JP2000066462A - Density unevenness evaluating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a density unevenness evaluating device capable of performing evaluation close to the evaluation performed by a skilled inspector by means of a densitometer. SOLUTION: This device is provided with an image input part 1 for reading density on a specified area including a density patch P formed on a recording sheet S and outputting the density as the density signal, an image memory part 3 for storing the density signal output from the image input part 1, a calculating part 4 for moving a certain measuring area in the density patch P based on the density signal stored in the image memory part 3 thereby calculating the dispersion of the density average in the measuring area, and a judging part 6 for judging the presence or absence of the density unevenness by comparing the density average dispersion calculated by the calculating part 4 with the preset allowable density average dispersion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for evaluating density unevenness for evaluating density performance of an image forming apparatus.

[0002]

2. Description of the Related Art Prior to shipment from a factory, a product inspection is performed to determine whether or not an image forming apparatus such as a printing apparatus, a copying machine, a printer, and a facsimile exhibits a predetermined performance. There is a concentration evaluation. In such a density evaluation, for example, in the case of a copying machine, an original for inspection having the same density or gradation density is actually copied on a recording sheet, or in the case of a printer, a density of a predetermined pattern and density built in the printer in advance. An inspector measures the density of an output image obtained by forming a pattern on a recording sheet at a predetermined number of places using a densitometer, and evaluates whether the density is a desired density.

FIG. 23 illustrates a method of measuring density using a reflection densitometer. The densitometer is roughly divided into a light emitting unit, a light receiving unit, and a density calculating unit. On the recording sheet, a square density patch having a side of about several tens mm is formed, and the density of the density patch at several locations is measured.
In the measurement, the light from the light emitting unit of the densitometer is applied to the density patch on the recording sheet, the reflected light is received by the light receiving unit, and the light receiving unit converts the reflected light into an electric signal, and based on the electric signal, A density calculator calculates the density of the density patch. The angle formed by the optical path of the light entering the density patch from the light emitting section and the optical path of the light reflected from the density patch to the light receiving section is 45 °. The measurement range in the density patch is called an aperture size, and has a circular shape with a diameter of about several mm.

[0004] Here, the inspection using a densitometer is performed in order to eliminate as much as possible a variation in judgment criteria which may be caused by the degree of fatigue among the inspectors or even by the same inspector, and to objectively remove the density unevenness. This is to determine the presence or absence. However, the quality of image quality should be judged based on human perceptual and subjective criteria, and it is different from human perception when judging the presence or absence of density unevenness based solely on the results of a densitometer. It can have consequences. Therefore, in practice, a skilled inspector first determines visually whether there is density unevenness, and if the level is sufficiently acceptable, finely adjusts the measurement position with a densitometer and checks the measurement results at multiple measurement points. Keep it constant,
"Passed".

In addition, since the inspection by an inspector takes time and effort, a technique for automatically performing a density inspection has been proposed. For example, JP-A-6-149126 discloses that an output image to be inspected is divided into minute regions,
From the maximum density and the minimum density, the presence / absence of density unevenness and its location are inspected. Also, JP-A-7-220
In Japanese Patent No. 042, the noise generated in advance is predicted, and the density is measured by correcting the expected noise when measuring the density.

[0006]

Indeed, according to these techniques, it is possible to measure the density unevenness of an image while reducing the work of the inspector. There are the following problems compared to First of all, it tends to be a ruler's rule that differs from the human sense. In other words, even when the concentration measurement device determines that the measurement is "failed", if a skilled inspector visually judges, there is only a sufficient level of concentration unevenness, and the actual measurement position is finely adjusted. In some cases, uneven density may not be detected. As described above, in the conventional concentration measuring device, whether the density unevenness actually occurs, or actually, the density unevenness is at a pass level, but the density unevenness is rejected because the measurement position is very slightly bad. It is difficult to distinguish between them.

Second, there is a case where an inspector measures a portion such as a white streak or a black streak, which can be easily avoided by the inspector, so that an accurate density measurement cannot be performed. In an image forming apparatus, image defects such as white streaks and black streaks may occur in a process direction of forming an image and in a direction orthogonal to the process for various reasons. When evaluating density unevenness, the inspector must measure the density while avoiding the image defect part, but since the conventional density measurement device does not actively avoid this image defect part, It is difficult to accurately evaluate the unevenness in density caused only by this.

Third, the dynamic range of an image sensor used in a density evaluation device is generally lower than that of a densitometer used by an inspector, and the output of the image sensor tends to be saturated particularly in a high density portion. It is difficult to measure an accurate concentration. For example, the measurement gradation of the conventional densitometer is from 1 to 1000 gradation to 1 to 10000 gradation, whereas the measurement gradation of the image sensor is from 1 to 256 gradation to about 1 to 512 gradation. Yes, and generally the measurement gradation is small. FIG. 24 is a graph showing the output characteristics of a general CCD image sensor.
This is a measurement value of a CD image sensor. Here, the absolute density difference D ₂ of the absolute density difference D ₁ and the high density portion of the low density portion, even though a D ₁ = D _2, CCD measurement differences G ₁ corresponding to the density difference, G ₂ satisfies G ₁ > G ₂ , and it can be seen that the output of the CCD is saturated particularly in a high density portion. As described above, in a density measuring device using a conventional image sensor, the measurement accuracy is particularly low in a high density portion as compared with a densitometer, and it is difficult to accurately measure the density.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a non-uniform density evaluation apparatus capable of performing an evaluation close to an evaluation performed by a skilled inspector using a densitometer.

[0010]

According to the present invention, a recording sheet S is provided.
An image input unit 1 for reading a predetermined range of density including the density patch P formed thereon and outputting the density signal as a density signal, and moving a certain measurement range in the density patch P from the density signal stored in the image memory unit 3 A calculating unit 4 for calculating the variation of the density average within the measurement range; and comparing the density average variation calculated by the calculating unit 4 with a preset allowable density average variation to thereby obtain the density unevenness. And a determination unit 6 for determining the presence or absence of density unevenness.

[0011] With such a configuration, in order to evaluate the density unevenness by comparing the measured average density unevenness with the preset density average unevenness, is there any inherent density unevenness? In addition, it is possible to distinguish and evaluate whether or not the density unevenness can be eliminated by the inspector by slightly moving the measurement position by the densitometer. further,
By matching the measurement range with the aperture size of the densitometer, it is possible to evaluate the density unevenness closer to the measurement by the densitometer.

In the present invention, the calculating section 4 calculates the density variation within a certain measurement range in the density patch P in addition to the density average variation, and the determining section 6 calculates the density variation in addition to the density average variation. The presence / absence of density unevenness may be determined by comparing the density unevenness with a preset allowable density unevenness.

Here, the term "average density variation" refers to an index indicating a plurality of density averages within a measurement range while moving the measurement range at a plurality of locations. On the other hand, the term “density variation” refers to an index indicating a variation in density of each pixel within a certain measurement range. By determining the presence or absence of density unevenness based on the density unevenness in addition to the density average unevenness, more accurate density unevenness evaluation can be performed.

In each case, the permissible density average variation and the density variation are set in the judgment section 6 in advance, but it is preferable that a plurality of these are set for each density range. This is because it has been experimentally revealed that the allowable density average variation and the density variation vary depending on the density.

Further, a display unit 7 for displaying the result determined by the determination unit 6 to the user from the viewpoint of user friendliness may be provided, or a plurality of recording sheets S may be displayed on the recording sheet S from the viewpoint of labor saving of measurement. A density patch P is provided, and a moving unit 2 that relatively moves the image input unit 1 and the recording sheet S so that the image input unit 1 can read a density in a predetermined range including each density patch P is provided. It may be something.

Further, according to the present invention, a measurement range adjusting section 5 for detecting an image defect portion in the density patch P and adjusting the measurement range so that the image defect portion is not included in the measurement range.
May be provided. By configuring the density unevenness evaluation apparatus as described above, the density evaluation is performed while actively avoiding the image defect portion, so that the density unevenness caused only by the original density can be accurately evaluated. The measurement range adjustment unit 5 may detect an image defect portion based on the density signal of the image defect detection chart CC. The image defect detection chart CC is formed in a range that can be read together with the density patch P. You. Since the image defect detection chart CC is for detecting image defects such as white streaks and black streaks in the density patch P, it is preferable to provide the image defect close to the density patch P. It is desirable to provide them close to the process direction and a direction perpendicular to the process direction. The streak-like image defect is likely to occur in a process direction of image formation or a direction perpendicular to the process direction due to its nature, and is for detecting the image defect effectively.

In the present invention, a density chart DC having a plurality of predetermined densities is provided in a range readable with the density patch P. A lighting device capable of changing the amount of light, an image sensor that reads the density patch P and the density chart DC and outputs a first density signal indicating their relative densities, and a step of measuring the amount of light incident from the lighting device. Patch P and density chart DC while changing
And outputs a second density signal indicating an absolute density based on an appropriate first density signal and a predetermined density of the density chart DC among the plurality of first density signals output from the image sensor. This is a non-uniform density evaluation device including a correction unit that performs correction.

With this configuration of the density unevenness evaluation apparatus, a second density signal is output based on the first density signal and a predetermined density of the density chart DC. An absolute density (second density signal) can be obtained regardless of a change in the measurement environment such as a performance error between the lots of the sensors, and a density output close to the density measured by the densitometer can be obtained. In particular, if the predetermined density of the density chart DC is measured by the densitometer, the output second density signal more accurately matches the measurement result by the densitometer. Further, a plurality of first density signals are obtained by changing the amount of incident light in a stepwise manner, an appropriate first density signal is selected from the first density signals, and a seventh density signal is output based on the selected first density signal. Therefore, it is possible to compensate for the lack of the number of gradations of the image sensor, to reduce the influence of the output saturation particularly in the high-density portion of the image sensor, and to evaluate the density unevenness close to the measurement by the densitometer. Further, since the density chart DC is provided in a range readable with the density patch P, the first density signal can be obtained under the same conditions as the density patch P, and a more accurate second density signal can be obtained. .

The illumination device includes a plurality of light sources having the same or different light amounts, and a plurality of shielding members capable of transmitting and shielding the light from the respective light sources. May be used to change the amount of incident light from the lighting device. With this configuration of the lighting device, it is possible to quickly and stably change the amount of incident light only by opening and closing the shielding member. In addition, by using a plurality of light sources in combination, the amount of incident light can be variously changed.

FIG. 1 shows the concept of the present invention.
The density patch P, the image defect detection chart CC, and the density chart DC are all within a predetermined range that can be read by the image input unit 1, and the image input unit 1 reads them and displays (the It is stored in the image memory unit 3 as a (one) density signal. The correction unit determines a new (absolute density) of the density patch from the density signals of the density chart and the density patch of the stored density signals and the density obtained by measuring the density of the density chart set in advance. To obtain a second) concentration signal. Further, the measurement range adjustment unit 5 specifies an image defect portion such as a white streak or a black streak in the density patch from the stored density signal of the image defect detection chart, and determines a measurement range avoiding the portion. In addition, the calculation unit 4 calculates the density average variation and the density variation of the measurement range determined by the measurement range adjustment unit 5 from the density signal of the density patch. The determination unit 6 evaluates and determines the density unevenness by comparing the calculated density average variation and the density variation with a preset allowable density average variation and the density variation. The result is transmitted to the user via the display unit 7. Note that the recording sheet and the image input unit 1 can be relatively moved by the moving unit 2.

[0021]

Next, preferred embodiments of the present invention will be described based on examples. FIG. 2 shows the overall appearance of the density unevenness evaluation apparatus according to the present embodiment. The evaluation device includes a computer 8, a display 71, an XY movement module 21, an XY movement module controller 22, an image input unit 14, and a lighting device 1.
1. It is composed of a density chart sheet S 'and the like,
The density unevenness on the recording sheet S is evaluated. The computer 8 includes a central processing unit 80, a primary storage device 81, a secondary storage device 82, interface devices 83a and 83b, and a bus connecting these components to each other. It performs various types of information processing based on a control program stored in the secondary storage device 82 by using it.

FIG. 3 is a block diagram illustrating the overall configuration of the evaluation apparatus. This density unevenness evaluation apparatus reads an image in a predetermined range including one chart group CG and outputs the image as a density signal.
A moving unit 2 for relatively moving the image input unit 1 with respect to the recording sheet S; an image memory unit 3 for storing the density signal output from the image input unit 1; A calculating unit for calculating a density variation within a measurement range within the density patch and a density average variation within a plurality of measurement ranges obtained by moving the measurement range from the density signal; and detecting an image defect portion within the density patch. The measurement range adjustment unit 5 that adjusts the measurement range so that the image defect portion is not included in the measurement range, the density variation calculated by the calculation unit 4 and the density average variation are set in advance. A judgment unit 6 for judging the quality of the image by comparing the allowable density variation and the average density variation.
And a display unit 7 for displaying the result determined by the determination unit 6 to the user.

FIG. 4 explains the chart group CG. One chart group CG includes a density patch P formed on the recording sheet S by the image forming apparatus, image defect detection charts CCa to CC formed close to the upper, lower, left and right thereof, and a plurality of charts provided on the density chart DC. And a density chart DC having a predetermined density. The recording sheet S and the density chart sheet S ′ are used in a state where the density chart sheet S ′ is overlapped with the image input unit side, and the density chart sheet S ′ is provided with a predetermined notch. The density patch P and the image defect chart can be observed from the image input unit side through the cutout portion. Also,
A density chart DC is provided near the notch on the density chart sheet S ′.
C, the density patch P, and the image defect detection chart CC exist close to each other, and constitute one chart group CG. In the present embodiment, such a chart group C
There are five G's on the recording sheet S and the density chart sheet S '.

FIG. 5 shows a more specific configuration of the image input unit 1. The image input unit 1 reads an illumination device 11 that can change the amount of light incident on a predetermined range on the recording sheet S in multiple steps, a density patch P and a density chart DC, and reads the relative densities of those. Image sensor 12 (hereinafter, referred to as “CCD 12”) that outputs a CCD measurement value (first density signal) indicating
The density patch P and the density chart DC are read while changing the amount of incident light from 1 stepwise, and an appropriate CCD measurement value is selected from a plurality of CCD measurement values output from the CCD, and the CCD measurement value and the density are selected. A correction unit 13 that outputs a density signal (second density signal) based on the predetermined density of the chart DC. The lighting device 11 includes three light emitting diodes (light sources) 111a to 111c having different light amounts.
And 3 that can shield light from each light emitting diode
The correcting unit 13 changes the amount of incident light by controlling the respective shutters 112a to 112c.

That is, as shown in FIG. 5 (a), the light from the light emitting diodes 111a to 111c is transmitted only when the shutters 112a to 112c are opened.
Light emitting unit 11 in image input unit 14 via 3a to 3c
4a to 4c, and irradiates a certain area on the recording sheet S and the density chart sheet S 'including one chart group CG. The reflected light is transmitted to the image input unit 14.
The light is received by the light receiving unit 121 in the inside. The light emitting unit and the light receiving unit 121 are provided in the image input unit 14. The shutters 112a to 112c are opened and closed by opening and closing controllers (not shown). The correction unit 13 controls opening and closing by sending a control signal to the opening and closing controller.

FIG. 5B shows the structure of the light emitting / receiving surface of the image input unit 14. A light emitting unit is provided in the image input unit 14 with the light receiving unit 121 as a center. Light incident from the light emitting units a to c irradiates a predetermined range including the chart group CG, and the reflected light is transmitted to the light receiving unit 121. Is received at. The distance between the recording sheet S and the image input unit 14 and the distance between the light emitting unit and the light receiving unit 121 are set so that the angle formed by the incident light and the reflected light is 45 °. The light received by the light receiving section 121 is applied to a CCD 12 (not shown) via a lens (not shown).

The moving unit 2 includes an XY moving module 21 and X
It comprises a Y moving module controller 22, a moving means 23 stored as a control program in a secondary storage device 82 of the computer 8, and the like. The XY movement module 21 includes an X-axis ball screw, a Y-axis ball screw, an X-axis servo motor for driving them, a Y-axis servo motor, and the like. Installed. A control signal from the moving means 23 is sent to the XY moving module controller 22 via the interface devices 83a and 83b of the computer 8, and the controller controls the rotations of the X-axis servo motor and the Y-axis servo motor, thereby obtaining an image. The input unit 14 is movable within a horizontal plane with respect to the recording sheet S and the density detection sheet.

The image memory unit 3 is assigned a partial area of the primary storage device 81 in the computer 8. The arithmetic unit 4, the measurement range adjustment unit 5, and the determination unit 6 are all stored as control programs in the secondary storage device 82 of the computer 8. The display unit 7 includes a display 7
1, a display means 72 stored as a control program in a secondary storage device 82 of the computer 8, a video memory (not shown), and the like. The result determined by the determination unit 6 is transmitted to the interface device 83b. This is displayed on the display 71 via the display.

FIG. 6 is a flowchart for explaining an evaluation procedure performed by the density unevenness evaluation apparatus according to this embodiment.

First, in S1 of FIG. 6, the image input unit 14 is moved to a position facing the chart group CG1. That is, the moving means 23 in the computer 8
Holds the positions of the chart groups CG in advance, and obtains the X position (X ₁ ) and the Y position (Y ₁ ) by referring to those corresponding to the chart group CG ₁ . This information shall be sent to the XY moving module controller 22 through the interface device 83a of the computer 8, to count the rotation this controller corresponding X-axis servo motor and the Y-axis servo motor in X ₁ and Y ₁ each Thereby, the image input unit 14 provided at the intersection of the X-axis ball screw and the Y-axis ball screw is moved to a position facing the chart group CG1.

At S2 in FIG. 6, the (second) density signal of the density patch P is obtained. It is preferable that the density signal is close to the density obtained by actually measuring the density patch P with a densitometer.
The density chart DC whose absolute density is clear is simultaneously read by the CCD 12. Further, in order to compensate for the relatively narrow dynamic range of the CCD 12, the amount of incident light is changed to obtain a plurality of CCD measurement values, and an appropriate CC
The density signal is obtained by selecting the D measurement value. FIG. 7 is a flowchart illustrating the procedure of S2 in more detail.

At S21 in FIG. 7, the incident light amount is changed. Here, the light emitting diodes a having different light amounts
A case in which the incident light from .about.c is used alone to change the amount of incident light will be described. The ratio of the incident light amounts is as follows: light emitting diode a: light emitting diode b: light emitting diode c is 4: 2:
It is one. It is assumed that all shutters are closed in an initial state. From this state, the correction unit 13 transmits a control signal to the opening / closing controller via the interface device 83a, and opens, for example, only the shutter a. Then, only the light from the light emitting diode a is emitted to the chart group CG1 via the light emitting unit 114a.

In S22 of FIG. 7, the density patch P and the density chart DC are read. Here, the density chart D
C has five predetermined densities d1 to d5 as a result of measurement by a densitometer in advance. The correction unit 13 transmits the density patch P and the density chart DC to the light emitting diode a.
The reflected light is read by the CCD 12, and the CCD measurement value Ga1 of the density patch P and the CCD measurement value ga1 of the density chart DC having five predetermined densities are read.
To ga5 are stored in the image memory unit 3. FIG.
(A) schematically shows the contents of the image memory unit 3 when the density patch P and the density chart DC are read by the incident light from the light emitting diode a.

In S23 of FIG. 7, it is determined whether or not the density patch P and the density chart DC have been read for all incident light amounts. That is, the correction unit 13 outputs the shutter b
Only, the density patch P and the density chart DC are irradiated with light from the light emitting diode b, and the reflected light
Read on CD12 and their CCD measurements Gb, gb
1 to gb5 are stored in the image memory unit 3, respectively.
Only the shutter c is opened, the density patch P and the density chart DC are irradiated by the light from the light emitting diode c, the reflected light is read by the CCD 12, and the measured values Gc and gc1 to gc5 of the CCD are respectively stored in the image memory unit 3. Repeat this process until you remember.

The amount of incident light can be changed by, for example, changing the amount of light emitted from the light emitting diode 111 or the light emitting diode 1.
Although it can be performed by inserting a neutral density filter in the optical path from the light emitting unit 11 to the light emitting unit 114, if the shutter 112 is opened and closed as in the present embodiment, the incident light amount can be stably and extremely short. Can be changed. FIG. 8B schematically shows the contents of the image memory unit 3 when the density patch P and the density chart DC are read by the incident light from the light emitting diodes a, b, and c. .

Here, a density signal (second density signal) and a CCD measurement value (first density signal) depending on the magnitude of the incident light amount
Will be described. In FIG. 9, the horizontal axis represents the density (second density signal) measured by the densitometer, and the vertical axis represents C.
FIG. 9A is a graph in which light is measured by a light emitting diode a, FIG. 9B is a light emitting diode b, and FIG. 9C is light by a light emitting diode c. It is a thing. From these graphs, the curves showing the relationship between the density and the CCD measurement values show that the slope is gentle (curve) when the incident light amount is large (light emitting diode a: 4), and is small (light emitting diode c: 1) when the incident light amount is small. It can be seen that the inclination is steep (curve) and the incident light amount is moderate (light emitting diode b: 2), and the inclination is also moderate (curve).

FIG. 10A shows these curves.
Are shown on the same graph. For the density D (second density signal) of a certain density patch P, the CCD measurement value (first density signal) is Ga, G
b and Gc.

In S24 of FIG. 7, the largest one of the measured values of the density patch P at each incident light amount and the measured value of the density chart DC at the incident light amount are selected.
Here, the CCD measurement values (Ga, Gb,
The largest one of Gc) is Gb. In this case, irradiation was performed by the light emitting diode b, and the CCD measurement values of the density chart DC at that time were gb1 to gb5 (see FIG. 8C).

In S25 of FIG. 7, the density of the density patch P is determined from the density patch P selected in S24 and the CCD measurement value of the density chart DC, and is used as a second density signal. As described above, since the density chart DC has five predetermined densities d1 to d5 as a result of measurement by the densitometer in advance, these and the CCD measured values gb1 to gb5
The density D is obtained from the measured value Gb of the density patch P using the relationship (see FIG. 8D).

FIG. 10B shows a method for obtaining the density D from the CCD measurement value Gb of the density patch P. First, the CCD measurement values gb1 to gb of the density chart DC
b5 (gb1 <gb2 <gb3 <gb4 <gb5) is compared with the CCD measurement value Gb of the density patch P, and the magnitude relationship is obtained. Here, it is assumed that gb2 <Gb <gb3. Next, the CCD measurement value gb2 of the density chart DC,
gb and their concentrations d2 and d3, two points P on the graph
2 (d2, gb2) and P3 (d3, gb3) are taken, a curve is linearly approximated from the two points, and the density D of the density patch P is obtained from the CCD measured value Gb. Of course, other P
A curve may be approximated using the points 1, P4, and P5, or an approximation other than the linear approximation may be used.

In this embodiment, since the density D of the density patch P is determined based on the predetermined density of the density chart measured in advance by the densitometer as described above, the density chart DC must be determined more accurately. Are preferably similar to the density of the density patch P. That is, when the density of the density patch P is relatively low, it is desirable to provide a density chart DC with a low density from 0.1 to 0.3 even for the same five gradations as shown in FIG. Conversely, when the density of the density patch P is relatively high, it is desirable to provide a density chart DC having a high density from 1.1 to 1.5 even at the same five gradations as shown in FIG. . Also, unlike the present embodiment, when the density patch P itself has a plurality of density gradations having a density range, it is necessary to provide a density chart DC having a wide range of densities as shown in FIG. There is. Also in this case, in order to obtain more accurate densities, it is desirable to have many density gradations as shown in FIG. 11D and to have a small density difference between the densities of the density chart DC.

In this embodiment, the density patch P is read by the CCD 12 while changing the amount of incident light, and the density of the density patch P is obtained by using the largest one of the measured values. That is, among the curves 1 to 3 in the graph of FIG. 10A, the portion indicated by the solid line is the measured value of the CCD of the density patch P, and it is possible to prevent the sensitivity of the CCD 12 from being saturated even in the high density portion. An accurate density signal can be obtained. Unlike the present embodiment, for example, the density patch P is read by the CCD 12 while changing the amount of incident light, and the density patch P is read using the average of a plurality of measured values.
May be obtained.

Further, in this embodiment, the light from the three light emitting diodes a to c having different light amounts is independently irradiated to change the incident light amount (FIG. 12A).
), And light from a plurality of light-emitting diodes may be combined for irradiation. FIG. 12B shows the same light emitting diodes a, b, and c as in the present embodiment (the light amount ratio is 4:
2: 1) indicates the amount of light emitted, and indicates that the light can be emitted in seven levels of 1 to 7. As described above, by irradiating a plurality of light emitting diodes in combination, it is possible to easily generate a multi-step light amount with a limited number of light emitting diodes and a limited light amount. In addition, for example, when irradiating light from the light emitting diode b and the light emitting diode c,
The correction unit 13 sends a control signal to the opening / closing controller via the interface devices 83a and 83b, opens the shutters b and c, and closes the shutter a so that the correction can be performed easily and quickly.

In S3 of FIG. 6, the measurement position is determined while avoiding image defects such as white streaks and black streaks. In order to perform more accurate density measurement of the density patch P, it is preferable to determine the measurement position while avoiding image defects such as white streaks and black streaks in the density patch P. Here, by specifying an image defect portion in the image defect detection chart CC provided near the density patch P, an image defect portion in the density patch is indirectly specified. FIG. 13 is a flowchart illustrating the procedure of S3 in more detail.

In S31 of FIG. 13, the measurement range adjusting unit 5 checks the image defect detection chart CC. This is performed by accumulating the density signals of the black and white portions of the image defect detection chart CC of the chart group CG already stored in the image memory unit 3 of the computer 8 in the X and Y directions. FIG. 14 shows Y of the density patch P.
FIG. 15 shows a cumulative graph of a density signal when a black streak image defect occurs in the axial direction, and FIG. 15 shows a cumulative signal of a density signal when a white streak image defect occurs in the X-axis direction of the density patch P. ing.

The line graph of FIG. 14 shows the cumulative value of the density signal of the black portion of the density defect detection charts CCa and CC. Here, since no image defect having a density greatly different from that of the black portion occurs in the Y direction, the line graph shows a substantially constant value. On the other hand, the line graph of FIG. 14 shows the accumulated value of the density signal of the white portion of the density detection charts CCa and CC. Here, the line graph shows a sharp rising peak in X _black because the density of the white portion is significantly different from that of the white portion in the Y direction, that is, a black streak image defect occurs.

Similarly, the line graph of FIG. 15 shows the cumulative value of the density signals of the black portions of the density defect detection charts 1b and 1d. Here, since the density is greatly different from the black portion in the Y direction, that is, a white image defect has occurred,
The line graph shows a sharp falling peak at Y _white .
On the other hand, the line graph of FIG.
It shows the accumulated value of the density signal of the white portion of d. Here, since no image defect having a significantly different density from the white portion occurs in the Y direction, the line graph shows a substantially constant value.

Next, in S32 of FIG. 13, the presence or absence of black streaks and white streaks and their positions are determined. This is shown in FIGS.
In is intended to determine, based on the graph described, for example, the presence of such black lines as in FIG. 14 compares the up-peak of black lines threshold TH _b and line graph preset, the up-peak as long as it exceeds the black streaking threshold TH _b, it is determined that there is an image defect black lines. Similarly, FIG.
The presence or absence of a white streak is determined in advance by a white streak threshold TH _w
And compared with the down-peak line chart, lowering peak as long as it exceeds the white streak threshold TH _w, it is determined that image defects white streaks are present. The position of the black streak can be determined from the X coordinate (X _black ) where the rising peak exists, and the position of the white streak can be determined from the Y coordinate (Y _white ) where the falling peak exists.

In S33 of FIG. 13, the measurement center position in the density patch P is determined. This is to determine the measurement center position in the density patch P such that the black streak and the white streak determined in S32 are not included in the measurement range. The streak-like image defect occurs due to its nature in a direction parallel or perpendicular to the normal image forming process, that is, in the X direction or the Y direction in FIGS. By determining the presence or absence of black streaks and white streaks in the chart and their positions, the presence or absence and positions of black streaks and white streaks in the density patch P are determined. The measurement center position in the density patch P is determined avoiding the defect.

In this embodiment, three density patches are included in one density patch P.
Measurement range, and the measurement range is
3 measurement center positions P_a0(X_a0, Y_a0), P
_b0(X_b0, Y _b0), P_c0(X_c0, Y_c0) Around half
Within a circle of diameter r. In addition, as will be described later, in the present invention, measurement is performed.
The density is measured by moving the fixed range.
Assuming that the separation is Δr and the safety margin is α, each center position P_a0,
P_b0, P_c0White streaks, black within a circle of radius (r + Δr + α) from
If there is an image defect such as a streak, the center position is moved.

FIG. 16 shows one measurement center position of the density patch P.
Place P_a0It shows the periphery. Image defects of black and white streaks
When there is no such image defect, there is such an image defect.
(A) As shown in FIG._a0, Radius (r + Δr +
When there is no image defect (black streak) in the circle of α) (| x_a0-X
_black|> R + Δr + α) indicates the measurement center position P_a0Is changed
do not do. On the other hand, as shown in FIG.
When there is an image defect (black streak) (| x_a0-X_black| <R
+ Δr + α) includes the measurement center position P_a0To P_a0’(X _a0+
Δx, ya) (| x_a0+ Δx-X_black｜ ＞
r + Δr + α) so that no image defect is included in the circle.
You.

In S4 in FIG. 6, the quality of the image forming apparatus to be inspected is judged by evaluating the density unevenness in the density patch P. Here, while moving the measurement range at a plurality of positions, the averager within the measurement range is taken in a plurality of concentrations, and a variation of the plurality of concentration averages is compared with a preset upper limit concentration average variation, so that the inspector can perform the measurement. Density unevenness that can be avoided by slightly adjusting the position is eliminated, and only the original density unevenness can be detected. Further, in the present embodiment, the accuracy of the density unevenness evaluation is further enhanced by comparing the density variation indicating the density variation of each pixel within a certain measurement range with a preset upper limit density variation. FIG. 17 shows this S
9 is a flowchart illustrating the procedure of No. 4 in more detail.

In S41 of FIG. 17, the average of the density within the measurement range centered on the measurement center position avoiding the white and black streaks in S3 of FIG. 6 is calculated. As described above, in this embodiment, there are three measurement ranges in one density patch P. FIG. 18A shows three measurement ranges in the density patch P. As described above, providing the measurement range avoiding the outer portion of the density patch P may cause the density to be higher in the outer portion due to the so-called edge effect. This is because, when the measurement is performed while avoiding the extension part, the evaluation by the concentration evaluation device and the evaluation performed by the inspector are more likely to coincide with each other. The reason why a plurality of measurement ranges are provided in one density patch P is to perform measurement more accurately.

Here, it is not necessary to change the measurement center position in S3 of FIG. 6 in order to avoid white and black streaks.
_a0 ( _xa0 , _ya0 ), _Pb0 ( _xb0 , _yb0 ), _Pc0 ( _xc0 ,
y _c0 ). FIG.
(B) is an enlarged view of one measurement range a. The calculation unit 4 calculates an average of the density of the pixels within the measurement range a from the density signals stored in the image memory unit 3. That is, pixels (x _i ,
When the concentration of y _j) and D, D is x _i, a function of y _j, also the density average _{D av} erage (hereinafter, "D _a" as to serial), there density average D _a in the measurement range = ΣD (x
_i , y _j ) / the total number of pixels in the measurement range｝. In this way, the average densities D _a (a), D _a (b), and D _a (c) of the measurement ranges a, b, and c are obtained.
Here, the radius r is 2 mm, which is substantially the same as the aperture size for density measurement by the densitometer. This is for improving the consistency with the measurement by the densitometer.

In S42 of FIG. 17, the measurement center position is slightly shifted, and the density average within the measurement range is calculated.
As shown in FIG. 18C, the measurement center position P in the initial state
Position _Pa1 ( _xa0 +) slightly moved from _a0 ( _xa0 , _ya0 )
.delta.x _1, the y _a0 + δy ₁₎ as a new measurement center position,
The inside of the circle having the radius r is set as a new measurement range a1. S in FIG.
Assuming that the density of the pixel (x _i , y _j ) within the new measurement range a1 is D, D is x _i , y
_j , and the average of the density is D _{averag e-moved1}
(Hereinafter referred to serial and "D _am1") as, be calculated as the average density D _am1 measuring range a1 (a) = ΣD (x i, y j) / { number of all pixels of the provided measurement range a1} it can.
Similarly, the average concentration D _am1 (b), D
_am1 (c) is obtained.

[0056] Note that the method of movement of the measurement center position is arbitrary and may be configured to perform a random, but considering the processing of S47 in FIG. 17 to be described later, for example, about the initial state measured center position P _a0 It is also possible to take several new measurement center positions on the concentric circle and move the measurement center position while changing the radius of the concentric circle.

In S43 of FIG. 17, the measurement center position is
Density average D obtained by shifting_amTo determine if there are enough
You. In this embodiment, the measurement center position is shifted by 20 places.
Therefore, the measurement ranges a1 to a20, b1 to b2
0, density average D for c1 to c20, respectively
_am1(A) -D_am20(A), D_am1(B) -D
_am20(B), D_am1(C) -D_am20Until (c) is obtained
To repeat the procedure of S43. Note that this
To move the measurement center position (δx^Two+ Δ
y^Two)^1/2Is set to 1 to 2 mm. this
Indicates that the measurement range is
The same distance that the switch is moved so that it does not protrude.
That's why. Also, move the measurement range slightly like this
Even if the measurement range does not include image defects such as white and black streaks
The initial value P of the measurement center position_a0(X_a,
y_a), P _b0(X_b, Y_b), P_c0(X_c, Y_c) Is the figure
6 (see S33 in FIG. 13).
See).

In S44 of FIG. 17, the calculation unit 4 calculates the variation of the density average when the measurement center position is shifted. Here, as an example, the standard deviation σ _moved (hereinafter referred to as “σ _m ”) is used to evaluate the density variation. The average of the above-mentioned concentration averages D _{am1 to} D _am20 is AD
standard deviation σ _m = 整数, where _am and k are integers of 1 ≦ k ≦ 20.
It can be calculated as [｛AD _am −D _amk ｝ ² ] ^1/2 . In this way, the measurement center position P _a0 (x _a ,
_{y a), P b0 (x} b, y b), P c0 (x c, standard deviation indicating the variation of the density average during a plurality move the measuring center position from _{y c) σ m (a)} , σ m ( b) and σ _m (c) are obtained.

At S45 in FIG. 17, the density variation within the measurement range is calculated. Here, as an example, the standard deviation σ
_Internal (hereinafter referred to as “σ _in ”) was used to evaluate the density variation. Σ _in (a) = Σ [｛D, where σ _in is the standard deviation indicating the concentration variation within the measurement range a.
_{a (a) -D (x i} , y j)} 2] can be calculated as ^1/2. Similarly, standard deviations σ _in (b) and σ _in (c) indicating the density variations in the measurement ranges b and c are obtained.

In S46 of FIG. 17, the calculated average density D _a , the standard deviation σ _in indicating the density variation, the standard deviation σ _m indicating the density average variation, and the density previously stored _in the evaluation table by the determination unit 6 the standard deviation sigma _in indicating the upper limit of the variation, and the standard deviation showing the upper limit of the density average variation sigma _m
To determine the density unevenness. FIG.
Is a diagram schematically showing a state in which the density average D _a , the density variation σ _in , and the density average variation σ _m for each of the measurement ranges a to c obtained by the _above are stored in the primary storage device 81 of the computer 8. . FIG. 20 schematically shows an evaluation table stored in the determination unit 6. In this embodiment, each standard deviation Σ _in1
~Σ in9, has a Σ _m1 ~Σ _m9. These are determined by repeating a sensory test by a skilled inspector in advance.

FIG. 21 is a flowchart for explaining the procedure in which the judgment section 6 evaluates the uneven density.
As an example, a procedure for evaluating uneven density in the measurement range a will be described. First, it is confirmed which density range the density average D _a (a) belongs to. Here, 0.8 <D _a (a) <
Let it be 1.0. Next, the concentration average variation σ
_In (a) and the upper limit Σ _{in 5} of the density average variation in the density range to which the density average D _a (a) belongs are compared in magnitude.
Here, when σ _in (a) < _Σin5 , it is evaluated that the density unevenness is at the “pass” level. Otherwise proceed to the next step.

Next, the magnitude of the density variation σ _m (a) and the upper limit Σ _m5 of the density variation in the density range to which the density average D _a (a) belongs will be compared. Here, σ _in (a) <Σ
_In the case of _in5 , the measurement of the measurement range a is performed again without evaluating the density unevenness. In other cases, it is evaluated that the density unevenness is at a “fail” level.

In S47 of FIG. 17, the judging section 6 judges a movement limit. That is, each measurement center position if how the mobile determines whether exceeds the upper limit value sigma _m of average density variation in the concentration range. For example, if the density average of the measurement range a is 0.8 <D _a (a) <1.0, a new concentric circle centered on the measurement center position P _a0 (x _a , y _a ) is newly added. A plurality of measurement center positions are provided to calculate the density average variation, and the radius of the concentric circle is gradually increased until the density average variation exceeds Σ _m5 which is the upper limit of the density range. Then, a radius δr _{limi t} (a) concentric immediately before exceeding the sigma _m5 (hereinafter, "[delta] r
_l (a) ”). Further, from the obtained average density variation sigma _m, assuming that the concentration variation is present in accordance with the normal distribution may be obtained [delta] r _l.

In this embodiment, the evaluation of the density unevenness is not performed.
And the average density unevenness σ_mAnd density unevenness σ _inAnd based on that
Judgment is made, but besides this, the density average D_aUsing
Decisions may be made, and priorities may be set for these decision factors.
It is also possible to make a judgment.

In S5 of FIG. 6, the result determined by the determination unit 6 is displayed to the user. FIG. 22 shows a screen displayed on the display 71 by the display means via the interface devices 83a and 83b. This screen displays the density range field F1 indicating the maximum value and the minimum value among the density averages D _a (a) to (c), the density average variation of each measurement range a to c, and the density unevenness determined by the density variation. An evaluation field F2, a movement allowable field F3 indicating a movement limit from each measurement center position, a density patch P, and a measurement center position within the density patch P and a density patch P indicating a movement limit.
It consists of field F4.

That is, in FIG. 22A, the display of the density field range F1 indicates that the maximum value and the minimum value of the density averages D _a (a) to (c) are 1.01 ± 0.05. To
The display of the evaluation field F2 indicates that all the measurement ranges a to c
Is determined to be a pass level, and the display of the movement allowable field F3 indicates that each of the measurement center positions P _a0 , P _b0 , P _c0 has a radius of 0.5.
Even if the measurement center position is moved within circles of mm, 0.4 mm, and 0.5 mm and measured, the average density variation σ _m does not exceed the upper limit Σ _m , that is, the density unevenness is at an acceptable level. are doing. Further, the density patch P field F4 indicates a range within a circle having a radius of 0.5 mm, 0.4 mm, and 0.5 mm from each of the measurement center positions _Pa0 , _Pb0 , and _Pc0 , respectively.

Similarly, in FIG. 22B, in the display of the density range field F1, the maximum value and the minimum value of the density averages D _a (a) to (c) are 0.50 ± 0.2. That is, the display of the evaluation field F2 indicates that the density average unevenness in a certain measurement range, the density unevenness determined from the density variation is the reject level, and the display of the movement allowable field F3 indicates that each of the measurement center positions P _a0 , If the measurement center position is moved within circles of radii of 0.1 mm, 0.2 mm, and 0.3 mm from P _b0 and P _c0 , respectively, the average density variation σ _m does not exceed the upper limit Σ _m , that is, density unevenness. Means reaching the passing level. Further, the density patch P field F4 indicates a range within a circle having a radius of 0.1 mm, 0.2 mm, and 0.3 mm from each of the measurement center positions _Pa0 , _Pb0 , and _Pc0 , respectively.

In S6 of FIG. 6, the last density patch P
It is determined whether or not. In this embodiment, one recording sheet S
Since five density patches P are provided above (see FIG. 4), if all the density evaluations have been performed, the process ends. If not, it moves to the next chart group CG (S1) and continues the density evaluation.

[0069]

As described above in detail, according to the present invention, it is possible to provide an apparatus for evaluating unevenness in density, which enables an expert inspector to perform an evaluation similar to that performed by a densitometer.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an overall configuration of a density unevenness evaluation apparatus according to an embodiment.

FIG. 2 is an external view of the entire density unevenness evaluation apparatus according to the embodiment.

FIG. 3 is a block diagram illustrating a configuration of an apparatus for evaluating density unevenness according to an embodiment;

FIG. 4 illustrates a chart group.

FIG. 5 illustrates an image input unit.

FIG. 6 is a flowchart illustrating a processing procedure of the entire density unevenness evaluation apparatus according to the embodiment;

FIG. 7 is a flowchart illustrating a process performed by a correction unit in more detail;

FIG. 8 is a diagram schematically illustrating a CCD measured value (first density signal) of a density patch and a density chart stored in an image memory unit.

FIG. 9 is a diagram for explaining a difference in output characteristics of the CCD image sensor due to a difference in incident light amount.

FIG. 10 is a view for explaining selection of an appropriate CCD measurement value by a correction unit and how to obtain the density of a density patch.

FIG. 11 illustrates a preferred embodiment of a density chart.

FIG. 12 illustrates a case where a plurality of light sources are used alone and a case where a plurality of light sources are used in combination.

FIG. 13 is a flowchart illustrating processing of a measurement range adjustment unit in more detail;

FIG. 14 shows a state of a density patch and an image defect detection chart when a black streak exists.

FIG. 15 is a diagram illustrating a state of a density patch and an image defect detection chart when a white streak exists.

FIG. 16 is a diagram for explaining a method of determining whether or not it is necessary to move a measurement range and a method of moving the measurement range.

FIG. 17 is a flowchart illustrating the processing of a calculation unit and a determination unit in more detail;

FIG. 18 illustrates the measurement range in more detail.

FIG. 19 is a table summarizing calculation results by a calculation unit;

FIG. 20 is a table summarizing the average density variation and the upper limit of the density variation for each density range that the determination unit has in advance.

FIG. 21 is a flowchart illustrating the evaluation of density unevenness by a determination unit in more detail;

FIG. 22 shows a screen displayed on the display device by the display unit.

FIG. 23 shows a method for measuring a concentration using a densitometer.

FIG. 24 shows output characteristics of a general CCD image sensor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image input part, 13 ... Correction part, 111 ... Light emitting diode (light source), 112 ... Shutter (shielding member), 2 ... Moving part, 3 ... Image memory part, 4 ... Calculation part, 5 ... Measurement range adjustment part, 6: judgment unit, 7: display unit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C061 AP03 AP04 KK22 KK25 KK28 KK35 2G059 AA01 EE02 GG03 KK04 MM03 MM05 MM10 2H027 DA09 DE02 DE07 DE09 EC06 EC07 EE08 FD08 GB01 GB05 2H077 DA03 DA49 DA62

Claims (9)

[Claims] An image input unit that reads a density in a predetermined range including a density patch formed on a recording sheet and outputs the density as a density signal; an image memory unit that stores a density signal output from the image input unit; A calculating unit that moves a certain measurement range in the density patch from the density signal stored in the image memory unit and calculates the variation of the density average within the measurement range; and the density average variation calculated by the calculation unit, A non-uniform density evaluation apparatus comprising: a determination unit configured to determine presence or absence of non-uniform density by comparing a set allowable density average variation. 2. The calculation unit calculates a density variation within a certain measurement range in a density patch, and the determination unit compares the density variation with a preset allowable density variation. The density unevenness evaluation device according to claim 1, wherein the presence / absence of the density unevenness is determined by the following. 3. A plurality of permissible density average variations and / or density variations are set for each density range.
Or the unevenness evaluation apparatus according to 2. 4. The density unevenness evaluation device according to claim 1, further comprising: a display unit that displays a result determined by the determination unit to a user. 5. A plurality of density patches are provided on the recording sheet, and the image input unit and the recording sheet are relatively positioned so that the image input unit can read a predetermined range of densities including each density patch. The density unevenness evaluation device according to any one of claims 1 to 4, further comprising a moving unit that moves. 6. Detecting an image defect portion in the density patch,
A measurement range adjustment unit that adjusts the measurement range so that the image defect portion is not included in the measurement range.
5. An apparatus for evaluating uneven density according to any one of 5. 7. The image defect detection chart is formed in a range that can be read together with the density patch, and the measurement range adjustment unit detects an image defect location based on a density signal of the image defect detection chart. Such an uneven density evaluation device. 8. A density chart having a plurality of predetermined densities in a range that can be read together with the density patch, wherein the image input unit can change the amount of light incident on a predetermined range on a recording sheet. An illumination device, an image sensor that reads a density patch and a density chart, and outputs a first density signal indicating their relative densities, and a density patch and a density chart while gradually changing the amount of incident light from the illumination device And outputs a second density signal indicating an absolute density based on an appropriate first density signal and a predetermined density on a density chart among a plurality of first density signals output from the image sensor. The density unevenness evaluation device according to claim 1, further comprising a correction unit. 9. The illumination device includes a plurality of light sources having the same or different amounts of light, and a plurality of shielding members capable of transmitting and shielding light from the respective light sources. The uneven density evaluation device according to claim 8, wherein the amount of incident light from the illumination device is changed by controlling the light intensity.