JP2002112034A - Image processor, image forming device, method for processing image, and method for forming image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the optimum sampling interval settable with the system constitution of a device. SOLUTION: One-line image data are divided into a plurality of blocks and pixel sampling is performed. Then the mean value of each block is found and the ground color level of an original is found from the peak holding value of the mean values. When a copying mode is selected in this case ('Y' in step S32), the sampling interval is set by selecting the interval by looking up a table in accordance with the selected mode (step S33). When the copying mode is not selected ('N' in step S32), the sampling interval which is set to default is set (step S34). Then ground color removal is made from image signals by performing sampling at the sampling interval set in steps S33 and S34 (step S38).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image processing apparatus,
The present invention relates to an image forming apparatus, an image processing method, and an image forming method.

[0002]

2. Description of the Related Art In a digital copying machine, a facsimile, or the like, when a background portion of a document has a predetermined density or more, for example, when a document such as a newspaper, a timetable, recycled paper, or a colored paper is a document, reading of the document is performed. When this is done, the density of the background of the original is high (for example, the background is slightly black). If the image data read by a photoelectric conversion element such as a CCD sensor is output as it is, the reproduced original becomes dirty due to the background. , The character portion, etc., are also difficult to see.

Conventionally, for a document having such a background having a predetermined density, a peak of the background density of the document is detected and held, and the read image is corrected based on the peak value. The removal process is in progress.

[0004] In this case, as a method of holding the background density peak, an analog method in which a peak level of an analog image reading signal is held by a capacitor (JP-A-6-225138).
And a digital method for holding the peak level of an image read signal after A / D conversion as a digital value (Japanese Patent Laid-Open No.
6-311359).

A method of performing peak hold of the background density by a digital method is to calculate an average value of a digitized image signal in line units and add a predetermined offset value to the average value to obtain a peak hold level. To determine.
In recent years, digital systems have been increasingly used in terms of cost, component variation, reliability, and the like.

[0006]

SUMMARY OF THE INVENTION
In the digital system disclosed in Japanese Patent Application Laid-Open No. 6-311359, when the conventional analog system is changed to the digital system, there is a problem that a difference occurs in the image characteristics due to a difference in the peak hold tracking characteristics of both systems.

Further, since the peak hold level is calculated from the average value in line units, the peak hold value does not rise to the background of the character portion for a document in which characters and patterns are combined (generally). In general, the background of the character portion has a low density, and the background of the picture portion has a high density.

In particular, when both digital and analog systems are mixed (in the case of double-sided printing, the front side is an analog system and the back side is a digital system. Here, the meaning of analog or digital is one line. This means whether the signal processing means for peak hold of the image signal is analog type or digital type.
There is a method described in JP-A-6-225138, in which a reference voltage of an A / D converter is controlled by a charge / discharge voltage value based on an R time constant. ), There is a problem that the image characteristics cannot be unified.

SUMMARY OF THE INVENTION It is an object of the present invention to accurately follow the background level of a document with a simple circuit configuration even for a document with mixed pictures and characters.

An object of the present invention is to set an optimum sampling interval according to the system configuration of the apparatus in this case.

An object of the present invention is to automatically set an optimum sampling interval in this case according to an image forming mode.

An object of the present invention is to improve the detection accuracy of a peak level even when an image signal is an image having a periodic vertical line pattern.

[0013]

According to a first aspect of the present invention, there is provided a sampling unit for dividing a digital image signal of a document into a plurality of blocks for each line and sampling pixels for each block, and a unit for each block. Averaging means for obtaining an average value of the sampling values of the above, peak holding means for detecting and holding the peak level of each average value in the one line, and the background level from the digital image signal using the peak level after the calculation. And a sampling interval setting unit that can set the sampling interval to a different size.

Accordingly, the average value of each block is obtained by dividing the image into a plurality of blocks for each line, and the peak level of each average value in one line is obtained. With a simple circuit configuration,
It is possible to accurately follow the background level of the document. In addition, if the sampling interval of pixels for each block is shortened, the accuracy of the peak level is improved, and if it is increased, the processing time of the circuit per unit time is shortened. It can be set.

According to a second aspect of the present invention, there is provided a sampling means for dividing a digital image signal of an original into a plurality of blocks for each line and sampling pixels for each block, and an average value of the sampling value for each block. , A peak hold means for detecting and holding a peak level of each average value in the one line, a calculating means for calculating a peak level of a subsequent line from the peak level and the digital image signal, A background removing unit for removing the background level from the digital image signal using the peak level after the calculation, wherein an appearance position of a sampling point of the sampling is irregular.

Therefore, each line is divided into a plurality of blocks to determine the average value of each block, and the peak level of each average value in one line is determined. With a simple circuit configuration,
It is possible to accurately follow the background level of the document. Further, since the appearance positions of the sampling points are irregular, the detection accuracy of the peak level can be improved even when the image signal is an image having a periodic vertical line pattern.

According to a third aspect of the present invention, in the image processing apparatus according to the second aspect, an appearance position of the sampling point is irregular due to a difference in a start position of the sampling depending on the block. Since the start position differs depending on the block, the appearance position of the sampling point is irregular, so that the peak level detection accuracy can be improved even if the image signal is a periodic vertical pattern image or the like.

The invention described in claim 4 is the invention according to claim 2 or 3
In the image processing device described in (1), an appearance position of the sampling point is irregular because the sampling cycle is different within the one line.

Therefore, since the sampling points appear irregularly due to different sampling periods within one line, the detection accuracy of the peak level can be reduced even if the image signal is of a vertical line pattern image. The invention according to claim 5, wherein the image processing apparatus according to any one of claims 1 to 4, wherein the photoelectric conversion element reads an image of a document, and processes the read image signal of the document. An image reading apparatus comprising:

Therefore, the same operation and effect as the invention according to any one of claims 1 to 4 can be obtained.

According to a sixth aspect of the present invention, there is provided an image forming apparatus comprising: the image reading apparatus according to the fifth aspect; and a printer engine for forming an image on a sheet based on the processed image signal. Device.

Therefore, the same operation and effect as those of the invention described in claim 5 can be obtained.

According to a seventh aspect of the present invention, there is provided a photoelectric conversion element for reading an image of an original, an image processing apparatus for processing the read image signal of the original, and an image processing apparatus for processing the image signal after the processing. A printer engine for forming an image on a paper based on the input device, and an input device for receiving a selection of the image forming mode, wherein the sampling interval setting means sets the sampling interval according to the selection. An image forming apparatus.

Therefore, according to the mode of image formation,
The optimum sampling interval can be selected, and the optimum sampling interval can be automatically set.

According to an eighth aspect of the present invention, there is provided a sampling step of dividing a digital image signal of a document into a plurality of blocks for each line and sampling pixels for each block, and an average value of the sampling value for each block. Averaging step, a peak hold step of detecting and holding a peak level of each average value in the one line as a background level of the document, and a peak level of a line subsequent to the peak level and the digital image signal. And a background removal step of removing the background level from the digital image signal using the calculated peak level, and a sampling interval setting step of setting the sampling interval before the sampling step. And an image processing method comprising:

Accordingly, each line is divided into a plurality of blocks, the average value of each block is obtained, and the peak level of each average value in one line is obtained. With a simple circuit configuration,
It is possible to accurately follow the background level of the document. In addition, if the sampling interval of pixels for each block is shortened, the accuracy of the peak level is improved, and if it is increased, the processing time of the circuit per unit time is shortened. It can be set.

According to a ninth aspect of the present invention, there is provided a sampling step of dividing a digital image signal of an original into a plurality of blocks for each line and sampling pixels for each block, and an average value of sampling values for each block. Averaging step, a peak hold step of detecting and holding a peak level of each average value in the one line as a background level of the document, and a peak level of a line subsequent to the peak level and the digital image signal. And a background removal step of removing the background level from the digital image signal by using the peak level after the calculation, whereby the appearance position of the sampling point of the sampling is made irregular. Processing method.

Therefore, each line is divided into a plurality of blocks, the average value of each block is determined, and the peak level of each average value in one line is determined. With a simple circuit configuration,
It is possible to accurately follow the background level of the document. Further, since the appearance positions of the sampling points are irregular, the detection accuracy of the peak level can be improved even when the image signal is an image having a periodic vertical line pattern.

According to a tenth aspect of the present invention, in the image processing method of the ninth aspect, an appearance position of the sampling point is irregular because a start position of the sampling is different depending on the block.

Therefore, since the sampling points appear at irregular positions due to the difference in the sampling start position between the blocks, the detection accuracy of the peak level is improved even if the image signal is of an image having a periodic vertical line pattern. Can be done.

According to an eleventh aspect of the present invention, in the image processing method of the ninth or tenth aspect, an appearance position of the sampling point is irregular due to a difference in the sampling cycle within the one line.

Therefore, since the sampling points appear irregularly due to the different sampling periods within one line, the detection accuracy of the peak level can be reduced even if the image signal is of an image having a periodic vertical line pattern. According to a twelfth aspect of the present invention, there is provided a reading step of reading an image of a document by a photoelectric conversion element, and an image processing step of processing the read image signal of the document by the image processing method according to the eighth aspect. And an image forming step of forming an image on paper by a printer engine based on the image signal after the processing, and a receiving step of receiving, by an input device, a selection of the image forming mode before the reading step. And the sampling interval setting step is an image forming method for setting the sampling interval according to the selection.

Therefore, according to the image forming mode,
The optimum sampling interval can be selected, and the optimum sampling interval can be automatically set.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described.

FIG. 1 is a side sectional view showing a schematic configuration of a copying machine according to an embodiment of the present invention. This copier 1
Are provided on the image scanner 2; an image scanner 2 as an image reading device for reading an image of a document; a printer unit 3 as a printer engine for forming an image on paper based on image data read by the image scanner 2; ADF (Automatic Document Feeder) 4.

A contact glass 5 on which an original to be read is placed is provided on the upper surface of the image scanner 2. Below the contact glass 5, a first carriage 8 including an illumination lamp 6 and a mirror 7 and capable of traveling along the contact glass 5, and a second carriage including mirrors 9 and 10 and capable of traveling along the contact glass 5. Carriage 11
, An imaging lens 12, and a CCD (Ch
scanning optical system 14 having an arge coupled device 13
Is provided. First and second carriages 8, 11
Is driven by a carriage motor (not shown) such as a stepping motor, and travels from the home position (right side) shown in FIG. 1 to the left side at a speed ratio of 2: 1.

In the printer unit 3, the paper is fed from a paper feed tray 15 for stacking paper to a paper output stacker 18 via a printer engine 16 for forming an image on paper in an electrophotographic system, a fixing device 17 and the like. A paper transport path 19 is formed. The printer engine 16 forms an electrostatic latent image by exposing the photoconductor 20 based on image data read by the image scanner 2 and a charger 21 for uniformly charging the surface of the photoconductor 20. Exposing device 22, developing device 23 for developing the electrostatic latent image formed on the surface of photoconductor 20 with toner, and transferring the toner image on photoconductor 20 to the paper conveyed in paper conveyance path 19. And a transfer unit 24 that performs the transfer.

The ADF 4 includes a document table 25 on which a document to be fed to the contact glass 5 by the ADF 4 is placed, and a paper discharge unit 26 for discharging the document that has been read. Inside the ADF 4, a paper output unit 2
6 is formed. A transport mechanism 31 such as an endless belt 29 wound around a plurality of pairs of rollers 28 and a transport roller 30 is provided in the document transport path 27. The transport mechanism 31 includes an A such as a stepping motor.
The document table 2 is driven by a DF motor (not shown).
The documents placed on the document 5 are conveyed one by one toward the contact glass 5. On the upper surface of the ADF 4, a main body operation panel 32 including a keyboard and a display is provided.

Next, the electrical connection of the control system of the copying machine 1 will be described with reference to FIG. Copier 1 has a CPU
And a main control section 33 for centrally controlling the driving of each section in the copying machine 1. This main control unit 33
Is connected to a main unit operation panel control unit 36 for controlling the main unit operation panel 32 as an input device, a scanner unit control unit 37 for controlling the image scanner 2, and a printer unit control unit 38 for controlling the printer unit 3. ing.

The main body operation panel control section 36 outputs an input signal corresponding to an input operation on the keyboard on the main body operation panel 32 to the main control section 33. Further, the main body operation panel control unit 36 causes the display to display information based on the display data output from the main control unit 33.

The scanner unit control section 37 includes the CCD 1
The image data of the document optically read in step 3 is output to the main control unit 35 as image data converted into an electric signal. An ADF controller 40 is connected to the scanner unit controller 37. The ADF controller 40 contacts an original by driving an ADF motor (not shown) according to a signal output from the scanner unit controller 37. Feed up to glass 5.

When the image data output from the main control unit 35 is input, the printer unit control unit 38 controls the driving of each unit in the printer unit 3 and
For the paper transported with the timing adjusted from 5,
An image based on the image data is formed.

FIG. 3 is a block diagram showing the electrical connection of the image processing apparatus 41 prepared in the scanner unit control section 37 or the main control section 35. As shown in FIG.
An analog image signal obtained by reading a document by the CCD 13 is converted into a digital image signal by an A / D converter 42, and further subjected to shading correction processing by a shading correction circuit 43. The background removal circuit 44 detects the background density of the digital image signal after the shading correction and performs the background removal processing. The image processing circuit 45 performs image processing such as MTF correction, scaling processing, γ correction, and binary / multi-value processing on the digital image signal after the background removal processing. The digital image signal after the image processing is transmitted to the printer unit control unit 38 and used for image formation.

FIG. 4 is a block diagram showing the electrical connection of the background removal circuit 44.

The background removal circuit 44 applies a block unit pixel sampling unit 5 to the digitized input image signal.
Each unit of the 1-Low Limit comparison unit 58 performs a process as described later, and the background removal unit 59 performs background removal processing of the input image signal using the detected background level as a threshold. FIG. 9 shows the input / output characteristics of the background removal unit 59. When the background level threshold (Dsh) is input, the output is white 2 if the output is an 8-bit monochrome level.
It has 55 levels, and its input / output characteristics are as shown by the solid line in FIG. If a gray-colored background from 255 levels of white to Dsh is input, all of them are output as 255 levels of white.

As shown in FIG. 4, the block unit pixel sampling unit 51 realizes a sampling unit, and divides an input digital image signal for one line into a plurality of blocks each having a fixed number of pixels. Each time, sampling is performed at a fixed number of pixel intervals. That is, as shown in FIG. 5, the lines [1] to [j] are divided into blocks [1] to [i], respectively. FIG. 6 shows an example of 1
FIG. 7 is a conceptual diagram in a case where a block unit is 196 pixels and sampling is performed at an interval of 7 pixels. In this case, as shown in FIG. 6, sampling is performed for 27 pixels in one block.

The number of blocks for dividing the digital image signal for one line (the number of peak level detection blocks) is calculated from the following equation.

Number of peak level detection blocks = PW_WI
DTH / BK_WIDTH (where, PW_WIDTH: the number of peak detection pixels in one line, BK_WIDTH: the number of pixels in one block) The block unit average calculation unit 52 implements an averaging unit, and as shown in FIG. For each block [1] to [i] of [1] to [j], the average value AV
E [1] to AVE [i] are calculated. That is, 2 sampled by the block unit pixel sampling unit 51
An average value is calculated from the sum of the seven pixels.

The block average value-PH (Peak Hold) value difference calculation unit 53 and the constant A rise calculation unit 54 correspond to the CR time constant of the conventional analog system, and are adapted to the characteristics of the analog system. Are the block average value-PH value difference calculation unit 53 and the constant A rise calculation unit 5
This can be achieved by changing the constant determined by 4.

As an example, in reading an image at 600 dpi, the rising characteristic of the peak hold
99% on white background skin (input image data) of 0 mm x 10 mm
A tracking characteristic of (5τ) is intended (all black data is assumed except for the white background). That is, for example, if a 200-level white background is input in a size of 10 mm (main scanning direction) × 10 mm (sub-scanning direction), a peak hold value of 200 × 0.99 level will be obtained after 10 mm in the sub-scanning direction. The aim is to have such an exponential function curve following characteristic. In the case of a 5 mm × 5 mm white background, the level on the exponential function characteristic at 5 mm in the sub-scanning direction becomes the peak level value.

In order to achieve the desired tracking characteristic, the number of pixels of 10 mm × 10 mm (236 pixels × 2
In the peak hold system of the copying machine 1, there are 236 lines having a white background in the sub-scanning direction. The following formula determines the ratio that needs to be raised in one line.

1-EXP (-5/236) = 0.020
96 (that is, about 2%) The above equation is obtained by adding about 2% of the difference between the “constant input data” and the “current peak hold value” in one line to the current peak hold value. Represents the peak hold value.

Here, when there is a white background of 236 pixels in one line, a value for increasing the current peak hold level in line units is obtained by the following equation.

Value for increasing current peak hold level =
(Input data-current peak hold level) x 236 x
0.02096 × (1/236) Here, if 0.02096 × (1/236) = 1 / α, α = 111260.

The technical meaning described above means that the input data level of 236 pixels exceeds the peak hold level by 1
/ Α is to increase the current peak hold level.

In the copying machine 1, since one line is divided into blocks to calculate one average value, the following-up constant A is as follows.

A = α / (the number of pixels in one block) By the above-described peak hold tracking operation, it is possible to obtain a peak hold tracking characteristic equivalent to that of the analog system in the digital system. A is a rising constant of the peak hold value of the digital system, and corresponds to changing the CR value of the conventional analog system.

Next, the multiple averaging unit 55 will be described.

That is, j: sub-scanning line variable IIRden [j]: denominator variable IIRnum [j]: numerator variable IIRrem [j-1]: remainder of summer averaging result of previous line PH [j]: current line peak hold level PH [j-1]: Assuming that the preceding line has a peak hold level, PH [j] = [IIRrem [j-1] + ｛PH [j-
1] × (IIRden [j] −IIRnum [j])｝
+ (PH [j] × IIRnum [j])] / IIRde
n [j].

Here, the meaning of the multiple averaging operation is to smooth the peak hold value in the sub-scanning direction. This amount averaging operation is performed by an IIR type (Infinite Impulse Res
(Ponse). IIR
The type filter is a feed hack type filter that uses the operation result of the previous line to perform the operation of the current line. That is, in order to perform the operation of the current line, the operation result of the previous line is required. To perform the operation of the previous line, the operation result of the line before the previous line is required.
finite) is subtracted from the influence of the past operation result. The influence becomes weaker as the past calculation result is obtained by multiplying the child averaging calculation coefficient many times. Thus, by bringing the calculation result of the infinite past line into the calculation of the current line, it is possible to obtain the same effect as performing the smoothing process by referring to the peak hold value over a wide range with a small amount of calculation. .

The reason why the multiple addition calculation is performed on the output of the constant A rise calculation unit 54 shown in FIG. 2 is that the peak hold value is increased even by a parameter other than the A parameter of the constant A calculation by changing the coefficient of the multiple addition. Is to be controllable.
In other words, it is possible to control the result of the constant A rise calculation unit 54 by the child averaging so as to further reduce the following speed.

Next, the constant B falling calculator 56 will be described. As an example, in the image reading of 600 dpi, the falling follow-up characteristic of the peak hold is 63% in the number of sub-scanning 420 mm lines (after a time of 1τ).
It is assumed that the following characteristic is pursued. Here, suppose 420mm
In order to calculate the constant B at which the peak hold value decreases by 63%, it is assumed that the peak hold value does not increase. However, the actual operation of the apparatus is as follows. Since both of the B operations are always performed, the lowering operation of the constant B is also performed for the line having the increased peak hold value.

In order to achieve the above-mentioned desired tracking characteristics,
In the analog system, the number of lines of sub-scanning 420 mm (992
In the time of (one line), the capacitor and the resistance become the discharge time constant of 1τ. In the peak hold system of the copying machine 1, the following level in one line is obtained by the following equation.

1−EXP (−1/9921) = 0.00010079 According to the above equation, the current peak hold value can be set to about 0.
The result is a 01% drop. The value for decreasing the current peak hold level in line units is given by the following equation.

Value for lowering current peak hold level =
(Current peak hold level) × 0.000100079 Here, if 0.00010079 = 1 / B, B = 9922 (B is a falling follow-up constant) That is, 1/1 of the current peak hold level for each line
This means that the current peak hold level is decreased by B. By the above-described peak hold tracking operation, it is possible to obtain a peak hold tracking characteristic equivalent to that of the analog method in the digital system. The output of the constant B falling calculator 56 is a value obtained by updating one peak hold value for one line.

Next, the offset addition / subtraction unit 57
An arbitrary constant is added or subtracted from the peak hold level determined by the falling calculation unit 56. This is for compensating, for example, a noise component of the characteristics of the CCD 13.

Next, the low limit comparing section 58
Under the following conditions, the peak hold level is set to an arbitrary value (Low Limit) set in advance.

That is, the peak hold level <Low Limit.

This is because, for a gray background color such as a close-up photograph, the gray is not output as a 255-level white image and the background is removed, but the gray is output as it is. is there. In addition, since the peak hold value is low at the leading edge of the document (the initial value is, for example, 0), even in the case of a character document, if there is no concept of a low limit, the character at the leading edge is skipped. It is also to solve this.

The block average value-PH value difference calculation section 53, the constant A rise calculation section 54, and the multiple addition average section 55
Constant B falling operation unit 56, offset addition / subtraction unit 57
And the low limit comparing unit 58 implement a peak hold unit and a calculation unit.

Next, the background removing section 59 will be described.
In the following description, the data width is 8 bits and 0
The case where the level is black and the level 255 is white will be described as an example. The background removing unit 59 implements a background removing unit. As shown in FIG. 9, when data equal to or greater than Dsh (current line quantization threshold level) is input, the output data becomes 255, as described below. Performs a formula operation.

Output data = (input data / Dsh) × 255 By the above operation, data of 0 to Dsh is requantized to 0 to 255.

Next, the procedure of the peak hold operation performed by the background removal circuit 44 will be described in detail with reference to the flowcharts of FIGS. The symbols used in the flowcharts of FIGS. 7 and 8 are defined in FIG.

First, j = 0, PH [j] = 0, Rrem
[J] = 0, Frem [j] = 0, IIRrem [j]
= 0, reset these values (step S
1) The sub-scanning line variable j is incremented by +1 (step S2).

The block unit pixel sampling unit 51 sets 1
The digital image data of a line is sampled by dividing the digital image data of the line into blocks, and an average value AVE [1] to an average value AVE [1] per block of one line are obtained by a block average calculator 52.
[K] is calculated (step S3). The number k of main-scanning effective blocks is calculated by the above-described “number of peak level detection blocks = P”.
W_WIDTH / BK_WIDTH ”.

Next, the block average value-PH value difference calculation section 53 resets the main scanning block variable m to m = 0 (step S4). Then, the difference between each block average value AVE [m] in one line and the peak hold level PH [j-1] of the previous line is calculated, and the following processing is performed. That is, when the difference is negative (Y in step S6), “Dif [m] = 0” is set (step S6).
7) When the difference is positive (N in step S6),
“Dif [m] = AVE [m] −PH [j−1]” is set (step S8). Then, the above calculation is performed for all the peak number detection blocks k in one line (Y in step S10), and the sum of the results is set to ｆDif (step S9). ΣDif is the sum of values of the input image exceeding the peak hold level in one line. That is, the peak hold value of the previous line is compared with the average value for each block of one line. If the average value is less than the peak hold value, the difference is set to 0 (step S7), and the average value is set to the peak hold value. If it exceeds, the difference is obtained (step S
8) Then, the excess difference is added for each block (step S9), and the sum of the input image of one line exceeding the peak hold value of the previous line is obtained.

Next, in the constant A rising operation section 54,
結果 Rquo [j] (quotient), Rrem [j] (remainder) as a result of dividing the sum of Dif and Rrem [j-1] (remainder of constant A operation result of previous line) by rising follow-up constant A
Is calculated (step S11). From the above results, PH [j] is increased under the following conditions.

That is, if Rquo [j] <1, PH [j] = PH [j]
(Y of step S12) When Rquo [j] ≧ 1, PH [j] = PH [j]
-Rquo [j] (N in step S12, S13) Rrem [j] is carried over to the constant A operation of the next line.

The multiple averaging unit 55 performs the following operation on PH [j] calculated by the constant A rising operation unit 54. Here, IIRrem [j-1] is the remainder of the child addition operation result of the previous line.

PH [j] = [IIRrem [j-1] +
｛PH [j-1] × (IIRden [j] -IIRnu
m [j])｝ + (PH [j] × IIRnum [j])]
/ IIRden [j] By this operation, PH [j] (quotient), IIRrem [j]
(Remainder) is calculated (step S14). Where I
IRrem [j] is carried over to the multiple averaging operation of the next line. In addition, arbitrary values can be set for the multiple addition denominator variable IIRden [j] and the multiple addition numerator variable IIRnum [j].

In the constant B falling calculating section 56, Frem is calculated based on PH [j] calculated by the multiple averaging section 55.
Fquo [j] is obtained by dividing the sum of [j-1] (the remainder of the previous line constant B operation result) by the falling follow-up constant B.
(Quotient) and Frem [j] (remainder) are calculated (step S15).

From this result, PH [j] is lowered under the following conditions.

When Fquo [j] <1, PH [j] =
PH [j] (Y in step S16) When Fquo [j] ≧ 1, PH [j] = PH [j] −
Fquo [j] (N in step S16, S17) Note that Frem [j] is carried over to the constant B calculation of the next line.

In the offset addition / subtraction unit 57, an arbitrary constant A
EREF addition / subtraction can be selected (steps S18 to S18).
S20). PH [j] in the offset addition / subtraction unit 57
Is the quantization threshold level Dsh [j] of the current line.

Next, in the Low Limit comparing section 58, when Dsh [j] <Low Limit (Y in step S21), Dsh [j] is set to a Low Limit in which an arbitrary value can be set (step S21).
22).

The processing in steps S2 to S22 is performed by j
Until the value of n becomes n, the value of j is incremented by 1 (step S2) and repeated (N of step S23), j
When the value of has become n (Y in step S23), a series of processing ends.

The threshold level D thus obtained
The sh [j] is output to the background removing unit 59 in line units, and the background threshold removing unit 59 updates the quantization threshold level Dsh [j] in line units.

The sampling step and the averaging step are realized by step S3, and the peak hold step and the calculation step are realized by steps S5 to S22.

By the way, in the copying machine 1, the appearance positions of the sampling points of the sampling performed by the block unit pixel sampling section 51 as described above are irregular. Specifically, the sampling start position differs for each block. Alternatively, the sampling cycle differs in each block.

FIG. 10 is an explanatory diagram of an example in which the sampling start position is shifted by one pixel for each block. The example of FIG. 10 shows an example in which the sampling start position of the block 2 is shifted by one pixel compared to the blocks 1 and 3 before and after it.

FIG. 11 is an explanatory diagram of an example in which the sampling period is varied within one block. In the example of FIG. 11, pixel sampling is repeated at the following intervals from the sampling start pixel in one block.

1, 2, 3... N-1, N As a result, the sampling periods in one block are all different. However, in this example, the variation pattern of the sampling period is the same between the blocks (this may be changed).

Next, an outline of a series of image forming processing will be described with reference to a flowchart of FIG.

That is, the user can select various image forming modes when copying a document with the copying machine 1. That is, whether the original is text or a photograph, whether the original is dark or light, and whether the original text is large or small, is selected by operating the main body operation panel 32, and the image quality mode according to the selection is set. To read the original.

That is, when there is an instruction to start copying by pressing the copy start button (step S3).
1) (Y), when the mode selection as described above has been performed (Y in step S32), the scanner unit control unit 37 then sets the sampling interval performed by the block unit pixel sampling unit 51 as described above. Select and set by table lookup according to the selected mode (step S33). If there is no such mode selection (N in step S32), a default sampling interval is set (step S34). The receiving step is realized by step S32. Steps S33 and S34 implement a sampling interval setting unit and a sampling interval setting step.

For example, in the example of FIG. 6 described above, the sampling interval of 196 pixels in one block is 27 pixels in units of 7 pixels, but if the sampling is performed in units of 3 pixels, as shown in FIG. It will be sampled.

Thereafter, as shown in FIG.
The carriages 8 and 11 are driven to read the original (step S35), and the image signal output from the CCD 13 is A / D converted by the A / D converter 42 (step S3).
6) The shading correction is performed by the shading correction circuit 43 (step S37). The reading step is realized by step S35. Then, steps S33 and S3
4 and the sampling start position or the sampling period as described above, the block unit pixel sampling unit 51
And the background is removed from the image signal as described above with reference to FIGS. 7 and 8 (step S38). The background removal step is realized by step S38. Then, after performing various types of image processing by the image processing circuit 45 as described above, an image signal is output to the printer unit 3.
An image processing step is realized by steps S36 to S38. Then, an image is formed by the printer unit 3 (step S39). This realizes the image forming process.

According to the copying machine 1 described above, in order to match the characteristics of the digital system with the characteristics of the analog system, various operations are performed on the value of the input image exceeding the peak hold level. In this case, in order to improve the accuracy, it is effective to execute the excess calculation for each pixel, but at the same time, the processing time of the circuit per unit time also increases. One line of the image signal is divided into blocks of a fixed pixel unit, and the excess can be calculated. This makes it possible to accurately follow the background level of a document with a simple circuit configuration even for a document with mixed pictures and characters.

Further, if the interval of sampling pixels for each block is shortened, the accuracy of the peak level is improved.
A longer time shortens the processing time of the circuit per unit time,
By setting the sampling interval, an optimum sampling interval can be set according to the system configuration of the apparatus.

In this case, the optimum sampling interval can be automatically set according to the copy mode.

Further, since the sampling start position differs depending on the block, the detection accuracy of the peak level can be improved even if the image signal is of an image having a periodic vertical line pattern.

Since the sampling period is different within one line, the detection accuracy of the peak level can be improved even if the image signal is an image having a periodic vertical line pattern.

[0103]

According to the first aspect of the present invention, an average value of each block is obtained by dividing a plurality of blocks for each line, and a peak level of each average value in one line is obtained. Even a document with mixed pictures and characters can accurately follow the background level of the document with a simple circuit configuration. In addition, if the sampling interval of pixels for each block is shortened, the accuracy of the peak level is improved, and if it is increased, the processing time of the circuit per unit time is shortened. It can be set.

According to the second aspect of the present invention, an average value of each block is obtained by dividing into a plurality of blocks for each line, and a peak level of each average value in one line is obtained. Even a document with mixed characters can accurately follow the background level of the document with a simple circuit configuration. Further, since the appearance positions of the sampling points are irregular, the detection accuracy of the peak level can be improved even when the image signal is an image having a periodic vertical line pattern.

According to a third aspect of the present invention, in the image processing apparatus according to the second aspect, since the sampling start position differs depending on the block, the appearance position of the sampling point is irregular. Even for an image having a vertical line pattern, the detection accuracy of the peak level can be improved.

The invention described in claim 4 is the invention according to claim 2 or 3
In the image processing apparatus described in 1 above, the appearance positions of the sampling points are irregular due to the difference in the sampling cycle within one line. Detection accuracy can be improved.

The invention described in claim 5 has the same operation and effect as the invention described in any one of claims 1 to 4.

The invention described in claim 6 has the same operation and effect as the invention described in claim 5.

According to the present invention, the optimum sampling interval can be selected according to the image forming mode, and the optimum sampling interval can be automatically set.

According to the eighth aspect of the present invention, since a line is divided into a plurality of blocks for each line, an average value is obtained for each block, and a peak level of each average value for one line is obtained. Even a document with mixed characters can accurately follow the background level of the document with a simple circuit configuration. In addition, if the sampling interval of pixels for each block is shortened, the accuracy of the peak level is improved, and if it is increased, the processing time of the circuit per unit time is shortened. It can be set.

According to the ninth aspect of the present invention, since a line is divided into a plurality of blocks for each line, an average value for each block is obtained, and a peak level of each average value for one line is obtained. Even a document with mixed characters can accurately follow the background level of the document with a simple circuit configuration. Further, since the appearance positions of the sampling points are irregular, the detection accuracy of the peak level can be improved even when the image signal is an image having a periodic vertical line pattern.

According to a tenth aspect of the present invention, in the image processing method of the ninth aspect, since the sampling start position is different for each block, the appearance position of the sampling point is irregular, so that the image signal is periodically generated. Even for an image having a vertical line pattern, the detection accuracy of the peak level can be improved.

According to an eleventh aspect of the present invention, in the image processing method according to the ninth or tenth aspect, the appearance positions of the sampling points are irregular due to the difference in the sampling period within one line. Even when the image has a periodic vertical line pattern, the detection accuracy of the peak level can be improved.

According to the twelfth aspect, the optimum sampling interval can be selected according to the image forming mode, and the optimum sampling interval can be automatically set.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a schematic configuration of a copying machine according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an electrical connection of a control system of the copying machine.

FIG. 3 is a block diagram showing an electrical connection of an image processing apparatus of the copying machine.

FIG. 4 is a block diagram showing an electrical connection of a background removal circuit of the image processing apparatus.

FIG. 5 is an explanatory diagram illustrating a case where a peak value is obtained from image data of each line in the background removal circuit.

FIG. 6 is an explanatory diagram illustrating sampling performed by the background removal circuit.

FIG. 7 is a flowchart illustrating in detail a procedure of a peak hold operation performed by the background removal circuit.

FIG. 8 is the same flowchart.

FIG. 9 is an explanatory diagram illustrating a background removal process performed by the background removal circuit.

FIG. 10 is an explanatory diagram of an example in which the background removal circuit shifts a sampling start position by one pixel for each block.

FIG. 11 is an explanatory diagram of an example in which the background removal circuit changes a sampling cycle within one block.

FIG. 12 is an explanatory diagram illustrating an example in which the background removal circuit changes a sampling interval.

FIG. 13 is an explanatory diagram illustrating sampling performed by the background removal circuit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 image forming device 2 image reading device 3 printer engine 13 photoelectric conversion element 32 input device 41 image processing device 42 A / D converter 51 sampling means 52 averaging means 53 to 58 peak hold means, calculation means 59 background removal means

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 DB01 DE02 DE07 DE09 EA18 EB03 FA30 5B047 AA01 BB02 CB21 DA03 DC02 DC11 5C076 AA36 AA40 BA06 BA08 5C077 LL19 MM03 PP21 PP25 PP43 PP46 PP68 PQ08 PQ12 TTQ06 RR18

Claims (12)

[Claims] A sampling means for dividing a digital image signal of a document into a plurality of blocks for each line and sampling pixels for each block; an averaging means for obtaining an average value of a sampling value for each block; Peak hold means for detecting and holding the peak level of each average value in one line; calculating means for calculating the peak level of a subsequent line from the peak level and the digital image signal; and calculating the peak level after the calculation. An image processing apparatus comprising: a background removing unit that removes the background level from the digital image signal using the digital image signal; and a sampling interval setting unit that can set the sampling interval to a different size. 2. A sampling means for dividing a digital image signal of a document into a plurality of blocks for each line and sampling pixels for each block; an averaging means for obtaining an average value of a sampling value for each block; Peak hold means for detecting and holding the peak level of each average value in one line; calculating means for calculating the peak level of a subsequent line from the peak level and the digital image signal; and calculating the peak level after the calculation. A background removing unit for removing the background level from the digital image signal using the image processing apparatus, wherein an appearance position of a sampling point of the sampling is irregular. 3. The image processing apparatus according to claim 2, wherein an appearance position of the sampling point is irregular because a start position of the sampling is different depending on the block. 4. The image processing apparatus according to claim 2, wherein an appearance position of the sampling point is irregular due to a difference in a cycle of the sampling within the one line. 5. A photoelectric conversion element for reading an image of a document, and processing the read image signal of the document.
An image reading apparatus comprising: the image processing apparatus according to any one of the above. 6. An image forming apparatus comprising: the image reading apparatus according to claim 5; and a printer engine that forms an image on a sheet based on the processed image signal. 7. A photoelectric conversion element for reading an image of a document, an image processing device according to claim 1 for processing an image signal of the read document, and an image processing device for processing an image on paper based on the processed image signal. An image forming apparatus comprising: a printer engine for forming; and an input device for receiving selection of the image forming mode, wherein the sampling interval setting means sets the sampling interval in accordance with the selection. 8. A sampling step of dividing a digital image signal of a document into a plurality of blocks for each line and sampling pixels for each block; an averaging step for obtaining an average value of a sampling value of each block; A peak holding step of detecting and holding a peak level of each average value in the one line as a background level of the document; and a calculating step of calculating a peak level of a subsequent line from the peak level and the digital image signal. An image processing comprising: a background removal step of removing the background level from the digital image signal using the peak level after the calculation; and a sampling interval setting step of setting the sampling interval before the sampling step. Method. 9. A sampling step of dividing a digital image signal of a document into a plurality of blocks for each line and sampling pixels for each block; an averaging step for obtaining an average value of sampling values of each block; A peak holding step of detecting and holding a peak level of each average value in the one line as a background level of the document; and a calculating step of calculating a peak level of a subsequent line from the peak level and the digital image signal. A background removal step of removing the background level from the digital image signal using the peak level after the calculation, wherein the appearance position of the sampling point of the sampling is made irregular. 10. The image processing method according to claim 9, wherein an appearance position of the sampling point is irregular because a start position of the sampling differs depending on the block. 11. The image processing method according to claim 9, wherein an appearance position of the sampling point is irregular due to a difference in a cycle of the sampling within the one line. 12. A reading step of reading an image of a document by a photoelectric conversion element, an image processing step of processing the read image signal of the document by the image processing method according to claim 8, and an image signal after the processing. An image forming step of forming an image on a sheet by a printer engine based on a printer engine, and a receiving step of receiving, by an input device, a selection of the image forming mode before the reading step. And an image forming method for setting the sampling interval according to the selection.