JPH06217116A - Image processor - Google Patents

Abstract

PURPOSE:To provide a best image for dispensing with eliminates instable intermediate density continuation by reducing density between adjacent pixels at the time of using an image output device for density gradation in the case of performing the multilevel dither processing of image information. CONSTITUTION:The pixel positions of respective lines in input image information are cyclically counted and outputted by a horizontal pixel position counter 201, the line positions of the input image information are cyclically counted and outputted by a vertical pixel position counter 202 with the fixed number of bits, corresponding to this counting, ROM 203a, 203b and 203c input the respective values of respectively stored matrix data Da, Db and Dc to comparators 204a, 204b and 204c as threshold levels Sa, Sb and Sc, and these image information density levels are compared with the levels Sa, Sb and Sc. Concerning the respective average values of the data Da-Dc, the Da is set as a minimum and the Dc is set as a maximum. Thus, the compared result expresses the image information of four gradations with three bits. On the other hand, since levels S1-S3 are fluctuated at the pixel positions, dither processing is performed to the image information, 64-gradation image information is modulated to four gradations, converted to the four gradations of binary two bits and outputted by an encoder 205.

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 having a function of converting multi-gradation image information into image information having a smaller number of gradations.

[0002]

2. Description of the Related Art A scanner device for reading an original image generally reads a gray-scale image with a large number of gradations such as 64 gradations or 256 gradations. Also, CR that outputs the image
The T display device or the like can display a grayscale image with the same number of gradations as the scanner device.

On the other hand, in the case of a printer for recording an image, even a printer capable of multi-gradation recording has about 16 gradations at most. Therefore, when the image read by the scanner device is recorded by the printer, the image information having a large gradation number is converted into the image information having a small gradation number. This conversion includes
Multivalued dithering is often used.

By the way, there are density gradation, area gradation, and quasi-density gradation in the multi-gradation expression system of a display device or a printer.

The density gradation changes the pixel density while keeping the size of the pixel constant. For example, a CRT display device corresponds to this system. In general, a device of density gradation can faithfully and stably display even at an intermediate density.

On the other hand, in the area gradation, the pixel density is kept constant and the size of the pixel is changed. For example, a pulse modulation type laser printer corresponds to this type.
In a pulse-modulation type laser printer, a photoconductor is scanned with a pulse-modulated laser beam. At this time, the pulse width is changed to change the size of the recording pixel.

Generally, in an area gradation printer or the like, when images of intermediate density are continuously recorded, the size of each pixel tends to vary. For this reason, for example, even if the original image has a constant density, the change in density of the recorded image is likely to occur and the image quality is likely to deteriorate.

Further, the quasi-density gradation changes both the density and the size of a pixel, and for example, a laser printer which uses both pulse modulation and power modulation corresponds to this method. The power modulation changes the emission power of the laser beam, which changes the size of the recording pixel.

In the semi-density gradation device, variations in recording density in the case of the above-mentioned area gradation are slightly improved.

[0010]

Conventionally, when displaying or recording an image, the same image information is always displayed or recorded by the device regardless of the multi-gradation expression system of the device used. Was there. Therefore, for example, a CRT display device may have a good image quality, but a printer may not have a good image quality.

Further, since the number of gradations of the image information to be output is always constant, when the CRT display device and the printer are properly used, the image information having a small number of gradations is output according to the printer. For this reason, even if the CRT display device has the capability of displaying with a large number of gradations, the display capability is not utilized and the image quality of the display image is deteriorated.

As described above, conventionally, there is a problem that the best image that can be output by various image output devices cannot be output.

It is an object of the present invention to solve the above problems and provide an image processing apparatus which can always output the best image with the image output apparatus used.

[0014]

To this end, one invention of the present application is to change the setting of dither matrix data which is a threshold level when quantizing pixel density when multi-valued dither processing is performed on image information. Further, a means for switching between outputting image information having a small density difference between adjacent pixels and outputting image information having a large density difference is provided. While outputting small image information, when outputting an image by a multi-tone expression method of area gradation, image information with a large density difference is output.

According to another aspect of the present invention, when converting multi-gradation image information into image information having a small gradation number, a means for arbitrarily changing the gradation number of the extracted image information is provided and always used. The image information of the highest gradation number that can be output by the image output device is taken out.

[0016]

The density gradation image output device can faithfully and stably display the intermediate density. In the above one invention,
When an image output device with a density gradation is used, the density difference between pixels is reduced, so that the original image density can be accurately expressed and the image quality is improved. On the other hand, in the image output device of area gradation, the pixel density becomes unstable when the pixels of the intermediate density are continuous. Therefore, the image quality is improved by increasing the density difference between the pixels and eliminating the continuation of the intermediate density. As a result, the best image can always be output.

According to another aspect of the invention, since the image is output with the maximum number of gradations that can be displayed by the image output device used, the best image can always be output.

[0018]

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 the first embodiment of the present invention. In the figure, a scanner 1 reads an original image line by line with a relatively large number of gradations. Multi-value dither processing unit 2
Is for converting image information into image information of four gradations by a multi-value dither method. The image output device 3 is a display device that displays an image on a screen, or a printer that records the image on recording paper.

In the multi-valued dither processing section 2, the horizontal pixel position counter 201 cyclically counts the pixel position of each line of image information to be processed with a fixed number of bits. The vertical pixel position counter 201 cyclically counts each line position of the image information to be processed in the sub-scanning direction with a fixed number of bits. ROM 203a-203c
Stores dither matrix data serving as a threshold level when quantizing the density level of image information. The comparators 204a to 204c respectively compare the density level and the threshold level of the input image information. The encoder 205 outputs image information of four gradations based on the comparison result.

With the above construction, in this embodiment, a CRT display device, a laser printer, and a thermal printer are prepared as the image output device 3. Also, laser printers
A pulse modulation method and a method using both pulse modulation and power modulation are prepared.

The multi-gradation expression method of the CRT display device is density gradation. A pulse modulation type laser printer is an area gradation. Laser printers and thermal printers that use both pulse modulation and power modulation have quasi-density gradation.

The user arbitrarily selects one of the above devices and uses it as the image output device 3.

Here, assuming that the matrix data stored in the ROM 203a is Da and the matrix data of the ROMs 203b and 203c are Da and Db, respectively, in this embodiment, depending on the device used as the image output device 3,
The contents of the matrix data Da to Dc are changed.

That is, when the CRT display device is used, as shown in FIG.
Is set to 5, 10, 15, and 20. Further, the matrix data Db includes 25, 30, 35, 4
0, the matrix data Dc has 45, 50, 55, 6
Set 0 respectively.

On the other hand, when a pulse-modulation type laser printer is used, as shown in FIG. 7B, the matrix data Da is 5, 20, 35, 50 and the matrix data Db is 10, 25 ,. 40, 55, and 15, 30, 45, 60 are set in the matrix data Dc, respectively.

When a laser printer or a thermal printer that uses both pulse modulation and power modulation is used, the matrix data Da includes 5, 10, 35, 40 and matrix data as shown in FIG. 15, 20, 15, and 50 are set to the data Db, and 25, 30, 55, and 60 are set to the matrix data Dc.

The matrix data Da to Dc are set, for example, by replacing the ROMs 203a to 203c.

Now, if the image processing apparatus is activated after such settings, the scanner 1 reads the original image line by line and sequentially outputs image information pixel by pixel.
In the present embodiment, it is assumed that the image information output here is represented by 64 gradations, that is, the pixel density is "0" to "63".

The horizontal pixel position counter 201 cyclically counts the pixel position of each line of the input image information with a fixed number of bits. In this embodiment, the counting operation is executed by 1 bit. Therefore, the horizontal pixel position counter 201 alternately outputs "1" and "0" data according to the pixel position of the image information.

The vertical pixel position counter 202 cyclically counts the line position of the input image information with a fixed number of bits. In this embodiment, the counting operation is executed by 1 bit as in the above. Therefore, the vertical pixel position counter 202 alternately outputs "1" and "0" data according to the line position of the image information.

The ROM 203a sequentially outputs each value of the matrix data Da as a threshold level Sa according to the output data of the horizontal pixel position counter 201 and the vertical pixel position counter 202. Similarly, the ROM 203
b and 203c sequentially output the respective values of the matrix data Db and Dc as threshold levels Sb and Sc.

The comparator 204a compares the density level of the input image information with the threshold level Sa. Similarly, the comparators 204b and 204c compare the density level of the input image information with the threshold levels Sb and Sc.

In each case, the average value of each of the matrix data Da to Dc is set so that the matrix data Da is the smallest, the matrix data Db is the next largest, and the matrix data Dc is the largest. As a result, the comparison result of the comparators 204a to 204c represents the image information of 4 gradations with 3 bits. Further, in this case, since the threshold levels S1 to S3 vary depending on the pixel position, the image information is dithered. As a result, the image information of 64 gradations is converted into 4 gradations.

The encoder 205 converts the 3-bit image information into 4-bit image information of binary 2-bit. Then, the image information of four gradations is displayed or recorded and output by the image output device 3.

By the way, as shown in FIGS. 2A to 2C, 12 kinds of the same data are set in the matrix data Da to Dc in any case. However, in the case of FIG. 2A, for example, 5 to 20 are matrix data Da, 25 to 40 are matrix data Db, 4
5 to 60 are set in the matrix data Dc, respectively. On the other hand, in the case of (b) and (c) of the same figure, the data of each of the above ranges is scattered in the matrix data Da to Dc.

Now, for example, as shown in FIG.
It is assumed that image information with a constant density of which the density level of adjacent four pixels is “21” is input.

Here, when the matrix data Da to Dc shown in FIG. 2A are set, the density level "2" is set.
Since “1” is larger than each value of the matrix data Da and smaller than each value of the matrix data Db, all the four pixels are converted to the density “1” as shown in FIG.

On the other hand, when the matrix data Da to Dc shown in FIG. 2B are set, the density level "21" is the value "" of the matrix data Dc at the upper left pixel position among the above four pixels. Since it exceeds 15 ", the pixel is converted to the density" 3 "as shown in FIG. At the upper right pixel position, the density level “21” is larger than the matrix data Da and smaller than the matrix data Db, so that the density level “21” is converted to the density “1”. In the lower two pixels, the density level "2
Since "1" is smaller than the matrix data Da, both are converted to the density "0".

Further, when the matrix data Da to Dc shown in FIG. 2C are set, as shown in FIG. 3D, the left two pixels have the density "2" and the right two pixels have the density "2". It is converted into image information of density "0".

That is, in the case of the matrix data Da to Dc of FIG. 2A, generally, the image information output has a small density difference between adjacent pixels, and in the case of the matrix data Da to Dc of FIG. , The density difference becomes large. Further, in the case of the matrix data Da to Dc of FIG.
The density difference is about the middle of the two.

In this embodiment, the matrix data Da to Dc of FIG. 2A are set when the CRT display device is used. Since the CRT display device expresses the image density by the density gradation, it is possible to faithfully and stably display even the intermediate density. Therefore, by displaying the image information in which the density difference between pixels is small in this way, the original image density can be accurately expressed and the image quality is improved.

On the other hand, the matrix data Da shown in FIG.
Dc to Dc are set when a pulse modulation type laser printer is used. The pulse modulation type laser printer is
Image density is expressed by area gradation, but in such a device, pixel density becomes unstable when pixels of intermediate density are continuous. In this embodiment, in this case, the density difference between the pixels is increased, so that the intermediate density does not continue. As a result, the image quality of the recorded image is improved.

Further, the matrix data Da shown in FIG.
Dc to Dc are set when a laser printer that uses both pulse modulation and power modulation or a thermal printer is used. These printers have quasi-density gradation, and the density becomes a little unstable when continuously recording pixels of constant density.
In this embodiment, in this case, the density difference between pixels is increased to some extent, so that the image quality is improved.

As described above, in the present embodiment, since the image information according to the characteristics of the image output device used is output, it is possible to always display or record the best image.

FIG. 4 is a block diagram showing the arrangement of an image processing apparatus according to the second embodiment of the present invention. In the figure,
The scanner 1 and the multi-valued dither processing unit 2 are the same as those in FIG. In this embodiment, the image information dithered by the multi-level dither processing unit 2 is transmitted by the transmitting unit 4 to another device via the communication line.

When transmitting the image information, as shown in FIG. 5, first, the other party's device is called (process 101). Then, the function information of the partner device is received. In this embodiment,
As one of the function information, the information indicating the multi-gradation expression method of the image output device on the partner device side is received (process 102).

As a result, the multi-tone expression method of the other party is judged (process 103). Here, when the multi-tone expression method of the other party is found (Y of processing 103), as described in FIG. 2, the matrix data Da to Dc corresponding to each multi-tone expression method are subjected to the multi-value dither processing. ROM 203 of part 2
It is set to a to 203c (process 104).

On the other hand, when the predetermined function information is not received and the partner's multi-tone expression method is unknown (N in process 103),
Matrix data D for quasi-density gradation shown in FIG.
a to Dc are set (process 105).

After such setting, the image information read by the scanner 1 is dithered and transmitted to the other party (Process 1
06).

As described above, in the present embodiment, when transmitting the dither-processed image information, the receiving side notifies the multi-gradation expression system of the image output device and is suitable for the multi-gradation expression system. Image information is sent. This allows
The receiving side will always be able to display and record the best image.

When the multi-gradation expression method of the image output device on the receiving side is unknown, the image information for the quasi-density gradation is transmitted. Since the image information for the semi-density gradation has an intermediate property between the density gradation and the area gradation, the image quality of the output image deteriorates regardless of the multi-gradation expression method on the receiving side. Is prevented.

In each of the above embodiments, the dither processing is executed with a matrix size of 2 × 2 to extract image information of four gradations. However, the matrix size and the number of gradations of the extracted image information are used. Needless to say, can be set arbitrarily.

FIG. 6 is a block diagram showing the arrangement of an image processing apparatus according to the third embodiment of the present invention. In this embodiment, the multi-gradation image information read by the scanner 1 is converted into a smaller number of gradations by the gradation number conversion unit 5, and the image output device 6 is converted.
I am trying to output.

The gradation number conversion unit 5 is a division circuit for converting a signal level by division, and has a function of arbitrarily setting a divisor at the time of division. Now, assuming that the density level of the input image information is f and the divisor to be set is 1, the gradation number conversion unit 5 outputs the image information of the density level g as shown in the following expression. g = f / l

With this configuration, in the present embodiment, as shown in FIG. 7, the scanner 1 reads image information with 64 gradations, and the image output device 6 includes a display device with 32 gradations and a display device with 4 gradations.
It is assumed that a gradation printer and a 16 gradation printer are prepared.

In this embodiment, when a display device with 32 gradations is used, "2" is set as the divisor l in the gradation number conversion section 5. When using a 4-gradation printer, the divisor l
When using a printer with "16" and 16 gradations,
“4” is set as the divisor l.

As a result, the image information of 64 gradations obtained by the scanner 1 is converted by the gradation number conversion unit 5 into the gradation number of the device used. Then, the device outputs an image with a predetermined number of gradations.

As described above, in this embodiment, when various devices having different gradation numbers are used as the image output device 6,
Image information of the maximum number of gradations that can be output by the device that is always used,
It is taken out from the gradation number conversion unit 5. Thereby, the grayscale image can be displayed or recorded more faithfully.

Further, since the gradation number converting section 5 is composed of a dividing circuit, and the gradation number of the image information to be taken out is changed by changing the divisor, the circuit structure of the gradation number converting section 5 is changed. Will be easier. Further, in the present embodiment, the divisor is 2
I am trying to set the factorial value of. In the case where the divisor is a factorial of 2, since division can be performed by bit-shifting the upper bits of binary data in the lower direction, the division circuit can be further easily configured.

FIG. 8 shows a block diagram of an image processing apparatus according to the fourth embodiment of the present invention. In the figure,
The scanner 1 and the gradation number conversion unit 5 are the same as those in FIG. 6, and in this embodiment, the image information obtained from the gradation number conversion unit 5 is transmitted to the transmission unit 4.
Thus, it is transmitted to the communication partner device.

In the case of transmitting the image information, as shown in FIG. 9, first, a call is made to the partner device (process 201). Then, in the present embodiment, information indicating the maximum number of gradations that can be output by the image output device of the other party is received (process 202).

Then, the maximum number of gradations is set in the gradation number conversion unit 5 by the method described in FIG. 7 (process 203).
After this operation, the image information read by the scanner 1 is converted by the gradation number conversion unit 5 and transmitted to the other party (process 204).

As described above, when the image information is transmitted, the notification of the number of gradations of the image output device is received from the receiving side, and the image information of the maximum number of gradations that the receiving side can output is transmitted.
The receiving side will always be able to display and record the best image.

[0065]

As described above, according to one invention of the present application, when multi-value dithering of image information is used and an image output device of density gradation is used, the density difference between adjacent pixels is increased. Since the original image density can be accurately expressed, the density difference between adjacent pixels is increased when an image output device with area gradation is used. Since there is no unstable continuous intermediate density, the best image can be output by the image output device that is always used.

In another invention, when converting multi-gradation image information into image information of a small number of gradations, the image information of the maximum number of gradations that can be output by the image output device used is output. Since this is set, the best image can always be output.

[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 an explanatory diagram of matrix data set in a multilevel dither processing unit.

FIG. 3 is an explanatory diagram showing an example of image information obtained by multi-value dither.

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

FIG. 5 is an operation flowchart of image information transmission processing in the embodiment.

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

FIG. 7 is an explanatory diagram showing a set value of a divisor to a division circuit in the embodiment.

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

FIG. 9 is an operation flowchart of image information transmission processing in the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 scanner 2 multi-value dither processing unit 3,6 image output device 4 transmission unit 5 gradation number conversion unit 201 horizontal pixel position counter 201 vertical pixel position counter 203a to 203c ROM 204a to 204c comparator 205 encoder

Claims (5)

[Claims] 1. A pixel density is quantized in an image processing apparatus for converting input multi-tone image information into image information of a smaller number of tones by multi-value dither processing and outputting the image information to various image output devices. The density difference switching means for changing the setting of the dither matrix data which is the threshold level at the time of outputting the image information having a small density difference between the adjacent pixels or the image information having a large density difference between the adjacent pixels, and the output image information for the density level Image information output means for density gradation, which outputs image information having a small density difference when outputting an image by a multi-tone gradation expression method,
An image processing apparatus comprising: an area gradation image information output unit that outputs image information having a large density difference when an image is output by a multi-tone expression method of area gradation. 2. A quasi-density gradation image information output means for outputting image information in which the density difference is set to a medium level when an image is output by a multi-gradation expression method that uses both density gradation and area gradation. The image processing apparatus according to claim 1, further comprising: 3. An image processing apparatus for converting input multi-gradation image information into image information having a smaller number of gradations by multi-value dither processing and transmitting the image information to a communication partner apparatus, wherein the pixel density is quantized. The density difference switching unit for changing the setting of the dither matrix data, which is the threshold level at the time, to output the image information having a small density difference between the adjacent pixels or the image information having a large density difference between the adjacent pixels, and the communication partner device. A destination multi-tone expression method determination means for determining the multi-tone expression method of the image output device used by the other party by communication, and a case where the partner outputs an image by the multi-tone expression method of density gradation. Image information transmitting means for density gradation which transmits the image information having a small density difference, and image information transmitting for area gradation which transmits the image information having a large density difference when outputting an image by a multi-tone expression method of area gradation Equipped with means An image processing device characterized by being provided. 4. An image processing apparatus for converting input multi-gradation image information into image information having a smaller number of gradations and outputting the image information to various image output devices, wherein the number of gradations of the image information to be converted is arbitrarily set. An image processing apparatus comprising: a gradation number varying means for changing; and an image information output means for outputting image information of the maximum gradation number that can be output by an image output apparatus which is always used. 5. An image processing apparatus for converting input multi-gradation image information into image information having a smaller number of gradations and transmitting the image information to a communication partner apparatus, wherein the number of gradations of the image information to be converted is arbitrarily set. The gradation number varying means for changing and the partner gradation number judging means for judging the maximum gradation number that can be output by the image output device used by the partner by communicating with the communication partner device are always discriminated. An image processing apparatus comprising: a transmitting unit that transmits the image information with the highest gradation number.