JP2947732B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, and more particularly, to a digital electronic forming apparatus that performs automatic density adjustment using a pixel density histogram to obtain an optimum image.

[0002]

2. Description of the Related Art In recent years, image forming apparatuses such as electronic copiers have
In addition to the conventional analog type, a digital type is widely used. A so-called automatic exposure function for obtaining the optimum image quality by changing the brightness of the document illumination lamp while detecting the document density with a sensor is a common function in analog copying machines. When this function is realized by a digital electronic copier,
Various techniques have been used. A method of obtaining an optimum image using a pixel density histogram is also generally used, and automatic density adjustment using a histogram is proposed in JP-B-64-6588 and JP-B-3-30143.

[0003]

In the automatic density adjustment of a digital electronic copying machine using a histogram, a reference value for density correction is obtained by referring to the numerical value of the histogram. If it is not faithfully represented, an appropriate correction reference value cannot be calculated,
There is a problem that automatic density adjustment is impossible or a defective image is output.

For example, as shown in FIG.
2, the original is placed without being pressed against the original scale 91, and the original cover is opened, all parts other than the original are read as black parts. Accumulated.

Therefore, the histogram created here is
It does not accurately reflect the density distribution of the document, and it is impossible to obtain an appropriate correction reference value. As a result, a good automatic density adjustment image cannot be obtained.

FIG. 19 shows a typical histogram tendency when image data is actually sampled and a histogram is created. FIG. 19A is a histogram when the document cover is opened. FIG. 19B is an example of a histogram when the document cover is closed (the document cover is white).

In FIG. 19A, data other than the original is inputted as a black portion, and the frequency of the black portion is increased. Originally, as shown in FIG. 19B, it is desirable that a black portion such as a character on a document appears as a peak on the black side.

Accordingly, it is an object of the present invention to provide a digital image copying machine capable of appropriately performing automatic density adjustment even when a document cover is open and obtaining a good copied image.

[0009]

In order to achieve the above object, an image forming apparatus according to the present invention reads a document in a main scanning direction and further repeats a reading operation along a sub-scanning direction different from the main scanning direction. Scanner means for providing the pixel density of each pixel in the original image for each scanning line, and each time pixel density data for one scanning line is received from the scanner means, A density histogram is created by using the pixel density, each pixel density included in the current scan line, and a weighting coefficient that changes according to the number of scan lines in the sub-scanning direction. Density correction for calculating a correction reference value for correction, correcting each received pixel density data based on the correction reference value, and providing corrected pixel density data Means, a mode setting means for setting an automatic density adjustment mode by the density correction means based on a user's input, a document cover for covering the document placed on the document table, and determining whether the document cover is open. And an image forming unit for forming an image based on the pixel density data. Further, when the automatic density adjustment is not set by the mode setting unit, the reading unit and the image forming unit Means for operating and forming an image, the automatic density adjustment is set by the mode setting means, and when the determination means determines that the document cover is closed, without performing pre-scanning by the reading means, A first automatic density adjusting unit configured to operate the reading unit, the density correcting unit, and the image forming unit to form a density-corrected image; When the automatic density adjusting means is set by the mode setting means and the judging means judges that the original cover is open, the reading means is controlled to prescan the original and placed on the original platen. Area setting means for detecting the position of the scanned document, and setting an area corresponding to this position as a histogram creation area; and scanning the document again by the scanner means, among pixel density data provided from the scanner means. And sampling means for sampling pixel density data corresponding to the histogram creation area set by the area setting means, and transferring the pixel density data from the sampling means to the density correction means, and obtaining from the density correction means. Providing the corrected density data to the image forming means, and forming a second density-corrected image; It includes an automatic density adjustment means. When the automatic density adjustment mode is set and the document cover is closed, the automatic density adjustment copy is performed without performing the prescan. When the document cover is open, prescanning is performed first to recognize the position of the document, a histogram is created only for the document area, and automatic density adjustment copying is performed without being affected by data outside the document. .

[0010]

[0011]

[0012]

[0013]

[0014]

[0015]

[0016]

[0017]

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of an image forming apparatus to which the present invention is applied. The image forming apparatus includes a scanner unit 1 for reading a document, and a printer unit 2 for forming an image on a sheet in accordance with an image signal supplied from the scanner unit 1 or an external device (not shown).

The scanner unit 1 includes a document table 117 on which a document to be copied is placed, an openable / closable document cover 109 for pressing a document placed on the document table 117, and a document placed on the document table 117. And a CCD type line sensor 4 as a photoelectric conversion means for photoelectrically converting reflected light from an original by irradiation of light from the fluorescent lamp 3. The fluorescent lamp 3 is provided with a lamp heater (not shown) as a heating means for heating the tube wall to a constant temperature. The document table 117 is provided with a document glass 92 on which a document is placed and a document scale 91 for abutting the document to measure the position of the document.

On the side of the fluorescent lamp 3, a reflector 115 for efficiently converging the light from the fluorescent lamp 3 to the original is provided. In addition, between the fluorescent lamp 3 and the line sensor 4, there are provided a plurality of mirrors 112 to 114 for bending an optical path through which light from the original to the line sensor 4, that is, reflected light from the original, passes; Lens unit 116 for focusing the reflected light on the light receiving surface of line sensor 4
And so on.

The original placed on the original table 117 is reciprocated by the scanning system including the fluorescent lamp 3 and the mirrors 112 to 114 reciprocatingly moving in the direction of arrow a along the lower surface of the original table 117. Sometimes it is exposed and scanned. In this case, the mirrors 113 and 114 move at half the speed of the mirror 112 so as to maintain the optical path length.

The reflected light from the original by the scanning of the scanning system, that is, the reflected light from the original due to the irradiation of the fluorescent lamp 3 is reflected by mirrors 112 to 114, passes through the lens unit 116, and passes through the line sensor 4 And an image of the original is formed on the light receiving surface of the line sensor 4.

The scanning unit 108 includes the fluorescent lamp 3, the line sensor 4, the mirrors 112 to 114, and the lens unit 116. The fluorescent lamp 3, the reflector 115, and the mirror 112 are provided on the first carriage 111, and the mirrors 113 and 114 are provided on the second carriage 110.
The motors 1 and 110 are moved by motors (not shown).

The printer unit 2 has a photosensitive drum 6 as an image carrier, and the photosensitive drum 6 is cylindrical,
It is configured to be rotatable in a desired direction by a motor or the like (not shown), is charged to a desired potential, and is irradiated with a light beam modulated in accordance with print data to form an electrostatic latent image.

Around the photosensitive drum 6, a charging device 102 for charging the surface of the photosensitive drum 6, a laser modulated according to print data as image information to be copied or output on the surface of the photosensitive drum 6. A laser unit 5 that outputs a light beam, a developing device 7 that develops the electrostatic latent image formed on the photosensitive drum 6 by attaching toner to the electrostatic latent image formed on the photosensitive drum 6 by the light beam from the laser unit 5, and a developed photosensitive drum 6 A transfer device 105 for transferring the upper toner image onto a sheet supplied from a sheet feeding unit 9 described later, and a peeling device 106 for peeling the sheet adsorbed on the photosensitive drum 6
And so on are arranged in order.

A cleaner unit 104 for removing toner remaining on the surface of the photosensitive drum 6 and a potential on the photosensitive drum 6 are provided around the photosensitive drum 6 and downstream of the peeling device 106. An erasing device 107 for erasing for the next image formation is arranged in order.

Between the developing device 7 and the transfer device 105,
A paper supply unit 9 that supplies paper for transferring the toner image formed on the photoconductor drum 6 toward between the photoconductor drum 6 and the transfer device 105 is provided.

In the direction in which the sheet on which the toner image has been transferred is separated from the photosensitive drum 6 by the peeling device 106, the fixing device 8 for fixing the toner image to the sheet, and the sheet peeled by the peeling device 106 A transport device 103 for transporting the toner toward the fixing device 8 is provided.

The sheet on which the toner image has been fixed by the fixing device 8 is discharged to a discharge tray 10 by a discharge roller 119.

FIG. 2 is a block diagram showing a schematic configuration of a control system of the image forming apparatus. This device has a main CPU 1
1, control panel CPU12, scanner CPU1
3 and the printer CPU 14.
The main CPU 11 communicates with and controls the control panel CPU 12, the scanner CPU 13, and the printer CPU 14.

Control panel (control panel) CPU1
2 is connected to a ROM 15 and a RAM 16 and detects a switch on a control panel 17 based on these data;
, Turning on and off, and controlling the display. The scanner CPU 13 is controlled by communication with the main CPU 11 and controls a mechanical controller (mechanical component) 23 such as a motor and a solenoid (not shown), an ADF (automatic document feeder) 24, and an editor 25 based on data in the ROM 21 and the RAM 22. , A / D (analog / digital conversion circuit) 26, SHD (shading correction circuit) 27, line memory 28, and the like.

The printer CPU 14 is controlled by communication with the main CPU 11, and has a ROM 31, RAM
Based on the data of 32, control of a mechanical controller 33 such as a motor and a solenoid (not shown), control of a sorter 34, an LCF (Large Cassette Feeder) 35, a laser modulation circuit 36, a laser drive circuit 37 and the like are performed.

The main CPU 11 comprehensively controls the image forming apparatus according to the control programs stored in the ROM 41 and the RAM 42. Data switching and buffer memory 4
3 indicates where to send the data read by the scanner unit 1;
Further, switching and buffering of data to be sent to the printer unit 2 are performed. The image processing unit 44 is provided with a circuit that creates a histogram from the image data, corrects the image data based on the histogram, and an automatic density adjustment unit according to the present invention. The compression / expansion circuit 45 performs compression / expansion of image data, and the page memory circuit 46 stores the image data for each page.

The display memory 48 stores the display 4
The printer controller 50 stores data of an image to be displayed on the personal computer (personal computer) 4.
9 is expanded into image data. The display font ROM 51 develops code data on the display memory 48 and print font ROM 52
Expands the code data on the page memory 46, and the compression memory 53 stores the data compressed by the compression / expansion circuit 45. In addition to the components described above, an I / F controller 57 that interfaces with the hard disk drive 54, the optical disk drive 55, and the facsimile adapter 56 is connected to the main CPU 11.

FIG. 3 is a block diagram showing a schematic configuration of the image processing section 44. The histogram creation circuit 80 creates a density histogram from the image data from the scanner unit 1. The correction reference value calculation unit 81 includes a histogram creation circuit 80
A correction reference value (to be described later) is calculated based on the histogram created in (1). The range correction circuit 82 corrects a density range (described later) using the correction reference value from the correction reference value calculation unit 81, and performs automatic density adjustment in real time.

The timing signal generator 83 is based on the clock signal from the clock generator 84, and
It generates various timing signals necessary for each block in the block. The image quality improvement circuit 85 includes a low-pass filter, a high-frequency emphasis circuit, and the like, and further improves the image quality of the image range-corrected by the range correction circuit 82. Enlargement / reduction circuit 8
6 enlarges / reduces the image as necessary, and executes a gradation processing circuit 8
7 processes the gradation of the image using the dither method or the error diffusion method. The image signal processed in this way is sent to the printer unit 2 to form an image.

FIG. 4 schematically shows a density histogram created by the histogram creating circuit 80. For example, A
In the case of reading one image of No. 4 at 400 dpi, the total number of pixels G is as follows.

G = 210 × 297 × (400 / 25.4) ² Each pixel having the number G of pixels has a density, and here, the density is expressed by 8 bits. The horizontal axis in FIG. 4A indicates this density, that is, the pixel value, and the vertical axis indicates the frequency (number of pixels) indicating how many pixels of which density existed with respect to the density.

As shown in FIG. 4A, in this embodiment, the density is divided into 16, and the 256 levels of density are simplified to 16 levels. That is, the lower 4 bits of the 8-bit pixel value are ignored. Employing 16 divisions greatly simplifies the hardware. The amount of information necessary as a histogram even in 16 divisions is sufficiently ensured in the automatic density adjustment function. FIG. 4B shows a method of equally dividing into 16 parts.
The division number 0 is in the range of pixel values 0 to F, the division number 1 is in the range of pixel values 10 to 1F, and so on.

Next, the range correction of the correction reference value calculation section 81 and the range correction circuit 82 will be described. The range correction is a function used for background cutting and the like in an automatic exposure function in an analog copying machine. Generally, when an original is read digitally and a density histogram is created, the result is as shown in FIG. In the case of an original such as a newspaper, the background density is considerable, so that one peak is formed in the background density portion as shown by M in FIG. 5A, and one peak is also formed in the character density portion such as N. Here, in an analog copying machine, the exposure lamp can be controlled to eliminate the background density portion, but in a digital copying machine, this cannot be done, so the same effect is obtained by the following method.

To explain with a simple example, the densities DW and DB corresponding to the peak points of the M peak and the N peak shown in FIG. 5A are obtained, and the following calculation is performed to obtain the density histogram of FIG. The distribution is converted as shown in FIG. Here, the densities DW and DB are called correction reference values, and are calculated by the correction reference value calculation unit 81 on the basis of the histogram on each scanning line created by the histogram creation circuit 80.

DN = (DI−DW) × FFH / (DB−DW) where DI is the input pixel density, DN is the corrected pixel density, and FFH is the maximum pixel density. That is, FIG.
The range (density range) between M and N in FIG.
h range.

Next, an outline of a histogram creation method will be described.
The following formula is a basic calculation formula for creating a histogram in the present invention, and the histogram is created for each main scanning line.
A reference value for range correction is obtained each time the histogram creation processing for one line is completed, and the range correction processing is performed based on the reference value. Further, the total number of data constituting the histogram is always a constant value.

A '= A-αA + αB where A': corrected frequency (number of pixels) corresponding to each density of the current line A: frequency corresponding to each density calculated up to the previous line B: current line Is a value multiplied by the frequency value accumulated in each line, and indicates the contribution rate to the histogram. This α
Is set in accordance with the number of lines as shown in FIG. 6, and 14 values (one power of 2), that is, 1,1 /
2, 1/4, 1/8, 1/16, 1/32, ..., 1 /
2048, 1/4096, 1/8192 (= 1/213)
Is selected from

Next, the histogram creation circuit 80 will be described. First, the histogram creation circuit 80 calculates A ′ = (A ′) + αB for each input pixel during one line reading, and secondly, during the period from one line reading to the next line reading,
That is, when no pixel density is input, (A ′) = A−αA is calculated for each density frequency of the histogram. In this way, the histogram creation circuit 80 calculates the corrected frequency value A ′ = A−αA + αB for the current line.
Generate A reference value for range correction is calculated by the correction reference value calculation unit 81 from the histogram thus created.

In addition, two modes, mode 0 and mode 1, are provided for creating a histogram, and one mode is selected as necessary.

Mode 0: Weighting coefficient variation addition mode depending on the number of sub-scanning lines Mode 1: Constant weighting coefficient addition mode for input pixels Mode 0 is, as described above, the value of coefficient α according to the number of main scanning lines counted. And create a histogram. In mode 1, a histogram is created with constant coefficients regardless of the count value of the main scanning line.

FIG. 7 is a block diagram showing a detailed configuration of the histogram creating circuit 80. One terminal of the switch 62 is connected to the pixel density signals IDAT4 to IAT4 from the scanner unit 1.
DAT7 is input, and output data signals CDT00 to CDT03 from counter 63 are input to the other terminal.
The switch 62 also selects one of the input signals according to the selection signal from the timing signal generator 83, and outputs the selected signals SLDT0 to SLDT3 to the selector 66 and the clock generator 64. Here, the pixel density signal IDAT4
To IDAT7 are the upper 4 bits of the pixel density.
AT0-3 are ignored for the reasons described above. The timing signal CTL0 from the timing signal generator 83 becomes high level between each line, that is, when the pixel density signal is not read, and the switch 62 selects and outputs the signal from the counter 63.

The counter 63 supplies a necessary value (count value) to the clock generator 64 and the selector 66 when calculating (A ') = A-αA. When the above-described pixel density signal is not read, the counter 63 generates a 4-bit count value for selecting and generating the 16 outputs of the clock generator 64 in order. The counter 63 receives the counter clock signal CT1C from the timing signal generator 83.
K is input and cleared by a counter clear signal CT1CL from the timing signal generator 83. The counter clear signal CT1CL becomes low level when the pixel density signal is read, and clears the counter 63.

The clock generating section 64 selects the input signal SLD
In response to T0 to T3, one of the 16 outputs FCK0 to FCK is selected and output at the cycle of the input clock signal MCK. FIG.
Indicates the relationship between the input and output signals of the clock generator 64.

The histogram registers (flip-flops) 65 1 to 65 F latch and output the corrected frequency (WDAT) for each pixel density when the input clock signals FCK 0 to FCK rise. The input signal WDAT is A′−αA or (A ′) + αB described above. The corrected frequency signal H from the histogram registers 651 to 65F
0 to HF are also output to the correction reference value calculation unit 81.

The selector 66 is connected to the histogram register 6
The frequency (the number of pixels) corresponding to each of the 16 levels of density H0 to HF from 51 to 65F is input. ) Is selected and the signal HSDT is output.

As shown in the timing chart of FIG. 14, the sub-scanning line number counter 76 receives the line synchronization signal HDEN from the timing signal generator 83 and outputs count value signals FDAT00 to FDAT12 to the clock generator 75. Clear signal CRST from main CPU 11
Is cleared each time one page of the document is scanned.

The clock generator 75 outputs the output signals FDAT0 to FDAT12 from the sub-scanning line number counter 76,
And the pixel synchronization clock signal GCK from the scanner unit 1 is input, and outputs the signal HCK to the counter 74 and the addition value generation unit 71. The clock generator 75 outputs the signal FDAT
Are 1, 3, 7, F, 1F, 3F, 7F, 1FF, 3
In any of FF, 7FF, FFF, 1FFF,
One clock of the input pixel synchronization clock signal is output. The clock generation unit 75 is configured by an AND circuit, and when all the line number signals FDAT are “1”, that is, FDAT = 1,
3 (11), 7 (111), F (1111) ...
Outputs one clock.

The counter 74 receives the clock signal HCK from the clock generator 75 and outputs the count value signals CDT20 to CDT23 to the selector 68 in the mode 0. The counter 74 is also cleared for each page by the clear signal CRST from the main CPU 11. The count values CDT20 to CDT23 are values for selecting α as shown in FIG.

The fixed coefficient value register 78 outputs a fixed coefficient value in the mode 1. The switch 79 is switched in response to a mode signal SL1 from the CPU 11, and is set on the counter 74 side in mode 0 and is set on the register 78 side in mode 1.

The subtraction value generator 67 calculates (A ') = A-αA
Is output at the time of calculating .alpha.A. Subtraction value generator 67
Receives the output signal HSDT from the selector 66,
A value is generated by dividing the signal HSDT by a power of 2 (shifting the signal HSDT).

The selector 68 performs an operation (A ') between each line, that is, when no pixel signal is read.
= A-αA, the input signals SSL0 to SSL3
Determined according to. That is, when the value of the input signals SSL0 to SSL3 is “1”, the selector 68 (the signal HSD
T value) / 2, when the input value is “2” (signal HSDT
) / 2 ² ,..., When the input value is C (signal HSD
T value) / 2 ¹³ is output.

The subtractor 70 performs subtraction (A ') = A-αA. The subtractor 70 outputs the density signal H from the selector 66.
SDT (A in the above equation) is input, a subtraction number signal SDT (αA in the above equation) is input from the selector 68, and a signal YDAT is output as a result of the subtraction.

The addition value generation section (shift register) 71
“ΑB” for calculating A ′ = (A ′) + αB is generated. The addition value generation unit 71 receives the clock signal HCK from the clock generation unit 75 and outputs the signal XDAT to the addition unit 69. The addition value generation unit 71 is also configured by the main CPU 11
Is cleared on a page-by-page basis by the clear signal CRST. FIG. 9 shows an output example of the addition value generation unit 71. When the clear signal CRST is input, the initial value output 2
000H, and outputs 1/2 of the current value every time the clock signal HCK from the clock generator 75 is input thereafter. Since this output is a hexadecimal number, for example, 1/2 of the current value of 2000H is 1000H, and 1/2 of the current value of 1000H.
Becomes 800H. FIG. 10 shows a change in each signal corresponding to a change in the signal FDAT.

The adder 69 calculates the addition A ′ = (A ′) + αB
Perform The addition unit 69 receives the frequency signal HSDT from the selector 66 and the addition data signal XDAT from the addition value generation unit 71, and outputs a signal ZDA as an addition result.
Output T. FIG. 10 shows an example of addition of the signal ZDAT.

The switch 77 determines that (A ′) = A−αA and A
The calculation of '= (A') + αB is switched. To one terminal of the switch 77, the addition result signal ZDAT from the addition unit 69 is input, and the subtraction result signal YDAT from the subtraction unit 70 is input to the other terminal, and the selection signal CTL1
, And outputs a selection result signal WDAT to the histogram registers 65 _{1 to} 65 _F.

Next, the creation of a histogram with the configuration shown in FIG. 7 will be described with reference to the timing charts of FIGS. 12, 13 and 14.

FIG. 12 is a timing chart showing a state of calculating A '= (A') + αB for each input pixel during one line reading. The signal MCK is a main clock and is synchronized with the pixel signal. The signal VDEN is a page synchronization signal, and the signal HDEN is a line synchronization signal. Pixel density signals IDAT4 to IDAT7 from the scanner unit 1
Are the upper four bits of the pixel density and are input to the switch 62. In this case, the sub-scanning valid signal CTL0 is enabled (low level), and the switch 62
T4 to IDAT7 are connected to the selector 66 and the clock generator 6
Send to 4.

The selector 66 outputs the pixel signals IDAT4 to IDAT.
AT7, that is, the outputs (frequency) of the histogram registers 65 _{1 to} 65 _F are selected according to the value of the selected input signal, and the selected frequency signal HSDT is output. The signal HSDT is added by the adder 69 to a coefficient (XDA
T) is added. The switch 77 is connected to the input signal C in this case.
The addition result signal ZDAT is set on the side of the addition unit 69 by TL1, and therefore the addition result signal ZDAT is stored in the histogram registers 65 _{1 to} 65 ₁
Return to _F.

Next, the clock generator 64 outputs the pixel signal ID
Clock signals FCK0 to FCKF according to AT4 to IDAT7
Outputs CKF. Each histogram register 65 _{1 to} 6
5 _F is a rising edge of each clock signal FCK0～FCKF, respectively latches i.e. stores the value of the output signal WDAT switch 77. By performing the above processing for each pixel of one line, a histogram of one line is generated, a reference value for pixel density adjustment is calculated, and the reference value is used for the processing of the next line.

Next, during the period from one line reading to the next line reading, that is, when no pixel density signal is input, the frequency of each density in the histogram is (A ') = A-αA
Is calculated.

FIG. 13 is a timing chart showing the state of the subtraction process. The switch 62 selects the selection signal CTL0.
Is switched to the counter 63 side, and the switch 77 is switched to the subtractor 70 side by the selection signal CTL1. The selector 68 subtracts each histogram value by a coefficient (mode 0) or a fixed coefficient (mode 1) determined by the number of sub-scanning counters. After the subtraction operation is completed, the process proceeds to a normal histogram creation operation. By repeating the above operation, when the mode is set to 0, a histogram having a constant total data amount is created every time each main scanning line is read. When the mode is set to 1 and the weighting coefficient is fixed, a histogram corresponding to a sudden change in the density of the original image can be obtained.

As described above, the histogram can be created in real time.
If is open, a good histogram cannot be created.

Next, an automatic density adjusting apparatus according to the present invention for solving the above problem will be described. FIG. 15 is a flowchart showing the operation of the copying machine according to the present invention.

That is, when the copy button is pressed and the start of copying is notified, it is determined whether or not the automatic density adjustment mode is set (ST1). If not, the copy operation is executed in the manual normal copy mode (ST2). . In this case, it is determined whether or not the document cover is open (ST3). If the document cover is closed, a normal automatic density adjustment copy operation is executed (ST3).
4) If it is open, the carriages 111 and 110 of the image reading scanner 1 start a pre-scan operation (ST5).

During the prescan operation, the CPU 11 recognizes the position of the document while reading the image data (ST6). In order to recognize the position of the document, the input image data is binarized with a predetermined threshold value, and it may be determined whether or not the document is a document portion based on the binarized data. FIG. 16 is a view for explaining an effective area for creating a histogram, and shows a case where a document is placed on a document glass with a displacement.
The CPU 11 recognizes the minimum rectangle (dotted line) circumscribing the document as a document density effective area for creating a histogram, and stores coordinates (x1, y1) and (x2, y2) at both ends of a diagonal line in a RAM.
42.

At this time, the binarized data can be illuminated, and the effective area can be calculated based on the illuminated binarized data. In this case, the processing speed is improved. Alternatively, only the actual document area that is inclined may be recorded as an effective area for creating a histogram. In this case, a large coordinate storage area and a long processing time are required.

After recognizing the position of the original, the histogram creation area is set to the histogram creation circuit 80 (ST7), the reading carriage is returned to the scan start position, and the automatic density adjustment copy operation is performed in the next main scan. (ST8), and a copy output is obtained.

Next, referring to FIG. 17, a description will be given of a histogram creation area setting unit according to the present invention. As shown in FIG. 17, the timing signal generator 83 of FIG. 3 includes a main scanning effective area signal generator 100 and a sub-scanning effective area signal generator 10.
1 is included.

The main scanning effective area signal generator 100 comprises a main scanning effective area start position register 94, a main scanning effective area end register 95, and a main scanning effective area signal generator 93. The two start and end registers 94 and 95 are provided from the CPU 11 with x2 and x1 in FIG.
Are set respectively. The main scanning effective area signal generating section 9
3 receives a horizontal synchronization signal and a basic clock, and outputs a main scanning effective area signal corresponding to a register value set by the CPU 11.

The sub-scanning effective area generating section 101 comprises a sub-scanning effective area start position register 97, a sub-scanning effective area end position register 98, and a sub-scanning effective area signal generating section 96. 9
The CPU 11 sets y1 and y2 in FIGS. The sub-scanning effective area signal generator 96 receives a page synchronization signal and a horizontal synchronization signal, and outputs a sub-scanning effective area signal corresponding to the value of the register set by the CPU 11.

That is, the histogram creating circuit creates a histogram for the logical product (dotted line in FIG. 16) of the main scanning effective area signal and the sub-scanning effective area signal output from the two generators 100 and 101.

[0079]

As described above, according to the present invention, since a histogram can be created without performing data sampling in a portion other than the original by the prescan operation, automatic density adjustment can be performed with an appropriate correction reference value. Can be.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a schematic configuration of an image forming apparatus according to the present invention.

FIG. 2 is a diagram showing a schematic configuration of a control system of the image forming apparatus according to the present invention.

FIG. 3 is a diagram showing a schematic configuration of an image processing unit in the image forming apparatus according to the present invention.

FIG. 4 is a diagram for explaining a histogram created in the present invention.

FIG. 5 is a histogram diagram for explaining a correction reference value and a range correction.

FIG. 6 is a diagram for explaining the number of sub-scanning lines in mode 0 and a coefficient α corresponding thereto.

FIG. 7 is a block diagram showing a configuration of a histogram creating circuit in the image forming apparatus according to one embodiment of the present invention.

FIG. 8 is a diagram for explaining the timing of an output clock signal corresponding to the input pixel density in the clock generation unit.

FIG. 9 is a diagram illustrating an output example of an addition value generation unit.

FIG. 10 is a diagram showing a change in each signal corresponding to a change in a signal FDAT.

FIG. 11 is a diagram illustrating an example of addition of a signal ZDAT;

FIG. 12 is a timing chart for explaining the operation of the histogram creation circuit.

FIG. 13 is a timing chart for explaining the operation of the histogram creation circuit.

FIG. 14 is a timing chart for explaining the operation of the histogram creation circuit.

FIG. 15 is a flowchart showing the operation of the copying machine according to the present invention.

FIG. 16 is a diagram for explaining an effective area for creating a histogram;

FIG. 17 is a diagram showing a configuration of a histogram creation area setting unit according to the present invention.

FIG. 18 is a diagram illustrating a document placed on a document glass.

FIG. 19 shows a representative histogram tendency when a histogram of a document image is created.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Scanner part 2 ... Printer part 3 ... Fluorescent light source 6 ... Photoconductor drum 7 ... Developing device 91 ... Original scale 92 ... Original glass 102 ... Charging device 104 ... Cleaner unit 105 ... Transfer device 106 ... Peeling device 107 ... Erasing device 108 scanning unit 116 lens unit 117 platen

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-95554 (JP, A) JP-A-60-218639 (JP, A) JP-A-63-30873 (JP, A) JP-A-60-1985 26366 (JP, A) JP-A-59-15264 (JP, A) JP-A-6-202449 (JP, A) JP-A-6-202448 (JP, A) JP-A 6-178099 (JP, A) JP-A-7-23224 (JP, A) JP-A-5-328129 (JP, A) JP-A-61-6634 (JP, A) JP-A-4-368058 (JP, A) JP-A-63-54151 (JP, U) JP-A 4-22739 (JP, U) (58) Fields surveyed (Int. Cl. ⁶ , DB name) G03G 15/00 303 G03G 21/00 370-540 H04N 1/40-1 / 409

Claims (1)

(57) [Claims] An original is read in a main scanning direction, and the original is read in the main scanning direction.
The reading operation is repeated along the sub-scanning direction different from the scanning direction.
The pixel density of each pixel in the original image for each scanning line.
Each pixel density included in the scanner means for providing, for each receiving pixel density data of one scan line from said scanner means, and the pixel density included in the first to the immediately preceding scan line, a current scan line And a weighting coefficient that changes according to the number of scanning lines in the sub-scanning direction, creates a density histogram, calculates a correction reference value for pixel density correction using the density histogram, and receives each pixel. Density correction means for correcting density data based on the correction reference value and providing corrected pixel density data; andmode setting means for setting an automatic density adjustment mode by the density correction means based on a user input. A document cover for covering the document placed on the document table; a determination unit for determining whether the document cover is open; and an image cover based on pixel density data. An image forming device for forming an image, wherein the image forming device further operates the reading device and the image forming device when the automatic density adjustment is not set by the mode setting device. The automatic density adjustment is set by the mode setting means, and if the document cover is determined to be closed by the determination means, the pre-scan is not performed by the reading means, A first automatic density adjusting unit for operating the reading unit, the density correcting unit and the image forming unit to form a density-corrected image; and the automatic density adjusting unit is set by the mode setting unit. If the means determines that the document cover is open, it controls the reading means to prescan the document and places it on the platen. The detection of the position of the document
The area corresponding to this position is defined as the histogram creation area.
An area setting means for setting, and again scanning the original by the scanner unit, the love
From the pixel density data provided by the
Transfer sampling means for sampling the pixel density data corresponding to the histogram creation area set by the area setting unit, the pixel density data to said density correction means from said sampling means, is corrected is obtained from the concentration correction means And a second automatic density adjusting unit for providing the density data to the image forming unit and forming a density-corrected image.