JPH0553350B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image enlarging/reducing method for at least one of enlarging or reducing an image.

(Prior art) As an image enlargement/reduction method for enlarging or reducing an image using a pixel density conversion method, the SPC method,
The logical sum method, 9-division method, projection method, etc. are known.

(Problems to be Solved by the Invention) Problems with these conventional methods include the fact that the lines are conspicuously blurred or missing.
The biggest problem is that moiré fringes occur when a halftone image with a periodic structure, such as a binarized image expressed using the systematic dither method, is enlarged or reduced.

The present invention has been made in view of this point, and its purpose is to provide an image enlargement/reduction method that can easily enlarge/reduce even a binarized image with a periodic structure without causing moiré fringes. There is a particular thing.

(Means for Solving the Problems) A typical overview of the present invention for solving the above problems is as follows.

That is, a step of dividing a binarized image to be enlarged/reduced into blocks of a predetermined size, and a step of counting at least one of the number of black pixels or the number of white pixels in each block. a step of estimating the density level of each block using the counting results; and a step of obtaining a density matrix pattern of a size corresponding to the enlargement/reduction magnification for each block based on the estimated density level of each block. and a density matrix pattern of a size corresponding to the enlargement/reduction magnification, are arranged and reconstructed according to the arrangement of the blocks, and the reconstructed image is made into an enlarged/reduced image. It is.

(Example) Hereinafter, the image enlargement/reduction method of the present invention will be specifically explained using FIGS. 1 to 4.

First, there is a binarized image that is to be enlarged/reduced.
can be easily obtained using a dither matrix of size as a threshold. For example, in the case of gradation painting, the setting width of the threshold values that make up this dither matrix is determined by the reflection density.
Set it as wide as 0.1 to 1.4, and set the reflection density for line drawings.
It is preferable to narrow it to about 0.1 to 0.3. This is to prevent the image from becoming blank or thick. Further, different types of dither matrices may be used for gradation drawings and line drawings. Note that the binarization method may be a method other than the dither method, such as a density pattern method or a dot method.

In an example of the method of the present invention illustrated in FIG. 1, first, if the image is not a binarized image, the above-mentioned binarization is performed (step). Figure 2 shows an original image A (see Figure 2 B) created by dithering using a dot-distributed (Bayer type) dither matrix DM1 (see Figure 2 A) with a size of 4 x 4.
An example is shown in which the image is binarized to obtain the binarized image B shown in FIG. 2C. In this figure, the numbers in the dither matrix DM1 and in the original image A indicate standardized density levels, and the pixels in the shaded area of the binarized image B indicate that they are black pixels.

In the next step, the binarized image is divided into blocks of appropriate size. In FIG. 2C, it is divided into 4×4 sizes. Then, the density level of each block is estimated by counting the number of black pixels (or the number of white pixels) in each block (step) to obtain a first density matrix pattern (step).
Here, the block size is the dither matrix (threshold value group) used to obtain the binarized image.
(4×4 or 8×8), preferably smaller than the dither matrix size. In this way, high resolution can be maintained while increasing the number of gradations. In FIG. 3B, the number of black pixels in each block is taken as the normalized average density level. Therefore, the numbers in each block in FIG. 3B indicate the number of black pixels in each block in FIG. 2C, as well as the average density level. Figure 3C shows the first density matrix pattern printed on each block based on the number of black pixels in each block.
The density pattern is determined by comparing the density level of each block with the dot concentration type (spiral type) dither matrix DM2. For example, in the case of block diagram BK1, its density level is 7, so the dither matrix in Figure 3A
A portion of DM2 with a density level of 7 or less becomes a black pixel, forming a density matrix pattern such as block BK1 in FIG. 3C.

After obtaining this first density matrix pattern, a second density matrix pattern of a size corresponding to the enlargement/reduction magnification is obtained for each block (step), and these are arranged in block order to form an enlarged/reduced image. Get (step). Figure 4A is an enlarged image obtained in this way with an enlargement factor of 5/4.
Figure b is a reduced image with a reduction magnification of 3/4. here,
The size ratio of the first and second density matrix patterns corresponds to the vertical and horizontal enlargement/reduction magnification,
The vertical and horizontal sizes of the second density matrix pattern are the vertical and horizontal sizes of the first density matrix pattern multiplied by the vertical and horizontal expansion/reduction magnification. Therefore, in the example of FIG. 4 where the vertical and horizontal magnifications are equal, the size in FIG. 4A is 5×5, and the size in FIG. 4B is 3×3.

In this example, we are trying to find a mother pattern obtained by two-dimensionally arranging the corresponding patterns of the first density matrix pattern when it is divided by the size of the second density matrix pattern. A pattern having the same positional relationship as the second density matrix pattern is cut out and used as the corresponding second density matrix pattern. FIG. 5 is an explanatory diagram (magnification: 5/4) showing an example of obtaining a second density matrix pattern from a first density matrix pattern.
density matrix pattern (size 4x4)
The plane consisting of blocks f ₁₁ , f ₁₂ , f ₁₃ , ..., f ₂₁ , f ₂₂ , ..., ... of the second density matrix pattern (size is 5×5) F ₁₁ , F ₁₂ , _F13 ,
..., F ₂₁ , F ₂₂ , ..., ... is shown. First, as a second density matrix pattern corresponding to block F ₁₁ , all blocks f ₁₁ ,
The position of block F ₁₁ is determined from the mother pattern assuming that f ₁₂ , f ₁₃ , ..., f ₂₁ , f ₂₂ , ..., ... contain the same first density matrix pattern corresponding to block f ₁₁ . Use a pattern cut out from . Similarly, the second density matrix pattern corresponding to block _f12 includes all blocks.
Blocks are added to f ₁₁ , f ₁₂ , f ₁₃ ,…, f ₂₁ , f ₂₂ ,…,…
From the mother pattern, which is assumed to contain the same first density matrix pattern corresponding to f ₁₂ ,
Use the pattern cut out at block F ₁₂ . That is, as the second density matrix pattern corresponding to block Fij, the same first density matrix pattern corresponding to block fij is applied to all blocks f ₁₁ , f ₁₂ , f ₁₃ , ..., f ₂₁ , f ₂₂ , ..., ... A pattern at the position of block Fij is cut out from a mother pattern that is assumed to contain a density matrix pattern of . The above-mentioned FIG. 4A shows the second density matrix pattern obtained in this way (FIG. 3C is taken as a column in the same figure) arranged on a plane. The same applies to Figure 4B.

In addition, in the above step, if you do not use the number of black pixels obtained in the step as is, but instead use a modified number of black pixels that takes into account the number of black pixels of surrounding blocks, etc., various image processing such as image enhancement can be performed at the same time. I can do it. Furthermore, if the matrices DM1 and DM2 are constructed of the same matrix, the capacity of the memory for storing them can be reduced.

Furthermore, in the method of the present invention, the above-mentioned steps are omitted, and the binarized image obtained in the step (corresponding to FIG. It can also be used as a density matrix pattern (corresponding to FIG. 3C).

Further, a specific method for obtaining the pattern of each block after scaling described above may be to actually configure the above-mentioned mother pattern in memory and read data at a predetermined address from it to obtain the pattern. , this would require an extremely large memory capacity. Therefore, instead of actually creating a mother pattern, attention may be paid to the periodicity of the pattern, and the density of each pixel may be determined in the following manner to obtain a pattern after scaling.

That is, in the case of enlargement (magnification m/n), the x-th pattern in the I-th block in the row direction of a new block (block after enlargement) is the same as the pattern in the I-th block in the row direction of the block before enlargement. AD1=mod[x+mod[(I-1)(m-n),n]
+1-2,n]+1 The pattern in the y-th column in the J-th block in the column direction, which is equal to the pattern in the +1st row, is AD2=mod in the J-th block in the column direction of the block before expansion. [y+mod[(J-1)(m-n),n]
+1-2,n]+1st column pattern; on the other hand, in the case of reduction (magnification m/n), the x-th row in the I-th block in the row direction of the new block (block after reduction) The pattern is AD1=mod[x+mod[(I-1)(n-ln-ml),
n]+1-2, n]+1 The pattern in the y-th column in the J-th block in the column direction of the new block, which is equal to the pattern in the row direction, is AD2 in the J-th block in the column direction of the block before reduction. =mod[y+mod[(J-1)(n-ln-ml),
n]+1-2, n]+1 Equivalent to the pattern in the 1st column.

Here, mod [p, q] is the remainder of p÷q,
Of course it is smaller than q.

Therefore, if the pixel density of each block before scaling is stored in memory, it can be easily updated by reading out the pixel density in the corresponding block before scaling by using AD1 and AD2 as addresses in the row and column directions. You can get various block patterns.

A specific configuration example for carrying out the above image enlargement/reduction method is shown in FIG.

In this configuration example, the black pixel counting means 4, the first density matrix pattern creation means 6, and the second density matrix pattern creation means 8 are connected via buffer memories 5 and 7, and the processing data is Processing is performed in a pipeline by repeating temporary storage and reading.

Further, the memory 3 is provided to temporarily store data imaged by the imaging system 1 and binarized by the binarization means 2 (for example, binarized using a dither threshold value). The black pixel counting means 4 reads data from the memory 3 and counts the total number of black pixels for each predetermined block size. Also, memory 9
is the second density matrix pattern creating means 8
and the printer 10.

(Effects of the Invention) As explained above, in the present invention, details at the 1-pixel level are ignored, and large The average concentration state is estimated for each block (division), and based on the estimation for each block, binarization (second sampling) is performed again for each block to obtain a first concentration matrix. Therefore, the correspondence (periodicity) for each pixel is no longer present between the first sampling and the second sampling, and therefore, the cause of moiré is eliminated. Then, by arranging this first density matrix to create a mother pattern, and cutting out a pattern according to the magnification from the mother pattern, the characteristics of each block are not destroyed (for example, the halftone dot pitch remains unchanged) and are Obtain an enlargement/reduction pattern corresponding to the block while making the most of it. Therefore,
It is possible to greatly reduce moiré and reproduce a continuous tone image by enlarging or reducing it as a binary image without significantly deforming the original image.

The resolution can be controlled by appropriately selecting the block size, and furthermore, since the first density matrix pattern is designed to break the periodicity at the pixel level and prevent moiré from occurring, When converting to the second density matrix, it becomes possible to apply and develop additional electrical processing such as gradation correction such as image enhancement and selection of various binarization patterns.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing an example of the method of the present invention, FIG. 2 is an explanatory diagram showing an example of binarization in FIG. 1, and FIG. 3 is an explanatory diagram of the first density matrix pattern in FIG. , FIG. 4 is an explanatory diagram of the second density matrix pattern (enlarged/reduced image) in FIG. 1, and FIG. 5 is an explanation of the method for obtaining the second density matrix pattern from the first density matrix pattern. 6 are block diagrams showing a specific example of the configuration for carrying out the image enlargement/reduction method of the present invention. 1... Imaging system, 2... Binarization means, 3, 5,
7, 9...memory, 4...black pixel counting means, 6...
...first density matrix pattern creation means, 8
...second density matrix pattern creation means,
10...Printer, DM1, DM2...Dither matrix, A...Original image, B...Binarized image, _f11 , _f12 ,..., _f21 , _f22 ,...First density matrix block of tux pattern, F ₁₁ , F ₁₂ ,
..., F ₂₁ , F ₂₂ , ... blocks of the second density matrix pattern.

Claims (1)

[Claims] 1. A step of dividing a binarized image to be subjected to enlargement/reduction conversion into blocks of a predetermined size, and for each block, determining at least one of the number of black pixels or the number of white pixels in the block. A step of counting, a step of estimating the concentration level of each block using the counting results, and a step of estimating the concentration level of each block based on the estimated concentration level of each block.
A step of obtaining a density matrix pattern of a size corresponding to the enlargement/reduction magnification for each block, and arranging the density matrix pattern of a size corresponding to the enlargement/reduction magnification according to the arrangement of the blocks. The reconstructed image is enlarged and
A method for enlarging/reducing an image, which is characterized by reducing the image. 2. The step of obtaining a density matrix pattern of a size corresponding to the enlargement/reduction magnification for each block based on the estimated density level of each block includes the following steps. The image enlargement/reduction method described in scope 1. Step: Obtain a binarized pattern of the same size as each block according to the estimated density level of each block. Step: Assuming that the binarization patterns of the same size are repeatedly lined up, a mother matrix of the binarization patterns is assumed, and a matrix pattern of a size corresponding to the enlargement/reduction magnification is cut out from the mother matrix. The cut out pattern is used as an enlarged/reduced density matrix pattern for the corresponding block.