JPH09261466A - Image processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To convert a binary image to a multi-valued image without deteriorating resolution with respect to a line picture/character and smoothly with respect to a natural picture by extracting a referring pixel for multi-value-converting a pixel of interest so as to generate multi-valued data of the interested pixel. SOLUTION: A dot array detection part 102 recognizes whether the pixel of interest is along an edge line or belongs to a flat part from dot arrangement in the periphery of the pixel and detects the connection of dots with the pixel in a center. A multi-valued referring pixel extracting part 103 extracts the referring pixel for multi-value-converting the pixel to extract referring data at the time of generating pixel multi-valued data. Data obtained by the multi- valued referring pixel extracting part 103 is inputted to a multi-valued signal generating part 104 and then converted to the multi-valued signal of the pixel. Then pixels are successively shifted to similarly process in each window to multi-value-contact the whole of a binary image 101 to obtain a multi-valued image 105.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for converting an image gradation-represented by a binary signal into a multivalued signal by, for example, a dither method or an error diffusion method.

[0002]

2. Description of the Related Art Conventionally, in an image processing apparatus for converting a binary image into a multi-valued image, the periphery of a target pixel (for example,
A method of generating a multi-valued image signal from an average value within a window of 5 × 5 pixels or 7 × 7 pixels is known.

However, as described above, when multi-valued data is generated with the average value of peripheral pixels, the image is smoothed, and particularly thin lines and characters are blurred due to this multi-valued. There is a problem. For example, there is an image composed of a flat portion of intermediate density and a line drawing as shown in 9-1 of FIG. 9, and enlarged views of respective binarized images are 9-2 and 9-3 in FIG. In this case, in 9-2, dots are randomly dispersed in the vicinity of the pixel of interest (pixel marked with x in the figure). It is desirable that the multivalued data at this time be represented by an average value in the window.

The data multi-valued in this way is 9
As represented by -4, smoothly averaged multi-valued data is generated over the entire window. But 9
-3, in the case of a line drawing, averaging within the window generates multi-valued data having density around the thin line, resulting in a blurred image as shown in 9-5.

The present invention has been made in view of the above problems, and an object of the present invention is not to reduce the resolution for line drawings / characters, and to smoothly perform binary conversion on natural images. An object is to provide an image processing device capable of converting an image into a multivalued image.

[0005]

In order to achieve the above object, the present invention provides an image processing apparatus for performing binary / multivalue conversion for converting a binary image represented by binary into a multivalued image. , Means for identifying a region consisting of a predetermined pixel centering on the pixel of interest of the binary image, means for detecting the arrangement state of pixels in the identified region, and based on the arrangement state of the detected pixels Means for extracting a reference pixel that is a target of the binary / multi-value conversion, and performs the binary / multi-value conversion on the extracted reference pixel.

[0006]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the configuration of an image processing apparatus according to an embodiment of the present invention. In the figure, 101
Is a 1-bit / pixel binary image represented by digital binary (0/1). This binary image is an image signal that has been binarized by another image processing device (not shown), and the gradation expression method includes a dither method, an average density storage method, an error diffusion method, and the like. In addition, when the image is a character or a line drawing, it may be a binary image generated by simple binarization using a certain threshold, and here, the binary image 101
However, it is unknown what kind of binarization method is used. Further, it is possible that a partial image of the binary image 101 is a mixed image in which a natural image is represented by error diffusion and another portion is represented by simple binarization by partial processing.

In order to multivalue the image as described above, in the present embodiment, first, a block of N × N pixels centering on the pixel of interest is cut out, and the dot array detection unit 10 is operated.
Enter 2 The dot array detection unit 102 recognizes from the dot arrangement around the target pixel whether the target pixel is a pixel along the edge line or a pixel belonging to a flat portion, and further, the target pixel becomes a natural image. It recognizes whether it belongs or a line drawing / character image.

Therefore, the larger the area of the window area N × N pixels input to the dot array detection unit 102, the more
Although considered to be good, here, a window of 7 × 7 pixels is taken as an example.

2 to 4 show a part of a line drawing and a natural drawing,
It is a figure which shows an example of a dot arrangement when it cuts out by the window of x7 pixel. FIG. 2 shows a thin line drawn by a line of 1 dot, and in the multi-valued signal conversion of the pixel of interest ◎, it is desirable to multi-value by referring to one horizontal line centering on the pixel of interest. I understand.

On the other hand, FIG. 3 shows the halftone densities of a landscape image, which is a natural image, in binary, and it can be seen that in a 7 × 7 pixel window, the dots are uniformly dispersed within the window. At this time, it is desirable to take the average value of all the pixels in the window for the multivalued signal conversion of the target pixel ⊚. Further, FIG. 4 shows a slender thin line. At this time, it is desirable to refer to the slanted direction for multi-value quantization.

As described above, for multi-value quantization, it is desirable to detect the dot arrangement of the peripheral pixels of the target pixel and extract the multi-value reference data according to the arrangement and arrangement direction. Therefore, the dot array detection unit 102 in FIG. 1 detects dot connectivity centered on the pixel of interest.

For example, in FIG. 2, it is detected that dots are arranged in the horizontal direction (the direction of the arrow in the figure), and in FIG.
The dots are uniformly distributed, and it is detected that there is no connectivity, and in FIG. 4, it is detected that the dots are lined up to the right (in the direction of the arrow in the figure).

Regarding the dot direction detection method,
Various methods are conceivable, for example, detecting the edge direction of the peripheral pixels, detecting the dot arrangement by checking the connectivity, or classifying the dot arrangement of all the pixels in the block into some patterns, A method of performing pattern matching of those patterns can be considered.

When the dot array detection unit 102 detects the dot array, the multi-valued reference pixel extraction unit 103 is next.
The reference pixel for multi-value conversion of the pixel of interest is extracted by. For example, in the dot arrays shown in FIGS. 2 and 4, along the arrow direction in the figure, the average value of 6 pixels in both horizontal directions of the target pixel is taken in FIG. 2, and in the case of FIG. Multi-valued with reference to 8 pixels along the arrow direction. But,
For example, in the case of the pixel arrangements shown in FIGS. 5, 6 and 7, that is, when the target pixel is located at the end of the line drawing, the average value of the pixels along the arrow direction in the drawing is calculated. Is desirable.

Particularly in the example as shown in FIG.
Continuity of dots is seen in three directions, but since random dots are diffused in the lower half area of the target pixel, this is not a line drawing, but this is the edge of the halftone density change area. It is more natural to see a part, and in this case, the lower half area is averaged.

As described above, the multi-valued reference pixel extraction unit 103
Then, the reference data for generating the target pixel multi-valued data is extracted.

Next, the data obtained by the multi-valued reference pixel extraction unit 103 is input to the multi-valued signal generation unit 104, where it is converted into a multi-valued signal of the pixel of interest. As the conversion method here, the simplest method of averaging the extracted pixels, a weighted average value weighted in proportion to the distance from the pixel of interest, or commonly known interpolation is used. There is a method of performing data interpolation.

Then, the pixel of interest is sequentially shifted, and the same processing is performed in each window, and the binary image 1
A multi-valued image 105 is obtained by performing multi-valued conversion on the whole 01.

As described above, according to the present embodiment, the dot connectivity and the direction of the neighboring pixels in the target pixel of the binary image are detected, and based on this dot connectivity and direction, A reference pixel for generating multi-valued data of a target pixel is extracted, and multi-valued data of the target pixel is generated based on the extracted reference pixel, thereby lowering the resolution for a line drawing / character. In addition, a natural image can be smoothly converted from a binary image to a multivalued image.

As shown in FIG. 8, an operation unit 401 may be added to and connected to the dot arrangement detection unit 102 of FIG. 1 to weight the dot orientation directivity detection (Wt). In this case, if the weighting is instructed most in the "line drawing" direction by operating the operation unit 401, the entire surface of the original image is regarded as a line drawing, whereas if the most weighting is instructed in the "natural image" direction, the entire original surface is Since it is regarded as a natural image, dots are not connected.

Even when the present invention is applied to a system composed of a plurality of devices (eg, host computer, interface device, reader, printer, etc.), a device composed of one device (eg, copying machine, facsimile device) Etc.)

Another object of the present invention is to supply a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or apparatus, and to supply a computer (or CP) of the system or apparatus.
It is needless to say that it is also achieved by (U or MPU) reading and executing the program code stored in the storage medium.

In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. As a storage medium for supplying the program code, for example, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, C
A D-ROM, a CD-R, a magnetic tape, a non-volatile memory card, a ROM, etc. can be used.

Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also the OS (operating system) running on the computer based on the instructions of the program code. It is needless to say that this also includes a case where the above) performs a part or all of the actual processing and the processing realizes the functions of the above-described embodiments.

Furthermore, after the program code read from the storage medium is written in the memory provided in the function expansion board inserted into the computer or the function expansion unit connected to the computer, based on the instruction of the program code, The CPU provided in the function expansion board or the function expansion unit performs a part or all of the actual processing,
It goes without saying that the processing may realize the functions of the above-described embodiments.

[0027]

As described above, according to the present invention,
Based on the arrangement state of predetermined pixels centering on the target pixel of the binary image, a reference pixel for performing multi-value conversion of the target pixel is extracted to generate multi-valued data of the target pixel.
It is possible to perform a binary / multi-value conversion smoothly on a natural image without lowering the resolution for a character.

[0028]

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a configuration of an image processing apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of dot arrangement when a part of a line drawing is cut out in a window.

FIG. 3 is a diagram showing an example of dot arrangement when a part of a natural image is cut out in a window.

FIG. 4 is a diagram showing an example of dot arrangement when a part of a line drawing is cut out in a window.

FIG. 5 is a binary image of a line drawing and its enlarged view.

FIG. 6 is a binary image of a line drawing and its enlarged view.

FIG. 7 is a binary image of a natural image and its enlarged view.

FIG. 8 is a diagram showing an example in which an operation unit is added to the dot array detection unit according to the embodiment.

FIG. 9 is a diagram for explaining a conventional line drawing and halftone.

[Explanation of symbols]

 101 Binary image 102 Dot array detection unit 103 Multi-valued reference pixel extraction unit 104 Multi-valued signal generation unit 105 Multi-valued image

Claims (6)

[Claims] 1. An image processing apparatus for performing a binary / multivalue conversion for converting a binary image represented by binary into a multivalued image, comprising a predetermined pixel centered on a pixel of interest of the binary image. Means for specifying a region, means for detecting an arrangement state of pixels in the specified area, and extracting a reference pixel to be a target of the binary / multi-value conversion based on the detected arrangement state of pixels. An image processing apparatus comprising: means for performing the binary / multivalue conversion on the extracted reference pixel. 2. The arrangement state of the pixels is detected based on the directionality of the pixels centered on the pixel of interest and the connectivity of the pixels based on the number of consecutive pixels. 1. The image processing device according to 1. 3. The image processing apparatus according to claim 2, wherein when the connectivity of the pixels is not detected, it is determined that the image corresponding to the pixel is not a character / line drawing. 4. The image processing apparatus according to claim 1, wherein the reference pixels are extracted along the arrangement direction when the arrangement state of the pixels has a constant arrangement direction. 5. The image processing apparatus according to claim 1, further comprising means for weighting detection of the arrangement state of the pixels. 6. The image processing apparatus according to claim 5, wherein the weighting includes weighting for a character / line drawing and weighting for a natural image.