JPH05328111A - Halftone picture recording circuit - Google Patents

Abstract

PURPOSE:To improve the picture quality at the time of quantization and to simplify the circuit constitution. CONSTITUTION:When input picture data is quantized, error distribution processing parts 70c, 71g, and 71c distribute the error between original picture data and quantized data to lines including the i-th line in the case of processing noticed line data ((i+1)-th line) and distribute it to lines including the (i+1)th line in the case of processing noticed line data (i-th line).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has an image reading means for inputting image data, a memory for temporarily storing the input image data, and an image output means for printing the stored image data on a recording material. The present invention relates to a halftone image recording circuit used in an image recording apparatus for recording at a density level lower than the density level of the input image data.

[0002]

2. Description of the Related Art Conventionally, image reading means, for example, a document is imaged by a CCD (charge coupled device) image pickup section through an optical system, and image pickup data (analog data) is converted to analog (A) /
Original image data is extracted as digital image data by a digital (D) conversion circuit and stored in a memory. The extracted image data is, for example, 0 (white) to 255.
It is assumed that each pixel is read in 256 gradations of (black).

In the data state as it is, one pixel is 0 to
In order to be represented by any of the gray scales of 255, an information amount of 8 bits (bit) per pixel is required, and therefore,
If this image data is to be stored as an entire image, a memory with a huge storage capacity is required. Further, in the data state as it is, the read image cannot be printed unless there is a device (printer) capable of printing one pixel with gradation of 0 to 255.

Therefore, a halftone image recording circuit is used, and the circuit quantizes image data to
The amount of data of pixels is reduced and the gradation of one pixel at the time of printing is reduced. As a result, the read image can be expressed even by a printing device having a small memory capacity and not very high gradation. However, in this case, if the data amount of one pixel is simply reduced by performing the quantization, an error from the original pixel appears in the printed image, and the image quality becomes low. Therefore, in order to improve the image quality, the quantization is performed. At this time, the error is distributed as shown in FIG.

Conventional error distribution has been performed only in one direction. That is, as shown in FIG. 23, the error of the pixel of interest (example B) is determined by the left side (example D) of the line adjacent in the scanning direction (right side, example C) and the preceding line (lower line in FIG. 23). ,
It was distributed to each pixel immediately below (example E) and lower right (example F).
The error distribution amount at this time is switched by using a random number,
The surplus remaining in the calculation after allocation is in a fixed direction (F in FIG. 23)
Was allocated to.

[0006]

However, in the above-mentioned conventional technique, since the error distribution occurring at the time of quantization is only one direction, there is a problem in image quality that a specific pattern occurs. It was In response to this, in order to improve the image quality, the error distribution direction is switched for each line as shown in FIG. However, this requires a circuit configuration for switching the distribution direction for each line as shown in FIG. 25, which causes a problem that the circuit configuration becomes complicated and the hardware cost increases.

Further, as shown in FIG. 23, since the error is distributed only toward the forward line and, conversely, the influence of the error from the forward line to the target line is not considered, The dots in the reproduced image lacked in detail, and there was a demand for improved image quality.

The present invention has been made to solve the above-mentioned conventional problems, and provides a halftone image recording circuit capable of improving the image quality at the time of quantization and simplifying the circuit configuration. This is an issue.

[0009]

The present invention is directed to an image reading means for inputting image data, a memory for temporarily storing the input image data, and an image output for printing the stored image data on a recording material. And a halftone image recording circuit for recording at a density level lower than the density level of the input image data, when quantizing the input image data,
Distributing the error between the original image data and the quantized data, including the rear line to the scan line data,
The above problem is solved by providing a means for carrying out the distribution including the destination line.

[0010]

In the present invention, when the input image is quantized, the error between the original image data and the quantized data is distributed to the scan data line including the rear line and Do it as well as distribute. Therefore, the error of the quantized data is distributed to the rear line and the front line of the data line of interest currently being scanned, so that a specific pattern does not occur in the image quality, and the image quality is high. Further, since the influence of the error of the front line is taken into consideration, the image quality is higher.
Moreover, since it is not necessary to switch the distribution direction for each line as in the conventional case, a circuit configuration for that is unnecessary, and therefore,
The circuit configuration can be simplified.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a digital copying machine 30 which is an embodiment of an image recording apparatus having a halftone image recording circuit according to the present invention.
It is a cross-sectional explanatory view of the overall configuration of. As shown in FIG.
The digital copying machine 30 of this embodiment includes a scanner unit 3
1, a laser printer unit 32, a multi-stage paper feeding unit 33, and a sorter 34 are provided.

The scanner unit 31 includes a document placing table 35 made of transparent glass and a double-sided automatic document feeder (RDF) 3.
6 and the scanner unit 40.

The multi-stage paper feeding unit 33 includes the first cassette 5
It has a first cassette 52, a second cassette 52, a third cassette 53, and a fifth cassette 55 which can be added by selection. In the multi-stage sheet feeding unit 33, the sheets are sent out one by one from the sheets stored in the cassettes of the respective stages and are conveyed toward the laser printer unit 32.

The RDF 36 sets a plurality of originals at one time, automatically feeds the originals one by one to the scanner unit 40, and one side or both sides of the original is scanned by the scanner unit 40 according to an operator's selection. It is configured to be read by.

The scanner unit 40 exposes a document to a lamp reflector assembly 41, a plurality of reflection mirrors 43 for guiding a reflected light image from the document to a photoelectric conversion element (CCD) 42, and a reflected light image from the document to the CCD 42. It includes a lens 44 for imaging.

When scanning a document placed on the document table 35, the scanner section 31 is configured to read the document image while the scanner unit 40 moves along the lower surface of the document table 35. When the RDF 36 is used, the document image is read while the document is being conveyed while the scanner unit 40 is stopped at a predetermined position below the RDF 36.

The image data obtained by reading the original image with the scanner unit 40 is sent to an image processing unit (not shown), which will be described later, and subjected to various processing, and then temporarily stored in the memory of the image processing unit. In response to the output instruction, the image data in the memory is given to the laser printer unit 32 to form an image on a sheet. The laser printer unit 32 includes a manual document tray 45, a laser writing unit 46, and an electrophotographic process unit 47 for forming an image.

The laser writing unit 46 is a semiconductor laser that emits a laser beam according to the image data from the above-mentioned memory, a polygon mirror that deflects the laser beam at a constant angular velocity, and a laser beam that is deflected at a constant angular velocity is an electrostatic photography process section. It has an f-θ lens and the like for correcting so as to deflect at a constant velocity on the photosensitive drum 43 of 47.

The electrophotographic process section 47 comprises a charging device, a developing device, a transfer device, a peeling device, a cleaning device, a static eliminator and a fixing device 49 arranged around the photosensitive drum 48 in accordance with a well-known mode. ..

A conveying path 50 is provided downstream of the fixing device 49 in the conveying direction of the sheet on which an image is to be formed. The conveying device 50 is connected to the conveying path 57 leading to the sorter 34 and the multi-stage paper feeding unit 33. It is branched to the communication path 58 which is in communication. The multi-stage paper feeding unit 33 includes a common transport path 56, and the common transport path 56 is configured to carry out the sheets from the first cassette 51, the second cassette 52, and the third cassette 53 toward the electrophotographic process section 47. It is configured.

The common transport path 56 joins the transport path 59 from the fifth cassette 55 on the way to the electrophotographic process 47 and communicates with the transport path 60.

The conveying path 60 joins the double-sided conveying path 50 and the conveying path 61 from the manual document tray 45 at a confluence point 62 to reach an image forming position between the photosensitive drum 48 of the electrophotographic process section 47 and the transfer device. The confluence point 62 of these three transport paths is provided at a position close to the image forming position.

Therefore, in the laser writing unit 46 and the electrophotographic process section 47, the image data read from the above-mentioned memory is the laser writing unit 46.
The laser image is scanned by a laser beam to form an electrostatic latent image on the surface of the photosensitive drum 43, and the toner image visualized by the toner is statically formed on the surface of the sheet conveyed from the multi-stage sheet feeding unit 33. It is electrotransferred and fixed. The sheet on which the image is formed in this manner is sent from the fixing device 49 to the sorter 34 via the transport paths 50 and 57, or is transported to the reverse transport path 50a via the transport paths 56 and 58.

Next, the digital copying machine 30 of this embodiment.
The configuration and function of the image processing apparatus included in the above will be described. 2 is a block diagram of an image processing apparatus included in the digital copying machine 30 of FIG.

The image processing apparatus included in the digital copying machine 30 includes an image data input section 70, an image processing section 71,
An image data output unit 72, a memory 73 including a RAM (random access memory), and a central processing unit (CPU) 74 are provided.

The image data input section 70 is a CCD section 70a.
Histogram processing unit 70b and error diffusion processing unit 70c
Is included. The image data input unit 70 is the CC of FIG.
The image data of the original document read from D42 is binarized and converted, and while the histogram is taken as a binary digital amount, the image data is processed by the error diffusion method and stored in the memory 7.
3 is configured to be stored once.

That is, in the CCD section 70a, after the analog electric signal corresponding to each pixel density of the image data is A / D converted, MTF correction, black and white correction or gamma correction is performed,
It is output to the histogram processing unit 70b as a digital signal of 256 gradations (8 bits).

In the histogram processing section 70b, density information (histogram data) added for each pixel density of 256 levels of the digital signal output from the CCD section 70a is obtained and, if necessary, the obtained histogram data is It is sent to the CPU 74 or as pixel data to the error diffusion processing unit 70c.

The error diffusion processing section 70c includes a CCD section 70a.
The digital signal of 8 bits / pixel output from is converted into 2 bits (4 values). The error diffusion processing unit 7
At 0c, an error diffusion method, which is a kind of pseudo-halftone processing, is performed, that is, a method of reflecting a quaternarization error in quaternarization determination of an adjacent pixel is performed to faithfully reproduce the local area density in the original image. Perform re-allocation calculation to reproduce.

The image processing unit 71 includes multi-valued processing units 71a and 71b, a synthesis processing unit 71c, a density conversion processing unit 71d, a scaling processing unit 71e, an image processing unit 71f, an error diffusion processing unit 71g, and a compression processing unit 71h. Is included.

The image processing unit 71 is a processing unit that performs various processes on the input image data according to various functions and finally converts the image data into image data desired by the operator. The processing unit is configured to process the output image data converted into the output image data. However, each of the above-described processing units included in the image processing unit 71 functions as necessary and may not function. That is, the multi-valued processing units 71a and 71a
In b, the data quaternized by the error diffusion processing unit 70c is converted into 256 gradations again.

In the synthesizing section 71c, a logical operation for each pixel, that is, a logical sum, a logical product, or an exclusive logical sum is selectively performed. The data to be calculated are pixel data stored in the memory 73 and bit data from the pattern generator (PG).

In the density conversion processing section 71d, the relationship between the input density and the output density is arbitrarily set for the 256 gradation digital signal based on a certain gradation conversion table.

In the scaling processing section 71e, the pixel data (density value) for the scaled target pixel is obtained by performing interpolation processing based on the input known data according to the instructed scaling ratio. After the scanning is scaled, the main scanning is scaled.

In the image process 71f, various image processings can be performed on the input image data according to various functions, and information collection such as feature extraction can be performed on the data string.

The error diffusion processing unit 71g performs the same processing as the error diffusion processing unit 70c of the image data input unit 70.

The compression processing unit 71h compresses the binary data by encoding it as a run length. Regarding the compression of the image data, the compression functions in the final processing loop when the final output image data is completed.

The image data output unit 72 includes a restoration unit 72a, a multi-value conversion processing unit 72b, an error diffusion processing unit 72c, and a laser output unit 72d. The image data output unit 72
The image data stored in the memory 73 in the compressed state is restored, converted back to the original 256 gradations, and the error diffusion of the four-valued data that is a smoother halftone expression than the binary data is performed. It is configured to transfer data to 72a.

That is, in the decompression unit 72a, the compression processing unit 71
The image data compressed by b is restored. In the multi-value quantization processing unit 72b, the multi-value quantization processing unit 71 of the image processing unit 71 is used.
Processing similar to that of a and 71b is performed. In the error diffusion processing unit 72c, the error diffusion processing unit 7 of the image data input unit 70 is used.
The same processing as 0c is performed. In the laser output section 72d, the digital pixel data is turned on / off of the laser based on a control signal from a sequence controller (not shown).
It is converted into an off signal, and the laser is turned on / off.

The data handled by the image data input section 70 and the image data output section 72 is basically stored in the memory 73 in the form of binary data in order to reduce the capacity of the memory 73. It is also possible to process in the form of four-valued data in consideration of deterioration of image data.

Next, the quantization and error diffusion processing performed by the error diffusion processing units 70c, 71g and 72c of the digital copying machine will be described. This quantization and difference diffusion processing is performed according to the procedure of FIG.

The image data input from the CCD 42 is
It is input to the histogram processing unit 70b via the CCD unit 70a, and the histogram processing unit 70b converts the image data of the gradation of the pixel into the level of 0 (white) to 255 (black) and the error diffusion processing unit 70c. Is entered.

First, 0 to 255 for this image data
Quantization is performed (step 1). That is, 0
255 is quantized at the W, X, Y, and Z points in FIG.
This quantization sets thresholds t1, t2, t3 to some extent, and then, based on this threshold, the input image data is assigned to W, X, Y, Z points by making the following determinations. Convert. Note that the input image data is f. When 255 ≧ f> t1 …… W, when t1 ≧ f> t2 ……
When X, t2 ≧ f> t3 ... Y, When t3 ≧ f ≧ 0 ...
... Z

Next, just by performing the quantization as described above, the image quality is not smooth because the density of the original data in the small area cannot be preserved. In order to eliminate this, the difference between the original data and the quantized data generated at the time of quantization is defined as an error component (error ε) (step 2).
The density of a small area is preserved by performing processing that affects the pixel density on the pixels around the pixel of interest.

This processing will be described in detail. First,
Quantization is performed with the processing target line as the i + 1 line.
At this time, the error .epsilon. To each of the distribution ratios (step 3). In FIG. 5, the error of the processing target pixel E on the i + 1 line is distributed to the pixels A, B, C, and D.
Distribution ratio (upper left 1/16, right above 3/16, upper right 1/1
6, 1/32 on the left side). With this distribution, when the pixels on the i-th line receive all the error distributions from the pixels on the i + 1-th line as shown in FIG. 5, the processing target line is moved to the i-th line as shown in FIG. Here, the processed pixel of interest is quantized again (by the method of FIG. 4) (step 4). The value quantized at this time is used as the result of quantization.

The error between the original data and the quantized data generated at this time is ε '(step 5). This error ε ′ is shown in FIG.
Allocate to each pixel on the lower right and on the right on the i-line at a certain allocation ratio. For example, in FIG. 7, the pixels are distributed to D, E, F, and G pixels. The remaining error ε ′ after distribution is D
A random number is used for each of the four G pixels, and one pixel is designated and distributed (step 6).

Next, the line of interest to be processed is moved to the line i + 2 (i is incremented by 1) (step 8), the process of step 3 is performed, and then the line of interest to be processed is moved to the line i + 1 and the processes of steps 4 to 7 are performed. I do. The above processing is sequentially performed up to the final line of the input image data (step 7).

By using the above-described procedure, in the conventional error distribution method using only step 7, since a specific pattern is found as a result, a process for changing the scan direction for each required line The image quality is improved without the need for a circuit, and the precision of dot expression is increased.

Next, the error distribution processing of the embodiment will be described in more detail with reference to the drawings. In this case, it is assumed that each pixel is read at a density level of 100 as shown in FIG.

First, the processing start pixel of the image data is set to (A).
And Then, an extra 0 is added to the upper side of the image data.
The dummy data containing the value of is also provided, and the dummy data for one column is also provided on the left side of the image data. Data having this dummy data is shown in FIG.

Next, the line of interest is set to the first line in order to perform the process of step 3 (the process shown in FIG. 6). First, when quantizing the density of the position (A) pixel, the threshold value t
Let 2 be (128). In this case, the pixel data of A is 1
Since it is 00, the value after quantization is (84). Further, the error component (error ε) at this time is 100−84 = 16 (1). This error amount ε is added to the surrounding pixels at the distribution ratio shown in FIG. This distribution amount is ε · 1/16 = 1 …… (2) ε · 3/16 = 3 …… (3) ε · 1/16 = 1 …… (4) ε · 1/32 = 0… … Calculate as in (5) (round down the decimal point). The remaining amount is calculated as 16-5 = 11 (6). This is left on the pixel of interest.

Next, the pixel of interest to be processed is moved to the pixel at position (B), and the process of step 3 is performed before. Since the density value of the pixel (B) is the same as that of the pixel (A), the same process is performed. This process is performed for all the lines of interest. After the processing, it becomes as shown in FIG. When the processing of the pixels of one line is completed, the processing target line is moved to the dummy line, and the processing of step 6 at the position (A0) is performed. Since the error of (A0) is 4 from the first line,
The sum of the original value and 0 is 0 + 4 = 4. This is
As shown in.

Quantization is performed based on the value thus obtained. First, the pixel of (A0) is quantized. Threshold t3 =
If it is 64, the result is 0 and the error component (error ε ') is 4. This error amount ε'is added to the pixels on the lower left, the lower right, and the right in the distribution of FIG. 12 according to the step 6 (step 2). The distribution amount is ε '・ 2/16 = 0 …… (7) ε' ・ 6/16 = 1 …… (8) ε '・ 2/16 = 0 …… (9) ε' ・ 6/16 = It is calculated as 0 ... (10) (round down to the nearest whole number). The remaining amount is 4-2 = 2. By using random numbers,
Determine and distribute one location. Here, the lower left direction is determined. At this point, the pixel (A0) is determined as shown in FIG.

Next, the pixel of interest is moved to (B0), and the process of step 6 is performed. Similarly, each pixel of the dummy line is processed, and the result is as shown in FIG.
This completes the process for the dummy line. Next, the process of step 3 is performed on the second line, and the result is as shown in FIG. Next, the process of step 6 is performed for the first line. For (A), the error ε'is redistributed as shown in FIG. The result is as shown in FIG. The above processing is performed until the final line.

If the output of this result is, for example, quantized into four values, it can be expressed by 00, 01, 10, and 11, the original 8 bits can be expressed by 2 bits, and the image in which the density is saved is 4 times. It can be expressed by a value. When this is processed by a circuit, it is possible to sequentially perform the processing of step 3 and step 6 with respect to the input data by only having one line buffer capable of storing the data of the hatched portion in FIG. Become. That is, the processing circuit is as shown in FIG. Therefore, since the switching processing circuit (FIG. 25) which is required for changing the line (FIG. 24) as in the prior art is not required, the circuit configuration is simplified as compared with the prior art.

As a result, by performing steps 3 and 6, the image quality is improved because the dots are finer and the density is preserved as compared with the conventional quantization.

FIG. 20 shows an example of the result of processing the input image data shown in FIG. 19 by the present invention, and FIG. 21 shows an example of the result of processing by the conventional circuit. In the circuit of the present invention, the line is not broken, but in the conventional circuit, the line is broken. Therefore, it is understood that the present invention can improve the image quality.

FIG. 22 is a structural explanatory view of a modified example of the image processing apparatus included in the digital copying machine of FIG.

The image processing apparatus of FIG. 22 mainly has an image data input section 80, an image processing section 81, an image data input section 82, and a memory 73, and is similar to the image processing apparatus of FIG. The same number is attached. In the image processing apparatus of FIG. 22, the image processing unit 81 includes a first density conversion processing unit 83,
It has a second density conversion processing 84, a 1/8 transformation processing section 85, and a synthesis processing section 86, and the image data output section 82 does not have the multi-value conversion processing section 72b and the error diffusion processing section 72c. ..

First and second density conversion processing units 83 and 84
Has the same function as the density conversion processing unit 71d.
The 1/8 transmutation processing unit 85 has a function of transposing the multi-valued image data to 1/8 times. Also, the synthesis processing unit 8
6f The combination processing unit 71c and the image processing unit 71f also have the functions.

[0061]

As described above, according to the present invention, since the dots are dense and the density is preserved during quantization, the image quality can be improved, and
An excellent effect that the circuit configuration can be simplified can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of a digital copying machine according to an embodiment of an image recording apparatus of the present invention.

FIG. 2 is a block diagram of an image processing apparatus included in the digital copying machine of FIG.

FIG. 3 is an explanatory diagram of a processing procedure of quantization and error diffusion processing performed by the digital copying machine of FIG.

FIG. 4 is an explanatory diagram of the quantization in FIG.

FIG. 5 is an explanatory diagram of the error diffusion processing of FIG.

FIG. 6 is an explanatory diagram of the error diffusion processing of FIG.

7 is an explanatory diagram of an error diffusion process of FIG.

FIG. 8 is an explanatory diagram of the error diffusion processing of FIG.

FIG. 9 is an explanatory diagram of the error diffusion processing of FIG.

FIG. 10 is an explanatory diagram of the error diffusion processing of FIG.

FIG. 11 is an explanatory diagram of the error diffusion processing of FIG.

FIG. 12 is an explanatory diagram of the error diffusion processing of FIG.

13 is an explanatory diagram of the error diffusion processing of FIG.

14 is an explanatory diagram of the error diffusion processing of FIG.

FIG. 15 is an explanatory diagram of the error diffusion processing of FIG.

16 is an explanatory diagram of the error diffusion processing of FIG.

17 is an explanatory diagram of the error diffusion processing of FIG.

18 is an explanatory diagram of the error diffusion processing of FIG.

FIG. 19 is an explanatory diagram of the error diffusion processing of the present invention.

FIG. 20 is an explanatory diagram of the error diffusion processing of the present invention.

FIG. 21 is an explanatory diagram of the error diffusion processing of the present invention.

22 is a block configuration diagram of a modified example of the image processing apparatus included in the digital copying machine of FIG. 1. FIG.

FIG. 23 is an explanatory diagram of a conventional error diffusion process.

FIG. 24 is an explanatory view of the same.

FIG. 25 is an explanatory view of the same.

[Explanation of symbols]

 30 Digital Copier 31 Scanner Section 32 Laser Printer Section 70 Pixel Data Input Section 70a CCD Section 70b Histogram Processing Section 70c Error Diffusion Processing Section 71 Image Processing Section 71a Multilevel Quantization Processing Section 71b Multilevel Quantization Processing Section 71c Error Diffusion Section 71d Density Conversion processing unit 71e Scale processing unit 71f Image processing unit 71g Error diffusion processing unit 71h Compression processing unit 72 Image data output unit 72a Restoration unit 72b Multi-valued processing unit 72c Error diffusion processing unit 72d Laser output unit 73 Memory 74 CPU central processing Computing device 80 Image data input unit 81 Image processing unit 82 Image data output unit

Claims (1)

[Claims] 1. An image recording apparatus having image reading means for inputting image data, a memory for temporarily storing input image data, and image output means for printing the stored image data on a recording material. In the halftone image recording circuit for recording at a density level lower than the density level of the input image data, when quantizing the input image data, an error between the original image data and the quantized data The halftone image recording circuit is provided with a means for performing both the distribution including the rear line and the distribution including the front line with respect to the scan data line.