JP2001063191A - Image forming apparatus capable of correcting image characteristics - Google Patents

Abstract

(57) Abstract: Provided is an image forming apparatus capable of adjusting reading characteristics and recording characteristics using a patch chart capable of accurately performing an error determination on a patch chart document for correcting color density characteristics. The purpose is to do. An image forming apparatus includes a scanner unit for reading a document image, a printer unit for printing an image, and an internal parameter correction unit for correcting the image characteristics of the scanner unit.
It has. The characteristic correction patch chart 54 in which patches having different densities are formed is output from the printer unit 2 based on the image signal 58 from the patch recording control unit 204 of the correction unit 70, and this patch chart is read by the scanner unit 1. . The image signal 52 is transmitted to the observation unit 206
The density of the patch chart document is determined by the determination unit 206 by comparing the average density with the expected value of the patch average density stored in the control unit 204 in the determination unit. To

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, and more particularly to an image forming apparatus capable of adjusting reading characteristics and recording characteristics using a patch chart.

[0002]

2. Description of the Related Art Recently, an image forming apparatus such as a so-called copying machine or printer includes a reading section (scanner section) such as a scanner for reading a document image and an image recording section (printer section) for image formation. In such image forming apparatuses, color printing is becoming mainstream, and accordingly, strict color density characteristics are also required for color density of printing. Conventionally, in such an image forming apparatus, in order to optimally set the color characteristics in a reading unit (scanner unit) and an image recording unit (printer unit), a reference chart is output from the printer unit and read by the scanner unit. The color density characteristics of the reading unit and the image recording unit are corrected based on the read image information.

As for the correction of the color density characteristics, Japanese Patent Application Laid-Open No. 1-61172 discloses an image forming apparatus having a function of correcting the image characteristics using a patch chart document. This publication discloses, as a reference patch chart original used for correction of image characteristics, a chart in which each of three reference colors (RGB) has eight levels of density gradation, and gradually changes from darker to lighter. Used. Further, examples of other patch chart originals include a cyan patch row, a magenta patch row, a yellow patch row,
It is assumed that a patch chart document having a black patch row is assumed, whereby the color density characteristics in the reading unit and the image recording unit can be corrected for each density of each hue.

[0004] In addition, the position error of the original is detected as a reading error determination when reading the patch chart original. For example, Japanese Patent Application Laid-Open No. 62-239662 discloses a method of detecting the position error. A method is disclosed in which a recorded mark is read and a positional shift of a document is detected. Furthermore, as a proposed technique, a high-density patch is arranged on the reading start side of a patch chart in Japanese Patent Application No. 10-365488 according to the prior patent application.
There is disclosed a method for detecting a position shift of a patch chart in a patch having a high density.

[0005]

Conventionally, there have been proposed various methods for detecting a position error of a patch chart document as a reading error determination and thereafter correcting the color density characteristics. However, in the determination of such a reading error, merely detecting the positional deviation of the original document can be performed even when an erroneous original document is placed on the reading table.
It is determined that the original is normal within a range in which the condition is satisfied, and the positional deviation correction is executed as it is. If it is determined that the data is normal, the document may be read later and erroneous correction data may be calculated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a reading characteristic using a patch chart that can accurately determine an error in a patch chart original for correcting color density characteristics. And an image forming apparatus capable of adjusting recording characteristics.

[0007]

According to the present invention, there is provided a reading means for reading an image set on a document table in a predetermined direction in units of areas, a read image generated by the reading means, or an externally input image. Recording means for directly recording the input image obtained on the recording medium, or transferring and recording the image on the recording medium after forming the image on the intermediate recording medium, and a plurality of patches having different densities, saturations, and hues are arranged. Patch recording control means for recording and outputting the adjusted patch chart document from the recording means, holding means for holding a plurality of patch arrays of different densities, saturations and hues, on the recording medium or on the recording intermediate medium Detecting means for obtaining an average density of each patch of the adjustment patch chart document, and reading characteristics of the reading means or the recording characteristics of the recording means by using the patch average density. Adjusting means for changing recording characteristics, and comparing the average density with the expected value of the average density of each patch held in the holding means. A determination unit for determining the validity of the received document.

According to the invention, there is provided a reading means for reading an image set on a document table in a predetermined direction in units of areas, a read image generated by the reading means, or
Recording means for directly recording an input image input from the outside on a recording medium, or transferring and recording the image on the recording medium after forming the image on an intermediate recording medium, and a plurality of patches of different densities, saturations, and hues Patch recording control means for causing the recording means to record and output the adjustment patch chart document in which is arranged, holding means for holding a plurality of patch arrangements of different densities, saturations, and hues, on the recording medium or the recording means. Detecting means for calculating an average density of each patch of the adjustment patch chart document on the intermediate medium, and adjusting means for changing a reading characteristic of the reading means or a recording characteristic of the recording means using the patch average density, A determination unit that determines the validity of the document used for the adjustment based on the regularity of the arrangement of the average densities. Image forming apparatus is provided, characterized in that it comprises.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus capable of adjusting reading characteristics and recording characteristics using a patch chart according to one embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram schematically showing a digital color copying machine according to an embodiment of the image forming apparatus of the present invention. As shown in FIG. 1, the image forming apparatus includes an operation panel 40 for operating the apparatus, a color scanner unit 1 that scans an original such as a color original and converts the original image into an electric signal, and converts the read original image into an electric signal. The printer includes a color printer unit 2 for printing on paper based on the image data, an operation panel 40 for operating these units, a main control unit 30 for controlling the color scanner unit 1 and the color printer unit 2.

The main control unit 30, the color scanner unit 1 and the color printer unit 2 include CPUs 91, 100, 1
10 is provided. That is, the main control unit 30 is connected to another CPU.
(A central processing unit) 91 for controlling the scanner, a color scanner unit 1 includes a scanner CPU 100 for controlling scanning of a document, and a color recording unit 2 includes a printer CP for controlling a printer.
U110 is provided.

The main CPU 91 is a printer CPU 11
The main CPU 91 issues an operation instruction to the printer CPU 1 through a shared RAM (random access memory) 35 shared with the CPU 0.
Numeral 10 returns a status status. The printer CPU 110 and the scanner CPU 100 perform serial communication, the printer CPU 110 issues an operation instruction, and the scanner CPU 100 returns a status.

The operation panel 40 has a liquid crystal display section 42 on which information relating to copying is displayed, various operation keys 43 for performing various settings relating to copying such as the number of copies, and a panel CPU 41 to which these are connected. It is connected to the main CPU91.

The main control unit 30 includes a main CPU 91, an RO
M (read only memory) 32, RAM 33, NV
It comprises a RAM 34, a shared RAM 35, an image processing unit 36, a page memory control unit 37, a page memory 38, a printer controller 39, and a printer font ROM 121.

The main CPU 91 controls the overall control. The ROM 32 stores a control program and the like. The RAM 33 temporarily stores data. NVRAM (non-volatile random access memory: non-volatile RAM) 34
This is a non-volatile memory that is backed up by a battery (not shown) and retains stored data even when the power is turned off. The shared RAM 35 is used for performing bidirectional communication between the main CPU 91 and the printer CPU 110. The page memory control section 37 stores and reads out image information from and to the page memory 38. The page memory 38 has an area in which image information for a plurality of pages can be stored, and is formed so that data obtained by compressing image information from the color scanner unit 1 can be stored for each page. The printer font ROM 121 stores font data corresponding to the print data. The printer controller 39 converts print data from an external device 122 such as a personal computer into a printer font ROM 121 at a resolution corresponding to data indicating the resolution given to the print data.
Is developed into image data using the font data stored in.

The color scanner unit 1 includes a scanner CPU 100 for controlling the entire system, a ROM 101 storing a control program and the like, a RAM 102 for storing data, a CCD driver 103 for driving the color image sensor 15, and the first carriage 8 A scanning motor driver 104 that controls the rotation of a scanning motor that moves
It is composed of an image correction unit 105 and the like.

The image correction unit 105 includes an A / D conversion circuit for converting R, G, and B analog signals output from the color image sensor 15 into digital signals, variations in the color image sensor 15, or ambient temperature. It comprises a shading correction circuit for correcting a threshold level fluctuation with respect to an output signal from the color image sensor 15 caused by a change, and a line memory for temporarily storing a digital signal subjected to shading correction from the shading correction circuit. ing.

The color recording section 2 includes a printer CPU 110 for controlling the entire system, a ROM 111 for storing a control program and the like, a RAM 112 for data storage, and a laser driver 11 for driving the semiconductor laser oscillator 60.
3. A polygon motor driver 114 for driving the polygon motor 54 of the exposure device 50, a conveyance control unit 115 for controlling the conveyance of the paper P by the conveyance mechanism 20, charging using the charging device, the developing roller, and the transfer device. Control unit 1 for controlling the process of developing, developing and transferring
16, a fixing control unit 117 for controlling the fixing device 80,
And an option control unit 118 for controlling options.

The image processing unit 36 and the page memory 3
8, the printer controller 39, the image correction unit 105, and the laser driver 113 are connected by an image data bus 120.

In the image forming apparatus having such a configuration,
The configuration of the image processing unit 36 for correcting the image characteristics and the process of correcting the characteristics will be described in detail below.

FIG. 2 is a block diagram schematically showing the image processing section 36 and its peripheral circuits of the digital color copying machine shown in FIG. The image processing section 36 optically reads a document image 50 and outputs an image signal 52. The scanner section (document reading section) 1 and the image signal 52 are directly used on a recording medium such as paper or an intermediate portion such as a photosensitive drum. It is connected to a printer unit (recording unit) 2 that forms a duplicate image 54 on a recording medium such as paper after an image is formed on the recording medium, and a color in the scanner unit (document reading unit) 1 and printer unit (recording unit) 2 An internal parameter correction unit 70 that corrects image density characteristics is provided. The internal parameter correction unit 70 calculates a parameter 56 for correcting the characteristics of the scanner unit 1 and the printer unit 2 and generates an internal parameter 56. The scanner unit 1 and the printer unit 2 correspond to the internal parameter 56. The processing contents will be changed.

Here, the internal parameter correction unit 70 operates when the patch recording control unit 204, which will be described later, is operated, and the adjustment patch document recorded as the duplicate image 54 is placed on the document table of the scanner unit 1. And is operated when the image of the patch document is read. In the latter case, the average density in each patch required for calculating the parameter 56 is measured while correcting the positional deviation of the original 50 on the original platen, and the parameter 56 is calculated based on the average density.

Next, the detailed configuration of the internal parameter correction unit 60 of the image processing unit 36 will be described in detail below, including its operation.

In the internal parameter correction unit 70, when the user operates the operation panel 40 to set the image adjustment mode and instructs the output of the patch chart document, the patch recording control unit 204 operates to operate the chart pattern in the patch recording document. An image signal 58 of the image chart of the patch chart for image adjustment stored in a memory (not shown) is sent to the printer unit 2 and has a plurality of patches of different densities, saturations, and hues as shown in FIG. The adjustment patch chart document 54 is output from the printer unit 2.

The output patch chart document is placed on a document reading table (not shown) by a user, and when an instruction to read the image is given, the patch chart document is read by the scanner unit 1. This image signal 52 is sent to the observation unit 205. The image signal 52 is input to the observation unit 205 on a line-by-line basis, and the partial line average value 60 of a plurality of regions in each line is output from the observation unit 205 to the determination unit 206. In the determination unit 206, each partial line average value 60 is compared with a certain threshold value, and from the comparison result,
The amount of displacement of the document 50, that is, the offset 61 in the horizontal direction (main scanning direction) and the offset 62 in the vertical direction (sub-scanning direction) of the document are obtained and output to the detection unit 207. The offset 62 in the sub-scanning direction is measured at two points as described later, and the difference is detected by the detection unit 207 as a slope. An error signal is output, and an error is displayed on the display unit 42. If the inclination is small, the average offsets 63 and 64 are sent to the detection unit 208 assuming that normal measurement is possible. The detection unit 208 considers the values of the average offsets 63 and 64, and
(Including the patch chart transferred and duplicated after the image is formed on the photosensitive drum), and the density average value 66 of each patch of the position-corrected patch chart document is calculated. 209. Adjustment unit 2
In step 09, the tone characteristics are obtained based on the average density value 66 of each patch, and the parameter 56 for correcting the tone characteristics of the image forming apparatus is calculated. The parameter 56 is transferred to the scanner unit 1 and the printer unit 2, and the tone characteristics of the scanner unit 1 and the printer unit 2 are corrected.

FIG. 3 shows a model of an adjustment patch chart document 50 used for correcting color conversion parameters and the like in the image forming apparatus, particularly in the scanner unit 1 and the printer unit 2. This adjustment patch chart document 5
0 indicates that high-density patches (cyan C: 100%, magenta M: 100%, yellow Y: 100%) are arranged on the reading start side of the patch chart document as in the example shown in FIG. By arranging a high-density patch on the reading start side, it is possible to detect the start point of the patch chart on the document as described later in detail.

The data such as the density of each patch of the adjustment patch chart document 50 is originally generated from the patch recording control unit 204 and is a known value, and is used as an expected value when measuring the average density of each patch. Is done. That is, by comparing the average density of each patch of the adjustment patch chart 50 read by the scanner unit 1 with its expected value, it is possible to determine whether or not the correct adjustment patch chart is used, that is, to determine the validity thereof. It becomes possible. That is, a document other than the adjustment patch chart is erroneously placed on the document table and read by the scanner unit 1, or an adjustment patch chart of another model is mounted on the document table and scanned by the scanner unit 1. An error in the user operation as read is determined. More specifically, in the detection unit 207, when the obtained actual average density and the expected value show values that are significantly different from each other, it is determined that the measurement is an erroneous measurement. It is possible to encourage.

The average density of each patch of the adjustment patch chart 50 read by the scanner unit 1 is sorted based on the density data stored in the patch recording control unit 104 so as to be continuous data. You. The sorted continuous density data increases in certain steps, but the difference between the previous and next values and the density step are compared. If the difference value shows a value that is significantly different from the density step, it is determined to be an erroneous measurement. Then, it is possible to encourage the measurer to perform the measurement again.

Referring to FIG. 4, the details of the processing operation in internal parameter correction section 70 shown in FIG. 2 will be described.

First, when the process in the image adjustment mode is started, in step 301, a patch chart pattern stored in advance is output from the printer unit 2 from the patch recording unit 204, and this is output to the adjustment patch chart original 50. Be prepared as

Next, the adjustment patch chart document 50
Is placed on the document reading table. In step 302, in order to more accurately read the adjustment patch chart document 50, the image reading CCD
Of the installation position is corrected. After that, the above-mentioned adjustment patch chart document 50 is pre-scanned by the scanner unit 1. Data 5 for each line by prescan
2 are read in order from the top. Then, the displacement (offset and inclination in the main and sub scanning directions) of the patch document 50 is detected. The procedure for detecting the displacement is different in the main scanning direction and the sub-scanning direction, and will be described separately below.

First, the procedure for detecting the offset amount and the tilt in the sub-scanning direction will be described in detail with reference to FIG. In step 303, the two positions X1 and X3 in the main scanning direction in each line j shown in FIG. 5 are set to the left end, and the partial line average values {d1, d2} 60, which are the average values of the data of the two regions of size W, respectively. Is obtained by the observation unit 105.

In step 304, the line position j at which the line average value d1 exceeds the threshold value Th1 for the first time is determined as the coordinate Y1 in the sub-scanning direction which is the offset 62 in the sub-scanning direction. Is the threshold
The line position j exceeding Th1 for the first time is set as a coordinate Y2 in the sub-scanning direction and stored in a register. If the coordinates Y1 and Y2 in the sub-scanning direction exceed a predetermined value, the coordinates are clipped to a predetermined value or an overflow bit is separately set. The reason why a high-density patch is arranged on the reading start side of the patch chart document is to increase the contrast between the plain density (normally white) and the patch density, thereby improving the detection accuracy.

In step 305, the detecting unit 10
At 7, the CPU reads the coordinates Y1 and Y2 in the sub-scanning direction, which is the offset 62, sets the average value Y0 of both as the sub-scanning average offset value 64, and detects the difference dY between them as the amount of inclination. When the coordinate dY in the sub-scanning direction is larger than a predetermined threshold value Th2 (dY ≧ Th2), it is determined that the inclination amount is large, and as shown in step 306, the measurer who is the user is given some form. Warn and urge re-measurement. In this case, the user again adjusts the orientation of the patch chart document on the document table and reads the image again as shown in step 302. Also,
If the coordinate dY in the sub-scanning direction is smaller than the predetermined threshold Th2 (dY <Th2), step 307 is executed.
Proceed to

The procedure for detecting the offset amount in the main scanning direction will be described in detail with reference to FIG. In step 303, the data of each line j is divided into blocks in units of 8 pixels, and the block average value d4 in the block is calculated as the partial line average value 60
Is obtained in the observation unit 205. Next, in step 304, the partial line average value d4 of each line j
The main scanning position Xj, which exceeds the threshold value Th3 for the first time from left to right, is determined by the determination unit 206 as the main scanning offset 61. If the main scanning position Xj exceeds a predetermined value, it is clipped to a predetermined value or an overflow bit is set separately. Then, Ys + Yp (where Y
s corresponds to the larger of Y1 and Y2. ) To 25
The six lines are divided into eight regions of 32 lines each, and the average value AVGXjj of Xj in the region jj (jj = 1 to 8) is determined by the determination unit 206 and stored in the register. CP
U reads AVGXjj (jj = 1 to 8) and averages them to obtain an average offset value X0 (63) in the main scanning direction. At this time, an abnormal value of AVGXjj due to noise or the like is checked, and if there is an abnormal value, it is excluded from the average calculation. In the main scanning direction, no tilt is detected,
Subsequently, the process proceeds to step 307.

In step 307, the main scan is executed, taking into account the average offset value X0 (63) in the main scanning direction and the average offset value Y0 (64) in the sub-scanning direction.
The reading range is shifted, and the patch is read. The patch size, the number of patches, and the patch arrangement are preset in the patch recording unit 204. In addition, the expected value of each patch is also set in advance in the patch recording unit 204, and when it is determined that there is an abnormal value, the measurer is prompted to re-measure. Further, the read data of the patches arranged in the reading order here is converted into continuous data in the order of density gradation. In the measurement of the density average value 66 of each patch, an area smaller than the patch size and arranged in a lattice is used as a measurement area.

In step 309, the density average value 66 obtained in step 307 is compared with the expected value. If the difference is larger than a predetermined value, a recording error of the adjustment patch chart 50 or a different document is used. This will prompt the measurer to re-measure. Further, the values before and after the density average value 66 of each patch sorted in the order of the density data are compared, and when the difference is larger than a predetermined value, a recording error of the adjustment patch chart 50 or a different original is used. This will prompt the measurer to re-measure.

In step 308, step 30
Based on the density average value 66 obtained in step 7, gamma conversion of the image forming apparatus is executed, and the internal parameters 56 such as shading correction are corrected (internal parameter correction unit). For example, a document 50 representing the gradation characteristics of the printer unit 2
Is read, and an approximation function D is obtained from the
[i] is required. Here, when there is a gradation inversion in the approximation function D [i], the inversion correction is performed by the following equation, and the inversion correction approximate function D ′ [i] is obtained. (Where Th4 is
This is a threshold value that bisects the gradation permutation i. ) i> = Th4 and D [i] <D [i-1] → D '[i] = D [i-1] i <Th4 and D [i]> D [i-1] → D' [i ] = D [i + 1] else → D ′ [i] = D [i] The inverse function of D ′ [i] is applied as a parameter 56 in a known γ-conversion unit inside the printer unit 2 so that the printer unit 2 Can be corrected.

[0039]

As described above, in the image forming apparatus according to the present invention, the average value of the read density of each patch of the adjustment patch chart is compared with the expected value, so that the adjustment patch chart can be accurately obtained. The validity of the patch read value is determined, for example, whether the patch has been read or the correct adjustment patch chart is used. On the other hand, since the read density average values sorted in the stored arrangement order are values of successive steps of monotonically increasing, the legitimacy of the patch read value can be determined also from the regularity thereof. If it is determined that an error has occurred, a message prompting the measurer to perform re-measurement is displayed.

The presence of these patch read value validity determining means can increase the accuracy of error determination.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of an image forming apparatus according to the present invention.

FIG. 2 is a block diagram showing in detail an image processing unit shown in FIG. 1 and peripheral parts related to the processing unit;

FIG. 3 is stored in a patch recording control unit shown in FIG. 2;
FIG. 4 is a plan view illustrating an example of a patch chart document output from a printer unit.

FIG. 4 is a flowchart showing a procedure in which the circuit shown in FIG. 2 determines the validity of a patch chart document and obtains an internal parameter for correction from the valid patch chart.

FIG. 5 is an explanatory diagram for explaining an offset amount and tilt detection procedure in the sub-scanning direction according to the present invention.

FIG. 6 is an explanatory diagram for describing a procedure for detecting an offset amount in the main scanning direction according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Color scanner part 2 ... Color printer part 36 ... Image processing part (internal parameter correction part) 30 ... Main control part 40 ... Operation panel 204 ... Patch chart output part 205 ... Observation part 206 ... Judgment part 207 ... Detection part 208 ... Detector 209… Adjuster

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G06T 5/00 G06F 15/68 310A 5B057 H04N 1/60 H04N 1/40 D 5C077 1/48 1/46 A 5C079 F-term (reference) 2C061 AP04 AQ06 AR01 KK18 KK25 2C087 AA09 AA15 AA16 AC08 BA07 BB10 CB04 2H027 DA09 EB03 EC03 EC06 2H030 AA03 AD12 5B021 BB02 LG07 LG08 PP04 PP06 QQ01 5B012 DC17 DA08 DCB PP37 PP46 PP59 PQ18 PQ22 TT06 5C079 HA16 JA10 LA12 LB01 MA01 MA19 PA02

Claims (5)

[Claims] A reading unit configured to read an image set on a document table in a predetermined direction in units of areas; and a reading image generated by the reading unit or an input image input from the outside is directly written on a recording medium. A recording unit for recording or transferring and recording an image on the intermediate recording medium after forming an image on the intermediate recording medium; and an adjustment patch chart original in which a plurality of patches having different densities, saturations, and hues are arranged. Patch recording control means for recording and outputting, a holding means for holding a plurality of patch arrangements of different densities, saturations and hues, and respective patches of the adjustment patch chart document on the recording medium or the recording intermediate medium Detecting means for calculating an average density of the patch means; adjusting means for changing a reading characteristic of the reading means or a recording characteristic of the recording means using the patch average density; In the image forming apparatus, a determination is made by comparing the respective average densities with expected values of the respective patch average densities held in the holding unit to determine the validity of the document used for the adjustment. And an image forming apparatus. 2. A reading means for reading an image set on a document table in a predetermined direction in units of an area, and a read image generated by the reading means or an input image inputted from the outside is directly written on a recording medium. A recording unit for recording or transferring and recording an image on the intermediate recording medium after forming an image on the intermediate recording medium; and an adjustment patch chart original in which a plurality of patches having different densities, saturations, and hues are arranged. Patch recording control means for recording and outputting, a holding means for holding a plurality of patch arrays of different densities, saturations, and hues, and respective patches of the adjustment patch chart document on the recording medium or the recording intermediate medium Detecting means for calculating an average density of the patch means; adjusting means for changing a reading characteristic of the reading means or a recording characteristic of the recording means using the patch average density; An image forming apparatus characterized by comprising, an image forming apparatus, characterized in that said from the regularity of the arrangement of the average density, and a determining means for determining validity of the document used to adjust 3. A decision means for judging the validity of a recording and reading signal of the adjustment patch chart document by comparing each of the average densities with an expected value of each of the patch average densities held in the holding means. 3. The semiconductor device according to claim 2,
Image forming apparatus 4. The validity of recording and reading signals of the adjustment patch chart document is determined by comparing the density difference between successive patches and a stored density step based on the regularity of the average density array. 3. The image forming apparatus according to claim 2, further comprising a determination unit that performs the determination. 5. The image forming apparatus according to claim 2, wherein when the determination unit determines that the measurement is not valid, the measurer is requested to perform re-measurement.