JPS63213084A - Picture processor - Google Patents

Abstract

PURPOSE:To reduce the capacity of a picture memory when the picture information is stored by converting a picture signal into a dither picture signal and applying the multi-value processing to the dither picture signal for production of a multi-value picture signal. CONSTITUTION:The picture of an original is converted into digital picture signals 11 via an input processing part 21 and supplied to a dither processing part 22. The part 22 applies the dither processing to the signals 11 to produce a 1-bit dither picture signal 12. This signal 12 is stored in a picture storing part 24 to be stored as the picture information and at the same time supplied to a picture processing part 23 to undergo the picture processing. The dither picture signal 13 processed by the part 23 is supplied to a density estimation processing part 25 forming a multi-value processing part and undergoes the multi-value processing for production of a multi-value output picture signal 14.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an image processing device that outputs an image having highly faithful gradation reproduction characteristics.

(Prior art) There is a need for an image processing device that can store, save, or transmit high-definition image information while maintaining high-fidelity tone reproduction characteristics, and output while maintaining high-fidelity tone reproduction characteristics. has been done.

(Problems to be Solved by the Invention) In such an apparatus, a large-capacity image memory is required to perform intensive image processing on image information.

On the other hand, in outputting image information that has been subjected to such advanced image processing, it is naturally required to output an image having tone reproduction characteristics that are highly faithful to the input image.

The present invention has been made in view of the above, and its purpose is to perform advanced image processing at a relatively low cost to shorten storage or transmission time, and to achieve high fidelity gradation. An object of the present invention is to provide an image processing device capable of outputting image information having reproduction characteristics.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, an image processing device of the present invention includes an input processing unit that converts image information into a digital image signal;
a dither processing section that converts the digital image signal into a dithered image signal using a dither matrix; and a multi-value processing section that performs multi-value processing on the dithered image signal to obtain a multi-value image signal. The main point is to have the following.

(Function) The image processing device of the present invention converts a digital image signal into a dithered image signal using a dither matrix, and performs multi-value processing on the dithered image signal to form a multi-value image signal. ing.

This allows the use of dithered image signals to store, store, or transmit image information, and output image information.

For reproduction, a multi-valued image signal obtained by converting this dithered image into multi-valued image is used.

(Example) Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a block diagram showing a circuit configuration of an image processing apparatus according to an embodiment of the present invention. The image processing apparatus shown in FIG.
It is sampled at a linear density of 6 lines/ml1 and converted into an 8-bit digital image signal 11, and this digital image signal 11 is supplied to the dither processing section 22. This dither processing unit 22 performs dither processing on the digital image signal 11,
A 1-bit dithered image signal 12 is formed. This 1-bit dithered image signal 12 is stored in the image storage section 24 to be saved as image information, and is also supplied to the image processing section 23 to perform image processing such as image editing such as enlargement/reduction and rotation. administered.

Dithered image signal 13 subjected to image processing by the image processing unit 23
is the density prediction processing section 2 constituting the multivalue processing section of the present invention.
5. This density prediction processing unit 25 predicts the image density from the input dithered image signal 13,
That is, by performing multi-value processing, the multi-value output image signal 14 is
form.

This multivalued output image signal 14 is sent to an output processing unit 26, for example 1
The image is supplied to an output processing unit such as a dye sublimation thermal transfer printer having a resolution of 6 lines/ram, and is reproduced by the output processing unit 26 into an image having an image density faithful to the original image and output.

That is, in the image processing apparatus of this embodiment, the input processing section 2
The 8-bit digital image signal 11 formed in step 1 is dithered in the dither processing unit 22 using the diagonal dither matrix shown in FIG. By performing binary conversion to a 1-bit dithered image signal 12, various types of image processing can be performed quickly and easily. That is, this deep image signal 12 is stored in an image storage section 24 consisting of, for example, a 20 MB magnetic disk device, and then subjected to various image processing, such as image data composition and affine transformation, under the control of the image processing section 23. image processing such as creation/editing of document images according to user requests. The dithered image signal 13 is thus subjected to image processing and then supplied to the 11-degree prediction processing section 25. The dithered image signal stored in the image storage section 24 may not be passed through the density prediction processing section 25 depending on what is added to the output processing section 26 . For example, when using a printer that can output the output of the output processing section 26 as a dithered image signal, or when connecting a data transmission system such as a telephone line, the dithered image signal is directly transmitted without going through the prediction processing section 25. 12, the processing time and transmission time will be shorter.

Therefore, it is desirable that the image processing section 23 include a selection section for selecting whether or not to use the density prediction processing section 25.

Here, the diagonal dither matrix will be explained.

In general, dither patterns that are two-dimensional expansions of dither matrices are shown in Fig. 5 (A>, (B)).

As shown in (C), there are a square dither pattern, a rectangular dither pattern, and a diagonal dither pattern.

Here, the reason why a diagonal dither pattern is used for a rectangular dither pattern consisting of a square dither pattern and a rectangular dither pattern is based on the results of the following study. Note that a diagonal dither pattern is defined as a threshold value located at the edge of each dither matrix that is in contact with at least two threshold values of an adjacent dither matrix (rOJ in the figure). If the number is represented by N, it corresponds to a dither matrix in which N is 5 or more. Incidentally, N is 4 for square and rectangular dither matrices.

The dither pattern is a two-dimensional expansion of the dither matrix according to its period. Therefore, Fig. 6(A)
The diagonal dither pattern shown in FIG.
It is thought that this corresponds to a rectangular dither pattern in which 2,83 is moved as shown in Figure 6 (B), (4X16)
This results in a rectangular dither pattern. Expressing this generally, the diagonal dither matrix is vertical and horizontal (m
xn2/-) can be expressed in association with a rectangular dither matrix (where n= represents the total number of threshold values of the dither matrix, and l is a divisor of n and represents the number of lines in the sub-scanning direction. ). Therefore, when processing is performed using this diagonal dither matrix, a gradation reproduction number of (n2+1) can be achieved in the same manner as when processing is performed using a square dither matrix in which the total number of thresholds is 02.

By the way, since the rectangular dither pattern has greater image asymmetry (vertical and horizontal resolution ratio) than the case of processing using the square dither pattern, the image quality deteriorates more. If the total number of threshold values of the dither matrix is expressed as 02, then the rectangular dither matrix can be expressed as (a+Xn27m) (where m is a divisor of n= and indicates the number of lines in the sub-scanning direction) . In this case, the image asymmetry Ar is defined by the following equation.

Ar=a/p...
- (1) Here, q and p represent the repetition pitch of the dither pattern in the horizontal and vertical directions, respectively. Based on this definition, we compare the image asymmetry between n=-64 and n=
-36 as an example, Figures 7 (A) and (B) respectively.
). The case of a rectangular dither matrix is indicated by "Δ", and the case of a diagonal dither matrix is indicated by "0". The results in this figure show that the diagonal dither matrix has smaller image asymmetry than the rectangular dither matrix.

In particular, it can be seen that the image asymmetry is the smallest when n=2111 and is close to the symmetry of a square dither pattern. In general, if the periods of the dither matrix in the main scanning direction and sub-scanning direction are Tl1l and TS, respectively, what is the diagonal dither matrix? Because of the shape, it is approximately Tl11
= (n 2/2m) +2. Ts=21. Therefore, the image asymmetry Ar is expressed by the following equation.

Ar=(n=/2m+2)/2m...---(2) Here, considering the relationship n=/2m>2m, in order for formula (2) to show the closest value to 1, It is necessary that the following conditions are met.

n 2 /2+n = 2111- (3) Therefore, when n = 2m, which satisfies this relationship, the image asymmetry is the smallest.

From the above results, it can be seen that processing using a diagonal dither matrix causes less image quality deterioration than processing using a rectangular dither matrix.

To summarize the above study results, when processing is performed using a square dither matrix with a total number of thresholds of 02, when processing is performed in dither matrix units, (n x n
) can only be processed in the window, so
Although n line buffer 7 memories are required for processing, if processing is performed using a diagonal dither matrix that can handle the same number of tone reproductions, the number of line buffer memories for processing only needs n/2, which is halved. . On the other hand, line buffer 7
If the memory is small (m x n27m), it is possible to process with a window of (m x n27m), but because of the large asymmetry of the image described above, the image cannot be satisfied. In other words, it can be seen that in order to reduce the image asymmetry to approximately 1 and reduce the amount of image memory, processing using a diagonal dither matrix is sufficient.

In other words, in this example, by processing with a diagonal dither matrix, the number of tone reproductions is exactly the same, and the asymmetry of the image (vertical and horizontal resolution ratio) is almost the same, compared to processing with a square dither matrix. Despite this, it is possible to reduce the amount of image memory in half.

The dither processing unit 22 converts the digital image signal into a dithered image signal 1 using such a diagonal dither matrix.
2, and this dithered image signal 12 is sent to the image processing section 2.
3 and the image storage unit 24 for image processing, the signal is input as a dithered image signal 13 to the density prediction processing unit 25.

As shown in detail in FIG. 2, the density prediction processing unit 25 stores the dithered image signal 13 in a memory 251 consisting of a line buffer of 4 lines, and
In order to predict the density of the original input image from the dithered image signal stored in the dithered image signal, that is, to reproduce the original input image by performing multivalue processing on the dithered image signal,
First, the dithered image signal from the memory 251 is supplied to the reference pixel selection section 252, and reference pixels are sequentially selected from the dithered image signal. Next, a reference pixel is selected in the reference pixel selection section 253 based on the selected reference pixel. Then, the density calculation section 254 determines the density of the reference pixel from the density of the reference pixel selected by the reference pixel selection section 253. By repeating the above processing, density prediction is performed for all pixels.

More specifically, the reference pixel selection section 252 sequentially determines the reference pixel (Of(i, j>) each time the address of the memory 251 where the dither image is temporarily stored is counted up.The reference pixel selection section 253 , this determined reference pixel (Of(i.

A reference pixel range centered on j)) is determined as a unit area based on the size of the dither matrix.

The reference pixel range obtained in this way is shown by broken lines in FIG. In this embodiment, the reference pixel range is an area of (4×16) pixels.

Furthermore, the density calculation unit 254 calculates 8IrJt (D
o (1, J)). The density of this reference pixel (
DQ (I, J)) can be expressed by the following formula.

Dq (1, J)=ΣDo (i, j
)/M (4) Here, M represents the total number of pixels in the dither matrix (64 in this example), and A represents a set of reference pixels.

When determining this density, by accumulating image data in a 4-line line buffer, it is possible to calculate the average density of the 64 dither matrices. Therefore, when dithered with a square dither matrix, 8
Although a line buffer for each line is required, the average density of each dither matrix can be accurately determined using a 4-line line buffer.

The 6-bit multi-value output image signal 14 determined in the above manner is supplied from the density calculation section 254 of the density prediction processing section 25 to the sublimation type thermal transfer printer forming the output processing section 26, so that it is faithful to the input image. An image output having tone reproduction characteristics can be obtained.

In the above embodiment, the case where the diagonal dither matrix shown in FIG. 3 is used has been described, but the invention is not limited to this. Moreover, the present invention is not necessarily limited to such a diagonal matrix, but can be similarly applied to a rectangular dither matrix. Further, in the case of the dither matrix shown in FIG. 9, it can be associated with a rectangular dither matrix as shown in FIG. 10, and the same effect as in the above embodiment can be obtained. Further, the threshold device may be of the dot concentrating type or dot dispersing type.

Furthermore, although the density prediction processing section 25 of the above embodiment performed density prediction based on the size of the dither matrix used in the dither processing section, the size of the reference range can be changed according to the output characteristics of the recording device. You may.

Further, in the above embodiment, an example of image editing of the image data of the image storage section 24 was shown, but the image processing section 23 may edit a plurality of input images, or the input image may be edited without image editing. This image processing device may also be used for copy output. Furthermore, when applied to facsimile and the like, since the dither matrix data is a two-chain system, the data transmission time is fast. By performing density prediction processing on the received binary image data, it is also possible to reproduce an image that is faithful to the original image.

[Effects of the Invention] As explained above, according to the present invention, an image signal is converted into a dithered image signal, and a multivalued image signal is formed by performing multivalue processing on the dithered image signal. Therefore, the capacity of the image memory for storing image information can be significantly reduced, and the device can be made smaller and less expensive.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an image processing device according to an embodiment of the present invention, FIG. 2 is a block diagram showing the detailed configuration of a density prediction processing section used in the image processing device of FIG. 1, and FIG. A diagram showing a diagonal dither matrix used in the device of FIG. 1, FIG. 4 a diagram showing a diagonal dither pattern used in the device of FIG. 1, and FIG. 5 a diagram showing various dither patterns.
Figure 6 is a diagram showing the correspondence between diagonal dither patterns and rectangular dither patterns, Figure 7 is a diagram showing the relationship between the size of the dither matrix and image asymmetry, and Figure 8 is the density of the device shown in Figure 1. FIGS. 9 and 10, which are explanatory diagrams of the reference pixel determination method in prediction processing, are diagrams showing other diagonal dither matrices and diagonal dither patterns, respectively. 21... Input processing section 22... Dither processing section 23... Image processing section

Claims (3)

[Claims] (1) An input processing unit that converts image information into a digital image signal, a dither processing unit that converts the digital image signal converted by this input processing unit into a dithered image signal using a dither matrix, and this dither processing An image processing device comprising: a multi-value processing section that performs multi-value processing on the dithered image signal converted by the section to obtain a multi-value image signal. (2) The image processing apparatus according to claim 1, wherein the dither matrix is a diagonal dither matrix. (3) an input processing section that converts image information into a digital image signal; a dither processing section that converts the digital image signal converted by this input processing section into a dithered image signal; and a dither processing section that converts the digital image signal converted by this input processing section into a dithered image signal; An image processing device comprising: a storage unit that stores image signals;