Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1997-11-06
2004-05-04
Garcia, Gabriel (Department: 2624)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S001160
Reexamination Certificate
active
06731401
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printing system with a printing head that successively forms dots in a predetermined direction on a printing object and records multi-tone images through a distribution of dots based on the error diffusion technique. The present invention also pertains to an image recording method and a recording medium, on which image conversion programs used therefor are recorded.
2. Description of the Related Art
Color printers, in which a plurality of color inks are discharged from a printing head, are widely used as an output device of a computer that records a multi-color, multi-tone image processed by the computer. Several methods are applicable to print a multi-color, multi-tone image with three color inks, cyan, magenta, and yellow (CMY). One method is a technique adopted in the conventional printers. This technique expresses the tone of a printed image by the density of dots (frequency of appearance of dots per unit area) while fixing the size of dots formed on a sheet of paper by a spout of ink. Another method adjusts the diameter of dots formed on a sheet of paper, in order to vary the density of dots per unit area. A monochromatic ink (generally black) forms a gray-scaled image. In this case, the tone of the image is also expressed by the distribution of dots.
In any of the above techniques, tone information of an original image is expressed by the distribution of dots, that is, the on/off state of dots, so that density error is inevitable in each pixel unit. An error diffusion technique has accordingly been proposed to distribute the density error causing in each pixel into the peripheral pixels and thereby make the whole density of a resulting image close to that of the original image. Many of the currently available printing systems adopt the error diffusion technique for distribution of dots.
The printing system based on the error diffusion technique scans a printing head in a direction of width of paper (hereinafter referred to as the primary scanning direction), while feeding the paper in a direction perpendicular to the primary scanning direction (hereinafter referred to as the secondary scanning direction), so as to form dots. The range of error diffusion is generally in the vicinity of a target pixel, that is, a plurality of adjoining pixels in the primary scanning direction and a plurality of adjoining pixels in the secondary scanning direction, as shown in FIG.
12
. The numerals allocated to the respective pixels shown in
FIG. 12
denote weights added to the distributed density errors. The total of weights is equal to one.
The printing system based on the error diffusion technique inputs print data for one scanning line in the primary scanning direction into an input data line buffer, determines formation or non-formation of dots with respect to the input data of one scanning line according to the error diffusion technique, stores the results of determination in a result line buffer, and stores results of error diffusion into an error diffusion line buffer. Since the error diffusion is carried out for pixels on a certain scanning line and pixels on a next scanning line, the error diffusion line buffer should have the capacity corresponding to at least two scanning lines.
The reduction in diameter of printing dots increases the number of dots printed on one line. The increased number of dots increases the required capacities of the input data line buffer, the result line buffer, and the error diffusion line buffer. By way of example, an image is recorded at the density of 1440 dpi in the direction of width of A4-size paper (210 millimeter). In this case, almost 12 thousand dots are formed on each line. The required capacity of the error diffusion line buffer for a certain scanning line and a next scanning line with respect to four colors CMYK then amounts to 96 kilobyte.
SUMMARY OF THE INVENTION
One object of the present invention is thus to reduce the required capacity of a memory for the error diffusion processing in a printing system with a printing head that successively forms dots along scanning lines in a predetermined scanning direction on a printing object and records an image through a distribution of dots based on an error diffusion technique. The required capacity of the memory for the error diffusion processing substantially corresponds to only one scanning line.
Another object of the present invention is to provide an image recording method for carrying out the error diffusion processing with a memory of such reduced capacity and a recording medium on which image conversion programs used therefor are recorded.
At least part of the above and the other related objects is realized by a first printing system with a printing head that successively forms dots along scanning lines in a predetermined scanning direction on a printing object and records an image through a distribution of dots based on an error diffusion technique. The first printing system of the invention includes: input means for inputting print data including tone information regarding an image to be recorded by a pixel unit; a plurality of storage buffers having a total capacity corresponding to a number of pixels included in only one scanning line, each storage buffer storing a cumulative error allocated to each pixel according to the error diffusion technique; diffused error registration means for registering the cumulative error into each of the storage buffers; corrected tone data computing means for computing corrected tone data with respect to a target pixel that is subjected to determination of formation or non-formation of a dot, based on tone information of the print data regarding the target pixel and the cumulative error regarding the target pixel and being registered in a storage buffer corresponding to the target pixel; density error computing means for calculating a difference between a printing density corresponding to the corrected tone data and a printing density realized by formation or non-formation of a dot as a density error; error distribution determination means for determining distribution of the density error into non-processed peripheral pixels in the vicinity of the target pixel with predetermined weights; and storage control means for storing errors allocated to adjacent pixels after the target pixel on an identical scanning line in a primary scanning direction into storage buffers corresponding to the adjacent pixels after the target pixel, and storing errors allocated to pixels existing on a next scanning line at positions corresponding to the target pixel and preceding pixels before the target pixel in the primary scanning direction into storage buffers corresponding to the target pixel and the preceding pixels before the target pixel, based on the distribution of the density error determined by the error distribution determination means.
In a printing system with a printing head that successively forms dots along scanning lines in a predetermined scanning direction on a printing object, the present invention is also directed to a first method of recording an image through a distribution of dots based on an error diffusion technique. The first method includes the steps of:
(a) inputting print data including tone information regarding an image to be recorded by a pixel unit;
(b) storing a cumulative error allocated to each pixel according to the error diffusion technique into each of a plurality of storage buffers, the storage buffers having a total capacity corresponding to a number of pixels included in only one scanning line;
(c) computing corrected tone data with respect to a target pixel that is subjected to determination of formation or non-formation of a dot, based on tone information of the print data regarding the target pixel and the cumulative error regarding the target pixel and being registered in a storage buffer corresponding to the target pixel;
(d) calculating a difference between a printing density corresponding to the corrected tone data and a printing densit
Garcia Gabriel
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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