JPH05191637A - Picture magnification device - Google Patents

Abstract

PURPOSE:To reduce the deterioration in the picture quality for a character picture (intermediate tone picture) by decreasing (increasing) the number of surrounding picture elements used for a parameter in the case of multi-value processing arithmetic operation when a magnification ratio is small (large). CONSTITUTION:A binary picture input section 1 receives binary picture information and a multi-value processing section 2 takes notice of multi-picture elements of the inputted binary picture information and applies multi-value processing to each picture element through the arithmetic operation employing its noted picture element and the surrounding picture elements as a parameter, and an arithmetic operation method changeover means 2a selects number of the surrounding picture elements being the parameter and the arithmetic operation equation in the case of the arithmetic operation. Furthermore, a magnification section 3 increases/decreases number of picture elements in response to the magnification of the picture size to magnify/reduce the picture size and a binarizing section 4 binarizes the multi-value picture information by the error spread method. When the magnification ratio of the picture size is small in the case of the arithmetic operation, number of the surrounding picture elements being the parameter is decreased and when the magnification ratio of the picture size is large in the case of the arithmetic operation, number of the surrounding picture elements being the parameter is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image scaling device for enlarging or reducing a binary image at an arbitrary magnification.

[0002]

2. Description of the Related Art A document image handled by a facsimile machine or various image processing apparatuses includes a black and white image such as a character or a line drawing (hereinafter referred to as a character image) and a halftone image such as a picture or a photograph. is there.

Usually, the image information of a character image is image information obtained by reading an original image with a scanner and simply binarizing the obtained image signal at a constant threshold level. On the other hand, the image information of the halftone image is image information obtained by binarizing the image signal obtained by reading the original image by pseudo halftone processing such as dither processing and error diffusion processing.

By the way, in the above apparatus, the number of pixels of the image information is increased or decreased by a linear interpolation method or the like, and the image size is often changed.

In general, a character image has little deterioration in image quality due to such scaling, but a halftone image has significant deterioration in image quality due to scaling. For example, when the halftone image is greatly enlarged by increasing the number of pixels, moire occurs in the image or the density change is noticeable, and the image quality deteriorates.

In order to reduce such image quality deterioration, for example, as disclosed in Japanese Patent Laid-Open No. 2-239380, binary image information is once multi-valued and scaled, and then binarized again. Things have been proposed. In this way, by scaling the multi-valued image information, in the case of a halftone image,
Image quality is improved by eliminating moire and unnatural changes in density.

However, conventionally, the binary image information has been multi-valued by a constant calculation method regardless of the type of image to be processed and the scaling ratio.

In this case, when the image information of the character image is multi-valued, the pixels that should originally have the white density or the black density have many intermediate areas, and the outline of the character becomes unclear. On the contrary, the image quality was deteriorated. Further, the edge portion of the halftone image also has an unclear contour and deteriorates the image quality, as in the case of the character image.

[0009]

As described above, the prior art is as follows.
When the binary image information is once multi-valued and scaled, there is a problem that the image quality deteriorates at the edge portion of the character image or the halftone image.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to provide an image scaling device which can always obtain good image quality for both character images and halftone images.

[0011]

To this end, in each invention of the present application, each pixel of the binary image information is focused, and each pixel is multi-valued by an operation using the pixel of interest and surrounding pixels as parameters. In the first aspect of the invention, however, in the calculation, the number of surrounding pixels as a parameter is reduced when the scaling ratio of the image size is small, and when the scaling ratio is large, the number is reduced. I try to do a lot.

According to the second aspect of the invention, it is determined whether each pixel is an edge portion or a non-edge portion of the image, and in the above calculation, when the pixel of the edge portion is multivalued, a parameter is set. The number of surrounding pixels is set to be small, and the number is increased when the pixels in the non-edge portion are multivalued.

According to the third aspect of the invention, when each pixel is an edge portion, the edge direction is further determined, and the positions of the surrounding pixels as parameters are changed according to the edge direction.

In the fourth invention, in the case of the above calculation, in the case of the image information obtained by simple binarization, the number of surrounding pixels as a parameter is reduced, and the image is obtained by the pseudo halftone process. In the case of image information, the number is increased.

In the fifth aspect of the invention, when the image information obtained by the simple binarization and the image information obtained by the pseudo halftone processing are mixed, they are discriminated from each other. In the case of pixels, the number of surrounding pixels as a parameter is reduced, and in the case of pixels in the pseudo halftone processing portion, the number is increased.

[0016]

When the number of surrounding pixels used as a parameter is increased during the above-described calculation for multi-value quantization, the difference in density between pixels is smoothed, so that the image quality of a halftone image is improved. On the other hand, in the character image or the edge portion of the image, the smaller the number of surrounding pixels as the parameter, the clearer the image.

In the first aspect of the invention, when the variable magnification ratio is small, the number of surrounding pixels used as the parameter is reduced, so that the deterioration of the image quality of the character image can be prevented. In addition, when the variable power ratio is large and the deterioration is apt to be noticeable in the halftone image, since the above number is increased, the deterioration of the halftone image can be reduced.

In the second invention, at the edge portion of the image,
Since the number of surrounding pixels is reduced and the number of peripheral pixels is increased, the image quality deterioration of each image portion is reduced.

In the third invention, since the positions of the surrounding pixels which are the above parameters are further changed according to the edge direction,
The pixel density is corrected according to the image content, and the image quality is further improved.

According to the fourth aspect of the invention, in the case of image information of a character image which is usually simple binarized, the number of surrounding pixels is reduced, so that the image quality deterioration of the character image is reduced and the normal pseudo halftone is used. In the case of processed image information, since the number of processed image information is increased, deterioration of the image quality of a halftone image is also reduced.

According to the fifth aspect of the invention, when the image information obtained by the simple binarization and the image information obtained by the halftone processing are mixed, the same effect as the above can be obtained.

[0022]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the configuration of an image scaling device according to the first embodiment of the present invention. In the figure, a binary image input unit 1 inputs binary image information, and is, for example, an image receiving unit of a scanner device or a facsimile device. The multi-value conversion unit 2 multi-values each pixel by paying attention to each pixel of the input binary image information and performing an operation using the pixel of interest and surrounding pixels as parameters.
The calculation method switching means 2a is for switching the number of surrounding pixels and the calculation formula used as parameters in the calculation.

The scaling unit 3 increases / decreases the image size by increasing / decreasing the number of pixels by a known technique according to the scaling ratio of the image size. The binarization unit 4 binarizes the multivalued image information by the error diffusion method. The image output unit 5 outputs the processed image information, and is, for example, an image transmission unit of an image recording device or a facsimile device.

Calculation method switching means 2a in the multi-value quantization section 2
Also, a signal for instructing a scaling ratio is input to the scaling unit 3.

If the image scaling apparatus of the present embodiment is activated with the above configuration, a signal indicating the scaling factor r is input from the outside. This scaling factor r is set by the operator or, in the case of a facsimile machine, determined by communication with the partner device.

The binary image input unit 1 sequentially inputs binary image information from an external device (not shown). The multi-value quantization unit 2 inputs the image information pixel by pixel and extracts eight surrounding pixels centered on the pixel of interest. Here, as shown in FIG. 2, it is assumed that the respective values of the surrounding pixels are A to H, the value of the target pixel is X, and the value obtained by multivalued the target pixel is X ′. In this embodiment, the number of gradations for multi-valued conversion is 8 gradations of densities “0” to “7”.

As shown in FIG. 3, when the scaling factor r is set to 95% or more and less than 105%, the multi-value quantization unit 2 multi-values the value X of the pixel of interest into X'according to the following equation. Turn into.

X ′ = 7 · X (1) Further, the scaling ratio r is 80% or more and less than 95% or 10
When it is 5% or more and less than 120%, it is multivalued by the following equation.

X ′ = 3 · X + B + D + E + G (2) Further, when the scaling factor r is less than 80% or 120% or more, it is multivalued by the following equation.

X ′ = X + B + D + E + G + (A + C + F + H) / 2 (3) The multi-value quantization unit 2 sequentially outputs image information multi-valued into 8 gradations by such calculation.

The scaling unit 3 enlarges or reduces the image size of the multi-valued image information by increasing or decreasing the number of pixels in the horizontal and vertical directions by a predetermined method. For example, in the case of enlargement, the number of pixels is increased according to the scaling ratio by the linear interpolation method.

The binarization unit 4 binarizes the variable-magnification multivalued image information by a known error diffusion method. The image output unit 5 outputs the binarized image information by a predetermined method.

As described above, in the present embodiment, when the binary image information is multivalued, if the scaling ratio is small, surrounding pixels are not included in the parameters of the arithmetic expression, and the target pixel is set to a predetermined value. The gradation level is converted to white or black. This prevents each pixel of the character image from changing to an intermediate density and deteriorating the image quality.

Further, the larger the variable power ratio, the larger the number of surrounding pixels as a parameter of the arithmetic expression. In the case of a halftone image, when the zoom ratio becomes large, a sharp change in density between pixels is noticeable and the image quality is apt to deteriorate, but by increasing the number of surrounding pixels as a parameter as described above, the density of the pixel of interest can be reduced. Since it is smoothed according to the density of surrounding pixels,
The deterioration of image quality is reduced.

In the above embodiment, the variable power ratio is divided into three ranks, but it is natural that the arithmetic expressions may be set by dividing into more ranks.

FIG. 4 shows a second embodiment of the present invention.

In the figure, the same reference numerals as those in FIG. 1 indicate the same parts, and in this embodiment, an edge portion judging portion 6 is newly provided. The edge determination unit 6 determines pixels in the edge portion that is the outline of the image.

With this configuration, when the image scaling apparatus of this embodiment is activated, the binary image input section 1 sequentially inputs binary image information, and the edge section determination section 6 determines that each input pixel is an edge section. It is determined whether or not it is a pixel. For this determination, for example, in the 3 × 3 pixel range shown in FIG. 2, each pixel pattern in the case where the target pixel corresponds to an edge portion is stored in advance, and those stored patterns are compared with the actual pixel pattern. By doing.

The multi-value quantization unit 2 multi-values the binary image information by each calculation method according to the above determination result. That is, as shown in FIG. 5, when the pixel to be processed is the pixel of the edge portion, the value X of the pixel of interest is multivalued into X ′ according to the equation (1). If the pixel is not the edge portion, it is multi-valued by the equation (3).

The scaling unit 3 scales the multi-valued image information at a predetermined scaling ratio, the binarization unit 4 binarizes the image information, and the image output unit 5 converts the image information to 2. Outputs the binarized image information.

As described above, in the present embodiment, when the pixel to be processed is the edge portion, the target pixel is multivalued without including the surrounding pixels in the parameter of the arithmetic expression. It is possible to prevent the pixel of (3) from changing to an intermediate density and degrading the image quality.

Further, in the non-edge portion, since the density of the pixel of interest is calculated by using many surrounding pixels as parameters of the arithmetic expression, each pixel density is smoothed according to the surrounding pixels, so that the image quality is deteriorated. Is reduced.

FIG. 6 shows a third embodiment of the present invention.

In the figure, the difference from FIG. 4 is that a direction-specific edge judgment unit 7 is provided instead of the edge judgment unit 6. The edge-by-direction edge determination unit 7 determines pixels in the edge portion, which is the contour of the image, by edge direction.

With this configuration, when the image scaling apparatus of this embodiment is activated, the binary image input unit 1 sequentially inputs binary image information. The edge-by-direction determination unit 7 determines whether or not each input pixel is an edge portion of an image for each edge direction.

That is, the edge patterns P1 to P in FIG.
4 shows an example of a pixel pattern determined by the direction-based edge portion determination unit 7. In each drawing, blank pixels are “white”, cross hatched pixels are “black”, and broken line hatched pixels are “white” or “black”. The edge pattern P1 is
When the pixel of interest is located at the left end of the white area of the image,
The edge pattern P2 is a case where the pixel of interest is located at the upper end of the white area. The edge pattern P3 is a case where the pixel of interest is located at the left end of the black region. Further, the edge pattern P4 is a case where the pixel of interest is located at the left end of the white region inclined at 45 degrees.

The direction-specific edge portion determination unit 7 determines various edge patterns in which the pixel of interest is located in each direction of the white or black area of the image as described above. Then, when one edge pattern is determined, the determination result is output. The multi-value quantization unit 2 multi-values the pixel of interest by a calculation method according to the determination result.

For example, when the input image information is determined to be the edge pattern P1 or P3, the value X of the pixel of interest is X '.
Multi-valued.

X ′ = 5 · X + C + H (4) When the edge pattern P2 is determined, the value is multivalued by the following equation. X ′ = 5 · X + F + H (5) Further, when the edge pattern P4 is determined, the value is multivalued by the following equation. X ′ = 5 · X + E + G (6) As described above, the direction-based edge portion determination unit 7 performs the calculation using the indeterminate pixel that may be “white” or “black” and the target pixel as parameters when determining the edge pattern. Thus, the pixel of interest is multivalued. On the other hand, when the edge pattern is not determined, multi-valued processing is performed by the calculation method for the non-edge pixel described in FIG. The multivalued image information is processed in the same manner as in the above-described embodiment.

As described above, in the present embodiment, when the pixel to be processed is the edge portion, the pixels around the image area in which the pixel is located are used as the parameters of the arithmetic expression. Is also corrected to the density corresponding to the image area, and the deterioration of the image quality is further reduced as compared with the embodiment of FIG.

FIG. 8 shows a facsimile apparatus according to the fourth embodiment of the present invention.

In the figure, the same reference numerals as in FIG. 6 indicate the same parts. In the figure, a photoelectric conversion unit 8 is a scanner device that reads an original image to obtain an analog image signal. A /
The D conversion 9 converts the analog image signal into a digital signal. The binarization unit 10 binarizes the image signal by a simple threshold value with a constant threshold level or by a halftone process such as an error diffusion method. The memory 11 stores the binary image information. The transmission unit 12 transmits an image to a communication partner according to a known procedure by making and receiving a call.

With this configuration, the facsimile apparatus of this embodiment first executes an image information accumulation operation during the transmission process. In this case, the operator can select the desired
Set the valuation method. The set binarization method is instructed to the binarization unit 10 and the multivalued unit 2.

When the facsimile apparatus starts reading the original image, the analog image signal output from the photoelectric conversion unit 8 is converted into a digital signal of a constant gradation by the A / D converter 9, and the binary signal is converted by the binarization unit 10. Valued. The binarized image information is temporarily stored in the memory 11.

After that, the transmitting unit 12 transmits to the other party and executes a known transmission control procedure. At this time, the recording paper size of the destination device is determined, and the scaling factor is determined if necessary.

After that, the binary image information is sequentially read from the memory 11 and multivalued by the multivalue conversion unit 2. in this case,
As shown in FIG. 9, when the binary image information is obtained by simple binarization, the multi-value quantization unit 2 increases the value X of the pixel of interest to X ′ according to the equation (1). Quantify. Further, when it is obtained by a pseudo halftone process such as an error diffusion method, it is multi-valued by the equation (3).

The image information scaling unit 3 thus multi-valued
To change the magnification. Then, the binarizing unit 4 re-binarizes the data, and then the transmitting unit 12 transmits the binarized data.

By the way, when reading a manuscript of a character image, the normal operator sets to simple binarization. Also,
When reading a document of a halftone image such as a photograph, the halftone processing is set.

In this embodiment, the image information obtained by the simple binarization is binarized without using the surrounding pixels as parameters, while the image information obtained by the halftone processing is binarized by using the surrounding pixels as parameters. ing. As a result, similarly to each of the above-described embodiments, the deterioration of the image quality of each of the character image and the halftone image is reduced.

FIG. 11 shows an image scaling device according to the fifth embodiment of the present invention.

6, the same reference numerals as those in FIG. 6 indicate the same parts, and the difference from FIG. 6 is that instead of the direction-specific edge part judgment part 7, a halftone part judgment part 13 and a character part judgment part 1
4 is provided. The halftone determination unit 13 determines the pixels of the halftone region in the image in which the character image and the halftone image are mixed in one page, and the character determination unit 14 determines the pixels of the character image region. Is determined.

With this configuration, when the image scaling device of this embodiment is activated, the binary image input section 1 sequentially inputs binary image information. The halftone part determination unit 13 determines whether or not each input pixel is a pixel in the intermediate density region, and outputs the determination result. Further, the character portion determination unit 14 determines whether the pixel is in the character image area and outputs the determination result. To determine these image areas, for example, in the 3 × 3 pixel range shown in FIG. 2, pixel patterns in various image areas are stored in advance and the stored patterns are compared with the actual pixel patterns. By doing.

By the way, in this case, the halftone judgment section 13
There is a case where the determination result of 1 and the determination result of the character part determination unit 14 are inconsistent. One is the case where the halftone portion determination unit 13 determines that the pixel of interest is a halftone region, and the character portion determination unit 14 determines that it is a character image region. The other is a case where neither area is determined. In the present embodiment, when one of the halftone portion determination unit 13 and the character portion determination unit 14 outputs a predetermined determination result, the determination result is validated. Then, when the determination result is output from both of them, or when the determination result is not output from either of them, the area is unclear.

As shown in FIG. 11, the multi-value quantization unit 2 multi-values the value X of the pixel of interest into X'in accordance with the equation (1) when it is determined that it is a character image area. In addition, when it is determined that the image is a halftone image area, it is multi-valued by the equation (3). Further, when the area is unknown, the value is multivalued by the equation (2).

As described above, in this embodiment, it is determined whether each pixel is a character image area or a halftone image area, and each pixel is multi-valued by an operation suitable for each. There is. As a result, the image to be scaled is reduced to 1
Even when a character image and a halftone image are mixed in a page, deterioration of image quality of each image can be suppressed.

In the above equation (1), the term of the parameter of the surrounding pixels is completely eliminated, but some terms of the parameter of the surrounding pixels may be set. In that case, the image quality of the halftone image is Of course, it can be improved.

In each of the above-described embodiments, an example in which the binary image information is converted into multi-valued image information of 8 gradations has been described. However, it goes without saying that the number of gradations can be set arbitrarily.

[0069]

As described above, according to the first aspect of the present invention, when the variable magnification ratio is small, the number of surrounding pixels used as a parameter in the multi-value quantization operation is reduced. When the deterioration is reduced and the variable magnification ratio is large, the number is increased, so that the deterioration of the image quality of the halftone image is reduced.

In the second aspect of the invention, the number of surrounding pixels used as the above parameter is reduced in the case of edge pixels and increased in the case of non-edge pixels, so that the image quality deterioration of each image portion is reduced.

In the third invention, the positions of the surrounding pixels used as the above parameters are further changed according to the edge direction.
Since the pixel density is corrected according to the image state, the image quality is further improved.

According to the fourth aspect of the invention, in the case of a character image that is normally simple-binarized, the number of surrounding pixels used as the above parameters is reduced, so that the deterioration of the image quality of the character image is reduced and normal pseudo halftone processing is performed. Since the number of halftone images is increased, deterioration of image quality of the halftone image is also reduced.

In the fifth aspect of the invention, it is determined whether each pixel is a character image area or a halftone image area, and multivalued by a suitable calculation method. Even when the toned image and the toned image are mixed in one page, the image quality deterioration of each image is reduced.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram of pixel positions of a target pixel and surrounding pixels used as parameters of an arithmetic expression.

FIG. 3 is an explanatory diagram showing correspondence between various scaling factors and calculation methods.

FIG. 4 is a block configuration diagram of an image scaling device according to a second embodiment of the present invention.

FIG. 5 is an explanatory diagram showing correspondence between pixel determination results and calculation methods.

FIG. 6 is a block configuration diagram of an image scaling device according to a third embodiment of the present invention.

FIG. 7 is an explanatory diagram showing correspondence between various edge patterns and calculation methods.

FIG. 8 is a block configuration diagram of a facsimile apparatus according to a fourth embodiment of the present invention.

FIG. 9 is an explanatory diagram showing a correspondence between each binarization method and a calculation method.

FIG. 10 is a block configuration diagram of an image scaling device according to a fifth embodiment of the present invention.

FIG. 11 is an explanatory diagram showing correspondence between various image areas and calculation methods.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Binary image input part 2 Multi-value conversion part 2a Calculation method switching means 3 Magnification part 4, 10 Binarization part 5 Image output part 6 Edge part judgment part 7 Directional edge part judgment part 8 Photoelectric conversion part 9 A / D conversion 11 memory 12 transmission unit 13 halftone determination unit 14 character determination unit

Claims (5)

[Claims] 1. In an image scaling apparatus which binarizes binary image information once, scales the image size by increasing or decreasing the number of pixels, and then binarizes it again, paying attention to each pixel of the binary image information. Multi-value conversion means for converting each pixel into a multi-value by calculation using the target pixel and surrounding pixels as parameters, and the number of surrounding pixels used as the above parameters when the scaling ratio of the image size is small in the above calculation. And an arithmetic method switching means for increasing the number when the zoom ratio is large. 2. In an image scaling apparatus which binarizes binary image information once, scales it by increasing or decreasing the number of pixels, and then binarizes it again, is each pixel of the binary image information an edge portion of the image? Edge determination means for determining whether or not it is a non-edge portion, and multi-value conversion means for converting each pixel into multi-value by performing an operation using the pixel of interest and surrounding pixels as parameters.
In the above calculation, when the pixel to be multivalued is the edge part, the number of surrounding pixels used as the parameter is reduced, and when it is the non-edge part, the calculation method switching means is increased. An image magnification / reduction device comprising: 3. An edge direction determining means for further determining an edge direction when each of the pixels is an edge portion, and the parameter according to the determined edge direction when the pixel to be multivalued is the edge portion. The image scaling apparatus according to claim 2, further comprising a reference pixel position changing unit that changes the positions of the surrounding pixels. 4. In an image scaling apparatus which binarizes binary image information once, scales it by increasing or decreasing the number of pixels, and then binarizes it again, paying attention to each of the pixels and distinguishing the pixel of interest and surrounding pixels. Multi-value conversion means for converting each pixel into a multi-value by a calculation as a parameter, and surrounding pixels used as the parameter when the binary image information is generated by simple binarization in the above calculation. And an arithmetic method switching means for increasing the number when the binary image information is generated by the pseudo halftone processing. 5. An image scaling apparatus which binarizes binary image information once, scales it by increasing or decreasing the number of pixels, and then binarizes it again, wherein the binary image information is generated by simple binarization. Determination means for discriminating each pixel of the binary image information into a pixel of the simple binarization portion and a pixel of the pseudo halftone processing portion in the case where both and the one generated by the pseudo halftone processing are mixed. And focusing on each of the above-mentioned pixels, and multi-value conversion means for converting each pixel into a multi-value by an operation using the pixel of interest and surrounding pixels as parameters; In the case of the digitized portion, the number of surrounding pixels used as the parameter is reduced, and in the case of the pixel of the pseudo halftone processing portion, an arithmetic method switching means for increasing the number is provided. Image scaling device.