Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
2000-10-27
2004-10-05
Rogers, Scott (Department: 2626)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S003260, C358S003210
Reexamination Certificate
active
06801338
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an image data binary coding method for use in a printer, a scanner, a copier, a facsimile, etc. for reproducing multi-gradation image data in the form of a bi-gradation image.
BACKGROUND OF THE INVENTION
An error diffusion method is well known for converting a multi-gradation image to a bi-gradation image.
FIG. 5
is a block diagram of a circuit for performing a conventional error diffusion method. Multi-gradation image data D
0
of a target pixel to be converted to bi-gradation image data is read from image memory
100
; a y-correction is performed, by reference to correction data stored in &ggr;-correction ROM
101
; the multi-gradation image data is transformed to multi-gradation image data pertinent to printing characteristics of an output device such as a printer. Multi-gradation image data D, after the &ggr;-correction, is added with error correction E of the target pixel by adder
102
in error diffusion processing unit
107
, and resultant output F is released as F=D+E.
Output F of the target pixel, added with error data E, is then compared with binary threshold Th by comparator
104
. When F=>Th, comparator
104
releases a binary signal B of 1 (B=1). If F<Th, a binary signal of 0 (B=0) is released. From the binary signal from comparator
104
, subtracter
106
determines binary coding error E′ as E′=F−B′. When an input data has 256 levels of gradation (0 to 255), B′ is given as B′=255B. When D=230 and Th=128, binary output B is 1 (B=1) and binary coding error E′ is determined as
E′=D−
255
B=
230−255=−25
For application to each pixel data thereafter, binary coding error E′ is weighted according to specific error matrix Mxy in weighting error calculator
105
, and then, calculator
105
calculates error correction E and saves correction E in error memory
103
. Adder
102
adds error correction E with succeeding multi-gradation pixel data, and the error diffuses.
In the above example, multi-gradation image data D of D=230 is compared with binary threshold Th of Th=128, and a resultant binary output is 1 at the level of 255 out of 256 levels. Then, a binary error of −25 is generated for multi-gradation image data D of 230. Weighting error calculator
105
weights and distributes the binary error to error memory
103
for adjacent pixels with the error matrix, and the error is reflected to the binary coding of the succeeding multi-gradation image data.
An example of error matrix Mxy used in the conventional error diffusion method is shown in FIG.
6
. The pixel denoted by the symbol “*” is a target pixel to be subjected to the binary coding. An error generated during the binary coding of the target pixel is weighted according to the weighting factors of 7, 1, 5, and 3 shown in
FIG. 6
, and weighted errors are applied to the succeeding image data before the binary coding. For binary coding of the multi-gradation image data of the target pixel denoted by “*”, the weighted error is read out from error memory
103
and used for correcting the image data received from image memory
100
.
The conventional error diffusion method permits a binary error generated during the binary coding of pixel data to be applied to the succeeding pixel data that is subjected to the binary coding, hence minimizing the error between the bi-gradation image data and the original multi-gradation image data.
The binary image generated by the error diffusion method has a smoother gradation and a higher resolution than a binary image generated by a common dithering matrix method. Hence, the error diffusion method is preferably applied to an ink jet printer or the like and regarded as an essential method for achieving a higher quality level of printing.
When a binary image generated by the error diffusion method is printed down with a common electronic photographic apparatus, dots of a printed pattern appear unstable hence causing a shape of a particle to be significantly deteriorated and making the quality of a printed image unfavorable.
This may be derived from the fact that the pattern of dots particularly in lower density regions is printed in an unstable manner by the electronic photographic apparatus and a dot gain is thus poor, while any ink jet printer can successfully print down discrete dots of a pattern. Also, in intermediate or high density regions, the dots of ink may be saturated too quickly, hence a declining reproducing of a gradation.
Moreover, printing with an electronic photographic apparatus possibly causes adjacent dots to overlap each other thus creating undesirably large dots. This may generate variations in the density throughout the regions at the same density, deteriorating the particles of dots.
Because of the above described aspects, the error diffusion method is not desirably applicable to the binary coding for an electronic photographic apparatus which produces a pattern of dots in an unstable manner in the reproduction. Yet, the error diffusion method is advantageous as higher in the smoothness of gradation and the resolution than the dithering methods. In a case that the error diffusion method is successfully used for binary coding with any electronic photographic apparatus, a resultant reproduced image will significantly be improved.
SUMMARY OF THE INVENTION
An image data binary coding method is provided for subjecting a pixel of a multi-gradation image to binary coding to generate a binary or bi-gradation image, which comprises acknowledging an arrangement of pixels around a target pixel through examining an on/off-state of each pixel of a binary form, calculating error correction data from the pixel arrangement, and carrying out the binary coding for multi-gradation image data.
As the error data for a binary form of the multi-gradation image data is corrected depending on a density of its actual printed form, unstable artifacts generated in the reproduction of printed dots can be suppressed during the binary coding. The bi-gradation image data processed by the error diffusion method can hence favorably be printed in dots.
REFERENCES:
patent: 5029226 (1991-07-01), Klein et al.
patent: 5361142 (1994-11-01), Semasa
patent: 0 272 147 (1988-06-01), None
Search Report corresponding to application No. GB 0025915.0 dated Apr. 20, 2001.
RatnerPrestia
Rogers Scott
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