Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
2000-02-11
2004-01-20
Rogers, Scott (Department: 2626)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S003200
Reexamination Certificate
active
06680786
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to image processing methods and image processing devices, and particularly relates to an image processing method and an image processing device which print a plurality of dots to generate a dot set that represents a half-tone level.
2. Description of the Related Art
Printers and printing presses reproduce images by applying ink or toner onto print sheets. A portion where ink or toner is applied represents a darker level in contrast with a portion with no ink or no toner applied thereto representing the lightest level.
When a half-tone level needs to be reproduced, however, it is not easy to control the amount of ink or toner applied onto a print sheet so as to achieve a right amount for a given half-tone level. Because of this, a half-tone is generally represented by controlling a size of an area where ink or toner is applied on a print sheet. This is generally referred to as a pseudo-half-tone scheme.
The pseudo-half-tone scheme includes a screen-dot method, a dither method, and an error-diffusion method, for example.
The screen-dot method is typically used in printing presses. A dot screen film having a periodical variation is superimposed on a transparent film representing an image, and the superimposed image is projected to expose a film. As a result of the exposure, dots are generated in such a fashion as to have area sizes corresponding to transparentness of the original image. An electronic means is utilized these days to generate a dot screen, and screen-dot processing is performed on such an electronic dot screen to generate dots by using a high-resolution image setter.
FIG. 1
is an illustrative drawing showing a circular dot set of the related art.
In
FIG. 1
, color-dot sets D
11
through D
15
and white-dot sets D
21
through D
24
are formed to have circular shapes around predetermined dot-set centers C
1
through C
9
.
In accordance with a specified gray level, an appropriate number of color dots are printed around dot-set centers to produce the color-dot sets D
11
through D
15
, leaving blank areas serving as the white-dot sets D
21
through D
24
. Each of the color-dot sets D
11
through D
15
is formed to be a circular dot set when the specified gray level corresponds to an area ratio substantially lower than 50%.
As the specified gray level increases, an area ratio of color-dot sets to white-dot sets (blank areas) increases. When the area ratio exceeds 50%, color dots are printed such as to leave circular blank areas, which form the white-dot sets D
21
through D
24
. Namely, the white-dot sets D
21
through D
24
are formed to be a circular dot set when the specified gray level is substantially higher than the area ratio of 50%.
When the area ratio is smaller than 50%, only those dots which are closer to a center of a color-dot set than to a center of a white-dot set are printed as color dots. In
FIG. 1
, for example, a dot d
0
is closer to the center of the white-dot set D
22
than to the center of the color-dot set D
13
, so that the dot d
0
will never be a color dot as long as the area ratio is smaller than 50%. As a result, the color-dot set D
13
ends up having a square shape when the area ratio is exactly 50%. The same applies in the case of the other color-dot sets D
11
, D
12
, D
14
, and D
15
in FIG.
1
.
FIG. 2
is an illustrative drawing showing an ellipse dot set of the related art.
In
FIG. 2
, the color-dot sets D
31
through D
35
and the white-dot sets D
41
through D
44
are formed to have ellipse shapes around predetermined dot-set centers C
11
through C
19
.
In accordance with a specified gray level, an appropriate number of color dots are printed around dot-set centers to produce the color-dot sets D
31
through D
35
, each of which is an ellipse shape when the specified gray level corresponds to an area ratio substantially lower than 50%.
When the area ratio is smaller than 50%, only those dots which are closer to a center of a color-dot set than to a center of a white-dot set are printed as color dots. As a result, the color-dot set D
33
ends up having a hexagon shape as shown in
FIG. 2
when the area ratio is exactly 50%. The same applies in the case of the other color-dot sets D
31
, D
32
, D
34
, and D
35
in FIG.
1
.
In the following, the dither method will be described.
The dither method is typically used in printers and display devices having low resolution. While there are several variations to the dither method, an organized dither method is most generally employed.
In this method, a threshold matrix called a dither matrix is used to convert an input image into a dot image by checking whether input-image data exceeds predetermined thresholds.
Choice of a type of a dither matrix determines which one of a half-tone dither image, a dot-concentrated dither image, etc is obtained.
FIGS. 3A through 3G
are illustrative drawings showing different types of dither matrixes.
FIG. 3A
shows a half-tone-type dither matrix, and
FIG. 3B
illustrates a screw-type dither matrix.
FIG. 3C
exhibits a variation of the screw-type dither matrix, and
FIG. 3D
demonstrates a half-tone-emphasized-type dither matrix. Further,
FIG. 3E
shows a dot-concentrated-type dither matrix, and
FIGS. 3F
illustrates a spiral-dot-type dither matrix. Finally,
FIG. 3G
shows a square-dot-type dither matrix.
The half-tone-type dither matrix has thresholds assigned to respective dots such that lower thresholds correspond to smaller ordinal numbers shown in FIG.
3
A. As a gray level of an image pixel increases, dots are generated in a scattered manner in an ascending order of the ordinal numbers. In this manner, a dot set corresponding to an image pixel is created.
In the screw-type dither matrix and the spiral-type dither matrix, thresholds are assigned such that lower thresholds correspond to smaller ordinal numbers as shown in FIG.
3
B and
FIG. 3F
, respectively, so as to generate dots in a spiral fashion. As a gray level of a pixel increases, dots are generated in an ascending order of the ordinal numbers so as to spread from a center to peripheral areas. A dot set corresponding to an image pixel is created in this manner.
As shown in
FIG. 3C
, the variation of the screw-type dither matrix has a different order of dot generation at the peripheral portion of the matrix as compared with the original screw-type dither matrix shown in FIG.
3
B. In comparison with the original screw type, this variation has a threshold arrangement insuring that a contour shape of the dot set is closer to a circle. Namely, the contour shape of the dot set more closely approximates a circular shape.
In the half-tone-emphasized-type dither matrix, the dot-concentrated-type dither matrix, and the square-dot-type dither matrix as shown in
FIGS. 3D
,
3
E, and
3
G, respectively, dot arrangement is concentrated at a center, and is scattered in the peripheral portion of the matrix.
Use of such dither matrixes described above or use of circular/ellipse dot sets previously described generates a plurality of dots that are so concentrated as to form a contiguous dot set. Hereinafter, these methods are referred to as a dot-concentrated-type method.
In the dot-concentrated-type methods, a size of a given dot set gradually increases as an input-image level increases. This results in a better gradation of half-tone representation despite lower resolution of obtained images compared to when other pseudo-half-tone schemes are used. Especially, when an image is printed on a print sheet by using ink or toner, the gradation of half-tone representation is smooth in relation to changes in dot-set sizes, thereby providing a stable representation of half-tone levels.
The dot-concentrated-type methods, however, are rather sensitive to an order of dot generation.
The screw-variation type, the half-tone-emphasized type, the dot-concentrated type, the square-dot type, and the spiral-dot type all suffer a drawback in that a contour shape of a dot set deviates from a circular shape. This results in unstable reprod
Oshio Hiroshi
Sato Kazuhiko
Fuji 'Xerox Co., Ltd.
Rogers Scott
Westerman Hattori Daniels & Adrian LLP
LandOfFree
Image processing method and device for half-tone representation does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image processing method and device for half-tone representation, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image processing method and device for half-tone representation will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3250172