Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1999-12-20
2004-01-06
Grant, II, Jerome (Department: 2626)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S002100, C358S003130
Reexamination Certificate
active
06674546
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image processing method which processes a multi-level input gradation image data on the basis of a multi-level dither method so as to convert into gradation image data having the smaller number of gradations, and an image processing apparatus therefore.
Conventionally, in an image forming apparatus which employs a line head such as a line LED (light emitting diode), a line thermal head and a line ink jet head, such as a printer and the like, a two-value image is formed by printing dots having the same size on a recording sheet according to a resolving power of the head, that is, according to an interval in a raster direction of a plurality of LED light emitting elements serving as recording elements arranged in a line in the case of the line LED head, according to an interval in a raster direction of a plurality of heat generating resistances serving as recording elements arranged in a line in the case of the line thermal head and according to an interval in a raster direction of a plurality of ink discharge ports serving as recording elements arranged in a line in the case of the line ink jet head. Further, the head is scanned plural times with changing a position in the raster direction so as to print the dots in a resolution more than the intervals of the respective recording elements, whereby the two-value image is formed.
In these image forming apparatuses, images of characters and lines are simply reproduced as a two-value image corresponding to the resolution of the head, and a photo image is reproduced according to a halftone process such as an ordered dither method or an error diffusing method. In the halftone process in this case, it is very hard to achieve both of a maintenance of high resolution and a reproduction of high gradation, and particularly in the ordered dither process, the resolution and the gradation have opposite characteristics.
To the contrary, in the image forming apparatus provided with the line head mentioned above, in recent years, there is known a structure which can express one pixel at some steps of gradations by modulating a printing area within one pixel with using the multi-level image data generated by processing the input gradation image data according to the multi-level dither method.
FIG. 14
shows a recording head
71
constituted by arranging a plurality of recording elements in a line, and a state of dots recorded by this recording head
71
. In this drawing, there is shown for simplification an example of the case of recording one pixel by three values including white. In this case, by arranging, for example, four or three recording heads
71
mentioned above in parallel, it is possible to record a color image constituted by a combination of four colors comprising C (cyan), M (magenta), Y (yellow) and K (black), or a combination of three colors comprising C, M and Y.
In the image forming apparatus which can record the multi-level image data, in order to reproduce the predetermined number of gradations peculiar to a printer engine actually performing an image recording operation after executing various image processes such as a color conversion process, an under color removal (UCR) process or a &ggr; correction, the structure is made such as to execute a multi-level halftone process such as a multi-level dither process employing a screen angle or a multi-level error diffusing process at each of colors so as to obtain the multi-level image data having some bits per one pixel. Then, it is intended to improve an image reproduction by concentrating more amount of information onto one pixel.
Further, the ordered dither process is generally light in processing, has a high speed and can reduce a cost, however, the error diffusing process is more excellent with respect to an image quality. However, in the case of the multi-level halftone process, a less difference in the image quality is generated in comparison with the case of two values. In particular, the more the number of gradation expressed by one pixel in a high resolution is, the smaller the difference of the image quality is.
In the multi-level dither process which is one of a multi-level halftone processes, there are two methods which are obtained by widely classifying according to a method of distributing a threshold value arrangement overriding each of planes. One is a method shown in
FIG. 16A
, that is, a method of filling up the threshold value in order of size from a smallest one at a unit of plane, and the other is a method shown in
FIG. 16B
, that is, a method of filling up the threshold value in order of size from a smallest one with respect to one optional pixel to be a subject to be processed.
For example, a multi-level dither process for converting image data of input 8 bits into an image having four values per one pixel (2 bits) according to the method shown in
FIG. 16A
by using a basic dither matrix of 2×2 shown in
FIG. 15
is a dither process used for a printer such as an ink jet printer, which is basically hard to be influenced by an appearance of a dot of an adjacent pixel and can stably reproduce an image formation at each pixel. A resolution thereof is substantially the same as a resolution performance of the printer engine section. That is, it is an ideal method in the case that the resolution is very high, the dot density is high and the image is reproduced in a density modulation. In this case, since the image is easily reproduced on a whole of a screen at an pixel of the same size or the similar size, it is easily affected by a printing accuracy.
Further, a multi-level dither process for converting image data of input 8 bits into an image having four values per one pixel (2 bits) according to the method shown in
FIG. 16B
by using a basic dither matrix of 2×2 shown in
FIG. 15
is a dither process frequently used for a printer such as a laser printer or a thermal printer, which is easily influenced by an appearance of a dot of an adjacent pixel and can be hard and unstable to form an image at each single pixel. A resolution thereof is low and a dot density is rough, and when setting a basic threshold value arrangement of the dither to a dot concentration type, an image called a dotted screen is formed. Since the resolution is low, a fine printing accuracy unevenness at a pixel unit is adsorbed.
To the contrary, with respect to a relationship between a recording head and a printing accuracy such as a printing position and a printing size, for example, in the case of the ink jet printer, a volume and a direction of an ink discharged from an ink discharge port corresponding to a recording element are in general frequently dispersed at each of ink discharge ports. It is possible to restrict the dispersion to a level equal to or less than a fixed value which generates no problem, however, a manufacturing cost becomes very expensive.
Further, in the case of forming an image at a high resolution equal to or more than an interval of the respective recording elements by scanning the head at plural times with changing a position in a raster direction, there is a possibility that a starting position for each of scanning is shifted, and a very high mechanical control is required for completely correcting this, so that it is a problem on cost.
When the volume and the direction of the ink are dispersed at each of the ink discharge ports, a density becomes higher at a portion having a large dot or a portion at which adjacent dots are closely arranged, in comparison with the other portion, whereby a density unevenness called as a black streak is generated, and further, a density becomes lower at a portion having a small dot and a portion at which adjacent dots are arranged apart from each other, in comparison with the other portions, whereby a density unevenness called as a white streak is generated. Accordingly, there is a problem that an image quality is deteriorated.
In order to prevent this, conventionally, the structure is made such that like a checkers-shaped thinned-out printing and the
Frishauf Holtz Goodman & Chick P.C.
Grant II Jerome
Toshiba Tec Kabushiki Kaisha
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