JP2002271624A - Imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrophotographic printer of a high density write group that can realize error diffusion processing at a highspeed and make improvement in the image quality, such as granularity and resolution of an image. SOLUTION: The imaging device that converts received multivalued image data with low resolution into output image data with high resolution, is provided with error arithmetic means (103, 104), that calculate error data caused by quantization in the unit of pixels with low resolution, a generating means 101 that generates multivalued data for pixels with high resolution corresponding to the received multivalued image data with low resolution, a correction means that uses the error data calculated by the error arithmetic means to correct the multivalued data with pixels having high resolution, and a quantization means 102 that quantizes corrected multivalued data of each pixel with high resolution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a laser printer, a digital copying machine, a color laser printer, and a digital color copying machine.

[0002]

2. Description of the Related Art Hitherto, a dither method, a density pattern method, and an error diffusion method have been generally used as a halftone reproducing method in an image forming apparatus. In the dither method, a color is expressed by a plurality of pixels and the combination thereof in a color image. The dither method used for general printing is excellent in graininess and smoothly expresses a halftone image. In the so-called area gradation method represented by the dither method, the resolution deteriorates in order to obtain gradation. Further, in the dither method for generating a periodic image with respect to a print image such as a halftone dot, moire tends to occur.

As a method for expressing gradation while maintaining resolution, there is an error diffusion method. The error diffusion method can obtain a resolution faithful to the original image and is suitable for character image reproduction.However, in halftone images such as photographic parts, isolated dots are arranged in a dispersed or irregularly connected manner. The graininess is poor, and a peculiar texture may occur. In particular, in an electrophotographic printer, an image is unstable because it is formed of isolated dots, and the graininess is deteriorated due to density unevenness and banding is likely to occur.

FIG. 27 is a block diagram of a conventional general error diffusion process. In the error diffusion processing, input multi-valued image data is compared with a threshold value to determine output data of 1 to 2 bits. Then, a difference between the output value and the image data is stored as an error of the pixel. In the next pixel, the output value of the pixel is determined by adding the product of the peripheral pixel and the error matrix coefficients (a to d) corresponding to the pixel to the image data of the target pixel and comparing the result with a threshold value. By repeating the above for each pixel, error diffusion processing in which the density of the image is stored is performed.

[0005] However, the error diffusion process is complicated because the product-sum operation is performed to diffuse the quantization error of peripheral pixels, and the processing time is extremely long. In particular, as the image output density increases, the number of pixels per unit area increases, and the amount of calculation increases. Specifically, the pixel density is changed from 600 dpi to 1
At 200 dpi, the number of pixels increases by 4 times and at 2400 dpi by 16 times, which increases in proportion to the square of the resolution. Therefore, it is necessary to speed up the processing to obtain the same productivity.

[0006] In each of the following two cases, the error diffusion process is performed in a state where the resolution of the input image data is low, and a high resolution binary image data is output. The operation and the circuit required for the error diffusion processing are smaller than those of the first embodiment, and high-speed processing can be performed.

Japanese Unexamined Patent Publication No. Hei 7 (1999) discloses a method in which input image data is converted into a higher resolution by converting the magnification, and the number of gradations is reduced by multi-value error diffusion, and the result is binarized to a higher resolution by a density pattern method or dither. -295527. The purpose of this is to reduce the operation time and prevent an increase in the circuit scale by the buffer memory, obtain a binary image signal with sufficient gradation at high speed, and eliminate moiré and rosette patterns. In this method, the gradation processing of reducing the number of gradations per pixel by multi-level error diffusion and the gradation processing of the density pattern method based on the result are performed twice.

Japanese Patent Application Laid-Open No. H11-155064 discloses a technique in which binary data obtained by error diffusion at low resolution (600 dpi) is converted into binary image data at high resolution (1200 dpi) by pattern matching. I have. This is also intended to greatly improve the granularity of highlight with a small amount of buffer memory and a small amount of processing.

[0009]

However, according to the method described in Japanese Patent Application Laid-Open No. Hei 7-295527, a high density writing such as 1200 dpi or more is required for the dot arrangement in a simple density pattern method or dither method.
In particular, in a printer using an electrophotograph, the higher the density, the lower the dot reproducibility becomes. Therefore, there is a problem that the image quality cannot be improved.Moreover, in the arrangement by the density pattern method or the dither method, the image has periodicity. There is a problem that moire may occur.

In the system described in Japanese Patent Application Laid-Open No. 11-155064, there is little change in the image as compared with the error diffusion processing of 600 dpi, and there is not much improvement.

The present invention has been made in view of the above, and in an electrophotographic printer of a high-density writing system, error diffusion processing is realized at high speed, and image quality such as graininess and resolution of an image is improved. It aims at improvement.

[0012]

According to an aspect of the present invention, there is provided an image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data. Error calculation means for calculating error data generated by quantization in low-resolution pixel units,
Generating means for generating multi-valued data of each corresponding high-resolution pixel from low-resolution input multi-valued image data, and correcting the multi-valued data of each high-resolution pixel using the error data calculated by the error calculating means; And a quantizing means for quantizing the corrected multi-value data of each pixel of high resolution.

According to the present invention, low-resolution input multi-value data can be rapidly converted to high-resolution binary data by error diffusion processing.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the dot size or the degree of concentration of the output dots is controlled using the generation unit. .

According to the present invention, an image can be formed with an optimum dot size (degree of dot concentration) according to the image output device.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the generating unit is configured to sequentially saturate each high-resolution pixel one pixel at a time or in the vicinity thereof. It is characterized in that data is distributed so that

According to the present invention, by dispersing the output dots, it is possible to form an image with good sharpness at an edge portion or a character portion of the image.

According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the generating unit is arranged such that the order of sequentially saturating the high resolution pixels one by one is dispersed. It is characterized by being.

According to the present invention, by dispersing the output dots, an image with good sharpness can be formed at an edge portion or a character portion of the image.

According to a fifth aspect of the present invention, in the image forming apparatus according to the third aspect, the generating means includes a step of setting at least one other pixel before a specific high-resolution pixel is saturated. Data is distributed.

According to the present invention, the output dots are concentrated as the density increases, so that an image having stable and good granularity can be formed in an area where the density change of the image is small.

According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the image forming apparatus further comprises a density region in which multi-value data of each high-resolution pixel is uniform.

According to the present invention, since the output dots are concentrated as the density increases, it is possible to form a stable image with good granularity in an area where the density change of the image is small.

According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, the density region is a medium density portion or a high density portion of the image.

According to the present invention, since the output dots are concentrated as the density increases, a stable image having good graininess can be formed in an area where the density change of the image is small.

According to an eighth aspect of the present invention, in the image forming apparatus according to the third or fifth aspect, the low-resolution input multi-valued image data is a sum of the multi-valued data of each corresponding high-resolution pixel. It is characterized by being equal to

According to the present invention, it is possible to form an output image in which the density is stored for the input image.

According to a ninth aspect of the present invention, in the image forming apparatus of the first aspect, the generation unit is switched in accordance with the characteristics of the image.

According to the present invention, it is possible to achieve both sharpness in an edge portion or a character portion of an image and granularity in a region where a change in image density is small.

The image forming apparatus according to claim 10 is
The image forming apparatus according to any one of claims 1 to 9, wherein a threshold value for binarization is 128 or less.

According to the present invention, it is possible to prevent a delay in the generation of dots peculiar to the error diffusion processing.

Further, according to the image forming apparatus of the present invention,
11. The image forming apparatus according to claim 1, wherein a resolution of the input multi-valued image data is 600 dpi, and a resolution of the output image data is 1200 dpi.

According to the present invention, density conversion of input multi-value data of 600 dpi into output data of 1200 dpi can be performed at high speed.

Further, the image forming apparatus according to claim 12 is
In an image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data, high-resolution output image data periodically generates dots and switches the order of generated dots in the main scanning direction. It is characterized by the following.

According to the present invention, in an image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data, by switching the order of generation of dots generated in the main scanning direction, the main scanning direction is changed. As a result, the spatial frequency of the image is lowered, and a stable image is formed.

The image forming apparatus according to claim 13 is
In an image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data, an error calculating means for calculating error data generated by quantization in low-resolution pixel units; Generating means for generating multi-valued data of each corresponding high-resolution pixel from image data, and correcting means for correcting the multi-valued data of each high-resolution pixel using the error data calculated by the error calculating means,
It is characterized by comprising quantization means for quantizing the multi-value data of each corrected high-resolution pixel, and switching means for switching the generation means in the main scanning direction.

According to the present invention, in an image forming apparatus for converting low-resolution input multi-valued image data (gradation number N) to high-resolution output image data (gradation number M <N), a low-resolution pixel By performing the error diffusion processing in units, the processing time is shortened, and the gradation data of the image is also stored. Also,
By generating multi-valued data of each pixel of high resolution and switching the means for generating multi-valued data of each pixel in the main scanning direction, both stable and highly granular high image quality can be achieved.

Further, according to the image forming apparatus of the present invention,
In an image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data, high-resolution output image data periodically generates dots and switches the order of generated dots in the sub-scanning direction. It is characterized by the following.

According to the present invention, in an image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data, the order of generation of dots generated in the sub-scanning direction is switched, so that As a result, the spatial frequency of the image is lowered, and a stable image is formed.

The image forming apparatus according to claim 15 is
In an image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data, an error calculating means for calculating error data generated by quantization in low-resolution pixel units; Generating means for generating multi-valued data of each corresponding high-resolution pixel from image data, and correcting means for correcting the multi-valued data of each high-resolution pixel using the error data calculated by the error calculating means,
It is characterized by comprising a quantizing means for quantizing the multi-value data of each corrected high-resolution pixel, and a switching means for switching the generating means in the sub-scanning direction.

According to the present invention, in an image forming apparatus for converting low-resolution input multi-valued image data (gradation number N) to high-resolution output image data (gradation number M <N), a low-resolution pixel By performing the error diffusion processing in units, the processing time is shortened, and the gradation data of the image is also stored. Also,
By generating multi-valued data of each pixel with high resolution and switching the means for generating multi-valued data of each pixel in the sub-scanning direction, both stable and highly granular high image quality can be achieved.

Further, according to the image forming apparatus of the present invention,
In an image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data, high-resolution output image data periodically generates dots, and the order of generated dots is determined by main scanning and sub-scanning. Switching in the direction.

According to the present invention, in an image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data, by switching the order of generation of dots generated in the sub-scanning direction, the main scanning direction is changed. Then, the spatial frequency of the image decreases in the sub-scanning direction, and a stable image is formed.

Further, according to the image forming apparatus of the present invention,
In an image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data, an error calculating means for calculating error data generated by quantization in low-resolution pixel units; Generating means for generating multi-valued data of each corresponding high-resolution pixel from image data, and correcting means for correcting the multi-valued data of each high-resolution pixel using the error data calculated by the error calculating means,
It is characterized by comprising a quantizing means for quantizing the multi-value data of each corrected high-resolution pixel, and a switching means for switching the generating means between a main scanning direction and a sub-scanning direction.

According to the present invention, in an image forming apparatus for converting low-resolution input multi-valued image data (gradation number N) to high-resolution output image data (gradation number M <N), a low-resolution pixel By performing the error diffusion processing in units, the processing time is shortened, and the gradation data of the image is also stored. Also,
By generating multi-valued data of each pixel with high resolution and switching the means for generating multi-valued data of each pixel in the sub-scanning direction, more stable and highly granular high image quality can be achieved.

The image forming apparatus according to claim 18 is
An image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data has switching means for periodically generating dots in the high-resolution output image data and switching the order of generated dots. Switching and non-switching are selected according to the characteristics of the image.

According to the present invention, in an image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data, a character portion and an edge portion of the image are periodically converted to high-resolution output image data. The high-resolution processing in which dots are generated and the processing of lowering the image spatial frequency are switched by switching the order in which dots are generated in the picture portion and non-edge portion of the image. Therefore, even in an image in which image types are mixed, an image having both resolution and gradation can be obtained according to the characteristics of the image.

Further, the image forming apparatus according to claim 19 is
An image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data has switching means for periodically generating dots in the high-resolution output image data and switching the order of generated dots. An image having a period twice as long as the input resolution (input 600 dpi and output 300 lines) is formed.

According to the present invention, an image in which the resolution of the input image matches the image spatial frequency of the output image can be obtained.
Even if the resolution of the output image is higher than the resolution of the input image, it is meaningless to form an output image at an excessively high image spatial frequency from the viewpoint of human visual characteristics. Double cycle (300 output with 600 dpi input)
It is desirable to form an image of the order of (line).

Further, the image forming apparatus according to claim 20 is
The image forming apparatus according to any one of claims 12 to 15, wherein control is performed such that dots formed by combining two dots in the main scanning direction or the sub-scanning direction are discretely arranged to form an image. .

According to the present invention, in an electrophotographic printer for high-density writing, by arranging dots in a two-dot combination in the main scanning direction or the sub-scanning direction discretely, the dots are inconspicuous visually. Since it is reproduced stably, it is excellent in gradation and graininess.

Further, the image forming apparatus according to claim 21 is
The image forming apparatus according to claim 16, wherein
It is characterized in that control is performed such that dots formed by combining 2 * 2 dots in the main scanning direction and the sub-scanning direction are discretely arranged to form an image.

According to the present invention, in the electrophotographic printer, by combining two discrete dots in each of the main scanning direction and the sub-scanning direction, the dots are more stable,
Excellent gradation and graininess.

Further, according to the image forming apparatus of the present invention,
The image forming apparatus according to claim 20, wherein
The combined dots are arranged in a staggered manner.

According to the present invention, by arranging the combined dots in a staggered pattern, the granularity is improved, and the resolution is reduced, and the image is compatible with both images, that is, both characters and photographs. The resulting image is obtained.

The image forming apparatus according to claim 23 is
An image forming apparatus according to any one of claims 11 to 17, wherein a continuous line-shaped image is formed in the sub-scanning direction.

According to the present invention, a stable image can be obtained by forming an image connected in a line in the image forming direction at the middle density portion of the image. Further, in the vertical line image, the change of the overlapping of the latent images of the exposure beam is small with respect to the unevenness of the image forming speed in the sub-scanning direction, and the banding is hardly generated.

[0058]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the image forming apparatus of the present invention will be described in detail with reference to the accompanying drawings.

(Embodiment 1) FIG. 1 is a schematic view showing an embodiment of an image forming apparatus comprising a digital copying machine to which the present invention is applied. The digital copying machine includes a scanner 400 as an image reading device, an image recording device 411 including a laser printer as an image forming unit, and a circuit described later. The scanner 400 illuminates an original such as a bookbinding original placed on a flat original platen 403 with an illumination lamp 502, and forms a reflected light image on a reading sensor 507 via mirror groups 503 to 505 and a lens 506. The illumination lamp 502 and the mirror groups 503 to 5
The document is scanned by reading the document information by moving the reference numeral 05, and is converted into an electric image signal. An image signal obtained by the reading sensor 507 is sent to the printer 411 via a circuit described later.

The scanner 400 transmits data read at 8 bits per pixel at 600 dpi, that is, at 256 gradations.

In the printer 411, a writing device 508 comprising a writing optical unit as exposure means
Converts an image signal into an optical signal and exposes it to an image carrier made of a photoconductor, for example, a photoconductor drum 509, and performs optical writing corresponding to a document image to form an electrostatic latent image. The writing optical unit 508 drives the semiconductor laser by the light emission drive control unit based on the image signal, emits a laser beam intensity-modulated by the image signal, and deflects and scans the laser beam by the rotary polygon mirror 510 to perform f / θ. Irradiate the photosensitive drum 509 via the lens and the reflection mirror 511.

The printer 411 writes binary data, that is, one dot on or off at 1200 dpi in both the main scanning and sub-scanning directions as a standard, and forms a high-definition image. In addition, a mode is provided in which the writing laser light is modulated at a high speed to write 2 bits of data per dot, that is, 4 values. Further, a function of changing the writing resolution according to the mode is provided, and writing can be performed at 2400 dpi, or at a vertical and horizontal flat pitch of 1200 dpi in the main scanning direction and 600 dpi in the sub-scanning direction.

The photosensitive drum 509 is rotated and driven clockwise as indicated by an arrow by a driving unit, and is uniformly charged by a charger 512 as a charging unit. A latent image is formed. The electrostatic latent image on the photosensitive drum 509 is developed into a toner image by a developing device 513, and a transfer material made of transfer paper is transferred to one of a plurality of paper feed units 514 to 518 and a manual paper feed unit 519. Is supplied to the registration roller 520 from the printer.

The registration roller 520 is connected to the photosensitive drum 50.
A transfer bias is applied from a transfer power supply to the transfer belt 521 to convey the transfer paper to the toner image on the photosensitive drum 50.
9 to transfer the toner image on the transfer paper. The transfer paper is conveyed by a conveyance belt 521, the toner image is fixed by a fixing unit 522, and is discharged to a discharge tray 523 as a copy. After the transfer of the toner image, the photosensitive drum 509 is cleaned by the cleaning device 524 and is gradually charged by the electric charger 525 to prepare for the next image forming operation.

FIG. 2 shows the image processing of the digital copying machine and the flow of image data. Scanner processing for correcting read data, digital image processing for processing and correcting a digital image, and writing processing for modulating a write LD are roughly classified. The data level of 600 dpi analog data read by the CCD is adjusted by AGC. Analog data of each pixel is converted to 8 bi per pixel by AD conversion.
The value is converted into a digital value of t, and variations in the pixels and illuminance of the read CCD are corrected by shading correction. Next, a filtering process is performed. Specifically, MTF correction for correcting the amplitude of an image generated by reading and smoothing processing for smoothly expressing a halftone image are performed. Then, scaling processing in the main scanning direction is performed in accordance with the copy magnification, and γ correction for converting the writing density into writing density is performed. Finally, halftone processing is performed, and 1 or 2 bits per dot
The data is converted and transmitted. In addition, background removal processing,
Unillustrated processes such as a flare removal process, a scanner γ, and image editing are added.

The error diffusion processing for quantizing image data according to the present invention is arranged in the halftone processing section.

FIG. 3 is a block diagram showing the multi-value data generation processing according to the first embodiment, and FIG. 4 is a processing flow. First, the low-resolution ( _RL ) 1
The multi-value data of each corresponding high-resolution (R _H ) pixel is generated from the input multi-value data of the pixel, and the peripheral error calculated for each low-resolution pixel is added. Next, the binarizing means 102
Then, the ON / OFF of each pixel is determined by binarizing the data to which the peripheral error has been added. Also, the output value calculation unit 103 calculates the output value of one pixel of low resolution from ON / OFF of each pixel of high resolution, and subtracts this output value from the sum of the input multi-valued data and the peripheral error to obtain the error. The value is diffused to peripheral pixels by the error buffer 104 as a value.

Hereinafter, the case where R _H = R _L × 2 (the case where the output resolution is twice the input resolution) will be specifically described. The multi-value data generation means 101 in FIG. 3 generates multi-value data of 2 × 2 pixels from input multi-value data of one pixel of low resolution. At this time, the average value of the data of 2 × 2 pixels is made equal to the input multi-value data of one pixel of low resolution. As an example, if the input multi-value data is 30, 70, 13
FIG. 5 shows a method for generating data of 2 × 2 pixels in the case of 5,200.
Shown in

As shown in FIG. 5, 2 × 2 pixels (A to D)
Data is concentrated on one pixel A, and when the data of pixel A reaches 255, data of A to D is determined by a method of distributing data to the next pixel B. When the input multi-valued data is 30, the data value of the pixel A becomes 120 by allocating the data only to the pixel A, and all the remaining pixels become 0. When the input multi-valued data is 70, the pixel A is 255, the pixel B is 25, and the pixels C and D are 0.
When the input multi-valued data is 135, pixels A and B are 25
5, the pixel C becomes 30, and the pixel D becomes 0. When the input multi-value data is 200, pixels A, B, and C are 255,
Becomes 35.

As described above, the data of each of the pixels A to D is determined, and the sum of the data value and the error calculated at the resolution _RL is compared with a threshold value (for example, 128). ON / OFF is determined. Also, A ~
An output value at the resolution _RL is calculated from the binarization result of D. The output value is 64 when one of the pixels A to D is ON, 128 when it is two pixels, 192 when it is three pixels, and 192 when it is three pixels.
In the case of four pixels, a value corresponding to the number of ON pixels, such as 255, is used. An error calculation is performed using the difference between the value obtained by adding the marginal error to the input multi-valued data and the output value as an error.

FIGS. 6A to 6D show the state of binary data after processing according to this embodiment. (A) is a low concentration part,
(D) represents a high density portion. In the low density portion, only the pixel corresponding to the pixel A is turned ON. As the density increases as shown in (b) to (d), pixels B, C, and D are turned on in this order.

As described above, the error calculation is performed in units of low-resolution pixels, and the binarization is performed in units of high-resolution pixels. Data can be obtained. Further, by arranging A to B and C to D in a staggered manner and sequentially generating dots from A, it is possible to form an image with high sharpness at an edge portion or a character portion of the image.

(Embodiment 2) In Embodiment 2 of the present invention, a low-resolution 1
Another method of generating 2 × 2 pixel multi-value data from pixel input multi-value data will be described.

FIG. 7 shows that the input multivalued data is 15, 30, 6
A method for generating data of 2 × 2 pixels at 0, 80, 100, and 150 will be described. The order of data distribution (A to D) is different from that of the first embodiment, and A and B are arranged so as to be continuous in the sub-scanning direction.

When the input multi-value data is 15, the pixel A becomes 60 by allocating the data only to the pixel A, and the other pixels become 0. When the number of input multi-value data is 30, the data is distributed to pixel A up to 100, and the remaining 20 is distributed to pixel B. Similarly, pixels B and C have data of 10
When it becomes 0, data is distributed to the next pixel. Therefore,
When the input multi-value data is 100, all four pixels are 10
It becomes 0. If the input multi-value data is 100 or more, 4
All pixels have the same value as the input multi-value data. In this manner, the data of each of the pixels A to D is determined, and the binarization and the error calculation are performed as in the first embodiment.

FIGS. 8A to 8D show the state of binary data after processing according to this embodiment. (A) is a low concentration part,
(D) represents a high density portion. In the low-density portion, only the pixel corresponding to the pixel A is turned ON as shown in (a). However, when the input data becomes 50 or more, the data of the pixel A and the pixel B become the same value (100). Only the corresponding pixel is not turned on. That is, as shown in FIG.
And the pixel B are turned ON at the same time. Further, the input data 75
Above, since the data of the pixel C becomes the same,
As shown in (c), three pixels are simultaneously turned on. When the input data is 100 or more, since all four pixels have the same value as the input data, the four pixels are simultaneously turned on as shown in (d).

With the above-described configuration, in the low density portion of the image, since the gradation is reproduced with the high-resolution isolated dots, an image in which the dots are inconspicuous and the granularity is good can be obtained. Further, since the output dots concentrate as the density increases, an image having stable and good granularity is formed in an area where the change of the input image data is small.

(Embodiment 3) In Embodiment 3 of the present invention, another method for generating multi-value data of 2 × 2 pixels from low-resolution input multi-value data of one pixel will be described.

FIG. 9 shows a method for generating data of 2 × 2 pixels for input multivalued data of 30 to 200. Up to 50 pieces of input multi-valued data, data is distributed up to 100 in the order of pixels A and B in the same manner as in the second embodiment. Input multi-valued data is 5
In the case of 0 to 80, the data of the pixels A and B are simultaneously increased. When the input multivalued data is 80 to 120, pixels A and B are set to 160, and the rest is allocated to pixel C. When the input multi-valued data is 120 to 160, the pixels A, B, and C are set to 160,
The rest is allocated to pixels D. When the input multi-value data is 160 or more, all four pixels have the same value as the input multi-value data.

Thus, even when the data of 2 × 2 pixels of high resolution is determined, the same effect as that of the second embodiment can be obtained. The difference from the second embodiment is that pixels A,
A state in which B and C are simultaneously turned on (a state shown in FIG. 8C).
However, it is slower than the second embodiment. The present invention is not limited to the second embodiment and the present embodiment, and it is possible to adjust the degree of concentration of output dots by changing the data generation method for each pixel with high resolution.

(Embodiment 4) In Embodiment 4 of the present invention, an example is shown in which a method for generating 2 × 2 pixel multi-value data from low-resolution 1-pixel input multi-value data is switched according to the characteristics of an image. . A case where an edge amount is used as a feature of an image will be described.

FIG. 10 shows a block diagram of this embodiment, and FIG. 11 shows a processing flow. In this embodiment, in addition to the configuration of the first embodiment, a means for determining an edge / non-edge based on an output from an edge extraction filter is added.

The edge extraction filter is a differential filter of a 5 * 5 matrix as shown in FIG. 12, and extracts a change in image data in a certain direction. FIG. 12A detects an image edge in the main scanning direction, and FIG. 12B detects an image edge in the sub-scanning direction. 12 (c) and 12 (d) similarly detect an image edge in an oblique 45 ° direction. Next, with respect to the detected image edge signals in the four directions, the largest value of the pixel, that is, the value in the direction in which the edge is the largest, is extracted for each pixel, and is set as the edge amount. When the edge amount of each pixel is larger than a predetermined value, the pixel is determined as an edge portion.

The method for generating 2 × 2 pixel multi-value data from low-resolution 1-pixel input multi-value data is switched according to the edge / non-edge determination result. In the edge / non-edge determination, if it is determined to be an edge portion, data is sequentially distributed from pixel A to 255 in the same manner as in the first embodiment. On the other hand, when it is determined that the pixel is a non-edge, data of each pixel is determined so that dots are concentrated as the density increases, as in the second or third embodiment. Error addition after each pixel data decision, binarization,
Output value calculation and error calculation are the same as in the first embodiment.

As described above, by switching the method of generating each pixel data of high resolution depending on the edge / non-edge of the image, the dots are dispersed and output one by one at the edge of the image, so that sharpness is reduced. And a good image is formed. On the other hand, in the non-edge portion of the image, dots are intensively output as the density increases, so that an image with stable and good granularity is formed. Therefore,
An image having both sharpness and graininess can be obtained even in an image in which characters and photographs are mixed.

In this embodiment, the edge amount by the edge extraction filter is used as a feature of the image. However, the method of detecting the feature of the image is not limited to this. Edge / non-edge of the image may be determined from the difference between the edge and the edge. Alternatively, a separate detection unit is provided to detect a character, a pattern, a halftone image of a specific frequency, and the like.
The generation method of each pixel data of high resolution may be switched according to the feature.

In the first to fourth embodiments, the case where the output resolution is twice as large as the input resolution has been described. By determining the data of the output pixel, high-speed error diffusion processing can be performed.

FIG. 13 shows an example in which the output resolution is four times the input resolution. In this case, multi-value data of 4 × 4 pixels (A to P) is generated from the input multi-value data of one pixel. In (a), since A to P are arranged in a dispersed manner, dots are dispersed and output by sequentially allocating data from the pixel A as in the first embodiment. Also,
In (b), since A to P are arranged so as to concentrate,
By the same data distribution as in the second or third embodiment, it is possible to concentrate output dots as the density increases.

FIG. 14 shows an example in which the output resolution is twice the input resolution in the main scanning direction and the same as the input resolution in the sub-scanning direction. In this case, high-speed error diffusion processing is possible by generating multi-value data of two pixels (A, B) from input multi-value data of one pixel.

(Embodiment 5) FIG. 15 shows Embodiment 5 of the present invention.
3 is a block diagram showing a multi-value data generation process of FIG. The fifth embodiment has basically the same configuration as that of the first embodiment shown in FIG. 3 except that the main scanning is performed by the multi-value data generating means 101 via the dot phase switching means 105. This is the point that the counter of the direction and the counter of the sub-scanning direction are input.

The multi-value data generating means 101 in the block diagram shown in FIG. 15 receives a counter in the main scanning direction and a counter in the sub-scanning direction. The counter in the main scanning direction is 1
The counter in the sub-scanning direction is synchronized with the pixel writing clock, and is synchronized with the writing one-line signal. Within the multi-value data generation means 101, the use of the counter in the main scanning direction and the counter in the sub-scanning direction, or both counters, are selectively switched.

When the above counter is not used, a dot pattern as shown in FIG. 6 is formed for each density by a regular arrangement of A to D as shown in FIG. The following process is performed by switching the arrangement cycle.

FIGS. 16 to 18 show examples of dot patterns generated when the regular phase from A to D is changed using a counter in the main scanning direction.

The basic pattern shown in FIG. 16A is a pattern alternately switched in the main scanning direction as shown in FIG. 16B. Since the uniform image portion generates dots in order from A due to the increase in density, a discrete pattern is generated in which two dots are combined in the main scanning direction as shown in FIG. Next, as shown in (d), a staggered pattern is formed by combining two dots at a time in the main scanning direction, and grows sequentially as shown in (e). The discrete staggered pattern has a relatively high spatial frequency of dot generation and maintains resolution, and is suitable for reproducing characters and fine lines.

The basic pattern shown in FIG. 17A is a pattern which is alternately switched in the main scanning direction as shown in FIG. 17B. The dot generation patterns of the low-density part (c) and the high-density part (e) of the image are the same as those in FIG. 16, but in the middle-density part shown in (d), two dots whose dot arrangement is connected to the sub-scanning direction It becomes a line with a width of 12
In the 00 dpi writing, a vertical line image of 300 LPI is formed. A line-shaped image is stable for image formation by an electrophotographic printer, and a line-shaped image connected to an image forming direction hardly causes banding.

The basic pattern shown in FIG. 18A is a pattern which is alternately switched in the main scanning direction as shown in FIG. The dot generation patterns in the low-density part (c) and high-density part (e) of the image are the same as those in A17 in FIG. 16, but in the middle-density part shown in (d), the dot arrangement is connected to the main scanning direction. It becomes a line with a width of one dot. In the 1200 dpi writing, a 600 LPI high-resolution horizontal line image is formed, and this line is not visually recognized.

FIGS. 19 to 21 show examples of dot patterns generated when the regular phase from A to D is changed using a counter in the sub-scanning direction.

The basic pattern shown in FIG. 19A is a pattern which is alternately switched in the sub-scanning direction as shown in FIG. Since the image uniform portion generates dots in order from A due to an increase in density, as shown in (c), a discrete pattern generated by combining two dots in the sub-scanning direction is generated. Next, as shown in (d), a staggered pattern is formed by combining two dots at a time in the main scanning direction, and grows sequentially as shown in (e).

The basic pattern shown in FIG. 20A is a pattern alternately switched in the sub-scanning direction as shown in FIG. The dot generation patterns of the low-density part (c) and the high-density part (e) of the image are the same as those in FIG. 19, but in the middle-density part shown in (d), one dot whose dot arrangement is connected to the sub-scanning direction It becomes a line with a width of 12
In the 00 dpi writing, a high-resolution vertical line image of 600 LPI is formed.

The basic pattern shown in FIG. 21A is a pattern alternately switched in the sub-scanning direction as shown in FIG. The dot generation patterns of the low density part (c) and the high density part (e) of the image are the same as those of A20 in FIG. 19, but in the middle density part shown in FIG. It becomes a line with a width of 2 dots.

FIGS. 22 to 24 show examples of dot pattern generation when the regular phases A to D are changed using the counters in the main and sub scanning directions.

The basic pattern shown in FIG. 22A is a pattern which is alternately switched in both the main scanning direction and the sub-scanning direction as shown in FIG. Since the image uniform portion generates dots in order from A due to an increase in density,
As shown in (c), a discrete pattern is generated in which four dots each consisting of two main scanning dots and two sub-scanning dots are combined.
Next, as shown in (d), a four-dot connection pattern is generated between the four-dot connection patterns, resulting in a staggered pattern. Thereafter, as shown in FIG. Since the stable combination patterns of four dots are arranged in a staggered manner so as to be discrete, the granularity and resolution of the image can be obtained. As in the above-described example, as the density shifts from the state (c) to the state (d), the spatial frequency of the image becomes twice as high, and the effect of increasing the resolution is obtained.

The basic pattern shown in FIG. 23A is a pattern alternately switched in both the main scanning direction and the sub-scanning direction as shown in FIG. The dot generation patterns in the low density part (c) and the high density part (e) of the image are the same as those in FIG. 22, but in the middle density part shown in FIG.
The dot arrangement becomes a 2-dot wide line extending in the sub-scanning direction and 300 LPI in 1200 dpi writing.
Is formed. The 300 LPI line is at a level that is not visually recognized and has high image stability.

The basic pattern shown in FIG. 24A is a pattern which is alternately switched in both the main scanning direction and the sub-scanning direction as shown in FIG. The dot generation patterns of the low density part (c) and the high density part (e) of the image are the same as those of A23 in FIG. 22, but in the middle density part shown in (d), the dot arrangement is connected to the main scanning direction. It becomes a line with a width of 2 dots.

FIG. 25 shows a flowchart including a process of converting the image period. As described above, the switching process is performed according to the features of the image. The features of the image detected from the image are classified into patterns such as patterns, characters, and line drawings, and spatial changes in the image in the form of edges and non-edges (image flat portions). Carve out. The image feature detection processing may be performed by a method different from that of the embodiment of the present invention. A character, a line drawing, or an edge portion where image resolution is required is formed such that the dot arrangement thereof has a high frequency as shown in FIGS. On the other hand, a non-edge portion of a picture or an image is controlled so as to be a low-frequency image so as to perform stable and smooth gradation reproduction. According to the set mode, mode 1 performs phase switching in the main scanning direction, mode 2 performs phase switching in the sub-scanning direction, and mode 3 selects a pattern in which phase switching has been performed in the main and sub-scanning directions. Subsequent processes are common, and are controlled in the same manner as in FIGS.

FIG. 26 shows an example of pattern generation orders A to P in the case of converting an image with an input of 600 dpi into an output of 2400 dpi, that is, a resolution of 4 * 4. Although all combinations are not shown, as shown in (c), by adopting a configuration in which the pixels are ranked from the end, the above-described dot combining process using the phase works efficiently. In this way, it is possible to adapt to different output resolutions, and it is possible to reproduce at an image frequency suitable for the output device.

It is possible to combine the phase processing of the present invention with the dot distribution of the multi-value data from A to D as shown in FIGS. 7 and 9. As a result, it is possible to set the dot size by combining dots in accordance with the characteristics of the output device and the spatial frequency of image formation.

[0108]

As described above, according to the image forming apparatus of the present invention (claim 1), low-resolution input multi-value data is rapidly converted to high-resolution binary data by error diffusion processing. Can be. That is, in an electrophotographic printer of a high-density writing system, error diffusion processing can be realized at high speed, and image quality such as image graininess and resolution can be improved.

Further, the image forming apparatus of the present invention (Claim 2)
According to this, an image can be formed with an optimum dot size (a degree of concentration of dots) according to an image output device.

Further, the image forming apparatus of the present invention (Claim 3,
According to 4), by dispersing the output dots, it is possible to form an image with good sharpness at an edge portion or a character portion of the image.

Further, the image forming apparatus of the present invention (Claims 5 to 5)
According to 7), the output dots are concentrated as the density increases, so that an image with stable and high granularity can be formed in an area where the density change of the image is small.

The image forming apparatus of the present invention (claim 8)
According to the above, it is possible to form an output image in which the density is stored for the input image.

The image forming apparatus according to the present invention (claim 9)
According to the method, by changing the degree of concentration of output dots in accordance with the characteristics of an image, it is possible to achieve both sharpness in an edge portion or a character portion of an image and granularity in a region where a change in image density is small.

Further, the image forming apparatus of the present invention (Claim 1)
According to 0), by setting the threshold value to 128 or less, it is possible to prevent a delay in dot generation in a low density portion.

Further, the image forming apparatus of the present invention (Claim 1)
According to 1), high-density conversion of input multi-valued data of 600 dpi to output data of 1200 dpi can be achieved at a high speed in an electrophotographic printer of 1200 dpi output.

The image forming apparatus according to the present invention (Claim 1)
According to 2), by switching the generation order of the dots generated in the main scanning direction, the spatial frequency of the image is reduced in the main scanning direction, and a stable image can be formed.

Further, the image forming apparatus of the present invention (Claim 1)
According to 3), the processing time is shortened by performing the error diffusion processing in units of low-resolution pixels, and the gradation data of the image can be stored. Further, by generating multi-value data of each pixel with high resolution and switching the means for generating multi-value data of each pixel in the main scanning direction, it is possible to achieve both stable and high-quality high-quality images.

Further, the image forming apparatus of the present invention (Claim 1)
According to 4), by switching the generation order of the dots generated in the sub-scanning direction, the spatial frequency of the image is reduced in the sub-scanning direction, and a stable image can be formed.

Further, the image forming apparatus of the present invention (Claim 1)
According to 5), the processing time is shortened by performing the error diffusion processing in units of low-resolution pixels, and the gradation data of the image is also stored. Further, by generating multi-value data of each pixel of high resolution and switching the means for generating multi-value data of each pixel in the sub-scanning direction, it is possible to achieve both stable and highly granular high image quality.

Further, the image forming apparatus of the present invention (Claim 1)
According to 6), by switching the generation order of the dots generated in the sub-scanning direction, the spatial frequency of the image is reduced in the main scanning direction and the sub-scanning direction, and a stable image can be formed.

Further, the image forming apparatus of the present invention (Claim 1)
According to 7), the processing time is shortened by performing the error diffusion processing in units of low-resolution pixels, and the gradation data of the image can be stored. Further, by generating multi-value data of each pixel of high resolution and switching the means for generating multi-value data of each pixel in the sub-scanning direction, it is possible to achieve both higher stability and higher image quality with higher granularity.

Further, the image forming apparatus of the present invention (Claim 1)
According to 8), high-resolution processing in which the character portion and the edge portion of the image have periodically generated dots in the output image data of high resolution, and the pattern portion and the non-edge portion of the image generate the generated dots. The order can be switched, and the process of lowering the image spatial frequency can be switched. Therefore, even in an image in which image types are mixed, an image having both resolution and gradation can be obtained according to the characteristics of the image.

Further, the image forming apparatus of the present invention (Claim 1)
According to 9), from the viewpoint of human visual characteristics, an image in which the resolution of the input image matches the image spatial frequency of the output image can be obtained. For example, a cycle twice as long as the input resolution (input 600d
It is desirable to form an image of about 300 lines at pi).

The image forming apparatus of the present invention (claim 2)
According to 0), in an electrophotographic printer of high-density writing, by discretely arranging dots that are two dots combined in the main scanning direction or the sub-scanning direction, the dots are inconspicuous visually and stably. Since the image is reproduced, an image excellent in gradation and graininess can be obtained.

Further, the image forming apparatus of the present invention (Claim 2)
According to 1), in an electrophotographic printer, by arranging two discrete dots in the main scanning direction and in the sub-scanning direction in a discrete manner, a more stable image excellent in gradation and graininess can be obtained. can get.

Further, the image forming apparatus of the present invention (Claim 2)
According to 2), by arranging the combined dots in a zigzag pattern, the graininess is improved, the resolution is reduced, and an image that is compatible with both, that is, an image that is compatible with both characters and photographs, is obtained. can get.

Further, the image forming apparatus of the present invention (Claim 2)
According to 3), by arranging the combined dots in a zigzag pattern, the graininess is improved, and the reduction in resolution is reduced, and an image compatible with both, that is, an image suitable for both characters and photographs is obtained. can get.

[Brief description of the drawings]

FIG. 1 shows the configuration of an image forming apparatus (Japanese Patent Application Laid-Open No. H11-41456).
20 (quoted from FIG. 19).

FIG. 2 is an explanatory diagram showing a flow of image processing and image data of a digital copying machine.

FIG. 3 is a block diagram illustrating multi-value data generation processing according to the first embodiment;

FIG. 4 is a flowchart of a multi-value data generation process according to the first embodiment.

FIG. 5 is an explanatory diagram illustrating a method for generating multi-value data of each pixel with high resolution according to the first embodiment;

FIG. 6 is an explanatory diagram showing binary data after processing according to the first embodiment;

FIG. 7 is an explanatory diagram showing a method for generating multi-value data of each pixel with high resolution according to the second embodiment.

FIG. 8 is an explanatory diagram showing binary data after processing according to the second embodiment.

FIG. 9 is an explanatory diagram illustrating a method for generating multi-value data of each pixel with high resolution according to the third embodiment.

FIG. 10 is a block diagram illustrating multi-value data generation processing according to a fourth embodiment.

FIG. 11 is a flowchart of a multi-value data generation process according to the fourth embodiment.

FIG. 12 is an explanatory diagram showing an edge extraction filter.

FIG. 13 is an explanatory diagram in the case of performing resolution conversion to 4 × 4 times.

FIG. 14 is an explanatory diagram in the case of performing resolution conversion to 2 × 1.

FIG. 15 is a block diagram of a fifth embodiment.

FIG. 16 is an explanatory diagram showing dot generation order according to the fifth embodiment.

FIG. 17 is an explanatory diagram showing dot generation order according to the fifth embodiment.

FIG. 18 is an explanatory diagram showing dot generation order according to the fifth embodiment.

FIG. 19 is an explanatory diagram showing dot generation order according to the fifth embodiment.

FIG. 20 is an explanatory diagram showing dot generation order according to the fifth embodiment.

FIG. 21 is an explanatory diagram showing dot generation order according to the fifth embodiment.

FIG. 22 is an explanatory diagram showing dot generation order according to the fifth embodiment.

FIG. 23 is an explanatory diagram showing the order of dot generation in the fifth embodiment.

FIG. 24 is an explanatory diagram showing dot generation order according to the fifth embodiment.

FIG. 25 is a flowchart including image cycle conversion according to the fifth embodiment.

FIG. 26 is an explanatory diagram in the case of performing resolution conversion to 4 × 4 times.

FIG. 27 is a block diagram showing a conventional error diffusion process.

[Explanation of symbols]

 400 scanner 411 image recording device 411 printer 101 multi-value data generation means 102 binarization means 103 output value calculation unit 104 error buffer 105 dot phase switching means

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshihiro Takesue 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. 5B057 CA08 CA16 CB07 CB12 CB16 CE13 5C077 LL18 LL19 NN04 NN07 NN11 PP20 PP28 PP47 PQ08 RR08

Claims (23)

[Claims] 1. An image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data, comprising: error calculating means for calculating error data generated by quantization in units of low-resolution pixels; Generating means for generating multi-valued data of each corresponding high-resolution pixel from input multi-valued image data of a resolution, and correcting the multi-valued data of each high-resolution pixel using the error data calculated by the error calculating means. An image forming apparatus, comprising: a correcting unit; and a quantizing unit that quantizes multi-value data of each corrected high-resolution pixel. 2. The image forming apparatus according to claim 1, wherein the generation unit controls a dot size of the output dots or a degree of concentration of the dots. 3. The image processing apparatus according to claim 1, wherein the generating unit stores each high-resolution pixel as one pixel.
2. The image forming apparatus according to claim 1, wherein the data is distributed so as to be sequentially saturated for each pixel or to be in the vicinity thereof. 4. The generating means sets each pixel of high resolution to 1
The image forming apparatus according to claim 3, wherein the order in which the pixels are sequentially saturated is dispersed. 5. The image forming apparatus according to claim 3, wherein the generation unit allocates data to at least one other pixel before a specific high resolution pixel is saturated. 6. The image forming apparatus according to claim 5, further comprising a density area in which multi-value data of each pixel of high resolution is equal. 7. The image forming apparatus according to claim 6, wherein the density region is a middle density portion or a high density portion of an image. 8. The image forming apparatus according to claim 3, wherein the low-resolution input multi-valued image data is equal to the sum of the multi-valued data of each corresponding high-resolution pixel. 9. The image forming apparatus according to claim 1, wherein the generation unit is switched according to characteristics of an image. 10. The image forming apparatus according to claim 1, wherein the binarization threshold is set to 128 or less. 11. The resolution of input multi-valued image data is 600
dpi and the resolution of the output image data is 1200 dpi
The image forming apparatus according to claim 1, wherein i is i. 12. An image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data, wherein the high-resolution output image data periodically generates dots,
An image forming apparatus characterized in that a generation order of generated dots is switched to a main scanning direction. 13. An image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data, comprising: error calculating means for calculating error data generated by quantization in units of low-resolution pixels; Generating means for generating multi-valued data of each corresponding high-resolution pixel from input multi-valued image data having a resolution, and correcting the multi-valued data of each high-resolution pixel using the error data calculated by the error calculating means. An image forming apparatus comprising: a correcting unit that performs quantization; a quantizing unit that quantizes multi-value data of each corrected high-resolution pixel; and a switching unit that switches the generating unit in a main scanning direction. . 14. An image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data, wherein the high-resolution output image data periodically generates dots,
An image forming apparatus characterized in that a generation order of generated dots is switched in a sub-scanning direction. 15. An image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data, comprising: error calculating means for calculating error data generated by quantization in units of low-resolution pixels; Generating means for generating multi-valued data of each corresponding high-resolution pixel from input multi-valued image data having a resolution, and correcting the multi-valued data of each high-resolution pixel using the error data calculated by the error calculating means. An image forming apparatus, comprising: a correcting unit that performs quantization; a quantizing unit that quantizes multi-value data of each corrected high-resolution pixel; and a switching unit that switches the generating unit in a sub-scanning direction. . 16. An image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data, wherein the high-resolution output image data periodically generates dots,
An image forming apparatus for switching the order of generated dots between a main scanning direction and a sub-scanning direction. 17. An image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data, comprising: an error calculating means for calculating error data generated by quantization in units of low-resolution pixels; Generating means for generating multi-value data of each corresponding high-resolution pixel from input multi-value image data of a resolution, and correcting the multi-value data of each high-resolution pixel using the error data calculated by the error calculating means. Correction means, a quantization means for quantizing the multi-value data of each corrected high-resolution pixel, and a switching means for switching the generation means between a main scanning direction and a sub-scanning direction. Image forming device. 18. An image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data, wherein the high-resolution output image data periodically generates dots,
Switching means for switching the generation order of generated dots,
An image forming apparatus, wherein switching and non-switching are selected according to characteristics of an image. 19. An image forming apparatus for converting low-resolution input multi-valued image data into high-resolution output image data, wherein the high-resolution output image data periodically generates dots,
Switching means for switching the generation order of generated dots,
An image forming apparatus which forms an image having a cycle twice as long as the input resolution (input 600 dpi and output 300 lines). 20. The image forming apparatus according to claim 12, wherein dots formed by combining two dots in the main scanning direction or the sub-scanning direction are arranged discretely to form an image. Image forming device. 21. The image forming apparatus according to claim 16, wherein dots are formed by discretely arranging 2 * 2 dots in the main scanning direction and the sub-scanning direction to form an image. . 22. The image forming apparatus according to claim 20, wherein the combined dots are arranged in a staggered manner. 23. The image forming apparatus according to claim 11, wherein a linear image continuous in the sub-scanning direction is formed.