JP2900907B2 - Image processing device - Google Patents

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 such as a facsimile or an image scanner, and more particularly, to a method of minimizing an average error of multivalued image data (also referred to as an error diffusion method).
The present invention relates to an image processing device that outputs a pseudo halftone image by binarizing the image.

[0002]

2. Description of the Related Art Conventionally, various types of so-called pseudo halftone binarization methods for binarizing read multi-value image data in an image processing apparatus have been proposed. Among these various binarization methods, the systematic dither method (or simply the dither method) is generally used. Here, dither means shaking, and is intended to express a gradation in a binary image by appropriately changing a threshold (Threshold) for binarizing multi-valued image data.

In this systematic dither method, m × m threshold values are prepared in advance in an m × m mask pattern, and (m × m + 1) levels of gradation can be expressed. The mask patterns are classified into a dot concentration type in which a threshold value is selected so that black dots gradually become thicker around a certain dot, and a dot dispersion type in which black dots appear in a dispersed manner.

According to this systematic dither method, the result of the binary data to be output is determined only by the magnitude relation between the value of the input multi-valued image data and the threshold value. However, this systematic dither method has a problem that it is still difficult to obtain good image quality. Therefore, the difference between the threshold value and the output binary data is added to the conditions for determining the image data of the peripheral pixels, and it is possible to obtain a good image quality by the conditional error minimization method. Is the law.

In the above-described average error minimizing method, difference (error) data between an input value and a threshold value is stored, and in processing a target pixel, the pixel data of the target pixel and the error data of neighboring pixels are weighted. In this method, the pixel is binarized by calculating the sum of the pixel value and the corrected density value of the target pixel and comparing the corrected density value with a threshold value.

The operation of the conventional average error minimizing method will be described with reference to FIG. FIG. 3 is a block diagram showing a configuration of a binarization processing unit based on a minimum average error method generally provided in a conventional image processing apparatus. This binarization processing unit adds the input multi-valued image data and the error data stored in the error memory 7 weighted by the weight matrix 8 and outputs the result as multi-valued image data after the addition. Is compared with the multi-valued image data after the addition output from the adder 13 and the threshold value stored in the fixed threshold value unit 5 to output binary data. It has a comparison unit 6 for outputting to the memory 7, an error memory 7 for storing the error data, and a weight matrix 8 for weighting and outputting the error data stored in the error memory 7.

In the mean error minimizing method, when binarization is performed by focusing on the y-th dot in the main scanning direction and the x-th line in the sub-scanning direction in the image space, the binarization is performed. An error generated in a binarized neighboring pixel is read out, and an added value is obtained based on a numerical value obtained by weighting the error. This added value is added to the data of the pixel of interest to obtain a corrected density value, which is compared with a fixed threshold to perform binarization. Here, the difference generated at the time of binarization is stored as a binarization error. By repeating the above process over the entire image space, binary data is obtained. By displaying and printing the binary data, a pseudo halftone image can be obtained.

Here, as the weighted error data added in the adder 13, the image data to be binarized is used as the image data of interest, and the error data of the pixels near the image data of interest is used. Specifically, in many cases, an error of four pixels, that is, a pixel on the left of the target pixel in the image space, a pixel on the upper left, a pixel on the upper right, and a pixel on the upper right is often used.

In general, a coefficient for weighting an error depends on a distance from a pixel of interest.

As described above, in the average error minimum method, a pseudo halftone image is obtained by adding the error data of the neighboring pixels to the image data of the pixel of interest by weighting it. It is excellent in terms of expressiveness and resolution, and it is difficult for moire to occur even for halftone printed originals,
It is an advantage that it is strong in reduction processing after binarization.

[0011]

However, the above-mentioned average error minimization method uses the number of neighboring pixels to be weighted when the sum of the pixel data of the target pixel and the error data of the neighboring pixels is weighted. It is necessary to perform addition, and since it is a sequential process, there is a problem that the processing time is long, and the higher the resolution, the more the number of pixels and therefore the processing time.

The present invention has been made in view of the above circumstances,
An object of the present invention is to provide an image processing apparatus that binarizes multi-valued image data using the average error minimization method and that can speed up image processing.

[0013]

According to the first aspect of the present invention,
An image processing apparatus having a binarization processing means for binarizing each of multi-valued image data photoelectrically converted by an image input device by pseudo halftone processing and outputting the binary data as binary data. Means for storing the multi-level image data, multi-level image data storing means, an error storing means for storing an error when the multi-level image data is binarized, and an error storing means for storing the error stored in the error storing means. Weighting means for weighting and outputting, and selecting and outputting only weighted errors which have not been added to the multi-valued image data among the weighted errors output from the weighting means. A selector for adding the multi-valued image data and the weighted error output from the selector, and adding the weighted error to the multi-valued image data. Threshold value storage means for storing a threshold value for conversion into multi-valued image data to which the weighted error is added based on the threshold value stored in the threshold value storage means. Binarizing means for binarizing multivalued image data based on the threshold value and binarized means for binarizing and outputting the binarized data as binary data; And an error output means for outputting an error generated at the time of the above to the error storage means.

Therefore, according to the present invention, the binarization processing means for binarizing multi-valued image data and outputting it as binary data is generated when the stored multi-valued image data is binarized. In addition to the multi-valued image data that is weighted and binarized, the error is stored, and the multi-valued image data after the error is added is binarized based on a threshold value. By selecting a weighted error added to the multi-valued image data by the selector, the speed of the image processing can be increased.

According to a second aspect of the present invention, in the first aspect of the present invention, the error stored in the error storage unit to which the weighting unit weights and outputs is weighted in the image space of the multi-valued image data. With respect to the position, it is characterized by an error of four pixels: a pixel on the left, a pixel on the upper left, a pixel on the upper right, and a pixel on the upper right.

Therefore, according to the present invention, the effect of the first aspect of the present invention can be obtained, and the error weighted by the weighting means is different from the position in the image space of the multivalued image data to be binarized. , An error that has not yet been added to the multi-valued image data to be binarized, because of the error of the four pixels of the pixel on the left, the pixel on the upper left, the pixel on the upper right and the pixel on the upper right And the upper right pixel becomes an error between the two pixels, and the weighted error of the two pixels is selected by the selector. Therefore, the error added by the adding means is halved, and the image processing speed is further improved. Can be achieved.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the image processing apparatus performs control based on the binary data and control means for controlling an operation of the image processing apparatus. It is characterized by having printing means and communication means for transmitting and receiving the binary data.

Therefore, according to the present invention, the operation of the invention described in claim 1 or 2 can be obtained, printing can be controlled by the control means, and the binary data can be transmitted and received by the communication means. Will be possible.

According to a fourth aspect of the present invention, in the third aspect of the invention, the binarization processing means and at least one of a control means, a printing means and a communication means are connected by a communication line. It is characterized by having.

Therefore, according to the present invention, the effect of the invention described in claim 3 is obtained, and the transmission and reception of the binary data between the binarization processing means and the control means, the printing means or the communication means. It can be performed.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of an image processing apparatus according to the present invention will be described with reference to the drawings. FIG. 2 is a block diagram showing the configuration of an embodiment of the image processing apparatus according to the present invention. The image processing apparatus includes a binarization processing unit 1 for binarizing input multi-valued image data by an average error minimization method,
A control unit 2 for controlling the operation of the image processing apparatus, a printing unit 3 for printing based on the output binary data, and a communication unit 4 having a communication line for transmitting and receiving image data are provided.

Here, in the present embodiment, an example is assumed in which the above-described block is built in one image processing apparatus. However, the present invention is not limited to this.
The binarization processing unit 1 may be provided in one device, the other blocks may be provided in another device, and these two devices may be connected to each other by a communication line. May be connected by a communication line.

Next, 2 in the image processing apparatus according to the present invention.
One embodiment of the binarization process will be described with reference to FIG. FIG. 1 is a block diagram showing a configuration of the binarization processing unit 1 shown in FIG.

The binarization processing section 1 determines an image data line buffer 9 for storing image data for each pixel, an error data line buffer 10 for storing error data, and a weighting coefficient corresponding to a pixel position. A weight matrix 11 for weighting the error data, and a selector 12 for outputting only the error data of the non-overlapping weighted neighboring pixels to the adder 13 except for the error data of the overlapping weighted neighboring pixels. An adder 13 that adds the pixel data stored in the image data line buffer 9 and the error data of the weighted neighboring pixels and outputs the result as addition data, and a fixed threshold value unit 16 that stores a fixed threshold value. Compares the threshold value S output from the fixed threshold value unit 16 with the addition data output from the adder 13, and outputs binary data. A binarizing section 15 for, the adder 13
And an adder 14 that compares the added data output from the binary data with the binary data output from the binarization unit 15 and outputs error data to the error data line buffer 10.

Next, the operation of the binarization processing of the multivalued image data by the binarization processing section 1 will be described with reference to FIGS.

Now, the pixel at the position of the x-th line and the y-th dot in the image space is noticed as an object of the binarization processing, and is set as the noticed pixel. The image data of the original image of the pixel at the position of the x-th line and the y-th dot is defined as I _{x, y} .

First, the target pixel data input to the binarization processing section 1 shown in FIG. 2 is stored at a corresponding position in the image data line buffer 9 in FIG. Further, an error E generated when binarizing pixels around the target pixel is stored in the error data line buffer 10. Note that, here, as the neighboring pixels, four pixels, that is, a pixel on the left of the pixel of interest in the image space, an upper left pixel, a pixel directly above, and a pixel on the upper right are defined as neighboring pixels.
It is not limited to one pixel.

Next, a weighting coefficient corresponding to each pixel position of the error data line buffer 10 is determined by the weight matrix 11, and error data associated with the weighting coefficient is output from the weight matrix 11.

In the prior art, as shown in FIG.
The image data I _{x, y} of the pixel of interest in the image data line buffer 9 is _added to the weighted error G _{x−1, y−1} ,
G _{x− 1, y} , G _{x−1, y + 1} , G _{x, y−1} are added to obtain an addition result I _{x, y} ′. However, with this method, it is difficult to speed up the image processing.

Therefore, in the image processing apparatus according to the present invention, the following operation is performed in order to speed up image processing. First, attention is paid to a pixel that has been processed before processing the pixel of interest that is the target of the current binarization processing.
In the present embodiment, the image data line buffer 9 shown in FIG.
Attention will be paid to I _{x, y-1} in the above. Since the image processing by the same binarization processing is performed on this pixel, errors G _{x-1, y-2} , G
_{x-1, y-1} , G _{x-1, y} , G _{x, y-2} are added, and the addition result I
_{x, y-1} 'has been obtained. _{Ix, y} 'and I
_{When x, y-1} 'is compared, it can be seen that the weighted errors G _{x-1, y-1} and G _{x-1, y of} the neighboring pixels are both added.

Therefore, in the present invention, as shown in FIG. 1, the selector 12 is provided in the preceding stage of the adder 13 to remove the error of the overlapped weighted neighboring pixels and remove the weighted neighboring pixels which are not overlapped. Only the error is input to the adder 13. That is, when the addition result I _{x, y} ′ of the target pixel is represented, the following expression (1) is obtained. I _{x, y} '= I _{x, y} + G _{x-1, y + 1} + G _{x, y-1} (1)

Then, the obtained addition result I _{x, y} ′ is
Input to a binarization unit (comparator) 15 and an adder 14,
First, the binarization unit (comparator) 15 compares the threshold value S stored in the fixed threshold unit 16 with a black pixel or a white pixel to obtain binary data O _{x, y} . . The binary data O _{x, y} is input to the adder 14 while being output. The adder 14 calculates a difference between the input data I _{x, y} ′ of the binarization unit (comparator) 15 and the output data O _{x, y,} and converts the difference into a binarization generated by the binarization of the target pixel. Error E
_{x and y} are stored in corresponding positions of the error data line buffer 10.

By repeating the above procedure over the entire image space, a binarized pseudo halftone image can be obtained.
In this embodiment, the error of the weighted neighboring pixels to be added is set to four pixels. However, the present invention is not limited to this, and errors of peripheral pixels in a wider range may be used.

Therefore, according to this embodiment, the adder 1
The weighted error data added by 3 is reduced by two compared to the case where there is no selector 13, so that the processing time in the image processing can be reduced, and therefore, the image processing can be speeded up. be able to.

[0035]

As is apparent from the above description, according to the present invention, in an image processing apparatus for obtaining a pseudo halftone image by binarizing multi-valued image data input by the average error minimizing method, Since only the weighted errors that have not been added to the multi-valued image data among the weighted errors output from the weighting means are selected and output, speeding up image processing is realized. In particular, it is possible to provide an image processing apparatus having a large effect of speeding up when performing image processing of high-resolution image data.

Further, since the binarization processing means and at least one of the control means, the printing means and the communication means are connected by a communication line, the transmission and reception of the binary data between the respective means is performed. An image processing device that can be easily performed can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of an image processing unit included in an image processing apparatus according to the present invention.

FIG. 2 is a block diagram illustrating a configuration of an embodiment of an image processing apparatus according to the present invention.

FIG. 3 is a block diagram of an embodiment of an image processing unit included in a conventional image processing apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Binarization processing part 2 Control part 3 Printing part 4 Communication part 9 Image data line buffer 10 Error data line buffer 11 Weight matrix 12 Selector 13, 14 Adder 15 Binarization part (comparator) 16 Fixed threshold part

Claims (4)

(57) [Claims] 1. An image processing apparatus having a binarization processing means for binarizing each of multi-value image data photoelectrically converted by an image input device by pseudo halftone processing and outputting the same as binary data, The binarization processing unit includes: a multi-value image data storage unit that stores the multi-value image data; an error storage unit that stores an error when the multi-value image data is binarized; Weighting means for weighting and outputting the stored errors, and among the weighted errors output from the weighting means, only weighted errors which have not yet been added to the multi-valued image data A selector for selecting and outputting the multi-valued image data and a weighted error output from the selector; and the weighted error is added. A threshold storing means for storing a threshold value for binarizing the value image data, based on the stored threshold storage unit threshold,
Binarizing means for binarizing the multi-valued image data to which the weighted error has been added and outputting this as binary data; and multi-valued image data to which the weighted error has been added. And an error output unit for outputting an error generated when binarizing the multi-valued image data based on the threshold value to the error storage unit. 2. An error stored in an error storage unit to which a weight is output by the weighting unit is a pixel adjacent to the left, an upper left pixel, and a position in an image space of the multi-valued image data. 2. The image processing apparatus according to claim 1, wherein the error is a difference between four pixels of a pixel immediately above and a pixel on the upper right. 3. An image processing apparatus comprising: a control unit that controls an operation of the image processing apparatus; a printing unit that performs printing based on the binary data; and a communication unit that transmits and receives the binary data. The image processing apparatus according to claim 1, further comprising: 4. An image processing apparatus according to claim 3, wherein said binarization processing means and at least one of a control means, a printing means and a communication means are respectively connected by a communication line. apparatus.