Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1998-03-31
2002-12-31
Rogers, Scott (Department: 2624)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S003260, C382S252000, C382S275000
Reexamination Certificate
active
06501566
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to image processing apparatuses, and more particularly to an image processing apparatus employing a multi-value error diffusion process.
2. Description of the Related Art
This application is based on Japanese Patent Application No. 9-084877 filed in Japan, the contents of which are hereby incorporated by reference.
In the field of the image processing apparatus employing the conventional multi-value error diffusion system, the art of comparing image data with a plurality of threshold values to generate output data of a plurality of bits corresponding to the comparison result is proposed as disclosed in, for example, Japanese Patent Laying-Open No. 4-2271.
FIG. 10
is a block diagram showing a structure of a conventional multi-value error diffusion process circuit.
Referring to
FIG. 10
, the multi-value error diffusion process circuit includes an adder
31
, a tone convertor
32
, a subtractor
33
, an error addition matrix
34
, an error memory
35
, and an address counter
36
.
Adder
31
adds a pixel density D (8 bits) of a pixel of interest (the pixel that is the subject of process) with a correction value R to output a corrected pixel density D′ (8 bits).
More specifically, as shown in
FIG. 11A
, the image (digital data) applied to the multi-value error diffusion process circuit is formed of pixels
0
-Xe in the x direction and pixels
0
-Ye in the y direction. The pixel of interest is indicated by * in the drawing. Density D of the pixel of interest is applied to adder
31
. Image process is carried out by scanning the pixel of interest in the input image.
Error memory
35
is formed of a plurality of pixels identical in number to the pixels of the input image as shown in FIG.
11
B. Address counter
36
designates a pixel in error memory
35
located at a position identical to the position of the pixel of interest.
In adder
31
, density D of the pixel of interest is added with the density (correction value R) of the pixel in error memory
35
designated by address counter
36
. Corrected pixel density D′ is output from adder
31
as shown in FIG.
11
C.
Tone convertor
32
converts the 8-bit converted pixel density D′ using a threshold value to output a 2-bit converted pixel density P. Tone convertor
32
also provides a data selector output Ti used for error computation at the same time. This data selector output Ti will be described afterwards.
Subtractor
33
subtracts data selector output Ti from corrected pixel density D′ to output the obtained value as error E.
Error addition matrix
34
distributes error E to the pixels around the pixel of interest in error memory
35
. Error memory
35
adds and stores the error for each pixel.
Error memory
35
provides the error of the addressed pixel designated by address counter
36
as correction value R.
The multi-value error diffusion process is completed by manipulating the pixel of interest in one image to alter pixel density D for all the pixels into converted pixel density P.
FIG. 12
is a block diagram showing a structure of tone convertor
32
of FIG.
10
.
Referring to
FIG. 12
, tone convertor
32
includes comparators CP
1
-CP
3
, an encoder ENC for adding the output of the comparator, and a data selector SEL for providing one threshold value or “0”.
Comparator CP
1
compares corrected pixel density D′ with a threshold value 192. When D′≧192, 1 is output. When D′<192, 0 is output.
Comparator CP
2
compares corrected pixel data D′ with a threshold value
128
. When D′≧128, 1 is output. When D′<128, 0 is output.
Comparator CP
3
compares corrected pixel density D′ with a threshold value
64
. When D′≧64, 1 is output. When D′<64, 0 is output.
Encoder ENC adds the outputs of comparators CP
1
-CP
3
to provide a converted pixel density P.
Data selector SEL selects any of the threshold values of 64, 128, and 192 or 0 according to converted pixel density P output from encoder ENC. The selected value is provided as data selector output Ti.
FIG. 13
shows the relationship of corrected pixel density D′, converted pixel density P, data selector output Ti, and error E.
When the value of corrected pixel density D′ is 0-63, converted pixel density P is 00. Here, data selector output Ti is 0. Therefore, the value of D′−0 is output from subtractor
33
as error E.
When the value of corrected pixel density D′ is 64-127, converted pixel density P is 01. Here, data selector output Ti is 64. Therefore, the value of D′−64 is output from subtractor
33
as error E.
When the value of corrected pixel density D′ is 128-191, converted pixel density P is 10. Here, data selector output Ti is 128. Therefore, the value of D′−128 is output from subtractor
33
as error E.
When the value of corrected pixel density D′ is 192-256, converted pixel density P is 11. Here, data selector output Ti is 192. Therefore, the value of D′−192 is output from subtractor
33
as error E.
Error addition matrix
34
adds error E generated by the tone conversion of the pixel of interest to the pixels around the pixel of interest in error memory
35
. More specifically, as shown in
FIG. 14
, error E of 1/6 generated by the tone conversion of the pixel of interest (*) is added to the two pixels in error memory
35
located below and to the left and right of the pixel of interest.
Error E of 2/6 is added to the two pixels located rightward and below the pixel of interest. Error diffusion is carried out in this way.
By using a multi-value error diffusion process circuit of the above-described structure, a pseudo tone can be applied on the image output. Furthermore, by providing the output data in a plurality of bits by each pixel, the tone gradation of the output data becomes more gentle than that of a binary output.
However, the conventional multi-value error diffusion process circuit had the disadvantage that the quality of the image data is degraded since the entire original document is subjected to the error diffusion process with a predetermined threshold value. For example, when there is a halftone image of uniform density in the original data such as halftone density text and that uniform density differs from the predetermined threshold value, data resolution is reduced to degrade the picture quality of the image.
When the error diffusion process is applied on the read out image data corresponding to halftone density text, the error is overlapped also on the text portion to degrade the picture quality of the text character. It may be desirable to not apply an error diffusion process in such a case. However, for original documents mixed with text characters and pictures, a better output may be obtained when the error diffusion process is applied.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an image processing apparatus that can carry out an error diffusion process without degrading the quality of image data.
Another object of the present invention is to provide an image processing apparatus that does not have the quality of text of halftone density degraded even when an error diffusion process is applied.
According to an aspect of the present invention, an image processing apparatus includes a reception unit for receiving image data represented in M gray levels, a detection unit for detecting image data having halftone density from the received image data, a set unit for setting a reference density used in an error diffusion process according to the detected image data, and a conversion unit to apply the error diffusion process on the received image data using the set reference density for converting the image data into image data of N(2<N<M) gray levels.
According to another aspect of the present invention, an image processing apparatus for converting image data represented by M gray levels into image data of N(2<N<M) gray levels using an error diffusion process
Hirota Soh
Ishiguro Kazuhiro
Tada Kaoru
Burns Doane , Swecker, Mathis LLP
Minolta Co. , Ltd.
Rogers Scott
LandOfFree
Image processing apparatus carrying out multi-value error... 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 apparatus carrying out multi-value error..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image processing apparatus carrying out multi-value error... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2989913