Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1999-11-01
2004-05-04
Lee, Thomas D. (Department: 2624)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S003280
Reexamination Certificate
active
06731407
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image processing method and device for carrying out pseudo-gradation processing on an image by a dither method.
2. Prior Art
When an image is to be out putted e.g. from a workstation, a personal computer, or a word processor (including a personal computer having a word processing program installed therein) to a display device (various kinds of displays) or a printing device (various kinds of printers), an original image cannot be output as it is, dependent on the specifications of the display device or the printing device. To output image data represented by matrix data (hereinafter simply referred to as a “matrix”) having gradation values representative of e.g. 256 gradation levels assigned to matrix elements thereof, that is, image data (gradation image data) having information of an n-valued gradation value (n=256 in this embodiment) assigned to each pixel, to a tape printing apparatus capable of processing only image data with a smaller (limited) number of gradation values representative of respective gradation levels, it is required to convert the above image data to one (pseudo-gradation image data) adapted to the limited number of gradation values. One of methods used in such image conversion (compression) processing, that is, pseudo-gradation processing is a so-called dither method. It should be noted that “n-valued gradation value” is intended throughout the specification to mean “gradation value capable of having any one of n possible numerical values”, and hence “5-valued gradation value”, for instance, is a “gradation value which can have any one of five possible values”. Further, “n-valued matrix” is intended throughout the specification to mean “matrix of matrix elements each capable of having any one of n possible numerical values”, and hence “5-valued matrix”, for instance, is a “matrix of matrix elements which can have any one of five possible values”.
The dither method is employed to superimpose noise on gradation values of pixels constituting gradation image data of an original image and then carry out binarization (binary dither method) or limited multi-valued conversion (multi-valued dither method) on values resulting from the superimposition. This method takes advantage of the integrating function of human eyes that recognize contents in an area as a shade or a color. In the binary dither method, for instance, the ratio of assignment of two numerical values (e.g. 1's and 0's) to matrix elements of a matrix are changed according to the gradation values of respective pixels of an input gradation image (for instance, by thinning “1's” in the matrix according to the gradation values under a predetermined rule) to thereby represent intermediate gradation (for instance, a gray color represented by setting 1's and 0's to black and white, respectively). A typical binary dither method is a systematic dither method.
In the systematic dither method, first, for comparison with n-valued gradation values each defined by any one of n possible numerical values (n is an integer equal to or larger than 3) and assigned to pixels forming an original gradation image, a dither matrix of thresholds each defined by any one of m possible numerical values (m is an integer satisfying a condition of n≧m≧2) and arranged therein as matrix elements is prepared beforehand. Next, (the matrix of) the original gradation image is divided into matrices each having the size of the dither matrix, and the gradation values of the respective elements of each of the divisional matrices and the corresponding thresholds of the dither matrix are compared with each other on an element-by-element basis to determine whether or not a gradation value satisfies a condition designated by a corresponding threshold. According to results of the determination, either of the numerical values 1 and 0 is assigned to each pixel to thereby form a pseudo-gradation image represented by a binary matrix. For instance, if the gradation value of a matrix element satisfies a condition designated by a corresponding threshold, a numerical value (e.g. 1) indicating validity of the gradation value is assigned to a corresponding matrix element, whereas if the gradation value does not satisfy the condition, a numerical value (e.g. 0) indicating invalidity of the gradation value is assigned to the corresponding matrix element, whereby a pseudo-gradation image represented by a two-valued (binary) matrix (i.e. of matrix elements each having a value 1 or 0) is formed.
By definition of relationship between gradation values and thresholds therefor, the gradation value of each matrix element which is equal to or larger than a corresponding threshold, larger than the threshold, equal to or smaller than the same, or smaller than the same, for instance, can be a gradation value satisfying a condition designated by the corresponding threshold. In the following, the dither method will be described based on a case, for example, in which a gradation value equal to a corresponding threshold also satisfies a condition (i.e. the condition is that the gradation value is equal to or larger than the threshold or that the gradation value is equal to or smaller than the corresponding threshold). Of course, even when the condition is defined such that it is not satisfied when a gradation value=a threshold holds, the gradation values can be processed based on the same principles.
The multi-valued dither method is a dither method in which, a converted (compressed) image, that is, a pseudo-gradation image is not an image represented by a binary matrix (binary image) but an image represented by a multi-gradation matrix of matrix elements having three or more gradation values (multi-valued image). However, it can be processed in the same manner as carried out in the binary dither method. For instance, when a gradation image with 256 gradation values ranging from 0 to 255 is processed, the 256 gradation values are classified into e.g. four ranges of gradation levels, that is, range
1
from 0 to 64, range
2
from 64 to 128, range
3
from 128 to 192 and range
4
from 192 to 255, and dither matrices are provided for application of the systematic dither method to respective ranges of gradation values. Further, two values representative of results of the application of the systematic dither method to range
1
are defined as 0 and 1, two values for range
2
as 1 and 2, two values for range
3
as 2 and 3, and two values for range
4
as 3 and 4. Then, when the systematic dither method is carried out on each range of gradation values, a 5-valued pseudo-gradation image represented by five gradation values of 0 to 4 can be formed. Of course, if the binary dither method is further carried out on such a multi-valued (e.g. 5-valued) pseudo-gradation image, it is also possible to finally obtain a two-valued or binary pseudo-gradation image.
The above pseudo-gradation processing by the dither method (hereinafter referred to as “dithering”) can be applied not only to a monochrome image (gradation image having gradation values of gray tones) but also to a color image. That is, in this case, it is only required to carry out the dithering (color dithering) on gradation values of each of basic colors, such as three primary colors. For instance, to form a pseudo-gradation image as a display image to be output to a display or the like, it is only required to carry out dithering of gradation values of each of three primary colors, i.e. R (red), G (green) and B (blue), separately, whereas to form a pseudo-gradation image as a print image for printing, it is only required to carry out dithering of gradation values of each of three primary colors, i.e. C (cyan), M (magenta) and Y (yellow), separately. In the latter case, alternatively, dithering of gradation values of each of four basic colors, i.e. C, M, Y plus K (black) may be separately performed.
In the above dithering, however, a gradation image represented by a matrix in which n-valued gradati
Brinich Stephen
Hogan & Hartson LLP
Lee Thomas D.
Seiko Epson Corporation
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