Facsimile and static presentation processing – Static presentation processing – Size – resolution – or scale control
Reexamination Certificate
1999-12-30
2004-05-04
Wallerson, Mark (Department: 2622)
Facsimile and static presentation processing
Static presentation processing
Size, resolution, or scale control
C358S001100, C358S001400, C358S001800
Reexamination Certificate
active
06731398
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technique that creates dots on a printing medium, so as to print a variety of images. More specifically the invention pertains to a technique that controls creation of dots on the contour of an image, so as to enhance the picture quality of the resulting image.
2. Description of the Related Art
Printing apparatuses that create ink dots on a printing medium to print an image are widely used as output devices of various images output from the computer, for example, natural images, letters, and figures. The printing apparatus divides an image into fine pixels and creates dots on the printing medium according to the tone values of the respective pixels, thereby printing the image. The technique applied for the printing apparatus determines creation or non-creation of a dot with regard to each pixel according to its tone value, in such a manner that dots are formed at a higher ratio in dark areas (where pixels have high tone values) of the printed image but formed at a lower ratio in light areas (where pixels having low tone values) of the printed image. The dots are created at the corresponding pixel positions, based on the results of the determination. The resulting printed image has a variation in brightness according to the density of dots and thus attains a wide range of tone value expression.
In the dark areas of the printed image, the control procedure determines creation of dots at a higher density. Namely dots are formed in most pixel positions in these areas. When the dots created there have a relatively small size, there is often a streak of clearance on the boundary between pixels, which is generally called banding and worsens the picture quality. The size of the dots formed on the printing medium is accordingly regulated to be greater than the interval between pixels.
Some proposed printers actively regulate the size of dots formed on the printing medium. In the case where the size of dots is not regulated, there are only two expressible levels, that is, creation or non-creation of the dot, in the respective pixels. In the case where the size of dots is regulated, on the other hand, there are a greater number of expressible levels in each pixel, which ensures the richer tone expression. The proposed technique allocates the larger-size dot to the pixels having high tone values and the smaller-size dot to the pixels having low tone values. Compared with the conventional technique that simply expresses the tone according to the density of dots, this proposed technique expands the degree of freedom in tone expression and enables a natural image having a wide range of tone values to be printed with a high quality.
These prior art printers, however, have a problem that the contour of a figure or a letter may be thickened in print. The figures and letters are generally expressed in black and have high tone values. The larger-size dot is accordingly allocated to such figures and letters. Since the size of the large dot is designed to be greater than the pixel, the printed contour is made thicker than expected. Allocation of the smaller-size dot to the contour may, however, cause the banding.
In these prior art printers, the printed figure or letter may have a relatively rough contour, which lowers the picture quality of the printed image. The dots are formed in the respective pixel positions, which are obtained by dividing the image as mentioned above. Unless the contour line coincides with the direction of alignment of pixels, the contour should be approximated by a broken line, which may result in a relatively rough contour. Increasing the number of divisions of the image to make the respective pixels smaller ensures the smooth contour. The time period required for printing the image, however, increases with an increase in number of pixels constituting the image.
SUMMARY OF THE INVENTION
The object of the present invention is thus to provide a technique that improves the picture quality of a printed image including figures or letters.
At least part of the above and the other related objects is actualized by a first printer having a print head that enables creation of at least two variable-size dots, that is, a larger-size dot and a smaller-size dot. The first printer drives the print head and carries out both main scan and sub-scan to print an image. The first printer includes: a contour pixel extraction unit that extracts contour pixels based on image data, the contour pixels representing the contour of a shape included in the image; a dot creation decision unit that determines creation or non-creation of each of the at least two variable-size dots with regard to each pixel based on the image data, and allocates the smaller-size dot to each of the contour pixels extracted by the contour pixel extraction unit; and a dot creation unit that actually creates the at least two variable-size dots, based on results of the determination and the allocation with regard to the respective pixels by the dot creation decision unit.
The present invention is also directed to a first method of printing that corresponds to the first printer. The invention accordingly provides the first method of driving a print head and carrying out both main scan and sub-scan to print an image, wherein the print head enables creation of at least two variable-size dots, that is, a larger-size dot and a smaller-size dot. The first method includes the steps of: (a) extracting contour pixels based on image data, the contour pixels representing the contour of a shape included in the image; (b) determining creation or non-creation of each of the at least two variable-size dots with regard to each pixel based on the image data, and allocating the smaller-size dot to each of the contour pixels extracted in the step (a); and (c) actually creating the at least two variable-size dots, based on results of the determination and the allocation with regard to the respective pixels in the step (b).
In the first printer and the corresponding first method, the technique of the present invention extracts contour pixels included in the image, determines creation or non-creation of each of the at least two variable-size dots with regard to each pixel based on the image data, and allocates the smaller-size dot to the extracted contour pixels. The at least two variable-size dots are formed according to the result of the determination with regard to the respective pixels. The smaller-size dot is allocated to the contour of a shape included in the image. This arrangement effectively prevents the contour from being undesirably thickened and thereby improves the picture quality of a resulting printed image.
The smaller-size dot is formed in the respective contour pixels, whereas the larger-size dot is created inside the shape. For example, in the case of printing black letters or figure, the larger-size dot is allocated to the inside of the respective letters or figure. This enables the contour of the shape to be printed clearly in deep black and effectively prevents banding from occurring even in solid areas of the figure.
In the first printer and the corresponding first method, one preferable application of the technique defines a plurality of adjoining pixels in a main scanning direction as one set, compares a tone value of each pixel included in the set with a predetermined threshold value, and extracts the contour pixels based on a result of the comparison and a preset relationship. The extraction of contour pixels according to this procedure desirably improves the picture quality of the resulting printed image.
In the first printer and the corresponding first method, another preferable application of the technique tentatively determines creation or non-creation of each of the at least two variable-size dots in each pixel based on the image data, stores a result of the tentative determination, rewrites the result of the tentative determination to create the smaller-size dot in the contour pixels, and settles the rewritten result as a result
Seiko Epson Corporation
Wallerson Mark
LandOfFree
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