JPH01186060A - Picture processing method - Google Patents

Abstract

PURPOSE:To obtain a picture data with fidelity to an original picture by estimating a density of the original picture based on a binarized data and a dither matrix and obtaining the binarized pseudo intermediate tone picture data subject to picture processing based on the estimated density. CONSTITUTION:A picture element calculation section 2 calculates the picture element of the original picture data corresponding to the selected picture element. Then a density estimate section 5 extracts a threshold value of the dither matrix corresponding to the position of the calculated picture element from the dither matrix storage section 3 and extracts the logic value of the calculated picture element. Based of the threshold value and the logic value, a table stored in the density estimate table storage section 4 is referenced to calculate the estimate density of the original picture at the location corresponding to the calculated picture element. The calculated estmate density is fed to a picture element decision section 6, which decides the logic value of the selected picture element based on the estimate density and the threshold value stored in the storage section 3 and stores it into the picture memory 1. Thus, the picture data with fidelity to the original picture is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION A) Industrial Application Field The present invention relates to an image processing method for performing image processing such as enlargement, reduction, or rotation on pseudo-halftone image data that has been binarized by dithering. In a conventional file storage or facsimile machine, an image read from an optical system is decomposed into dot-shaped pixels, and image data is formed in which each pixel is represented as a binary signal of black and white. Further, in such an apparatus, when reading a multi-tone image such as a photograph as a digital image, a dithering method is used to express halftones in a pseudo manner.

On the other hand, it is desirable that such an apparatus be capable of enlarging and reducing the formed binary image data through data processing, and various circuits for this purpose have been proposed. for example,
According to the circuit disclosed in Japanese Patent Application Laid-Open No. 61-179671, each pixel of the original image is output approximately twice in the vertical and horizontal directions, thereby performing double enlargement.

l/j Problem to be Solved by the Invention Incidentally, pseudo-halftone image data created by the dither method expresses the density of the original image by the distribution state of black and white pixels. When enlarged or reduced by the conventional method as described above, the distribution state of white and black pixels becomes the original (
In other words, the image data (before being enlarged or reduced) changes, the iUE changes, or the images become cluttered.

For example, if a 4x4 dither matrix as shown in Figure 5(a) is used for 3 units in the horizontal direction, it has a size of 12x4 pixels as shown in Figure 5('b); The original image data of fcl in the same figure, which is obtained by binarizing the original image in which half the density is at a density level of 12.5 out of 16 levels and the right half is at a density level of 6.5, is converted to If the image is enlarged twice vertically and horizontally using this method, the distance between the white pixel and the black pixel becomes large, resulting in a very rough image, as shown in 1dl of the same figure. Note that one square in the figure represents one pixel, and the shaded area represents a black pixel.

B) Means for Solving the Problems The present invention provides image processing that performs image processing such as enlargement, reduction, and rotation on pseudo-halftone image data obtained by binarizing an original image by a dithering method using a dithering matrix. The method is characterized in that the density of the original image is estimated from the dither matrix and image data, and the estimated density is used to form binarized pseudo-halftone image data that has been subjected to image processing.

(e) Function The present invention performs various image processing ( When enlarging, reducing, rotating, etc.), the density of the original image corresponding to this pixel is estimated from the relationship between the logical value of the pixel of the original image data and the threshold value of the matrix that determined the logical value of this pixel. The logical value of the pixel of the image-processed image data at the position corresponding to this pixel of the original image data is determined from the estimated density and the dither matrix.

(F) Embodiment Figure 1 is a block diagram showing an embodiment for carrying out the image processing method of the present invention. (1) shows original image data and image data obtained by performing image processing on this original image data. Image memory that stores individual images, +
2J is a pixel calculation unit that calculates the pixel of the original image data corresponding to each pixel of the image data after image processing, and (3) is the threshold value of the dither matrix (in this example, the 4× shown in FIG. (41 is a dither matrix storage unit that stores the dither matrix (IJ threshold)), which is created to estimate the density of the original image from the relationship between the pixel of the original image data and the threshold of the dither matrix at this pixel position. This is a density estimation table storage unit that stores a table.The principle of creating such a density estimation table is explained when the density of the original image is 0.
~N (N is a positive real number of 16 or less), and the larger the number, the higher the concentration, and the threshold of the dither matrix is 1 to T (T is a positive integer of 16 or less), The logical value of a certain pixel in the binarized pseudo-halftone image data is aO'', which means that the density of the original image at the position corresponding to this pixel is 0≦D<T (however, T is This indicates that it can be estimated that the threshold value of the dither matrix at the position corresponding to this pixel is
This indicates that the density [D of the original image can be estimated to be T≦D≦N. Based on this principle, a large number of concentration estimation tables can be created, but in this example, a concentration estimation table as shown in FIG. 2 is adopted from among them, and this is stored in the concentration estimation table memory. It is stored in section (4). (5) calculates the logical value of the pixel from the original image data stored in the image memo (Jan. ), and based on these logical values and thresholds, refer to the table stored in the density estimation table storage section (4), a density estimation unit that calculates an estimated density of the original image at a position corresponding to a pixel;
(6) calculates the logical value of the pixel of the image data after image processing based on the estimated density calculated by the estimation unit (5) and the threshold value of the dither matrix stored in the dither matrix storage unit (3). This is a pixel determining unit that determines.

Regarding the operation of the block diagram of such a configuration, please refer to the operation flowchart shown in FIG.
Explanation will be given using a case in which ×4 original image data is enlarged twice in the vertical and horizontal directions. Note that, according to the present invention, FIG.
) shows 24×8 image data obtained by enlarging the 12×4 original image data twice in the vertical and horizontal directions.

First, when obtaining 24×8 enlarged image data, one pixel (for example, the pixel in the first row and first column) constituting such data is selected (Sl), and the pixel calculation unit (2) selects the selected pixel (Sl). Calculate the pixel of the original image data corresponding to the pixel (S
l). In this example, the upper left corner of the image data after processing is
×2 41! pixel group l is located at the upper left corner of the original image data (first
The four 2×2 pixel groups to the right of these four pixel groups correspond to one pixel in the second row and first column of the original image data. Finally, the 2×2 411ii pixel group at the right end of the processed image data corresponds to one pixel at the right end (12th row, 4th column) of the original image data. The pixel calculation unit (2) calculates pixels so that each of the four 2×2 pixel groups of the processed image data corresponds to one pixel of the original image data. , the first row in the pixel group at the upper left corner of the image data after processing
The pixel corresponding to the pixel in the column becomes the pixel in the first row and first column of the original image data.

When the pixel of the original image data is calculated in this way, the density estimation unit (5) retrieves the threshold value of the dither matrix corresponding to the position of the calculated pixel from the dither matrix storage unit (3) (S5), and Based on these threshold values and logical values, refer to the table stored in the density estimation table storage section (4) to extract the original position of the calculated pixel. Calculate the estimated density of the image. In this embodiment, the threshold value "1" and the logical value '1'' are extracted for the pixel in the first row and first column calculated by the pixel calculation unit (2), and based on these, the estimated density is 9.
．． It is calculated as 0.

The calculated estimate 11M is sent to the pixel determining unit (6), which determines the logic of the selected pixel based on the estimated density and the threshold value stored in the IJ storage unit (3). According to this embodiment, based on the estimated density of 9.0 and the dither matrix threshold value "1", the selected pixel in the first row and first column has a logical value. It is determined as "1".

Thereafter, the logical values of all pixels constituting the 24x8 image data after the enlargement process are determined, and therefore the 12x4 original image data shown in Fig. 5 [cl] becomes a 24x8 image as shown in Fig. 4. The data is enlarged.

As seen from FIG. 4, compared to the pseudo-halftone image data enlarged by the conventional method shown in FIG. 5(d), the pseudo-halftone image data enlarged by the present invention is
Black pixels can be distributed densely, and the image becomes less coarse.

In the above explanation, since the original image data is expanded twice in the vertical and horizontal directions, the pixel calculation unit (2) divides the pixels that make up the image data after the expansion process into four pixel groups of roughly 2×2. The calculation is performed assuming that each corresponds to one pixel of the original image data, but if the original image data is multiplied by X in the horizontal direction and by 7 in the vertical direction, the pixel calculation unit (2) is XX7 in the pixels constituting the image data after the enlargement process.
The calculation is performed on the assumption that each of the pixel groups corresponds to one pixel of the original image data.

Note that, according to this embodiment, 1 of the calculated original image data
The density estimating unit (5) determines the estimated density of the original image corresponding to each pixel. ), the estimated density of the original image at the position corresponding to the surrounding pixels of one pixel in the calculated original image data is also determined, and these determined If the average value of the estimated density is used as the estimated density of the original image at the position corresponding to the calculated pixel, a more accurate estimated density can be determined.

On the other hand, the 24x8 image data shown in Figure 4 is used as the original image data, and it is reduced to 1/2 in length and width as shown in Figure 5 (
In the case of 12×4 image data as shown in C), the pixel calculation unit (2) calculates four pixels of 2×′2 of the original image data for one pixel that constitutes the image data after thinning. Calculate the pixel groups as corresponding ones. Specifically, the pixel in the first row and first column of the image data after reduction corresponds to the 2×2 four pixel group at the upper left corner of the original image data, and the pixel in the second row and column of the image data after reduction corresponds to The pixels in the first column correspond to the four 2×2 pixel groups to the right of the above pixel group in the original image data, and finally, the pixels in the 12th row and 4th column of the reduced image data correspond to the pixels in the original image data. This corresponds to a group of four 2×2 pixels at the lower right corner.

In this way, for each of the four pixels of the original image data calculated by the pixel calculation unit (2), the density estimation unit (51 is the position corresponding to the four pixels in the same manner as in the explanation of the above-mentioned enlargement process) Determine the estimated density of the original image of the determined 4
The average value of the two estimated densities is calculated and the result is sent to the pixel determining section (6). This point is different from the case of the enlargement processing described above.

Thereafter, the pixel determination unit (6) determines the logical value of the selected pixel in the same manner as in the above-described enlargement process.

In this way, the original image data can be reduced. Note that the 12×4 image data in FIG. 5 [cl] does not necessarily represent data obtained by reducing the 24×8 image data in FIG. 4 by the method described above.

Also, in the reduction process, when reducing the original image data to 1/x in the horizontal direction and 1/y in the vertical direction, the pixel calculation unit (21 constitutes the image data after the reduction process) Each pixel is calculated as corresponding to a group of xXy pixels of the original image data.

Note that the present invention can be applied to perform various image processing such as rotation processing in addition to the above-described enlargement and reduction processing.

(G) Effects of the Invention According to the present invention, the dither method using a dither matrix is used to enlarge pseudo-halftone image data that has been binarized.
When performing image processing such as reduction or rotation, the density of the original image is estimated based on the binarized image data and the dither matrix, and a binarized pseudo-halftone image is image-processed based on this estimated density. Get data. As a result, the density of image-processed image data does not change from the original image data or become rough, and image data faithful to the original image can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a schematic diagram showing an example of an ai estimation table, FIG. 3 is a flowchart showing the operation of the present invention, and FIG. 4 is a block diagram showing an example of an ai estimation table. FIG. 5) to fd) are schematic diagrams showing an example of enlarged image data to be used, and FIG.
Tol in the same figure shows the original image, fc) in the same figure shows original image data, and fdl in the same figure shows enlarged image data obtained by the conventional method. (3)... Dither matrix storage unit, (4)... Density estimation table storage unit, (5)... Density estimation unit, (6
)...Pixel determination section.

Claims (1)

[Claims] (1) An image processing method that performs image processing such as enlargement, reduction, rotation, etc. on pseudo-halftone image data obtained by binarizing an original image by a dithering method using a dithering matrix, the method comprising: and an image processing method, comprising estimating the density of the original image from the image data, and forming binarized pseudo-halftone image data subjected to image processing using the estimated density.