JPH06217114A - Halftone image processor - Google Patents

Abstract

PURPOSE:To improve the gradation expression of print picture quality in a halftone by reducing driving nonuniformity at a printing part in the case of recording an image. CONSTITUTION:Concernng data inputted by an image reader, data quantized by a halftone image processing circuit are successively processed for the unit of two pixels. Concerning these data of two pixels, first of all, whether it is an edge or not is decided by an edge decision part 1. Based on the result of this decision, an objective image for performing arithmetic operation between pixels is switched. When it is not the edge, arithmetic operation is executed by an arithmetic part 2 and when it is the edge, correction emphasis is performed. Thus, even when a dot is moved by driving nonuniformity at the printer part, it does not stand out and picture quality is improved especially concerning the halftone part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a halftone image processing apparatus, and more particularly, to an improvement in halftone print image quality by performing inter-pixel calculation on data quantized by halftone image processing. The present invention relates to a halftone image processing device.

[0002]

2. Description of the Related Art In conventional halftone image processing, a quantized value is printed as it is. That is, one pixel of the image data input as digital information is read with a gradation of 0 to 255, for example. In this state, 8-bit information is required to be expressed by one pixel 0 to 255, and an enormous memory is required to store this information in the entire image. Further, in this state, the read image cannot be printed unless there is a device capable of printing one pixel with gradation of 0 to 255. Therefore, the amount of data for one pixel is reduced to
By reducing the gradation of pixels, it is possible to represent even a printing device having a small memory amount and gradation not so high.

As a processing procedure, the gradation of a pixel at the time of image input is read at a level of 0 to 255. Figure 20
First, as shown in FIG.
Quantize ~ 255. That is, 0 to 255 are quantized at the points W, X, Y, and Z in FIG. In this quantization, by setting certain fixed threshold values t1, t2, t3, the following determination is performed and quantization is performed. Let the input data be f. 255 ≧ f> t1 W t1 ≧ f> t2 X t2 ≧ f> t3 Y t3 ≧ f ≧ 0 Z Next, if the quantization is performed, The image quality is not smooth because the density cannot be saved. In order to eliminate this, as shown in FIG. 21, the difference from the original data generated at the time of quantization is set as an error amount, and the difference is processed so as to affect the pixel density around the pixel of interest. Save the density in a small area with.

FIG. 22 is a flow chart for explaining the conventional halftone image processing. First, as shown in FIG. 21, each of the lower left pixel, the lower right pixel, the lower right pixel, and the right pixel on the attention line i of the attention pixel arranged in the line direction of the line i + 1 immediately after the attention line i, respectively. Then, the error ε is distributed at a certain allocation ratio (step 1). Next, it is judged whether or not all the image data have been processed (step 2). If all the image data have been processed, the process ends. If not all processed, i = i
It is set to +1 (step 3), the process returns to step 1 and the process is repeated.

[0005]

As described above, the quantized value in the conventional halftone image processing is printed as it is, and the gradation expression is expressed by the area. The dot expression is random, and when the printing position of the dot changes due to uneven driving of the printer, there may occur a case where the dot intervals are close to each other, a separated part, or the dots are connected to each other. For this reason, the image quality is easily affected by other than image processing. Further, since the relationship between the gradation expression on the 0 to 255 level and the copy density is as shown by the dotted line in FIG. 10, the density change drastically changes and smoothness does not appear (halftone part). There was a point.
Further, in the halftone image processing circuit that does not determine the non-edge or edge regions, there is a problem that the image quality of only the halftone portion cannot be corrected.

The present invention has been made in view of such a situation, and performs halftone image processing on data input by an image reading device, and the inter-pixels are equally spaced with respect to the quantized data. Calculation is performed to reduce driving unevenness in the printer unit such as image recording in terms of image quality and improve gradation expression of halftone print image quality. Also, based on the array of quantized data, By improving the gradation expression of halftone print image quality by determining the edge part and switching the target image for inter-pixel calculation, a means for determining the area of the edge part or the non-edge part is provided. An object of the present invention is to provide a halftone image processing apparatus in which inter-pixel calculation is executed for a non-edge portion and correction emphasis is performed for the edge portion by switching the target of the inter-pixel calculation.

[0007]

In order to achieve the above object, the present invention provides (1) an image data input unit for binarizing and converting image data of an original, and an image processing for finally converting the image data. Section, a storage section that stores the image data processed by the image processing section, and an image data output section that restores the image data stored in the storage section and performs error diffusion of the data that is a halftone expression. And an arithmetic means for performing inter-pixel arithmetic after the error diffusion processing of the data in the image data output portion, and further, (2) an edge portion judging means provided before the arithmetic means. , And even
(3) In the above (2), the edge determination unit is composed of a main scanning direction edge determination unit and a sub scanning direction determination unit for determining an edge in the main scanning direction and an edge in the sub scanning direction. Further, (4) in (2) or (3) above, the edge portion determination means determines the area of the edge portion and the non-edge portion.

[0008]

With respect to the data input by the image reading device, the data quantized by the halftone image processing is processed in units of two pixels. For the data of the two pixels, the edge determination unit first determines whether or not it is an edge.
Based on the result of this determination, the target image for which the inter-pixel calculation is performed is switched. If it is not an edge, calculation is executed by the calculation unit, and if it is an edge, correction enhancement is performed. in this way,
By performing pixel-to-pixel calculations at equal intervals on the quantized data in the halftone image processing, the influence on the image quality due to drive unevenness in the printer unit during image recording is reduced, and the print quality of the halftone image is reduced. Improve gradation expression. In addition, the target image for inter-pixel calculation is switched by performing edge determination, and the edge portion is saved. In the edge determination, first, for two target pixels in the main scanning direction to be processed, an area larger than the target pixel is set, the area is divided, and the quantized value in the divided area is divided. Calculate and determine the maximum and minimum values among the calculated values. When the difference between the maximum value and the minimum value of the quantized value is larger than a predetermined value, it is determined as the edge portion in the main scanning direction, and when it is smaller, it is determined as the non-edge portion. The same edge judgment is performed for one of the two target pixels in the main scanning direction.
This is also performed for one target pixel in the sub-scanning direction.

[0009]

Embodiments will be described below with reference to the drawings. First, FIG. 1 is a flowchart for explaining the positioning of a print data conversion method in a halftone image processing apparatus according to the present invention. In this method, inter-pixel calculation at equal intervals is performed in the conventional halftone image processing (step 1). The flow has (step 2) added. The data quantized by the conventional halftone image processing is set to W, X, Y, and Z for the input data of 0 to 255. With respect to this quantized value, calculation processing is performed in the following procedure. First, for the main scanning direction,
The following calculation is performed at equal intervals. First, in FIG. 2, A and B
When is the target pixel, it is determined whether these two pixels correspond to the edge in the image. The judgment is made on the target pixels A and B.
Including E, F, A, B, C, and D in FIG. As shown in FIG. 3, if these 6 pixels match a pattern determined to be a predetermined edge portion, the calculation is not performed between the target pixels A and B, and the pixels are held in the through state.

Further, for the target pixel to be processed, the information on the area of n × m (n ≧ 1, m ≧ the number of target pixel) is divided as shown in FIG. This divided area a, b,
The sum of the quantized values of c and d is calculated (Fig. 5 step
1) Then, determine the maximum and minimum values (Fig. 5, step 2),
If the difference between the maximum value and the minimum value is smaller than the fixed threshold value th, the next process is executed. In FIG.
When A and B are the target pixels, it is determined whether or not these two pixels correspond to the edge in the image (steps 3 and 4). The determination includes the target pixels A and B, and E, F, and
A, B, C and D are used as judgment materials. As shown in FIG. 3, if the 6 pixels match the pattern that is determined to be the edge portion in advance, the target pixel portion is set as the edge portion, and the processing of the equation (2) described later is performed (step 6). On the contrary, if it does not match the pattern, it is set as a non-edge portion, and the processing of equation (1) described later is performed (step 5). Further, in step 2, if it is larger than the fixed threshold value th, it is regarded as an edge portion, and the processing of equation (2) described later is performed (step 6).

The inter-pixel calculation is executed as follows. A, B
Where n is the number of pixels to be processed and the number of quantized values is n, and the processing results of each pixel are A ′ and B ′, the following expression 1 is obtained.

[0012]

[Equation 1]

When the determination is for the edge portion, the processing shown in the following equation 2 is performed to correct and emphasize the edge portion.

[0014]

[Equation 2]

Next, (C, D) is the target pixel. This is realized by performing the process to the end of the quantized data. By using this method, it is possible to improve the image quality printed by using only the quantized value in the conventional halftone image processing. That is,
An inter-pixel calculation means for performing quantization on the input image data by halftone image processing and performing a predetermined process on the quantized data at a constant pixel interval in the main scanning direction (during printing). The provision reduces the drive unevenness in the printer unit during image recording in terms of image quality, and improves the gradation expression of the halftone print image quality.

In short, the inter-pixel calculation according to the present invention is the following processing. Pixel interval to be processed: m Number of quantized values: n Target pixel: A ₁ A ₂ A ₃ ... _Am Result: A ′ ₁ , A ′ ₂ , A ′ ₃ ... A ′ _m A ′ _m = A ₁ + A _{2 + a 3 + ... + a} m If, a _'m> n-1 if _{a' n-1 = a 1} + ... + a m - performing to _{(n-1) a 'm} = n-1 m = 2.

Further, by using a method of determining the edge portion on the image based on the array of quantized data, the target pixel for inter-pixel calculation is switched. The inter-pixel calculation is executed under the following conditions. Edge part: Quantized value as it is Not edge part: Target pixel is A ₀ A ₁ ... _Am .
(A ₀ , A ₁ , ..., A _m = 0, to, n-1 (number of quantized values)) _Am = A _m + A _m-1 + ... + A ₁ + A ₀ If A _m > n-1 At time A _m = n−1 m = j to m = 0 is executed (the number of calculation target pixels is j).

Further, by using the method of determining the areas of the edge portion and the non-edge portion in the image based on the array of the quantized data, the inter-pixel calculation is performed on the non-edge portion, and
Correction enhancement is applied to the edge portion. At this time, the inter-pixel calculation is executed as follows. Edge part: Correction enhancement is performed. The quantized value is one level higher. (n-1: number of quantized values) target pixel A ₀ A ₁ ...
When _{A m A m = A m +} A m +1 non-edge _{portions: A m = A m + A} m-1 + ... + A 1 + A 0 If the A _m = n-1 when A _m> n-1 _m = Execute from j to m = 0 (j: number of calculation target pixels).

FIG. 6 is a block diagram showing an embodiment of a halftone image processing apparatus according to the present invention. In the figure, 1 is an edge determination unit and 2 is a calculation unit. Data (step 1 in FIG. 1) quantized by the conventional halftone image processing with respect to the input data is shown in FIG. 7A, FIG. 8A, FIG. 9A, and FIG. 11A. , (B). This data is processed in units of two pixels in the main scanning direction shown in FIG. Here, the number of quantized values is four. The edge determination unit 1 first determines whether or not the data of these two pixels is an edge. Based on the result of this determination, the target image for which the inter-pixel calculation is performed is switched. If it is not an edge, the calculation unit 2 executes the calculation.

In this block diagram, the processing is executed so that the input is rearranged in units of two pixels. For example, if the input is for four pixels, the calculation processing is executed for the pixel of (A, B) first, and for the pixel of (C, D), the processing is delayed and executed at the next time. The results thus obtained are shown in FIGS. 7 (b), 8 (b), (c), and 9 (b), (c). In addition, in this method, the printing state at the density 90 of the original data is shown in FIG.
It shows in (d). As described above, by implementing this method, even if the dots are moved in the sub-scanning direction due to the unevenness of driving in the printer unit, the dots are less noticeable and the image quality is improved. According to the present invention, the operation panel 54 of the image forming apparatus, such as a digital copying machine, is provided with an image mode instruction key or the like for instructing the image formation as shown in the block diagram of FIG. There is. In FIG. 6, reference numeral 54a is a character mode, and if the read original or the like is only characters, the character mode key 54a is operated. If the original is a photograph, the photograph mode key 54b is operated, and if the original is an image in which characters and photographs are mixed, the character / photograph mode key 54c is operated.
Therefore, in accordance with the operation of the above keys, step 1 shown in FIG.
Between step 2 and step 2, the following processing is executed depending on which of the keys 54a to 54c instructing the image processing mode on the operation panel 54 has been operated. For example, if the manuscript is a text manuscript, the output may be performed as it is without executing the equations related to the halftone processing of step 5 and step 6. If the original is a photographic original, the inter-pixel calculation for the intermediate image processing according to the present invention is executed according to the equation (1) in step 5. Further, when the original includes both characters and photographs, the above-described processing from step 2 is executed based on the edge determination according to the instruction of the key 54c, and finally the calculation of the equation (1) or (2) is executed. To do.

However, as described above, when the quantized value is unconditionally subjected to the pixel-to-pixel arithmetic processing on the entire image at equal intervals, as in the case of a character original or a photograph / character original. Since the pixel-to-pixel calculation is also performed on an image having an edge portion, a defect that the edge portion is popped out or chipped occurs. In addition, as a result of the erroneous determination of the halftone edge portion as an edge in the halftone image, a problem occurs that the edge in the halftone is emphasized, and conversely, the edge in the halftone is a blank image. It causes problems such as.
In order to eliminate this problem, as shown in FIG.
The edge determination is performed in the sub-scanning direction similarly to the determination as to whether or not there is an edge in the main scanning direction with the pixels A and B as the target pixels. In this case, for example, the images J, K, G, H, and I including the target pixel A are used as the determination material.

That is, for two target pixels in the main scanning direction to be processed, an area larger than the target pixel is set, the area is divided, and the quantized value in the divided area is calculated. , Determine the maximum and minimum of the calculated values. It is determined that the difference between the maximum value and the minimum value of the quantized value is larger than the predetermined value as the edge portion in the main scanning direction, and if the difference is smaller than the predetermined value, it is determined as the non-edge portion. Similar edge determination is performed in the sub-scanning direction for one of the two target pixels in the main scanning direction.

FIG. 13 is a diagram showing the pattern condition of the edge in the sub-scanning direction. The numerical values represent the quantized density, and as shown in the figure, 6 pixels J, K, A, arranged in the sub-scanning direction.
If G, H, and I match a pattern that is determined to be an edge portion in advance, A and G are edge portions, and conversely, those that do not match this pattern are non-edge portions. Here, when the determination result is the edge portion, it is assumed that the quantized data of the target pixels A and B is passed through as it is.

If the determination result is a non-edge portion, in the figure showing the quantization processing of FIG.
With B as the pixel of interest, 6 pixels in the main scanning direction of E, F, A, B, C, and D are used as the determination material, and these 6 pixels are as shown in the edge part pattern condition in the main scanning direction of FIG. If it matches the pattern that is determined as the edge part in advance, the edge part,
If it does not match the pattern, it is determined as a non-edge portion and the determination process is performed again. Here, when it is finally determined to be a non-edge part,
Inter-pixel calculation is performed in the same manner as above. The processing content is the same as that of equation (1). When it is determined that the edge portion is present, the quantized data of the target pixels A and B is passed through as it is. Thus, in this method,
By accurately determining the edge / non-edge portion based on the determination information in the area division and the determination information in the main scanning direction and the sub-scanning direction, it is possible to perform the arithmetic processing between pixels on the entire image unconditionally in the past. The image quality is better than the printed one.

FIG. 14 is a flowchart in which the edge determination in the sub-scanning direction is added to the flowchart for determining the edge in the main scanning direction shown in FIG. That is, the n × m area including the pixel of interest is selected from the quantized pixel input, and this is divided into a, b, c, and d divided areas. Among the quantized values of the divided areas a, b, c, d, the pixel density information of the maximum value and the minimum value is obtained (step 1). The difference between the maximum value and the minimum value of the quantized values of the divided areas a, b, c, d is
It is determined whether it is larger or smaller than a predetermined fixed threshold value th (step 2). The difference value obtained in step 2 is
When it is determined that it is smaller than the fixed threshold th, the pattern of the main scanning line is checked for a match with a predetermined pattern (step 3). When it is determined that the difference value obtained in step 2 is equal to or larger than the fixed threshold value th, the pattern of the sub-scanning line is checked for matching with a predetermined pattern (s
tep4). When the pattern of the sub-scanning line is determined to be non-edge, the process proceeds to step 3, and when it is determined to be the edge portion, the process is directly performed (step 5). In step 3, it is determined whether the pattern of the main scanning line matches the predetermined pattern, that is, the non-edge portion or the edge portion. If it is an edge part, it is directly passed through (step 6). When it is determined that the pattern of the main scanning line and the sub-scanning line is the non-edge portion, the calculation processing of the target pixel is performed by the equation (1) (step 7).

In the output result of the prior art of FIG. 16, the boundary between the edge portion and the non-edge portion (shown by a thick frame in the figure) is compared with the data quantized by the halftone image processing of FIG. In contrast to the low fidelity, the output result according to the present invention in FIG. 17 faithfully reproduces the edge portion.

FIG. 18 is a sectional view showing the overall construction of a digital copying machine having a halftone image processing function according to the present invention. In the figure, 10 is a digital multi-function peripheral, 11 is a scanner section, 12 is a laser printer section, 13 is a multi-stage paper feeding unit, 14 is a sorter, 15 is a document placing table, 16 is a double-sided automatic document feeder (RDF), 20 is a scanner unit, 21 is a lamp reflector assembly, 22 is a photoelectric conversion element (CCD), and 23. Is a reflection mirror, 24 is a lens,
25 is a manual document tray, 26 is a laser writing unit, 27 is an electrophotographic process section, 28 is a photoconductor drum,
29 is a fixing device, 30 is a conveying path, 31 is a first cassette, 3
2 is a second cassette, 33 is a third cassette, 35 is a fifth cassette, 36 is a common conveyance path, and 37 to 41 are conveyance paths.

The digital copying machine 10 includes a scanner section 11
A laser printer unit 12, a multi-stage paper feeding unit 13, and a sorter 14 are provided. The scanner unit 11 includes a document placing table 15 made of transparent glass, a double-sided automatic document feeder (RDF) 16 and a scanner unit 20, and the multi-stage paper feeding unit 13 includes a first cassette 31 and a first cassette 31.
It has a second cassette 32, a third cassette 33 and a fifth cassette 35 which can be added by selection. Further, in the multi-stage sheet feeding unit 13, the sheets are fed out one by one from the sheets stored in the cassettes of the respective stages and are conveyed toward the laser printer unit 12.

The RDF 16 sets a plurality of originals at one time and automatically feeds the originals one by one to the scanner unit 20 so that one side or both sides of the original can be scanned according to the operator's selection. To read. The scanner unit 20 forms a lamp reflector assembly 21 for exposing a document, a plurality of reflection mirrors 23 for guiding a reflected light image from the document to a photoelectric conversion element (CCD) 22, and a reflected light image from the document on the CCD 22. Lens 24 for

When scanning a document placed on the document placing table 15, the scanner section 11 is configured to read the document image while the scanner unit 20 moves along the lower surface of the document placing table 15. When the RDF 16 is used, the document image is read while the document is conveyed while the scanner unit 20 is stopped at a predetermined position below the RDF 16. The image data obtained by reading the original image with the scanner unit 20 is sent to the image processing unit and subjected to various processes.
The image data is temporarily stored in the memory of the image processing unit, and the image data in the memory is given to the laser printer unit 12 according to an output instruction to form an image on a sheet.

The laser printer unit 12 is provided with a manual document tray 25, a laser writing unit 26, and an electrophotographic process unit 27 for forming an image. Also,
The laser writing unit 26 is a semiconductor laser that emits a laser beam according to the image data from the above-described memory, and a polygon mirror that deflects the laser beam at a constant angular velocity. The drum 28 has an f-θ lens and the like for performing correction so that it tends to have a constant velocity. The electrophotographic process unit 27 includes a charging device, a developing device, a transfer device, a peeling device,
A cleaning device, a static eliminator and a fixing device 29 are arranged. A transport path 30 is provided on the downstream side of the fixing device 29 in the transport direction of the sheet on which the image is to be formed. The transport path 30 communicates with the transport path 37 leading to the sorter 14 and the multi-stage sheet feeding unit 13. It branches to the transport path 38 that is located.

The conveyance path 38 is branched in the multi-stage sheet feeding unit 13, and the reversal conveyance path 3 is formed as a conveyance path after branching.
0a and a double-sided / composite transport path 30b are provided. The reversal conveyance path 30a is a conveyance path for reversing the front and back sides of a sheet in a double-sided copy mode for copying both sides of a document. The double-sided / composite conveyance path 30b conveys a sheet from the reverse conveyance path 30a to the image forming position of the photosensitive drum 28 in the double-sided copying mode, or images on one side of the sheet with images of different originals or toners of different colors. This is a conveyance path for conveying the sheet to the image forming position of the photosensitive drum 28 without reversing the sheet in the single-sided synthetic copy mode for performing the synthetic copy to be formed.

The multi-stage paper feeding unit 13 includes a common transport path 36, which feeds the sheets from the first cassette 31, the second cassette 32, and the third cassette 33 to the electrophotographic process section 27. It is configured to be conveyed toward. Further, the common conveyance path 36 joins the conveyance path 39 from the fifth cassette 35 on the way to the electrophotographic process section 27 and communicates with the conveyance path 40. The transport path 4
0 indicates the double-sided / composite transport path 30b and the manual feed tray 2
It is configured so that it merges with the conveyance path 41 from 5 at the confluence point 42 and leads to the image forming position between the photoconductor drum 28 of the electrostatic photography process section 27 and the transfer device. The confluence point 42 is provided at a position close to the image forming position.

Therefore, in the laser writing unit 26 and the electrophotographic process section 27, the image data read from the above-mentioned memory is stored in the laser writing unit 26.
The toner image formed as an electrostatic latent image on the surface of the photoconductor drum 28 by being scanned with a laser beam by the toner is visualized by the toner.
It is electrostatically transferred and fixed on the surface of the sheet conveyed from.
The sheet on which the image is formed in this way is fixed in the fixing unit 29.
Is sent to the sorter 14 via the transport paths 30 and 37, or is transported to the reverse transport path 30a via the transport paths 30 and 38.

Next, the configuration and function of the image processing unit and each control system included in the digital copying machine will be described with reference to FIG.
It will be described based on. FIG. 19 is a block configuration diagram of an image processing unit and each control system included in the digital copying machine with a facsimile function shown in FIG. 18, in which 50 is an image data input unit, 50a is a CCD unit, and 50b is a control unit. Histogram processing section, 50c error diffusion processing section, 51 image processing section, 51a and 51b multi-value processing section, 51c combining processing section, 51d density conversion processing section, 51e scaling processing section, 5e.
1f is an image processing unit, 51g is an error diffusion processing unit, 51
h is a compression processing unit, 52 is an image data output unit, 52a is a decompression unit, 52b is a multi-value quantization processing unit, 52c is an error diffusion processing unit, 52d is a laser output unit, 53 is a memory, 54 is an operation panel, 54a is A character mode key, 54b is a photograph mode key, 54c is a character / photograph mode key, 55 is a copy density key, 56 is a magnification key, and 57 is an image processing CPU (central processing unit).

The image processing unit included in the digital copying machine 10 includes an image data input unit 50, an image processing unit 51, an image data output unit 52, a memory 53 including a RAM (random access memory), and an image processing unit. A central processing unit (CPU) 57 is provided. The image data input unit 50 includes a CCD unit 50a and a histogram processing unit 50b.
And an error diffusion processing unit 50c. The image data input unit 50 processes the image data by the error diffusion method while binarizing and converting the image data of the original read from the CCD 22 of FIG. 18 and taking a histogram as a binary digital amount. , And is temporarily stored in the memory 53. That is, in the CCD unit 50a,
The analog electric signal corresponding to each image density of the image data is A
After D / D conversion, MTF (Modulation Transfer Func
correction), black and white correction or gamma correction is performed.
It is output to the histogram processing section 50b as a gradation (8-bit) digital signal.

In the histogram processing section 50b, the digital signal output from the CCD section 50a is added for each pixel density of 256 gradations to obtain density information (histogram data).
And the obtained histogram data is sent to the image processing CPU 57 or as pixel data to the error diffusion processing unit 50c as necessary. In the error diffusion processing unit 50c, the error diffusion method which is a kind of the pseudo halftone processing unit, that is, the method of reflecting the binarization error in the binarization judgment of the adjacent pixel, is output from the CCD unit 50a. Bit / pixel digital signal is 1 bit (2
Value), and the redistribution operation is performed to faithfully reproduce the local area density in the original.

The image processing unit 51 is a multi-valued processing unit 51a, 5
1b, a combination processing unit 51c, a density conversion processing unit 51d, a scaling processing unit 51e, an image processing unit 51f, an error diffusion processing unit 51g, and a compression processing unit 51b. The image processing unit 51 is a processing unit that finally converts the image data input according to the image processing mode instructed by the operation panel 54 into image data desired by the operator, and is finally converted into the memory 53. The processing unit is configured to process the data until it is stored as output image data. However, each of the above-described processing units included in the image processing unit 51 functions as necessary and may not function.

That is, in the multi-value quantization processing units 51a and 51b, the data binarized by the error diffusion processing unit 50c is converted again into 256 gradations. In the combination processing unit 51c, a logical operation for each pixel, that is, an operation of a logical sum, a logical product, or an exclusive logical sum is selectively performed. The data to be the target of this calculation are the image data stored in the memory 53 and the bit data from the pattern generator (PG). In the density conversion processing unit 51d, according to the instruction of the copy density key 55 of the operation panel 54, the relationship between the input density and the output density is arbitrarily set for the digital signal of 256 gradations based on a predetermined gradation conversion table. It In the scaling processing unit 51e, the pixel data (density value for the target pixel after scaling is performed by performing interpolation processing with known data that is input according to the scaling ratio designated by the scaling key 56 of the operation panel 54. ) Is calculated, the main scanning is scaled after the sub-scanning is scaled.

In the image processing section 51f, various image processings may be performed on the input pixel data, and information collection such as feature extraction may be performed on the data string. The error diffusion processing unit 51g performs the same processing as the error diffusion processing unit 50c of the image data input unit 50. Compression processing unit 51h
Then, binary data is compressed by the encoding called run length. Regarding the compression of image data, the compression functions in the final processing loop when the final output image data is completed.

The image data output unit 52 includes a restoration unit 52a, a multi-value quantization processing unit 52b, an error diffusion processing unit 52c, and a laser output unit 52d. The print data conversion method of the halftone image processing apparatus according to the present invention is applied between the error diffusion processing section 52c and the laser output section 52d. The image data output unit 52 restores the image data stored in the memory 53 in a compressed state, converts the image data into the original 256 gradations again, and corrects the error of the four-valued data which is a smoother halftone expression than the binary data. It is configured to perform diffusion and transfer the data to the laser output unit 52d. That is, the restoration unit 52a restores the image data compressed by the compression processing unit 51b. The multilevel halftoning processing unit 52b performs the same processing as the multilevel halftoning processing units 51a and 51b of the image processing unit 51. The error diffusion processing unit 52c performs the same processing as the error diffusion processing unit 50c of the image data input unit 50. In the laser output unit 52d, the print control CP
Based on the control signal from U, the digital image data is converted into a laser on / off signal, and the laser is turned on / off. The data handled by the image data input unit 50 and the image data output unit 52 is basically stored in the memory 53 in the form of binary data in order to reduce the capacity of the memory 53. It is also possible to process in the form of four-valued data in consideration of deterioration.

[0042]

As is apparent from the above description, the present invention has the following effects. That is, in the past, as a method for solving the problem in image quality that occurs because the value quantized by the halftone image processing circuit is printed as it is, the data quantized by the halftone image processing circuit is By performing the pixel-to-pixel calculation at equal intervals, the influence on the image quality due to the drive unevenness in the printer unit during image recording is reduced, and the gradation expression of the halftone print image quality is improved.
Further, it can be realized by adding the processing unit of this system without changing the conventional halftone image processing. Furthermore, by providing a means for determining the edge, it is possible to save the edge portion by switching the target image of the inter-pixel calculation.
Furthermore, the maximum value and the minimum value of the quantized values of the pixels in the divided area are calculated, the difference value is obtained, and the fixed value is compared with the fixed threshold value in the main scanning direction and the sub scanning direction to obtain an accurate value. It is now possible to determine the non-edge portion and the edge portion. As a result, it is possible to reduce the image defects such as the protrusion at the edge portion and the chipping that have conventionally occurred. From this point, it is possible to perform the print expression according to both the character and the photograph portion on the document in which the character and the photograph are mixed.

[Brief description of drawings]

FIG. 1 is a flowchart for explaining the positioning of a print data conversion method in a halftone image processing apparatus according to the present invention.

FIG. 2 is a diagram showing processing directions according to the present invention.

FIG. 3 is a diagram showing a determination pattern for a target pixel according to the present invention.

FIG. 4 is a diagram showing an example of a quantization processing method according to the present invention.

FIG. 5 is a flowchart showing an edge determination process of the present invention.

FIG. 6 is a configuration diagram for explaining an embodiment of a halftone image processing device according to the present invention.

FIG. 7 is a diagram for comparing data quantized by halftone image processing according to the present invention with conventional output data.

FIG. 8 is a diagram for comparing data quantized by another halftone image processing according to the present invention with conventional output data.

FIG. 9 is a diagram for comparing data quantized by another halftone image processing according to the present invention with conventional output data.

FIG. 10 is a diagram showing the relationship between each data and the density at the time of printing according to the present invention and that of the prior art.

FIG. 11 is a diagram for comparing a printing state at a density of 90 of original data according to the present invention and that of a conventional technique.

FIG. 12 is a diagram for explaining another example of the quantized value processing method according to the present invention.

FIG. 13 is a diagram showing a determination pattern of an edge in the sub-scanning direction.

FIG. 14 is a diagram showing a flowchart of an intermediate image processing apparatus according to the present invention.

FIG. 15 is a diagram for explaining the effect of the halftone image processing apparatus according to the present invention.

FIG. 16 is a diagram for explaining the effect of the halftone image processing device according to the present invention.

FIG. 17 is a diagram for explaining the effect of the halftone image processing device according to the present invention.

FIG. 18 is a sectional view showing the overall configuration of a digital copying machine having a halftone image processing function according to the present invention.

19 is a block configuration diagram of an image processing unit and each control system included in the digital copying machine in FIG.

FIG. 20 is a diagram for explaining a conventional quantization processing procedure.

FIG. 21 is a diagram for explaining conventional density storage.

FIG. 22 is a flowchart for explaining conventional halftone image processing.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Edge determination unit, 2 ... Calculation unit, 10 ... Digital multi-function peripheral, 11 ... Scanner unit, 12 ... Laser printer unit, 13
... multi-stage paper feeding unit, 14 ... sorter, 15 ... document placing table, 16 ... double-sided automatic document feeder (RDF), 20
... Scanner unit, 21 ... Lamp reflector assembly, 22 ... Photoelectric conversion element (CCD), 23 ... Reflecting mirror, 24 ... Lens, 25 ... Manual document tray, 26 ... Laser writing unit, 27 ... Electrophotographic process section, 2
8 ... Photosensitive drum, 29 ... Fixing device, 30 ... Transport path, 31
... 1st cassette, 32 ... 2nd cassette, 33 ... 3rd cassette, 35 ... 5th cassette, 36 ... Common conveyance path, 37-
41 ... Conveyance path, 50 ... Image data input section, 51 ... Image processing section, 52 ... Image data output section, 53 ... Memory, 54 ...
Operation panel, 55 ... Copy density key, 56 ... Magnification key,
57 ... Image processing CPU (central processing unit).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Norihide Kunikawa 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka Prefecture

Claims (4)

[Claims] 1. An image data input unit for binarizing and converting image data of a document, an image processing unit for finally converting the image data, and a storage unit for storing the image data processed by the image processing unit. , An image data output unit that restores the image data stored in the storage unit and performs error diffusion of data that is a halftone expression. After the error diffusion processing of the data in the image data output unit, An intermediate-tone image processing device, characterized in that it is provided with a calculation means for performing an interval calculation. 2. The halftone image processing apparatus according to claim 1, further comprising an edge determination unit provided in front of the calculation unit. 3. The edge portion determining means comprises main scanning direction edge portion determining means and sub scanning direction determining means for determining an edge portion in the main scanning direction and an edge portion in the sub scanning direction. Item 2. The halftone image processing device according to item 2. 4. The halftone image processing apparatus according to claim 2, wherein the edge portion determination means determines an area of an edge portion and a non-edge portion.