the edge between two color areas, attempting to predict when two abutting colors could cause a thin line problem if the printing system misregisters. The solution used is to generate a fixed-width, constant color fill (a “frame” or “trap”) whose color and position is calculated with various methods from the two abutting colors, and to superimpose that new digital signal with the original signal to produce prints that show the misregistration problem less.
For example, the method of Taniguchi, described in U.S. Pat. No. 4,931,861, finds the border between abutting or overlapping colors using logical operations, shrinks one of the color borders, and defines a “linkage” portion as a frame or trap to be superimposed at the border between the two colors.
The method of Yosefi, described in U.S. Pat. No. 5,113,249 uses a set of automated rules as the basis for deciding, for each pair of abutting or overlapping colors, whether or not to create a frame, and, if so, the constant (fill) color to use and the position of the created frame. Yosefi describes rules to follow after finding an edge and knowing the two colors. There are 24 rules based on the two colors. Once the frames are made, they are combined with the original data to print an image having reduced defects.
U.S. Pat. No. 4,583,116 to Hennig et. al describes a trapping process that evaluates the weighted separations on both sides of an edge in or
Coleman Robert M.
Nickell Eric S.
Rumph David E.
Carter Tia A.
Coles Edward
Xerox Corporation
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