JP2000341524A - Electrophotographic device, method for image processing of electrophotographic picture, and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce capacity of a memory without deteriorating the image quality. SOLUTION: On a screen table TB1 of a pixel 1, the drive pulse width data corresponding to gradation data '0' to '42' need to be stored because the data change, but the drive pulse width data corresponding to gradation data '43' to '255' are not required to be stored, because the data are constant at '255'. Therefore, the table TB1 is constituted of the drive pulse width data corresponding to the minimum gradation value '0' and maximum gradation value '42' of an area, where the output varies and the driving pulse width data corresponding to the gradation data '0' to '42', and accordingly, the data amount of the table TB1 is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus, an image processing method for electrophotography, and a recording medium, and more particularly to an electrophotographic apparatus for expressing gradation by halftone dots formed from a plurality of dots. The present invention relates to an electrophotographic apparatus, an electrophotographic image processing method, and a recording medium that can reduce the data amount of a gamma (γ) table to be referred to when performing tone processing.

[0002]

FIG. 1 shows an example of an electrophotographic system for reproducing a color image using cyan (C), magenta (M), yellow (Y) and black (K) toners. .

In a personal computer (PC) 1,
The operator generates character data and graphic data by using an application program 11 (for example, a word processor, a graphic tool, or the like) installed in advance. The data generated by the application program 11 is supplied to a driver 12 for the printer 2 installed in the personal computer 1 in advance. The driver 12 converts the supplied data into RGB data for each pixel.
The image data is converted into image data composed of (8 bits × 3 = 24 bits) gradation data. This image data is supplied to the printer 2 via the cable 3. The printer 2 includes a controller 21 and an engine 22, and reproduces a color image based on the supplied image data.

The controller 21 includes a color conversion unit 31, a halftone processing unit 32, and a pulse width modulation (PWM (Pulse Wi
dth Modulation)) section 33. The color conversion unit 31 converts the supplied RGB gradation data of each pixel into R
The data is converted into CMYK gradation data D1 having a complementary color relationship with GB.
The CMYK gradation data D1 is composed of 8 bits each and has a maximum of 256 gradations. The CMYK gradation data D1 output from the color conversion unit 31 is supplied to the halftone processing unit 32.

FIG. 2 shows an example of the configuration of the halftone processing unit 32. As shown in FIG. 2, the halftone processing unit 32 includes a page memory 51, a screen processing unit 52, and a screen table memory 53.
The page memory 51 stores the CM supplied from the color conversion unit 31.
YK gradation data D1 is stored. A screen table (gamma table) is stored in the screen table memory 53 in advance. This screen table has correspondence between gradation data and laser drive pulse width data as image reproduction information for each pixel.

The screen processing unit 52 includes a page memory 5
1 is read out, and the screen table corresponding to the read out pixel is selected. The screen processing unit 52 reads the drive pulse width data D2 corresponding to the gradation data with reference to the selected screen table, and supplies the read drive pulse width data D2 to the pulse width modulation unit 33. The pulse width modulation unit 33 generates a pulse width modulation signal D3 for driving a laser diode (LD) 42 in the engine 22 based on the supplied drive pulse width data D2, and generates the generated pulse width modulation signal D3 Is supplied to the engine 22.

The engine 22 includes a laser driver 41, a laser diode (LD) 42, a photosensitive drum (not shown), a transfer drum (not shown), and the like. The laser driver 41 drives a laser diode 42 for image drawing based on the supplied pulse width modulation signal D3.
The laser beam emitted by the laser diode 42 is applied to a predetermined area of the photosensitive drum (not shown) to form a latent image having a predetermined surface potential on the photosensitive drum. The charged toner adheres to the latent image formed on the photosensitive drum, and the toner is transferred to printing paper via a transfer drum (not shown). Thereby, a color image is reproduced.

Next, a screen constituting an image reproduced by the engine 22 will be described with reference to FIG.
FIG. 3 shows a screen (or cell) 61 composed of 3 × 3 (vertical × horizontal) pixels as an example. In a predetermined area in each of the pixels 1 to 9, a dot which is an area (hatched area in the figure) to which toner is attached is formed based on the pulse width modulation signal D3. A halftone dot 62 is formed by a plurality of dots, and the halftone (halftone) gradation is expressed by the size of the halftone dot. As described above, the method of reproducing the halftone of the grayscale image by the size of the halftone dot is called a dither method, and is widely used. In the screen 61, dots 1 to 5 are formed in the pixels 1 to 5, respectively, and the dots 1 to 5 form a halftone dot 62.

Next, the density (gradation) expressed on the screen 61 will be described with reference to FIG. FIG.
As shown in (A), the screen 61 is composed of, for example, nine pixels and can express a density of 0 (0/9) to 1 (9/9). Here, the density 0 is the minimum density and the density 1 is the maximum density. Screen 61
The density expressed above is based on the pulse width modulation signal D3 generated in the pulse width modulation section 33.

For example, when a density of 1/9 is expressed on the screen 61, the pulse width modulation unit 33 applies three scanning lines each having three pixels to each of the three scanning lines shown in FIG.
The pulse width modulation signal shown in FIG. in this case,
The pulse width modulation signal becomes H (High) level at the position of the pixel 1. When expressing the density from 0/9 to 1/9, the pulse width modulation unit 33 changes the pulse width of the pulse width modulation signal in the pixel 1 according to the density. When the density 2/9 is expressed on the screen 61, the pulse width modulation unit 33 outputs a pulse width modulation signal as shown in FIG. 4C for three scanning lines. That is, the pulse width modulation signal becomes H level at the positions of the pixel 1 and the pixel 2. When the density 4/9 is expressed on the screen 61, the pulse width modulation unit 33 outputs a pulse width modulation signal as shown in FIG. 4D for three scanning lines. That is, the pulse width modulation signal goes high at the positions of pixel 1, pixel 2, pixel 3, and pixel 4. Similarly, when expressing a density other than the above, the pulse width modulation unit 33 outputs a pulse width modulation signal having a pulse width corresponding to the density (256 gradations at maximum) to a predetermined scanning line.

As described above, by changing the pulse width of the pulse width modulation signal for each pixel on the screen 61, up to 256 gradations can be expressed per pixel. However, in the engine 22, the type of the area of the dot formed per pixel is actually about 20 due to the particle diameter of the toner and the like, so that 256 gradations cannot be expressed. However, if the number of gradations that can be expressed on the screen 61 is 20 gradations per pixel,
Nine pixels provide 180 (20 × 9) gradations.

Next, the processing operation of the controller 21 will be specifically described with reference to FIG. First, the processing of the gradation data of the pixel 1 will be described below. The screen processing unit 52 reads out the gradation data “42” of the pixel 1 stored in the page memory 51 (FIG. 5A),
A screen table (gamma table) corresponding to pixel 1 is selected (FIG. 5B). Screen processing unit 52
Refers to the selected screen table, reads the drive pulse width data “255” corresponding to the gradation data “42” (FIG. 5C), and modulates the read drive pulse width data “255” by pulse width modulation. To the unit 33. The pulse width modulation unit 33 supplies the supplied drive pulse width data “25”.
A pulse width modulation signal D3 is generated based on 5 ”(FIG. 5).
(D)), the generated pulse width modulation signal D3 is output to the engine 2
2 to a laser driver 41.

In the case of processing the gradation data of the pixel 2, the screen processing section 52 reads the gradation data "41" of the pixel 2 stored in the page memory 51 (see FIG. 5).
(A)), a screen table (gamma table) corresponding to the pixel 2 is selected (FIG. 5B). The screen processing unit 52 refers to the selected screen table,
Driving pulse width data “1” corresponding to gradation data “41”
20 ”is read (FIG. 5C), and the read drive pulse width data“ 120 ”is supplied to the pulse width modulator 33. The pulse width modulator 33 is based on the supplied drive pulse width data“ 120 ”. A pulse width modulation signal D3 is generated (FIG. 5D), and the generated pulse width modulation signal D3 is supplied to a laser driver 41 in the engine 22.

The processing of the gradation data of each of the pixels 3 to 9 is the same as that of the above-described pixels 1 and 2, and the description thereof is omitted. However, in the example of FIG. 5, the pulse width modulation signals corresponding to each of the pixels 3 to 9 are all 0.

Next, an example of the input / output characteristics of the screen table (gamma table) shown in FIG. 5B is shown in FIG. 6A shows an example of the input / output characteristics of the screen table for the pixel 1, FIG. 6B shows an example of the input / output characteristics of the screen table for the pixel 2, and FIG. 4 shows an example of input / output characteristics. The horizontal axis represents the gradation data (input) of the pixel, and the vertical axis represents the drive pulse width data (output).

As shown in FIG. 6A, in the input / output characteristics of the screen table corresponding to the pixel 1, the drive pulse width data sharply rises to 256 gradations in a region where the gradation data of the pixel is small. On the other hand, the input / output characteristics of the screen table corresponding to the pixel 2 gradually rise with respect to the gradation data of the pixel, as shown in FIG. As shown in FIG. 6C, in the input / output characteristics of the screen table corresponding to the pixel 9, the drive pulse width data sharply rises to 256 gradations in a region where the gradation data of the pixel is large. The input pixel gradation data is 25
It has 6 gradations, and the output drive pulse width data is also composed of 8 bits, and has a resolution of 256. As a result, the screen table memory 53 requires a memory capacity of (256 gradations × 8 bits) × 9 pixels.

[0017]

However, the size of the screen (cell) 61 actually has many pixels, and as a result, the screen table memory 53 stores 25 pixels.
It is necessary to store data of a capacity of one pixel consisting of 6 gradations × 8 bits by the number of pixels, and there is a problem that the capacity of the screen table memory 53 becomes very large.

Further, the screen table memory 53 includes:
Usually, it is constituted by a high-speed SRAM (Static Random Access Memory), and there is a problem that an increase in the memory capacity causes an increase in cost.

An object of the present invention is to provide an electrophotographic apparatus in which the capacity of a screen table memory is reduced without deteriorating image quality.

[0020]

In order to achieve the above object, according to one aspect of the present invention, a screen table (conversion table) for each pixel is stored in a partial area of all gradation values of gradation data. And the correspondence between the gradation data and the image reproduction information. In halftone processing using halftone dots, the conversion table for each pixel may change the output image reproduction information only in a part of the entire gradation value. Therefore, according to the present invention, only the conversion data for the partial area is provided in the conversion table. As a result, the number of data in the screen table can be reduced.

In order to achieve the above object, the present invention provides:
2. Description of the Related Art In an electrophotographic apparatus that reproduces an image by expressing a gradation by halftone dots formed from a plurality of dots, the gradation data to be input has a correspondence between the gradation data and the image reproduction information for each pixel. A halftone processing unit that outputs the image reproduction information with reference to the conversion table, wherein the conversion table for each pixel includes the grayscale data in a partial area of all grayscale values of the grayscale data; It is characterized by being configured in correspondence with image reproduction information.

According to the present invention, the capacity of the screen table (conversion table) memory can be further reduced without deteriorating the image quality of the reproduced image.

[0023] To achieve the above object, the present invention provides:
In an electrophotographic image processing method for reproducing an image by expressing a gradation by using a halftone dot formed of a plurality of dots, the gradation data and the image reproduction information for each pixel are compared with the input gradation data. A halftone processing step of outputting the image reproduction information with reference to a conversion table having correspondence, wherein the conversion table for each pixel includes the halftone value in a partial area of all the grayscale values of the grayscale data. It is characterized by being constituted by the correspondence between key data and image reproduction information.

[0024] To achieve the above object, the present invention provides:
In a recording medium recording a program for causing a computer to execute an image processing procedure of an electrophotograph that reproduces an image by expressing a gradation by halftone dots formed from a plurality of dots,
The image processing procedure includes:
A halftone processing step of outputting the image reproduction information with reference to a conversion table having a correspondence between the gradation data and the image reproduction information for each pixel, and the conversion table for each pixel includes: It is characterized by comprising the correspondence between the gradation data and the image reproduction information in a part of the entire gradation value.

According to another aspect of the present invention, the conversion table is composed of discrete tone values at predetermined intervals and image reproduction information corresponding to the discrete tone values. The corresponding image reproduction information is interpolated to obtain the corresponding output image reproduction information. By doing so, the memory capacity of the conversion table can be further reduced.

In order to achieve the above object, the present invention provides:
2. Description of the Related Art In an electrophotographic apparatus that reproduces an image by expressing a gradation by halftone dots formed from a plurality of dots, the gradation data to be input has a correspondence between the gradation data and the image reproduction information for each pixel. A halftone processing unit that outputs the image reproduction information with reference to the conversion table, the conversion table includes intermittent gradation values at predetermined intervals and image reproduction information corresponding thereto, and the halftone The processing unit obtains the image reproduction information by an interpolation operation on the input gradation data according to the image reproduction information corresponding to the gradation value in the conversion table.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. However, such embodiments do not limit the technical scope of the present invention.

FIG. 7 shows an example of input / output characteristics of a screen table (gamma table) as a conversion table. The horizontal axis represents the pixel gradation data (input), and the vertical axis represents drive pulse width data (output) as image reproduction information. In the example of FIG. 7, gamma tables (input / output characteristics) γ1 to γ corresponding to nine pixels forming the screen 61 are shown.
9 is shown. In the gamma table γ1, the drive pulse width data rapidly rises in a region where the gradation data of the pixel is small, and then rises relatively slowly to the maximum drive pulse width “255”. Conventional gamma table γ
1 indicates that the output drive pulse width data has a maximum value of “255”.
In the region where the input grayscale data is high after reaching the maximum value, the drive corresponding to all the grayscale regions of 0 to 255 of the input grayscale data although most of the output has the maximum value “255”. The pulse width data is stored.

In the gamma tables γ2 and γ3, the drive pulse width data rises relatively slowly with respect to the gradation data of the pixel. In the conventional gamma tables γ2 and γ3, most of the output drive pulse width data has a minimum value “0” in an area where input gradation data is low or high.
Alternatively, the drive pulse width data corresponding to all the gray scale areas from 0 to 255 of the input gray scale data is stored although the maximum value is “255”.

In the gamma table γ9, the drive pulse width data has a maximum value of “25” in a region where the gradation data of the pixel is large.
5 ". In the conventional gamma table γ9, in the region where the input grayscale data is low, the input grayscale , Driving pulse width data corresponding to all the gradation ranges from 0 to 255.

As described above, the gamma tables γ1 to γ9 indicate that the output drive pulse width data is 0 to 255 only in a certain limited range of all the input grayscale data.
The drive pulse width data is the minimum value “0” or the maximum value “255” in other ranges. That is, in the gamma tables γ1 to γ9, although most of the drive pulse width data has the minimum value “0” or the maximum value “255”, the drive pulse Storing the width data leads to increasing the capacity of the screen table memory 53.

The example of the input / output characteristics of the screen table shown in FIG. 7 shows that, for example, in the area (γ1) where the density (gradation value) of the screen (cell) is close to zero, the output value sharply rises, and In a region (γ2, γ3) where the density is relatively low, the change in gradation can be clearly recognized by the human eye, so that the output value rises relatively slowly. Then, in the high density region (γ9), the change in gradation is hardly recognized by the human eye, so the output value is rapidly increased. As described above, in the halftone processing using the screen table, it is necessary to provide a gamma table having different input / output characteristics for each pixel, so that an ideal density change can be given to the human eye. it can.

FIG. 8 shows an example of a screen table (conversion table) for each pixel to which the present invention is applied and its input / output characteristics. FIG. 8A shows an example of a screen table TB1 relating to pixel 1 and its input / output characteristics γ1.
8B shows an example of a screen table TB2 relating to the pixel 2 and its input / output characteristics γ2, and FIG. 8C shows an example of a screen table TB9 relating to the pixel 9 and its input / output characteristics γ9. The horizontal axis of the input / output characteristics represents the gradation data (input) of the pixel, and the vertical axis represents the drive pulse width data (output) as the image reproduction information.

As shown in FIG. 8A, in the screen table of the pixel 1, the drive pulse width data corresponding to the gradation data "0" to "42" changes and needs to be stored. Since the drive pulse width data corresponding to data “43” to “255” is constant at “255”,
In the areas "43" to "255", it is not necessary to store all the drive pulse width data of the output corresponding to the input gradation data. Therefore, here, the minimum grayscale value “0”, the maximum grayscale value “42”, and the grayscale data “0” to “42” of the input grayscale data in the area where the drive pulse width data changes.
Is stored only for the drive pulse width data corresponding to. That is,
Only the part indicated by the solid line in FIG. 8A is the screen table TB.
It is stored as 1.

As shown in FIG. 8B, in the screen table of the pixel 2, the drive pulse width data corresponding to the gradation data "0" to "29" is constant at "0".
In the area from “0” to “29”, it is not necessary to store all of the output drive pulse width data corresponding to the input gradation data. The drive pulse width data corresponding to the gradation data “30” to “50” changes and needs to be stored. However, the drive pulse width data corresponding to the gradation data “51” to “255” is “255”. , It is not necessary to store all of the output drive pulse width data corresponding to the input grayscale data in the area from “51” to “255”. Therefore, here, only the minimum gradation value “30”, the maximum gradation value “50”, and the driving pulse width data corresponding to the gradation data “30” to “50” in the area where the output changes are stored. That is, only the part indicated by the solid line in FIG. 8B is stored as the screen table TB2.

As shown in FIG. 8C, in the screen table of the pixel 9, since the drive pulse width data corresponding to the gradation data "0" to "244" is "0" and constant, this area is It is not necessary to store all of them, but the drive pulse width data corresponding to the gradation data “245” to “255” needs to be stored because they change. Therefore, here, only the minimum gradation value “245”, the maximum gradation value “255”, and the driving pulse width data corresponding to the gradation data “245” to “255” in the area where the output changes are stored. That is, only the portion indicated by the solid line in FIG. 8C is stored as the screen table TB9.

As described above, by reducing the driving pulse width data to be stored, the capacity of the screen table memory 53 can be further reduced. Also,
The area where the screen table changes (change amount) is shown in FIG.
As shown in FIG. 8A, when the gamma table γ1 rises slowly, the length becomes longer, and as shown in FIG. 8C, when the gamma table γ9 rises sharply, the length becomes shorter.
That is, the minimum required table length for each pixel may be secured as the memory capacity.

The configuration of an embodiment of an electrophotographic system to which the present invention is applied is the same as that shown in FIGS. Also in the present embodiment, the page memory 51 stores the supplied CMYK gradation data. Similarly, the screen table memory 53 previously stores a screen table (gamma table) indicating the correspondence between the gradation data and the drive pulse width data (image reproduction information) for each pixel. However, in the present embodiment, the screen table memory 53 stores the minimum gradation value and the maximum gradation value in the area where the driving pulse width data changes, and the image reproduction information (the driving pulse width data) in the area between them. ) Is stored. Thereby, as described above, the data amount of the screen table can be reduced.

FIG. 9 is a flowchart for explaining the processing operation of the controller 21. FIG. 10 is for specifically explaining the processing of the controller 21. 10A shows an example of the gradation data D1 stored in the page memory 51, FIG. 10B shows an example of the screen table 53, and FIG. 10C shows data D2 output by the screen processing unit 52. FIG. 10D shows an example of data D3 output from the pulse width modulation unit 33.

Next, the processing operation of the controller 21 will be described with reference to the flowchart of FIG. 9 and FIG. First, in step S <b> 1, the personal computer 1 supplies RGB gradation data to the color conversion unit 31 via the cable 3.

In step S2, the color conversion section 31
The supplied RGB gradation data is converted into CMYK gradation data, and the CMYK gradation data is stored in the page memory 51.

In step S3, the screen processing section 52 reads out the gradation data for each pixel stored in the page memory 51 (see FIG. 10 (A)).
In step 4, a screen table (gamma table) corresponding to the read pixels is selected (see FIG. 10B).

In step S5, the screen processing section 52 compares the read gradation data of the pixel with the minimum gradation value of the selected screen table.

If it is determined in step S6 that the gradation data of the pixel is equal to or smaller than the minimum gradation value, the process proceeds to step S6.
Then, the screen processing unit 52 generates “0” as the drive pulse width data (see, for example, pixels 3 to 9 in FIG. 10C). If it is determined in step S6 that the gradation data of the pixel is not smaller than the minimum gradation value (greater than the minimum gradation value), the process proceeds to step S8.

In step S8, the screen processing section 52 compares the gradation data of the pixel with the maximum gradation value.
If it is determined that the gradation data of the pixel is equal to or greater than the maximum gradation value, the process proceeds to step S9, where the screen processing unit 52 generates “255” as the driving pulse width data (for example, FIG. 10C). Pixel 1). Step S
In step 8, when it is determined that the gradation data of the pixel is not equal to or larger than the maximum gradation value (smaller than the maximum gradation value), the process proceeds to step S10, where the screen processing unit 52 refers to the screen table 53 and responds. The driving pulse width data is read (for example, refer to the pixel 2 in FIG. 10C).

In step S11, the screen processing section 52 supplies the generated or read drive pulse width data to the pulse width modulation section 33. Pulse width modulator 33
Generates a pulse width modulation signal D3 based on the supplied drive pulse width data (see FIG. 10D), and supplies the generated pulse width modulation signal D3 to the laser driver 41;
The processing operation ends.

FIG. 11 shows a screen table memory 53.
2 shows the configuration of the second embodiment. In the example of FIG. 11, the screen table memory 53 stores the minimum gradation value and the maximum gradation value of the area where the output of each of the pixels 1 to 9 changes, and stores a change table TB11 common to each pixel. Have. This change table TB11
Is a data in which the data of the area where the drive pulse width data (image reproduction information) changes is shared with the gradation data and stored, and has a fixed length for the pixels 1 to 9. The drive pulse width data is composed of 8 bits. First
In the configuration of this embodiment, the screen table is provided for each pixel. However, in the configuration of the second embodiment, a common change table is provided for a plurality of pixels, so that the screen table memory 53 The capacity can be further reduced. However, in this example, as shown in FIG. 7, in order to provide different input / output characteristics for each pixel, predetermined input / output characteristics are determined based on the common change table TB11 and the minimum and maximum gradation values for each pixel. Is required.

FIG. 12 shows a screen table memory 53.
Shows the configuration of the third embodiment. In the example of FIG. 12, the common change table TB11 is omitted from the structure of the second embodiment shown in FIG. 11, and only the minimum gradation value and the maximum gradation value of the output change area in each pixel are included. It has become. Thus, the capacity of the screen table memory 53 can be further reduced. For example, as shown in FIG. 13, the gradation data and the corresponding change in the driving pulse width data are obtained by linear interpolation approximation from the minimum gradation value and the maximum gradation value and the corresponding driving pulse width data. Required by According to such an operation,
It is possible to realize a screen table having input / output characteristics having different inclinations at least for each pixel.

FIG. 14 shows a screen table memory 53.
Of the fourth embodiment is shown. In the example of FIG. 14, in order to reduce the driving pulse width data to be stored, the pixel gradation data “0” (or the minimum gradation value) is set to “X0”.
, And “X7” is made to correspond to the gradation data “255” (or the maximum gradation value) of the pixel, and the interval between them is divided into seven equal parts at a predetermined interval. The gradation data and the corresponding drive pulse width data are stored. The drive pulse width data corresponding to the input gradation data other than the stored eight gradation data is obtained by interpolation approximation.

That is, the drive pulse width data Y0 to Y7 corresponding to the grayscale values X0 to X7 on both sides adjacent to the input grayscale data are read out, and the two drive pulse width data are converted into the input grayscale data by interpolation. Find the corresponding drive pulse width data. At this time, the driving pulse width data corresponding to the even-numbered gradation value and the driving pulse width data corresponding to the odd-numbered gradation value are required. In the example of FIG. 14, an even table TB20 composed of even-numbered gradation values and corresponding drive pulse width data, an odd-numbered gradation value and corresponding driving signals are provided so that data can be read simultaneously. An odd table TB21 composed of pulse width data is provided. Also, the even table T
The drive pulse width data Y0 to Y7 in B20 and the odd number table TB21 are each composed of 8 bits.

FIG. 15 shows the screen tables (even table TB20 and odd table TB2) shown in FIG.
An example of the input / output characteristics of 1) is shown. In the input / output characteristics of FIG. 15, data other than the stored data is
As described above, it is obtained by interpolation approximation. For example, input grayscale data “X2” intermediate between grayscale data “X2” and “X3”
The drive pulse width data “Y23” corresponding to “3” is calculated by the following equation (1) according to linear interpolation.

Y 23 = Y 2 + {(Y 3 −Y 2) × (X 23 −X 2)} / (X 3 −X 2) (1) The screen processing section 52 requires a drive pulse width required for calculating the above equation (1). Data "Y2" and "Y3"
Can be simultaneously read from the even table TB20 and the odd table TB21, respectively. As a result, it is possible to shorten the memory read time and the halftone processing time. Note that the linear interpolation approximation in FIG. 15 has higher accuracy as the input / output characteristics of the screen table rise more rapidly.

If the interval between the gradation data X0 to X7 is d, it is not necessary to store the respective values of the gradation data X0 to X7, so that the capacity of the screen table memory 53 can be further reduced. it can. For example, “X2” and “X3” are obtained by the following equations (2) and (3).

X2 = INT (X23 / d) × d (2) X3 = X2 + d (3) Here, INT indicates that a decimal point in parentheses is rounded down to be converted into an integer.

Further, if each interval of the gradation data X0 to X7 is a power of 2 (X3−X2 = 2 ⁿ ),
In an arithmetic circuit for calculating binary data, (1)
Since the division of the expression (2) can be performed only by the shift operation, the operation time can be shortened.

FIG. 16 is a block diagram showing the configuration of another embodiment of the electrophotographic system. The electrophotographic system shown in FIG. 16 is realized by incorporating the color conversion function and the halftone processing function on the printer 2 side of the electrophotographic system shown in FIG. The driver 92 is a computer program installed in the personal computer 81 in advance. The functions of the application program 91, the color conversion unit 112, the halftone processing unit 113, the pulse width modulation unit 121, the laser driver 131, and the laser diode 132 are the same as those of the application program 11, the color conversion unit 31, This is the same as the halftone processing unit 32, the pulse width modulation unit 33, the laser driver 41, and the laser diode.

In the system example shown in FIG. 16, color conversion processing and halftone processing are performed by the driver 92 installed on the personal computer 81 side. FIG.
In the system example described above, the color conversion processing and the halftone processing are performed by the controller 21 in the printer 2.
In the example of the system shown in FIG.
Do it on the side. If lower price of the printer 82 is required,
It is effective to reduce the capability of the controller 101 and realize the color conversion processing and the halftone processing by the driver program installed in the personal computer 81. When halftone processing is realized by the driver 92, a recording medium in which a program for causing a computer to execute the above halftone processing procedure is stored in the personal computer 81.

The recording medium for providing the user with a computer program for executing the above processing includes information recording media such as a magnetic disk and a CD-ROM, as well as the Internet,
Transmission media via networks such as digital satellites are also included.

Further, in the present embodiment, the interpolation calculation is not limited to linear interpolation. For example, a secondary approximation curve or a tertiary approximation curve may be obtained from nearby values to perform the interpolation calculation.

[0060]

As described above, according to the present invention, since the data amount of the screen table is reduced, the capacity of the screen table memory can be further reduced. Therefore, the cost of the screen table memory can be further reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of an electrophotographic system.

FIG. 2 is a diagram illustrating a configuration example of a halftone processing unit 32 in FIG. 1;

FIG. 3 is a diagram for explaining a screen 61;

FIG. 4 is a diagram for explaining a relationship between a screen 61 and a pulse width modulation signal.

FIG. 5 is a diagram for specifically explaining processing in a controller 21;

6 is a diagram illustrating an example of input / output characteristics of the screen table in FIG.

FIG. 7 is a diagram illustrating an example of input / output characteristics of a screen table.

FIG. 8 is a diagram showing an example of a screen table to which the present invention is applied and its input / output characteristics.

FIG. 9 is a flowchart for explaining a processing operation of the controller 21;

FIG. 10 is a diagram for specifically explaining processing in the controller 21;

FIG. 11 is a diagram showing a configuration of a screen table memory 53 according to a second embodiment.

FIG. 12 is a diagram showing a configuration of a screen table memory 53 according to a third embodiment.

FIG. 13 is a diagram for explaining a method for calculating intermediate data.

FIG. 14 is a diagram showing a configuration of a screen table memory 53 according to a fourth embodiment.

FIG. 15 is a diagram illustrating a technique for calculating intermediate data.

FIG. 16 is a block diagram showing a configuration of another embodiment of the electrophotographic system.

[Description of Signs] 1 Personal computer 2 Printer 21 Controller 22 Engine 31 Color conversion unit 32 Halftone processing unit 33 Pulse width modulation unit 41 Laser driver 42 Laser diode 51 Page memory 52 Screen processing unit 53 Screen table memory (conversion table)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C262 AA05 AA24 AA27 AB07 BB03 BB06 BB10 BB14 BB19 BB23 BB44 BC01 BC07 BC09 BC10 5B057 AA11 CA08 CA12 CB07 CB12 CE13 CH07 DB02 DB09 5C077 LL17 MP02 NN04Q NN17 PP

Claims (10)

[Claims] 1. An electrophotographic apparatus which reproduces an image by expressing a gradation by using halftone dots formed by a plurality of dots. And a halftone processing unit that outputs the image reproduction information with reference to a conversion table having a correspondence with the conversion table. An electrophotographic apparatus comprising a correspondence between the gradation data and image reproduction information. 2. The method according to claim 1, wherein the conversion table for each pixel has a minimum gradation value and a maximum gradation value of an area where the image reproduction information changes in response to a change in the gradation data. An electrophotographic apparatus according to claim 1. 3. The pixel conversion table according to claim 2, wherein the conversion table for each pixel further includes image reproduction information corresponding to gradation data between the minimum gradation value and the maximum gradation value. Electrophotographic equipment. 4. The conversion table for each pixel, wherein a plurality of pixels commonly provide image reproduction information corresponding to gradation data between the minimum gradation value and the maximum gradation value. Item 3. An electrophotographic apparatus according to Item 2. 5. An electrophotographic image processing method for reproducing an image by expressing a gradation by using halftone dots formed by a plurality of dots. A halftone processing step of outputting the image reproduction information with reference to a conversion table having correspondence with image reproduction information, wherein the conversion table for each pixel is a part of all gradation values of the gradation data. An image processing method for an electrophotograph, wherein the image processing method is constituted by the correspondence between the gradation data and the image reproduction information in the region of (1). 6. A recording medium storing a program for causing a computer to execute an image processing procedure of an electrophotograph for reproducing an image by expressing a gradation by using halftone dots formed by a plurality of dots, wherein the image processing procedure comprises: A halftone processing step of outputting the image reproduction information by referring to a conversion table having correspondence between the gradation data and the image reproduction information for each pixel with respect to the inputted gradation data, Wherein the conversion table is configured to correspond to the gradation data and image reproduction information in a part of all gradation values of the gradation data. 7. An electrophotographic apparatus that reproduces an image by expressing a gradation by halftone dots formed from a plurality of dots, wherein the gradation data and the image reproduction information are input for each pixel with respect to the inputted gradation data. A halftone processing unit that outputs the image reproduction information with reference to a conversion table having a correspondence with the conversion table. The conversion table has intermittent gradation values at predetermined intervals and image reproduction information corresponding thereto. The halftone processing unit obtains the image reproduction information by interpolation on the input gradation data according to the image reproduction information corresponding to the gradation value in the conversion table. Photo equipment. 8. The conversion table includes a first conversion table having even-numbered gradation values and corresponding image reproduction information, and a second conversion table having odd-numbered gradation values and corresponding image reproduction information. A conversion table, wherein the halftone processing unit refers to the first and second conversion tables to determine image reproduction information corresponding to the tone values on both sides adjacent to each other. Item 8. An electrophotographic apparatus according to Item 7. 9. An image processing method for an electrophotograph which reproduces an image by expressing a gradation by a halftone dot formed by a plurality of dots, wherein the input gradation data is replaced with gradation data for each pixel. A halftone processing step of outputting the image reproduction information by referring to a conversion table having a correspondence with the image reproduction information, wherein the conversion table includes an intermittent gradation value at a predetermined interval and a corresponding image reproduction The halftone processing step comprises: performing an interpolation operation on the image reproduction information with respect to the input gradation data according to the image reproduction information corresponding to the gradation values on both sides adjacent to each other in the conversion table. An image processing method for an electrophotograph, characterized in that it is obtained. 10. A recording medium storing a program for causing a computer to execute an image processing procedure of an electrophotograph for reproducing an image by expressing a gradation by using halftone dots formed by a plurality of dots, wherein the image processing procedure comprises: A halftone processing step of outputting the image reproduction information by referring to a conversion table having correspondence between the gradation data and the image reproduction information for each pixel with respect to the input gradation data, Has an intermittent gradation value at a predetermined interval and image reproduction information corresponding to the intermittent gradation value, and the halftone processing step includes: A recording medium on which an image processing program is recorded, wherein the image processing program is obtained by an interpolation operation in accordance with image reproduction information corresponding to the gradation values on both sides.