JPH07123246A - Binary picture reduction device - Google Patents

Abstract

PURPOSE:To prevent deterioration in picture quality due to error spread of a line drawing by calculating a 1st tentative reduction picture element value of a picture element block based on a counted black picture element number and a reduction rate and calculating a 2nd tentative reduced picture element based on an exception processing condition. CONSTITUTION:An adder section 2 counts number of block picture elements Gxy in a picture element block of a line buffer 1. A comparator section 3 compares the number of block picture elements Gxy with a preset threshold level T to set a 1st tentative reduced picture element Txy of the picture element block as Txy=1 (black level) in the case of Gxxy>=T and (to set the 1st tentative reduced picture element T., of the picture element block as Txy=0 (white level) in the case of Gxy<T. An except processing section 4 uses a conversion picture element block already converted and a picture element block processed at present to discriminate whether or not the picture element block has an except pattern. When the picture element block is the except pattern, a 2nd tentative picture element value Exy is set to 0 (white level) to provide an except discrimination signal s=0 and when not the except pattern, an exception discrimination signal s-1 is outputted. A reduced picture element decision section 5 sets the conversion picture element Qxy to be Txy in the case of s=1 and sets the conversion picture element Qxy to be Exy in the case of s=0.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binary image reducing apparatus for reducing a binary image consisting of pixels having a value of 0 or 1, and more particularly to a software fax for displaying a facsimile image on a display.

[0002]

2. Description of the Related Art In many conventionally used binary image conversion methods, the value of an original pixel around the converted pixel is referred to determine the value of the converted pixel. Here, a typical example is SP
The C method, the projection method, and the ETP method will be described. Hereinafter, the pixel value is set to 1 for black pixels and 0 for white pixels.

In the SPC method, the value of the original pixel closest to the converted pixel is used as the value of the converted pixel, and FIG. 2 shows a projected image of the converted image on the original image. It is used for conversion pixels.

Further, in the projection method, as shown in FIG. 3, the original pixel indicated by a dotted line and the conversion pixel indicated by a solid line are rectangular regions, and white pixels are determined depending on the area ratio of the conversion pixels. It determines a black pixel.

Specifically, if the sum I of the original pixel values P _{i, j} weighted by the area S _{i, j} occupied by the original pixels is greater than or equal to a certain threshold T, the value Q of the converted pixel should be 1 and smaller than the threshold. If it is 0. When this is expressed by an equation, I = S _1,1 P _1,1 + ... + S _{1, m} P _{1, m} (1) (1, m ≧ 0) If I ≧ T, then Q = 1 I <T Then Q = 0.

Further, the ETP method is a reduction method which is an improvement of the SPC method and prevents the disappearance of fine lines. An example of conditions for determining fine lines and a method of preventing the disappearance will be described with reference to FIG.

FIG. 4 shows the positional relationship between the current pixel and the converted pixel.

The following is a logical formula for determining a thin line having a line width of 2 between the pixels P _-1 , P ₀ closest to the converted pixels Q _-1 , Q ₀ .

[0009] _{(P 0,0 = P -3,0 = ~P} -1,0 = ~P -2,0) = (~P -1,0 + ~P -1, -1 + ~P -2 _{, -1} + to P _{-3, -1} ) = (to P _0,1 + to P _-1,1 + to P _-2,1 + to P _-3,1 ) (2) If the above equation is satisfied, It is determined that there is a thin line with a line width of 2.

Here, +, P _{i, j} , and P _{i, j} are respectively
Logical sum (or), pixel, inverted pixel (if P _{i, j} = 1
If P _{i, j} = 0 and P _{i, j} = 0, then ~ P _{i, j} = 1) is represented.

In FIG. 4, even if it is determined that there is a black thin line with a line width of 2 according to the above-described thin line determination condition, SP
In the C method, both the converted pixels Q ₋₁ and Q ₀ become white, and the black thin line disappears in the reduced image, but in the ETP method, Q ₀
The thin lines are preserved by converting to black.

[0012]

When binarizing a character or figure, a certain threshold is used, but when binarizing a halftone image such as a photograph, gradation is expressed by the density of black pixels. A dither method that changes the threshold is used. The error diffusion method, which is one of the dither methods, is currently in the mainstream because it has a large resolution and a large number of gradations and can produce a high-quality binary image without moire.

Therefore, the reduction of the line image and the error diffusion image will be described below.

An example of the error diffusion image is enlarged and shown in FIG.

In discussing the reduced image quality of a binary image,
The following matters are important for line images such as characters and figures and reduced images of dither images.

(A) Reduced image of line drawing A thin line is saved. This prevents missing and blurring.

(B) Reduced image of error diffusion image The gradation is output. Make sure that the density of the original image is not reversed. Pixel connection is reduced as in the original image.

Next, what happens when the conventional reduction method is applied to a line drawing will be described.

In the SPC method, a white pixel is selected even if there is a black line between converted pixels, so that missing occurs.

In the projection method, when the threshold value T is large, blanks occur, and when the threshold value T is small, the line becomes thick.

In the ETP method, thin lines between converted pixels are preserved.

Next, let us look at the reduction of the error diffusion image.

In the SPC method, since the error diffusion image has no periodicity in the arrangement of black pixels, the color of the original pixel selected as the conversion pixel becomes random. Therefore, in the reduced image, some black pixels are formed, and the image quality deteriorates.

In the projection method, since the area of the black pixel among the converted pixels is processed by the threshold value, the density can be expressed even in the reduced image, and the image quality is not extremely deteriorated.

In the ETP method, basically, as in the SPC method, a reduced image with black pixels is formed. Where the thin line saving process is performed, the color is reversed from that of the SPC method, and therefore, the gradation is reversed compared to the original image.

Table 1 summarizes the features of the reduced image according to the above-described conventional reduction method.

[0027]

[Table 1]

As shown in Table 1, none of the conventional reduction methods are effective for both line drawing and error diffusion image.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a binary image reducing apparatus that does not deteriorate the image quality of both a line drawing and an error diffusion image.

[0030]

An object of the present invention described above is to provide an extracting means for extracting a pixel block having a predetermined size according to a reduction rate from an original image which is a binary image, and the extracting means. Counting means for counting the number of black pixels in the extracted pixel block is compared with the number of black pixels counted by the counting means and a threshold value set in advance according to the reduction ratio, and according to the result. The first of the pixel blocks
First calculating means for calculating the provisional reduced pixel value of the pixel block and an exceptional process in which the pixel block and the pixel block for which the reduced image value has already been determined are preset for the pixel block according to the reduction rate. Determining means for determining whether the condition is met, second calculating means for calculating a second provisional reduced pixel value of the pixel block when the determining means determines that the condition is an exceptional processing condition, and the determining means. The selection means selects one of the first temporary reduced pixel value and the second temporary reduced pixel value as the reduced pixel value of the pixel block in accordance with the determination result by This is achieved by a binary image reduction device.

[0031]

The extracting means extracts a pixel block having a predetermined size according to the reduction rate from the original image which is a binary image.

The counting means counts the number of black pixels in the pixel block extracted by the extracting means.

The first calculating means compares the number of black pixels counted by the counting means with a preset threshold value according to the reduction rate, and according to the result, the first temporary value of the pixel block is compared. The reduced pixel value of is calculated.

The determining means determines whether or not the pixel block meets an exception processing condition preset according to the reduction rate, using the pixel block and the pixel block for which the reduced image value has already been determined.

The second calculating means determines the second value of the pixel block when the judging means judges that the condition is an exceptional processing condition.
The provisional reduced pixel value of is calculated.

The selecting means selects one of the first tentative reduced pixel value and the second tentative reduced pixel value as the reduced pixel value of the pixel block according to the determination result of the determining means. , Output to the next stage.

[0037]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a binary image reducing apparatus according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an embodiment of a binary image reduction device according to the present invention.

A line buffer 1 is connected to the binary image reducing apparatus according to the present embodiment for storing binary original image data input line by line.

The binary image reducing apparatus according to this embodiment extracts from the line buffer 1 a pixel block which is connected to the line buffer 1 and which is predetermined according to the reduction ratio, and is included in the pixel block. The addition unit 2 that counts the number of black pixels is compared with the number of black pixels counted by the addition unit 2 and a threshold value determined according to the reduction ratio, and the first provisional reduced pixel is obtained according to the result. An exception determination signal indicating whether or not the pixel block is an exception based on the reduction rate using the comparison unit 3 that calculates the value T _{x, y} and the pixel block and the converted pixel block that has been converted, and that indicates the determination result. Exception processing unit 4 for calculating and outputting s and the second provisional reduced pixel value E _{x, y}
And the value of the exception determination signal s output from the exception processing unit 4, the first temporary reduced pixel value T _{x, y} and the second
And a reduced pixel value determination unit 5 that selects and outputs one of the temporary pixel values E _{x, y} as a reduced pixel value.

The reduced pixel value output from the reduced pixel value determination unit 5 is stored in the line buffer 7 for storing.

Further, a reduction rate setting section 6 is connected so as to supply the reduction rate inputted from the outside to each of the adding section 2, the comparing section 3 and the exception processing section 4.

The operation of the binary image reducing apparatus having the above configuration will be described below by taking the case of a reduction rate 1 / n (n is an integer of 2 or more) as an example.

The line buffer 1 stores binary original image data input line by line.

The adder unit 2 has n × of the line buffer 1.
n pixel block g _x, the number of black pixels in the _y c _x, counts the _y.

As an example, FIG. 8 shows the case where n = 3.

The pixel block g _x indicated by the solid _line, the number of black pixels in the _y G _x, after counting the _y, then the main scanning direction right adjacent pixel blocks g _{x + 1,} the _y indicated by a dotted line Number of black pixels G
Count _{x + 1, y} .

Similarly, the pixel blocks are sequentially n (=
3) Moving in the main scanning direction or the sub-scanning line direction one by one.

The comparator 3, number of black pixels G _x, is compared with a threshold value T set in advance and _y, the pixel block g _x, a first temporary reduced pixel values T _x of _y, a _y G _{If x, y} ≧ T, T _{x, y} = 1 (black), and if G _{x, y} <T, set T _{x, y} = 0 (white).

When the reduction ratio is 1 / n, the threshold value T = n
By setting a low value, you can prevent missing lines.

In order to prevent thickening of characters and figures, the exception processing unit 4 uses the n × n pixel block currently being processed and the converted pixel block that has already been converted to determine whether the pixel block is an exceptional pattern. Make a decision.

Even if the pixel block includes three black pixels, the second tentative pixel value is used in the case of an exceptional pattern located beside the black pixel block as shown in FIGS. 9 (a) and 9 (b). _{Ex, y}
= 0 (white), and an exception determination signal s = 0 indicating whether or not exception processing has been performed is output.

If the pattern composed of the pixel block and the converted pixel block is not an exceptional pattern, s = 1 is output.

Here, the exception judgment signal s and the second temporary pixel value E _{x, y} may be the same value.

In the reduced pixel value determination unit 5, when s = 1, the converted pixel value Q _{x, y} = T _{x, y} is set, and when s = 0,
The converted pixel value Q _{x, y} = E _{x, y} .

First, the case where the image reducing apparatus of the present embodiment is applied to a line drawing will be described below in comparison with other reducing methods.

As an example, the case where the image shown in FIG. 5A is used as an original image and this image is reduced at a reduction ratio of 1/3 will be described.

In the SPC method, as shown in FIG.
Even if there is a black line between the converted pixels, white pixels are selected, resulting in missing.

In the projection method, when the threshold value T is large, blanks occur, and when it is small, the line becomes thick. Where 1 /
At the time of reduction by 3, the number of original pixels in the converted pixels is 3 × 3, which is nine. Therefore, I in the equation (1) is the number of black pixels.

Therefore, when the threshold value T = 4, that is, when there are four or more black original pixels among the converted pixels, as shown in (c) of FIG. 5, missing occurs. On the other hand, if T = 3 or less, FIG.
On the contrary, as shown in (d) of FIG.

In the ETP method, as shown in FIG.
Preserve thin lines between transformed pixels.

On the other hand, in the present embodiment, as shown in FIG. 5 (f), an image is obtained that is clearer than the threshold processing and the line is not thickened by the exceptional processing.

Next, in the case where the image reducing apparatus of this embodiment is applied to the error diffusion image, the image shown in FIG. 7A is used as an original image, and the image is reduced at a reduction ratio of 1/3. It will be described below in comparison with other reduction methods.

In the SPC method, since the error diffusion image has no periodicity in the arrangement of black pixels as shown in FIG. 7B,
The color of the original pixel selected as the conversion pixel becomes random. Therefore, in the reduced image, some black pixels are formed, which deteriorates the image quality.

In the projection method, as shown in FIG. 7C, the area of the black pixel in the converted pixels is processed by the threshold value, so that the density can be expressed even in the reduced image, and the extreme image quality can be obtained. There is no deterioration.

On the other hand, in the ETP method, as shown in (d) of FIG. 7, a reduced image in which black pixels are formed is basically formed as in the SPC method. Where the thin line storage processing is performed, the color is reversed from that of the SPC method, so that the gradation is reversed in some areas as compared with the original image. In the present embodiment, as shown in (e) of FIG. 7, since the ratio of the exceptional processing is small, the projection method with the threshold value T = n is substantially used, and a reduced image that represents gradation and has no deterioration in image quality is obtained. can get.

[0067]

According to the binary image reducing apparatus of the present invention, an image having no missing lines and no thick lines can be obtained in a line drawing. Further, in the error diffusion image, it is possible to obtain a reduced image that represents gradation and has no deterioration in image quality.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a value image reducing device according to the present invention.

FIG. 2 is an explanatory diagram of an SPC method.

FIG. 3 is an explanatory diagram of a projection method.

FIG. 4 is a diagram used for explaining a thin line determination condition of the ETP method.

FIG. 5 is an example of a reduced image with a line image reduction ratio of 1/3.

FIG. 6 is an enlarged view of an error diffusion image.

FIG. 7 is an example of a reduced image with a reduction rate of 1/3 of the error diffusion image.

FIG. 8 is an example of the number of black pixels in a pixel block when the reduction ratio is 1/3.

FIG. 9 shows a pattern of exception processing.

[Explanation of symbols]

 1, 7 Line buffer 2 Addition unit 3 Comparison unit 4 Exception processing unit 5 Reduced pixel value determination unit 6 Reduction ratio setting unit

Claims (1)

[Claims] 1. A binary image reducing apparatus for reducing a binary image composed of pixels having a value of 0 or 1, which has a predetermined size from an original image which is a binary image according to a reduction rate. Extraction means for extracting a pixel block, counting means for counting the number of black pixels in the pixel block extracted by the extraction means, and preset according to the number of black pixels counted by the counting means and the reduction rate And a threshold value that has been determined, and a first calculation unit that calculates a first provisional reduced pixel value of the pixel block according to the result, and the pixel block and the pixel block whose reduced image value has already been determined. Determining means for determining whether the pixel block corresponds to a preset exceptional processing condition according to the reduction ratio, and if the determining means determines the exceptional processing condition, Two Second calculating means for calculating a temporary reduced pixel value, and one of the first temporary reduced pixel value and the second temporary reduced pixel value depending on the judgment result by the judging means. A binary image reduction device, comprising: a selecting unit that selects as a reduced pixel value of a block.