JPH06178108A - Image processor - Google Patents

Abstract

PURPOSE:To make it possible to arbitrarily change the number of gradation of image information to be taken out according to processing contents by converting the multi- level image information to the image information of a designated number of gradation when an operator designates the number of gradation of image information. CONSTITUTION:An operator sets an original to a scanner 1 and designates a desired processing and the number of gradation of image information to be taken out in a non-illustrated operation part. Thus, the scanner 1 reads original image information one line by one line and outputs image information one picture element by one picture element. An adder 21 inputs the image information and adds the correction value calculated in an error distribution calculation part 25. The image information to which the correction value is added is inputted in comparators 221 to 221. A selection part 228 selects the comparators to be operated of the comparators 221 to 227 according to the designated number of gradation. Namely, when eight number of gradation is designated, the comparators 221 to 221 are operated, in the case of four number of gradation, the comparators 222, 224 and 226 are operated, in the case of two number of gradation, the only comparator 224 is operated, and input image information can be expressed by a small designated number of gradation.

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 converting input multi-tone image information into smaller fixed tone image information and outputting the image information.

[0002]

2. Description of the Related Art In many image processing apparatuses such as facsimile machines, a plotter for recording an image with two gradations of white and black is used. Therefore, in these devices, the image information is always binarized and recorded or transmitted.

On the other hand, in recent years, a plotter has been developed which can record a grayscale image to some extent, for example, 4 or 8 gradations. An image processing apparatus equipped with such a plotter for recording and transmitting multi-gradation image information is also in practical use.

By the way, when a grayscale image such as a picture or a photograph is handled, it is better to process the image information with multiple gradations so that the reproducibility of the image is better. On the other hand, in the case of transmitting an image without light and shade such as a character image, the image information of two gradations has an advantage that the data amount is small and communication can be performed in a short time.

[0005]

As described above, although both the two-gradation image information and the multi-gradation image information have their respective characteristics, the conventional various image processing apparatuses always generate images with a constant number of gradations. Since the information is processed, there is a problem that the operator cannot change the number of gradations according to the processing content.

It is an object of the present invention to solve the above problems and provide an image processing apparatus capable of arbitrarily changing the number of gradations of image information to be extracted.

[0007]

To this end, according to the present invention, when an operator arbitrarily designates the number of gradations of image information to be output, the image processing apparatus causes the image information of multi-gradation to be designated gradations. It is characterized in that it is converted into a number of image information and outputted.

[0008]

As a result, the operator can arbitrarily change the number of gradations of the image information to be extracted according to the processing content.

[0009]

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

FIG. 1 is a block diagram showing the arrangement of an image processing apparatus according to an embodiment of the present invention. In the figure, a scanner 1 reads an original image with a relatively large number of gradations, such as 64 gradations. The error diffusion processing unit 2 converts multi-tone image information into image information of, for example, 2 to 8 tone by error diffusion processing.
The switching circuit 3 switches whether to output the converted image information to the plotter 4 or the transmission unit 5.
The plotter 4 records an image on recording paper, and has a function of recording a grayscale image at a fixed gradation of 8 gradations, for example. The transmission unit 5 transmits the processed image information to the communication partner.

In the error diffusion processing unit 2, an adder 21
Is to add a correction value to the pixel of interest of the image information.
The quantizer 22 quantizes input image information into image information having a certain number of gradations. The error detection unit 23 detects a quantization error that occurs during quantization. The storage unit 24 stores the quantization error of each pixel in a fixed range around the target pixel. The error distribution calculation unit 25 calculates the correction value to be added to the pixel of interest. An error diffusion filter indicating the surrounding pixel position to be referred to and a coefficient for calculating a correction value is set in the error distribution calculation unit 25.

FIG. 2 shows a block diagram of the quantizer 22. In the figure, comparators 221 to 227 are for comparing the density level of the image information to be respectively input with a preset threshold value. Selection unit 228
Is for selectively operating all or part of the comparators 221 to 227. The encoder 229 is for generating binary image information data having a fixed number of gradations based on the comparison result of the comparators 221 to 227.

With the above configuration, when the operator uses the image processing apparatus of this embodiment, the operator sets a document on the scanner 1 and uses an operation unit (not shown) to perform desired processing and the number of gradations of image information to be extracted. Is specified. For example, when the original image is a grayscale image, the number of gradations is designated as 8 gradations. If the original image is a character image, two gradations are designated. Further, when it is desired to transmit even a grayscale image to the communication partner in a short time, 4 gradations or 2 gradations are designated. Then, the image processing device is activated.

As a result, the scanner 1 scans the original image one by one.
Each line is read and image information is output pixel by pixel. The adder 21 inputs the image information, and the error distribution calculation unit 2
The correction value calculated in 5 is added. The image information to which the correction value has been added is input to the comparators 221 to 227.

Here, assuming that the seven boundary levels when the section from the density 0 of the image information to the maximum density is divided into 8 at constant intervals are threshold values S1 to S7, the comparator 221
The threshold value S1 is set in advance. The comparator 221 is
It has a function of comparing the density level of the input image information with the threshold value S1. Similarly, the comparators 222-2
Also in 27, constant threshold values S2 to S7 are respectively set, and it has a function of comparing the density level of the input image information with the set threshold values S1 to S7.

The selection unit 228 selects one of the comparators 221 to 227 to be operated according to the designated gradation number. That is, when the number of gray scales is specified, all the comparators 221 to 227 are operated. Further, when the number of gradations is designated to four, the comparators 222, 224 and 22
6 is operated. Further, when the number of gray scales is designated, only the comparator 224 is operated.

As a result, the comparison result of the comparators 221 to 227 represents the input multi-gradation image information by the designated constant gradation number. The encoder 229 converts the comparison result into binary-numbered image information data having a constant gradation. Thereby, the image information of 64 gradations is quantized into the image information of 2 to 8 gradations.

The error detection unit 23 detects a quantization error generated in the quantization for each pixel of image information. Storage unit 24
Temporarily stores the detected quantization error for each pixel position. The error distribution calculation unit 25 pays attention to one pixel of the image information input to the adder 21, and calculates a correction value for the pixel of interest. This correction value is calculated by summing the quantization errors of the surrounding pixels designated by the error diffusion filter at the designated ratio. The adder 21 adds the correction value thus calculated to the pixel of interest to correct the density.

The error diffusion processing unit 2 outputs the image information converted into a fixed number of gradations by the above error diffusion method.

The switching circuit 3 outputs the image information to the plotter 4 when the image is recorded, and to the transmitter 5 when the image is transmitted.

The plotter 4, when image information is input,
An image is recorded with the number of gradations of the image information. Also, the transmitter 5
When the image information is input, transmits the image information to the communication partner.

As described above, in this embodiment, when the operator specifies the number of gradations of image information, the multi-gradational image information read from the original is converted into the specified number of gradations for recording or recording. I am trying to send it.

Thus, for example, when the image is recorded by the plotter 4, it is recorded at 8 gradations, and when the image is transmitted by the transmitting unit 5, it is recorded at 8 gradations. The operator can arbitrarily change the number of gradations of the extracted image information according to the processing content such as transmitting and shortening the communication time.

Further, when the image information of each gradation number is obtained, a necessary one of the comparators 221 to 227 is selectively used. Therefore, one quantizing unit 22 can generate the image information of each gradation number. Can be obtained.

In the above embodiment, the error diffusion processing unit 2
The image information obtained from the above-mentioned processing is only executed in two kinds of processing, that is, recording or transmission, but other processing such as displaying on a display device or accumulating in a storage device may be executed. . In this case, it suffices to extract the image information of a desired number of gradations according to the processing.

In the above embodiments, the image processing apparatus has been described, but a facsimile apparatus can have such an apparatus configuration. When the facsimile apparatus has such a configuration, when the original image is copied, the number of gradations is increased to obtain a good recorded image, and when the original image is transmitted, the original image is transmitted with two gradations in a short time. Can be said to communicate.

Next, a second embodiment of the present invention will be described.

The image processing apparatus of this embodiment has the same configuration as that of FIG. 1, and the quantizing unit 22 has a divider 23 as shown in FIG.
It consists of 0.

With this configuration, it is assumed that the quantizing unit 22 is input with image information of 64 gradations, as in the above embodiment. In this embodiment, as shown in FIG. 4, when the image information to be extracted is designated as 8 gradations, the divisor i is “8”, and when the gradation information is designated as 4 gradations, the divisor i is “16”, the second floor. When designated as a key, “8” is input to the divider 230 as the divisor i.

The divider 230 divides the density f by the divisor i, where f is the density of the input image information, and the obtained quotient g
The image information having the density of is output. When the quotient g is a decimal number, an integer value is obtained by rounding up or down after the decimal point. As a result, the image information of 64 gradations is 2,
It is converted into image information of 4 or 8 gradations.

In this way, the quantizer 22 is divided by the divider 230.
With this configuration, the image information of each gradation can be extracted by a simple process of changing the divisor.

Next, a third embodiment of the present invention will be described.

The image processing apparatus of the present embodiment has the same configuration as that of FIG. 1, and the error distribution calculation unit 25 is provided with two types of error diffusion filters.

With this configuration, in the present embodiment, as shown in FIG. 5, when the image information to be extracted has 2 or 4 gradations, the error distribution calculation unit 25 uses one of the error diffusion filters 25a to obtain the correction value. calculate.

In the figure, "*" indicates the pixel of interest, and each number indicates the position of the surrounding pixel to be referred to and the coefficient for calculating the correction value. For example, the error diffusion filter 25
In a, the sum of each number is "16", but the number is "1"
For the pixel of, 1/1 of the quantization error that occurred in that pixel
6 will be calculated as the correction value for the pixel of interest. When the image information to be extracted has 2 gradations or 4 gradations, the correction values of the seven surrounding pixels are calculated and added to the target pixel according to the error diffusion filter 25a.

On the other hand, when the image information to be taken out has 8 gradations, the error distribution calculating section 25 calculates the correction value by the other error diffusion filter 25b. In this case, the quantization error generated in two adjacent pixels is added to the target pixel as a correction value of 1/2.

The error diffusion processing unit 2 converts the image information by switching the error diffusion filter to be used according to the number of gradations of the extracted image information.

If the image information input to the error diffusion processing unit 2 has 64 gradations, the density of the image information is 0 to 63.
It is represented by. When converting this image information into, for example, 8 gradations, it is equivalent to dividing the density by 8, so that a level of 0 to 7 corresponding to the remainder of the division will occur as a quantization error. Here, when the correction value is calculated according to the error diffusion filter 25a for the quantization error of 0 to 7, the calculated value becomes 1 or less in many cases. Therefore, when rounding down below the decimal point, the target pixel cannot be corrected, and if the calculated value is rounded up to 1, the correction amount becomes excessive.

In this case, in this embodiment, since the correction value of each pixel is calculated according to the error diffusion filter 25b, the calculated value is relatively less than 1 or less. As a result, the pixel of interest can be corrected more accurately.

On the other hand, when the image information is converted into 2 gradations, the levels 0 to 31 occur as a quantization error. In this case, even if the correction value is calculated according to the error diffusion filter 25a, the calculated value rarely becomes 1 or less. Further, in this case, since the error is distributed from the seven surrounding pixels to the target pixel, the target pixel can be corrected more correctly.

As described above, in this embodiment, when the number of gradations of the image information to be extracted is as large as 8 gradations, the number of surrounding pixels to be referred to is reduced to 2 pixels, and at the same time, the reference pixels from each pixel are reduced. The ratio of error distribution is increased. When the number of gradations is as small as 4 gradations or less,
The number of surrounding pixels to be referred to is increased to 7 pixels to reduce the ratio of error distribution from each pixel.
As a result, the error diffusion process is executed more accurately, and the image quality of the image information to be extracted is improved.

Next, a fourth embodiment of the present invention will be described.

The image processing apparatus of this embodiment has the same configuration as that of FIG. 1, and the error distribution calculating section 25 is provided with one error diffusion filter 25a as shown in FIG.

With this configuration, in the present embodiment, when the image information to be extracted has 2 gradations or 4 gradations, the error distribution calculating section 25.
Reads each number from the entire A1 of the error diffusion filter 25a and processes the image information in the same manner as in the third embodiment.

On the other hand, when the image information to be extracted has 8 gradations, the error distribution calculation unit 25 reads two numbers from the partial area A2 of the error diffusion filter 25a and processes the image information in the same manner. In this case, the two numbers in the specific area A2 are
Since both are "4", the error diffusion filter 2 of FIG.
The same correction value as in the case of using 5b can be calculated and processed in the same manner.

In this way, by changing the reading area of the error diffusion filter according to the number of gradations of the image information to be taken out, the same processing as that of the third embodiment can be executed, and the error diffusion filter provided is Only one is enough.

Next, a fifth embodiment of the present invention will be described.

The image processing apparatus of this embodiment has the same configuration as that of FIG. 1, and the error distribution calculating unit 25 is configured as shown in FIG. That is, as shown in FIG. 8, the surrounding pixel position designating section 251 designates each of the seven pixel positions around the target pixel “*”. The arithmetic circuits 252 and 253 each perform a constant arithmetic operation with the quantization error of each pixel as a factor. The adder 254 includes the arithmetic circuits 252 and 2
The calculated value of 53 is added. The bit shift circuits 255 and 256 are for shifting the input data by a fixed number of bits.

With this configuration, the quantization error of each pixel around the target pixel is input from the storage unit 24 to the arithmetic circuits 252 and 253. Here, as shown in FIG. 8, assuming that the quantization errors of the seven surrounding pixels designated by the surrounding pixel position designating unit 251 are A to G, the arithmetic circuit 252 sets the variable X1,
The arithmetic circuit 253 calculates the variable X2 by the following equations. X1 = 4C + 4G X2 = A + 2B + 2D + E + 2F Then, the adder 254 adds the calculated variables X1 and X2.

The variable X1 calculated by the arithmetic circuit 252 is 2
It is input to the bit shift circuit 255 as data of a base number. The value of (X1 + X2) calculated by the adder 254 is also input to the bit shift circuit 256 as binary data.

In this embodiment, the bit shift circuit 255
Operates when the number of gradations of the extracted image information is eight,
The bit shift circuit 256 operates when there are two gradations or four gradations.

Now, assuming that the bit shift circuit 255 operates, the bit shift circuit 255 shifts each bit of the data of the variable X1 by 3 bits in the lower direction. By this bit shift, the value of the variable X1 becomes 1/8. Since the variable X1 has a value of (4C + 4G), the same value as the correction value calculated based on the error diffusion filter 25b of FIG. 5 is obtained.

On the other hand, if the bit shift circuit 256 operates, the bit shift circuit 256 operates as (X1 + X2).
4 bits of each bit of the data are shifted downward.
This bit shift reduces the data value to 1/16. As a result, the same value as the correction value calculated based on the error diffusion filter 25a of FIG. 5 is obtained.

As described above, in the present embodiment, the correction value is calculated by two kinds of calculation methods, but since the calculation unit 252 is shared in each calculation, the hardware can be reduced. .

In each of the above embodiments, the calculation method of the correction value of the pixel of interest is set to two types, but it is natural that it may be set to three or more types.

The number of gradations of the image information to be extracted is 2, 4
Alternatively, the number of gradations is fixed to three, but the number of gradations may be set arbitrarily. Also, in the scanner 1, 6
It goes without saying that the number of gradations can also be set arbitrarily, whether or not the original image is read in four gradations.

[0057]

As described above, according to the present invention, when the operator specifies the gradation number of the image information, the multi-gradation image information is converted into the image information of the specified gradation number. It is possible to arbitrarily change the number of gradations of the extracted image information according to the processing content.

[Brief description of drawings]

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

FIG. 2 is a block configuration diagram of a quantization unit.

FIG. 3 is a block configuration diagram of a quantization unit in a second exemplary embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a method of controlling the quantizer.

FIG. 5 is an explanatory diagram of an error diffusion filter switching method according to a third embodiment of the present invention.

FIG. 6 is an explanatory diagram of a method of using the error diffusion filter according to the fourth embodiment of the present invention.

FIG. 7 is a block configuration diagram of an error distribution calculation unit in a fifth embodiment of the present invention.

FIG. 8 is an explanatory diagram of surrounding pixel positions for reference.

[Explanation of symbols]

 1 Scanner 2 Error Diffusion Processing Section 3 Switching Circuit 4 Plotter 5 Transmission Section 21,254 Adder 22 Quantization Section 23 Error Detection Section 24 Storage Section 25 Error Distribution Calculation Section 25a, 25b Error Diffusion Filter 221-227 Comparator 228 Selection Section 229 Encoder 230 Divider 251 Surrounding pixel position designator 252, 253 Arithmetic circuit 255, 256 bit shift circuit

Claims (4)

[Claims] 1. An image processing apparatus for converting multi-gradation image information into smaller fixed gradation number of image information and outputting the image information, the gradation number designating unit arbitrarily specifying the gradation number of the image information to be output. And an image number conversion means for converting the multi-tone image information into image information of the specified number of tones. 2. An image processing apparatus for converting multi-gradation image information into smaller fixed gradation number of image information by an error diffusion method and outputting the image information, the gradation number specifying the gradation number of the image information to be output. When performing the error diffusion process of adding the quantizing error generated in the individual surrounding pixels to the target pixel at a set ratio when the gradation number of the image information to be output is large, An error distribution changing means is provided to decrease the number and set the ratio to a large value, while increasing the number of the surrounding pixels to set the ratio to a small value when the gradation number is small. An image processing device characterized by the above. 3. An image processing apparatus for converting multi-gradation image information into image information having a smaller number of fixed gradations and outputting the image information, wherein each pixel density of the multi-gradation image information and a preset threshold value. A plurality of comparators that compare the values with each other; a gradation number designating unit that specifies the number of gradations of the image information to be output; and a specific one less than the number of gradations designated from the plurality of comparators. An image processing apparatus comprising: a comparator selecting unit that extracts a comparison result from a comparator; and an encoder that converts the extracted comparison result into image information of the specified gradation number. 4. An image processing device for converting multi-gradation image information into image information having a smaller fixed number of gradations and outputting the image information, and a gradation number specifying means for specifying the number of gradations of the image information to be converted, And dividing means for obtaining image information of the specified gradation number by dividing each pixel density of the multi-gradation image information by a divisor determined according to the specified gradation number. An image processing device characterized by the above.