JPH09238258A - Image processing unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To print out with high image quality an image obtained from a scanner whose resolution is low onto a multi-value printer. SOLUTION: A filter processing section 3 applies spatial filter processing to an image read by a scanner section, a magnification processing section 4 applies magnification processing conversion to the image processed by the filter processing section 3 into a line density in matching with the line density of a multi-value printer 9, and the image processed by the magnification processing section 4 is converted into a gradation number in matching with the recording characteristic of the multi-value printer 9 by a gradation processing section 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for inputting / outputting multivalued images such as digital copy, facsimile, optical file and the like.

[0002]

2. Description of the Related Art FIG. 10 shows a conventional image processing apparatus in which an image read by a scanner having a low linear density is recorded by a printer having a high linear density, which is disclosed in, for example, Japanese Patent Laid-Open No. 252273/1987. Have been described.

The original 101 is sequentially read line by line by the reading sensor 102, and is transmitted from the transmission control unit 103.
The transmitted document is received by the reception control unit 104, and is recorded on the recording paper 107 by the recording device 106 directly through the switch 105 or through the image information expansion unit.

In this case, when the switch 5 is switched to the position shown in the figure and the received original is not processed by the image information enlarging section 108, the original 101 is reduced and the recording paper 1 is printed.
When the switch 105 is connected to the side opposite to that shown in the figure, the image information of the original 101 is enlarged by the image information enlargement unit 108 and is recorded on the recording paper 107 at the same size.

This is because the linear density of the recording device 106 of the recording unit is higher than the linear density of the reading sensor 102 of the reading unit, and if the transmission document 101 is recorded as it is, the reception document 107 is automatically reduced. Therefore, it is necessary to enlarge the image information in order to record the received original at the same size as the transmitted original.

[0006]

As described above, in the conventional image processing apparatus, when the recording unit is a laser beam printer using plain paper, for example, the pixel density and linear density of the laser beam printer are , Because it is larger than the scanner of the reading unit, when the original is read by the scanner on the sending side and transmitted, the received side is reduced and recorded, and the received original of the same size as the sending original is recorded.
It was necessary to enlarge the image information vertically and horizontally.

In the case of a reduced original, there is no problem because the image information read by the scanner is recorded as it is without thinning, but in the case of enlargement processing,
For example, when doubling the height and width, it is particularly considered that the same one pixel is changed to the length and width of four pixels to perform the image processing accompanying the enlargement processing and the image processing suitable for a multi-value printer such as a laser beam printer as a recording unit. However, there is a problem that the image quality deteriorates.

In view of the above points, the present invention has as its object to provide a low-cost image processing apparatus which projects a high-quality image from a low-resolution scanner to a multi-valued printer.

[0009]

According to a first aspect of the present invention, in an image processing apparatus having a structure in which the linear density of the scanner is smaller than the linear density of the printer, the linear density of the printer with respect to the multi-valued image read by the scanner. It is characterized in that a high-quality image can be output by performing enlarging processing for conversion according to the above, and then performing gradation conversion processing according to the characteristics of the printer.

According to a second aspect of the present invention, the edge detection processing is performed on the image after the enlargement processing, and the edge enhancement processing is performed on the pixel determined to be the edge portion, so that the reproducibility of the thin line portion is improved and the low reproducibility is improved. It is characterized in that it is designed to solve a problem when using a scanner of resolution.

According to the third aspect of the present invention, the coefficient of the spatial filter can be selected by the user, and the reproducibility of the output image is improved by switching and using the original image depending on the type such as a character or a photograph. The feature is that they are allowed to do so.

[0012]

1 is a block diagram of an image processing apparatus according to the present invention, in which a scanner section 1 is an apparatus for reading a document as a black and white multivalued image, and the reading linear density is multivalued. It is lower than the linear density of the printer 9. Memory unit 2
Temporarily saves the image data. Filter processing unit 3
Performs a convolution operation on n × m pixels around the target pixel with a filter having a specific coefficient as shown in FIG. The enlargement processing unit 4 performs the enlargement processing with the ratio of the linear density of the printer / the linear density of the scanner. The edge determination unit 5
It is detected whether or not the pixel of interest is an edge pixel. The edge enhancement unit 6 calculates the edge enhancement coefficient shown in FIG. 7 for n × m pixels around the target pixel, and performs enhancement processing. Selector 7
Is a device that selects and outputs an input image. Gradation processing unit 8
Is an apparatus for converting a multi-valued image into the number of gradations matching the characteristics of the printer 9. The multi-valued printer unit 9 is a recording device that records multi-valued images. The control unit 10 controls the present device.

FIG. 2 shows a processing block diagram for performing the enlargement processing and gradation processing according to the present invention. Here, as an example, the linear density of the scanner is 200 dpi and the number of gradations is 25.
The description will be made assuming that the value is 6 values, the linear density of the printer is 400 dpi, and the number of gradations is 16 values.

An image read from the scanner section 1 is subjected to a convolution operation with a filter coefficient shown in FIG. The filter-processed image is enlarged by the enlargement processing unit 4. The magnification of the enlargement processing is a value of (printer linear density) / (scanner linear density). In this configuration example, 400/200 = 2 times.

As the enlarging processing method, the method of directly interpolating the value of the pixel of interest as the value of the pixel to be interpolated in the main scanning direction or the sub scanning direction is used, or the pixel value obtained by performing the interpolation calculation between adjacent pixels. Method is used.

Further, the filter processing section 3 and the enlargement processing section 4 are combined into one circuit, and the output of the filter processing section is 1 in this case.
The pixels may be output as four pixels that are twice the vertical and horizontal.

The image vertically and horizontally doubled is subjected to gradation conversion processing in the gradation processing unit 8 in accordance with the characteristics of the printer. Generally, since the gradation reproduction capability per pixel of a multi-valued printer is a numerical value or 10 numerical values, the gradation processing unit 8 uses a multi-valued error diffusion process or a pseudo halftone process such as a multi-valued dither process to calculate the number of gradations. Is reduced to a value suitable for the printer, and is recorded as a multivalued image by the multivalued printer unit 9.

As described above, the spatial filter processing is performed on the input image from the scanner 1 to suppress the occurrence of moire, and the gradation conversion processing according to the characteristics of the printer is performed after the enlargement processing is performed. It is possible to output from the high-density printer an image of the same image quality as when a high-performance scanner is used.

The processing for the binary image stored in the file 11 or the like is performed by setting the density value (0, 1) of the binary image to the maximum value of the output value of the scanner (when the output of the scanner is 8 bits ( 0, 255)) is converted to multi-bit by the multi-bit conversion processing unit 12 and then input to the filter processing unit 3. The subsequent operation is the same as that of the image read by the scanner. However, the coefficient of the filter processing unit 3 uses the value for the binary image.

Thus, for a binary input image,
By using a multi-valued filter as a spatial filter and performing conversion processing on a multi-valued image, a high-quality image matching the characteristics of the printer can be obtained.

When applied to a device for accumulating an image such as an image file, the image read by a scanner having a low linear density is accumulated as a multi-valued or binary image and enlarged at the time of output to perform image processing and output. By configuring to perform
The memory size required for image storage can be reduced to realize a low-cost device.

FIG. 4 shows a processing block diagram for performing the edge enhancement processing according to the present invention. The image enlarged by the enlargement processing unit 4 is input to the edge determination unit 5 and the edge emphasis unit 6. The structure of the edge determination unit 5 is shown in FIG. The edge determination unit 5 uses four types of coefficients 13 having a matrix size of 5 × 5 and performs a convolution operation with peripheral pixels of the pixel of interest. Of the absolute values of the respective output values, the maximum value detection unit 14 detects the maximum value and sets the value as the edge amount indicating the size of the edge in the target pixel. If the value of the edge amount is equal to or greater than a certain value, the determination circuit 15 determines the pixel of interest as an edge. Edge enhancement unit 6 in FIG.
Then, the edge enhancement processing is performed by the filter processing. In the selector 7, based on the result of the edge determination unit 5, the edge emphasis unit 6
The image from which the edge is emphasized and the image from the enlargement processing unit 4 which is not selected are selected and output.

Further, as shown in FIG. 6, the edge enhancing section 6
A plurality of coefficients such as a strong emphasis coefficient 6a and a weak emphasis coefficient 6b, and depending on the size of the edge amount obtained by the edge determination unit 5, when the edge amount is large, when the emphasis amount is strong, and when the edge amount is small, It is also possible to adopt a configuration in which the output from the coefficient with weak emphasis is switched by the selector 7 and output. FIG. 7 shows an example of a coefficient used for the edge emphasis processing. FIG. 7A shows an example of a weak emphasis coefficient, and FIG. 7B shows an example of a strong emphasis coefficient.

Thus, the reproducibility of characters and fine line portions in the image can be improved by detecting the edge portion in the image and performing the emphasis processing on the edge portion according to the size of the edge.

FIG. 8 is a block diagram of the filtering process according to the present invention. A plurality of coefficients of the spatial filter shown in FIG. 3 are prepared, a filter 3a for photographs and a filter 3b for characters are provided in the filter processing unit 3, and the user can select them by the switch unit 16 or the like. The user switches and uses the spatial filters according to the type of the input image such as a character image or a photographic image. An example of the coefficients of this spatial filter is shown in FIG. 9, where (a) is an example of a photographic image filter and (b) is an example of a character image filter. As described above, by preparing the coefficients suitable for the character image and the photographic image, it becomes possible to perform the multi-valued output processing optimal for each image, and the quality of the output image can be improved.

[0026]

According to the first aspect of the present invention, the image input / output processing apparatus using the scanner having a low linear density due to the linear density of the printer causes a moire by performing the spatial filter processing. By suppressing the image and enlarging the image read by the scanner and then performing gradation conversion processing that matches the characteristics of the printer, an image processing device with the same image quality as when using a scanner with high linear density is provided at low cost. You can do it.

According to the second aspect of the present invention, the edge portion in the image is detected, and the edge portion is emphasized in accordance with the size of the edge. Reproducibility is improved.

According to the third aspect of the present invention, the user selects the coefficient of the spatial filter according to the type of the input image and prepares the coefficient suitable for the character image and the photographic image. This makes it possible to perform the multi-valued output processing most suitable for the image, and the quality of the output image is improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an image processing apparatus according to the present invention.

FIG. 2 is a processing block diagram for performing enlargement processing and gradation processing according to the present invention.

FIG. 3 is an explanatory diagram showing coefficients of a spatial filter used in the image processing apparatus of the present invention.

FIG. 4 is a processing block diagram for performing edge enhancement processing according to the present invention.

FIG. 5 is a configuration diagram of an edge determination unit according to the present invention.

FIG. 6 is a configuration diagram showing another example of the edge determination unit according to the present invention.

FIG. 7 is an explanatory diagram of an edge enhancement filter used in the image processing apparatus of the present invention.

FIG. 8 is a configuration diagram of a filter processing unit according to the present invention.

FIG. 9 is an explanatory diagram of spatial filter coefficients used in the filter processing unit of the image processing apparatus according to the present invention.

FIG. 10 is a block diagram of a conventional image processing apparatus.

[Explanation of symbols]

 3 Filter processing unit 4 Enlargement processing unit 5 Edge determination unit 6 Edge enhancement unit 7 Selector 8 Gradation processing unit

Claims (3)

[Claims] 1. An image processing apparatus for processing an image read by a scanner unit and recording it by a multi-valued printer unit having a linear density larger than that of the scanner unit, wherein an image read by the scanner unit is processed. A filter processing unit that performs spatial filter processing, an enlargement processing unit that converts the image processed by the filter processing unit according to the linear density of the printer unit, and an image processed by the enlargement processing unit in the printer. An image processing apparatus, comprising: a gradation processing unit that converts the number of gradations according to characteristics. 2. An edge enhancement process based on the edge size, comprising an edge determination unit that detects an edge size of the image processed by the enlargement processing unit and an edge enhancement process unit that performs an edge enhancement process. The method according to claim 1, wherein
The image processing apparatus according to any one of the preceding claims. 3. The image processing apparatus according to claim 1, wherein a coefficient of the filter processing unit can be set according to a type of an input image read by the scanner unit.