JP3253171B2 - Image density unevenness measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image density unevenness measuring apparatus for measuring density unevenness of an image obtained by an image recording apparatus such as a laser printer which scans a photosensitive member with a light beam to record an image. About.

[0002]

2. Description of the Related Art In an image recording apparatus such as a laser printer that uses a light beam to scan an image on a photosensitive member to record an image or a laser imager used in medicine, density unevenness may occur in a recorded image. Density unevenness in the perpendicular direction is likely to occur, which is a problem in image quality.

The causes of density unevenness in the direction perpendicular to the scanning line of a recorded image can be roughly classified into unevenness in the scanning line pitch and unevenness in the light beam intensity. convenient.

Conventionally, there is no apparatus for evaluating unevenness in density of an image recorded by a laser imager or the like used for recording an image obtained by a CT scanner, MRI, or the like. Although the presence or absence of unevenness could be identified, the cause could not be determined. For this reason, the light beam irradiation unit, the transport unit for the recording film, and the like are independently inspected to estimate the cause of the density unevenness and take a countermeasure.

[0005] As a device for evaluating image density unevenness of an image of a general laser printer or the like, there is known a method for evaluating the image density unevenness itself (for example, Japanese Patent Application Laid-Open Nos. 4-2847771 and 4-335363). Has been
Apparatus for evaluating scanning line pitch (for example, see Japanese Patent Application Laid-Open
No. 82684, JP-A-4-229287) are known.

[0006]

However, when the density unevenness is evaluated by visual observation, a quantitative evaluation cannot be performed because individual evaluators vary. Also, even if density unevenness is found by visual inspection, the cause was only estimated from the results of unit inspection of the light beam irradiation unit and the recording film transport unit, etc., so the direct cause of the actual density unevenness was It takes time to take measures without grasping.

Further, in the case of an image density unevenness evaluation apparatus for an image such as a general laser printer or the like, the density unevenness itself and the scanning line pitch are measured separately, so that the relationship between the density unevenness and the scanning line pitch cannot be grasped. It is not known whether the cause is uneven scanning line pitch. For this reason, the direct cause of the density unevenness cannot be determined, and it takes time to take measures.
In addition, since the density distribution used for measuring the scanning line pitch does not correspond to the visual sense, it is difficult to grasp how the scanning line pitch unevenness affects the density unevenness. Furthermore, there is no conventional image density unevenness evaluation apparatus capable of measuring even light beam intensity unevenness.

The present invention has been made in view of the above points, and is directed to a direction perpendicular to a scanning line with respect to an image obtained by an image recording apparatus such as a laser imager or a laser printer which performs image recording by scanning a light beam. It is an object of the present invention to measure and evaluate the density unevenness with high accuracy by linking the causes (unevenness of scanning line pitch, unevenness of light beam intensity).

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is directed to a method of scanning a light beam in a direction perpendicular to a scanning line of an image sample, which may have a density difference for each scanning line. In a device for measuring the density unevenness, a density measuring means for measuring the density of an area of the image sample having a finer width than the pitch of the scanning lines, and a density measuring position of the image sample in a direction perpendicular to the scanning lines. Moving means for moving, position measuring means for measuring the density measuring position, the image sample based on the density measuring position measured by the position measuring means and the density measured by the density measuring means at each density measuring position A density distribution creating means for creating a density distribution of the density distribution, a density unevenness distribution creating means for creating a density unevenness distribution by spatially filtering the density distribution, and a scanning line peak from the density distribution. A first scanning line pitch unevenness distribution creating means for obtaining a scanning line pitch unevenness distribution from the scanning line pitch, and obtaining a value corresponding to the intensity of the light beam from the density distribution to obtain the light beam intensity unevenness distribution from the value. Light beam intensity unevenness distribution creating means to be created, and the concentration distribution creating means
Created by the density distribution created by
Density unevenness distribution, the first scan line pitch unevenness distribution
Scanning line pitch unevenness distribution created by the
Light beam intensity created by the light beam intensity unevenness distribution creation means
Can display at least one of the uneven distributions
The image density unevenness measuring device is constituted by the display means .

[0010]

According to the present invention, the density measuring position moved by the moving means is measured by the position measuring means, and the density at the density measuring position is measured by the density measuring means. The density distribution creating means creates the density distribution, the density unevenness distribution creating means creates the density unevenness distribution based on the density distribution, and the first scanning line pitch unevenness distribution creating means creates the scanning line pitch unevenness distribution based on the density distribution. Then, the light beam intensity unevenness distribution creating means creates the light beam intensity unevenness distribution based on the density distribution.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an apparatus for evaluating uneven image density according to the present invention.

Reference numeral 1 denotes a He-Ne laser, which emits a laser beam 2 indicated by a broken line. The cylinder 3 indicated by a dashed line is provided around the optical path of the laser light 2 to prevent the laser light 2 from being refracted under the influence of air fluctuation and changing the optical path. Reference numeral 4 denotes a beam expander, which enlarges the diameter of the laser beam 2. The cross-sectional diameter of the laser beam 2 irradiated by the He-Ne laser 1 is about 0.8 mm, and is expanded to about 4 mm by the beam expander 4.

The cross section of the laser beam 2 expanded by the beam expander 4 is deformed by a cylindrical lens 5 into a vertically long slit shape, and then the upper and lower portions are cut by a slit 6 to have a width of about 20 μm and a height of about 20 μm. A cross section of 1000 μm becomes a rectangular light beam. By using the vertically elongated slit light as described above, the granular noise of the sample is suppressed. Also, if the sample surface is set slightly before the beam waist of the lateral diameter (for example, the He-Ne laser 1 side of about 0.1 mm), the sample is irradiated with a converged beam, so that the granular noise is more effectively reduced. Can be suppressed. The cylindrical lens 5 and the slit 6 are arranged on a gonio stage 17 so that the azimuth angle between the scanning line recorded on the image-recorded sample 9 and the laser beam 2 passing through the slit 6 can be adjusted. By adjusting the angle, the accuracy of the concentration measurement of the sample 9 can be improved.

Reference numeral 7 denotes a single-axis mechanical stage,
It is controlled by the stage controller 12 which receives a command from U15, and moves in the left-right direction. The sample 9 is fixed to the sample holder 8 and arranged on the uniaxial mechanical stage 7.
Is moved left and right, thereby moving the sample 9 left and right to micro trace the sample 9.

The position (moving distance) of the uniaxial mechanical stage 7 is precisely measured by a laser
15 reported. The sample 9 used in this embodiment is a film on which an image is recorded by a laser imager, and the density of the sample 9 is measured based on the amount of the laser beam 2 transmitted through the sample 9. Recording of an image on the sample 9 by the laser imager is performed by repeatedly scanning the light beam in the horizontal direction of the sample 9 while transporting the sample 9 in the vertical direction. The sample 9 on which the image is recorded in this manner is fixed to the sample holder 8 with the length and width reversed.

The laser beam 2 that has passed through the slit 6
And is received by the photodiode 10. The photodiode 10 generates a current according to the amount of the received laser beam 2. This current is voltage-converted and amplified by the amplifier 13, converted into a digital value by the A / D converter 14, and then input to the CPU 15. Reference numeral 16 denotes a display device,
It is connected to U15 and displays measurement results such as density unevenness, scanning line pitch unevenness, light beam intensity unevenness, etc., which will be described later.

The CPU 15 obtains the density of the sample 9 based on the transmitted light amount input from the A / D converter 14 and the light amount of the light source irradiated by the He-Ne laser 1 using Equation 1. In Equation 1, D is the concentration of the sample, I ₀ is the light source light amount, and I is the transmitted light amount.

[0019]

D = log (I ₀ / I) The density of the sample 9 obtained by the _equation 1 is expressed by the following formula:
The data is stored in a memory (not shown) provided in the CPU 15 in association with the irradiation position of the laser beam 2 on the sample 9 precisely measured in 1. By the way, since the measurement of the irradiation position of the laser beam 2 on the sample 9 requires precision, the concentration of the sample 9 is measured after the first measurement is performed by the laser length measuring device 11, and then the laser length measuring device is measured. If the second measurement is performed at 11 and the average value of the first and second measurement results is used as the irradiation position of the laser beam 2 on the sample 9, a more accurate position can be measured.

Next, the CPU 15 gives a command to the stage controller 12 to move the one-axis mechanical stage 7 to 1 μm.
Just move laterally. After the movement, the uniaxial mechanical stage 7 is temporarily stopped, the density of the sample 9 is determined at the position after the movement in the same manner as described above, and the density is measured by the laser beam on the sample 9 precisely measured by the laser length measuring device 11. The data is stored in the memory provided in the CPU 15 in association with the irradiation position of No. 2. As described above, the density distribution of the sample 9 can be obtained by obtaining and storing the density of the sample 9 at each position on the sample 9.

FIG. 2 shows the concentration distribution of the sample 9.

The concentration distribution shows a wavy line as shown in FIG.
The ridge of the wavy line corresponds to the scanning line when an image is recorded on the sample 9.

FIG. 3 and FIG. 4 are flowcharts of the processing for analyzing the density distribution shown in FIG.

Referring to FIG. 3, first, the center position of each mountain having the density distribution shown in FIG. 2 is obtained (F-1).

FIG. 5 is an explanatory diagram of a method for obtaining the center position of a mountain.

For example, to determine the center position of the peak a in FIG. 5, a threshold is provided between the highest point and the lowest point of the peak a, and two points a _U and a _{D at} which the peak a reaches this threshold are determined. Ask. Then, thus determined the midpoint a _C two points a _U and a _D determined, considered the position of the middle point a _C (the value of the horizontal axis) and the center position of the mountain a. In step (F-1) of FIG. 3, the center positions of all the peaks in the density distribution are obtained in this way.

Returning to the description of FIG. 3, in step (F-2), the cycle average of the density distribution shown in FIG. Find the uneven distribution.

FIG. 6 is an explanatory diagram of a method for obtaining the cycle average of the density distribution.

Using the center positions of the respective mountains obtained in step (F-1), the area between the center positions of adjacent mountains as shown in FIG. 6 (the area of the hatched portion) as shown in FIG. Is obtained, and this area is divided by the scanning line pitch to obtain a cycle average. For example, the CPU 15 associates the cycle average and the position on the sample 9 with the CPU 15 such that the cycle average of the peaks a and b is data at the center position between the center position of the peak a and the center position of the peak b. It is stored in the provided memory. In this way, by obtaining and storing the cycle average corresponding to the position on the sample 9, the uneven density distribution of the sample 9 can be obtained.

FIG. 7 shows an uneven density distribution.

In FIG. 7, the vertical axis is the cycle average, and the horizontal axis is the position on the sample 9. The density unevenness distribution is obtained by removing components due to the influence of the scanning line cycle during image recording from the density distribution shown in FIG.

In step (F-3) of FIG. 3, the density unevenness distribution shown in FIG. 7 is Fourier-transformed to obtain the density unevenness frequency distribution.

FIG. 8 shows a frequency distribution of uneven density.

In FIG. 8, the ordinate represents the density in decibels, and the density 1 corresponds to 0 dB. The horizontal axis is the spatial frequency, which indicates the frequency of the fluctuation of the concentration on the sample 9. The evaluator can see by looking at the density unevenness frequency distribution in FIG.
Thus, in this density unevenness frequency distribution, the density unevenness m, p,
q and r show prominent values, indicating that the evaluator should pay attention to the density unevenness m, p, q, and r as the density unevenness on the sample 9.

In step (F-4) of FIG. 3, the scanning line pitch obtained by using the center position of each mountain obtained in step (F-1) is stored in the memory provided in the CPU 15 in the order of measurement. Remember. This makes it possible to obtain the scanning line pitch uneven distribution of the sample 9 corresponding to the number of scanning lines.

FIG. 9 shows a distribution of scanning line pitch unevenness.

In FIG. 9, the vertical axis is the scanning line pitch, and the horizontal axis is the number of scanning lines indicating the position of the scanning line on the sample 9. Since the number of scanning lines corresponds to the position on the sample 9, this uneven scanning line pitch distribution can be compared with the uneven density distribution shown in FIG. The scanning line pitch unevenness distribution in FIG. 9 shows only the density unevenness caused by the scanning line pitch unevenness in the density unevenness distribution shown in FIG.

Returning to FIG. 3 again, in step (F-5), the scanning line pitch unevenness distribution shown in FIG. 9 is Fourier-transformed to obtain the scanning line pitch unevenness frequency distribution.

FIG. 10 shows the frequency distribution of scanning line pitch unevenness.

In FIG. 10, the vertical axis represents the scanning line pitch in decibels.
Corresponds to B. The horizontal axis indicates the spatial frequency, which indicates the frequency of the fluctuation of the scanning line pitch on the sample 9. The evaluator ran in FIG.
As can be seen by looking at the frequency distribution of the
In the frequency distribution of the pitch variation, the pitch variation s, t, u
Indicates a prominent value, indicating that the evaluator should pay attention to the pitch unevenness s, t, and u as the scanning line pitch unevenness on the sample 9.

Subsequently, in step (F-6) of FIG.
Scan line pitch unevenness due to polygon (rotating polygon mirror) is obtained. A light beam is used for recording an image on a sample, and a polygon is used to deflect and scan the light beam, for example. In this embodiment, when recording an image on the sample 9, eight polygons are used. Depending on the surface of the polygon, there may be a defect such as surface tilt, and the defect of the polygon surface may cause unevenness of the scanning line pitch.
Therefore, the data of the scanning line pitch unevenness distribution shown in FIG. 9 is classified for each face of the polygon, and the scanning line pitch unevenness due to the polygon is examined.

FIG. 11 shows scanning line pitch unevenness due to polygons.

In FIG. 11, the vertical axis is the scanning line pitch, and the horizontal axis is between the surfaces of the eight polygons. In the figure, the vertical line connects the maximum value and the minimum value of the scanning line pitch for each surface of the classified polygon, and further connects the average value of the scanning line pitch for each surface of the classified polygon by a polygonal line. It is.

Proceeding to FIG. 4, in step (F-7), FIG.
From the data of the scanning line pitch unevenness distribution shown in FIG.
(Average value shown in (2)) is subtracted to obtain a scanning line pitch uneven distribution other than polygons.

FIG. 12 shows a scanning line pitch unevenness distribution other than polygons.

In FIG. 12, the vertical axis is obtained by subtracting the average value for each polygon surface from the scanning line pitch shown in FIG. 9, and the horizontal axis is the number of the scanning line on the sample 9. It is the number of scanning lines shown. The nonuniform scanning line pitch distribution other than polygons represents only the nonuniform scanning line pitch caused by defects other than the polygon surface defect in the nonuniform scanning line pitch distribution shown in FIG.

Returning to FIG. 4, in step (F-8), the scanning line pitch unevenness distribution other than polygons shown in FIG. 12 is subjected to Fourier transform, and the scanning line pitch unevenness frequency distribution other than polygons is obtained.

FIG. 13 shows a scanning line pitch uneven frequency distribution other than polygons.

In FIG. 13, the vertical axis represents the scanning line pitch in decibels.
Corresponds to B. The horizontal axis indicates the spatial frequency, which indicates the frequency of the fluctuation of the scanning line pitch on the sample 9. The evaluator runs in Fig. 13.
As can be seen from the frequency distribution of the scanning line pitch unevenness,
In the frequency distribution of scanning line pitch unevenness due to other than Rigon, the pitch unevennesses v and w show prominent values, and the evaluator regards the pitch unevenness v and w as scanning line pitches other than polygons on the sample 9. It is clear that attention should be paid to unevenness.

Subsequently, in step (F-9) of FIG.
The density at the highest point of each peak of the density distribution shown in FIG. 2 is stored in a memory provided in the CPU 15 in association with the position on the sample 9 as the density corresponding to the intensity of the light beam, and is stored in the memory provided in the CPU 15. I do.

FIG. 14 is an explanatory diagram of a method for obtaining the density corresponding to the intensity of the light beam.

Since the density of the image on the sample 9 is higher as the light beam used for recording the image of the sample 9 is higher, the density of the highest point of each peak is stored in correspondence with the position on the sample 9. The light beam intensity uneven distribution of the sample 9 can be obtained.

FIG. 15 shows the light beam intensity unevenness distribution obtained as shown in FIG.

In FIG. 15, the vertical axis represents the density corresponding to the intensity of the light beam, and the horizontal axis represents the position on the sample 9. This uneven light beam intensity distribution shows only the uneven density caused by the uneven light beam intensity in the uneven density distribution shown in FIG.

Finally, in step (F-10) of FIG. 4, the light beam intensity non-uniformity distribution shown in FIG. 15 is Fourier-transformed to obtain a light beam intensity non-uniformity frequency distribution.

FIG. 16 shows the frequency distribution of light beam intensity unevenness.

In FIG. 16, the vertical axis represents the density corresponding to the intensity of the light beam in decibels, and the density 1 corresponds to 0 dB. The horizontal axis is the spatial frequency, which indicates the frequency of the fluctuation of the concentration on the sample 9. The evaluator uses the light beam shown in FIG.
As can be seen from the frequency distribution,
The uneven intensity frequency distribution shows a value at which the uneven intensity z is prominent, and it is understood that the evaluator should pay attention to the uneven intensity z as the light beam intensity unevenness on the sample 9.

Here, the evaluation of the density unevenness performed using each distribution obtained by the processing for analyzing the density distribution shown in FIGS. 3 and 4 will be described. This evaluation is performed by the evaluator
It is.

Here, looking at the frequency distribution of the density unevenness shown in FIG. 8, since the density levels of the density unevenness m, p, q, and r are high, the cause of the density unevenness m, p, q, and r is high. The procedure for locating is described.

Looking at the frequency distribution of the scanning line pitch unevenness in FIG. 10, the pitch unevenness s corresponding to the density unevenness p in FIG.
It can be seen that the pitch unevenness t corresponding to the density unevenness q and the pitch unevenness u corresponding to the density unevenness r in FIG. 8 appear, but the pitch unevenness corresponding to the density unevenness m in FIG. 8 does not appear.

Looking at the frequency distribution of scanning line pitch unevenness other than polygons in FIG. 13, pitch unevenness v corresponding to density unevenness q in FIG. 8 and pitch unevenness w corresponding to density unevenness r in FIG. 8 appear. However, it can be seen that pitch unevenness corresponding to the density unevenness m in FIG. 8 and pitch unevenness corresponding to the density unevenness p in FIG. 8 do not appear.

On the other hand, looking at the frequency distribution of the light beam intensity unevenness in FIG. 16, the intensity unevenness z corresponding to the unevenness density m in FIG. 8 appears, but the intensity unevenness corresponding to the density unevenness p in FIG.
It can be seen that there is no intensity unevenness corresponding to the density unevenness q in FIG. 8 and the intensity unevenness corresponding to the density unevenness r in FIG.

From the above, the density unevenness m in FIG. 8 is caused by the light beam intensity unevenness, the density unevenness p in FIG. 8 is caused by the scanning line pitch unevenness due to a defective polygon, and the density unevenness q in FIG. It can be seen that and r are caused by scanning line pitch unevenness due to non-polygon (for example, uneven transport of the sample or vibration of the image recording apparatus).

Further, according to the above evaluation, the level of each unevenness (unevenness of density, unevenness of pitch, unevenness of intensity) is quantitatively expressed, so that quantitative evaluation of unevenness of density and quantitative estimation of the cause thereof are performed. It can be carried out.

The above description has been made on the evaluation of the density unevenness of the sample using each frequency distribution. However, the density unevenness distribution before the Fourier transform of each frequency distribution, the scanning line pitch unevenness distribution, and the scanning line pitch unevenness other than polygons. By using the distribution and the light beam intensity unevenness distribution, it is possible to grasp at which position on the sample the density unevenness occurs.

In the above-described embodiment, the density unevenness distribution is obtained by cycle averaging in step (F-2) of FIG. 3. Here, the density unevenness distribution applicable to the image density unevenness evaluation apparatus according to the present invention is obtained. Another method will be described.

FIG. 17 is a diagram showing the distribution of the level of unevenness in the visual limit (“Applied Optics, Vol. 25, No. 21).
No. (Issued November 1, 1986), p. 3880, a graph described in a paper by Paul Schubert entitled "Periodic Image Artifacts in Continuous Tone Laser Scanners". ).

Conventionally, the level of visual limit unevenness (visual contrast sensitivity to a sine wave pattern), which indicates the limit at which density unevenness can be visually identified, is known. If it is above the curve in FIG. Uneven concentration on the sample can be identified. Therefore, the present method utilizes this visibility limit level.

First, the density distribution shown in FIG. 2 is Fourier-transformed to obtain a density frequency distribution, and then the density frequency distribution and the distribution of the visual limit level are combined to obtain a density uneven frequency distribution. This makes it possible to attenuate components that are not visually recognized in the density frequency distribution, and to obtain the density unevenness frequency distribution corresponding to the eyes. In addition,
In order to obtain the density unevenness distribution, the density unevenness frequency distribution may be inverse Fourier transformed.

Further, in the above embodiment, the center position of the peak of the density distribution (the center position of the scanning line) was obtained by providing one threshold in step (F-1) in FIG. Instead, the center position of the scanning line may be obtained by another method.

For example, in the “scanning line pitch measurement method” filed on the same day as the present application, a plurality of threshold values are set, and the center point of two points (up and down of a mountain) at which the curve of the density distribution reaches the threshold value is obtained for each threshold value. Straight line approximation is performed on the center point for each threshold value, and the position of the point at which the obtained approximate straight line reaches the highest peak density is regarded as the center position of the scanning line.
It goes without saying that this method can be applied to the present invention.

Further, in the above embodiment, the density distribution at the center of the peak of the density distribution is plotted in step (F-9) in FIG. Although the density unevenness distribution is obtained, the light beam intensity unevenness distribution may be obtained by actually obtaining the light beam intensity. Here, a method for obtaining the light beam intensity will be described.

FIG. 18 is a diagram showing the waveform of the intensity of the light beam of the laser imager used when recording an image on the sample 9.

In FIG. 18, the vertical axis represents the intensity of the light beam, and the horizontal axis represents the distance from the center of the cross section of the light beam. FIG. 18 shows an example of a light beam having an intensity of 1 and a beam diameter of 120 μm. The intensity distribution of the light beam is the strongest at the center point, and is represented by a Gaussian distribution curve as shown in FIG. Although the radius of this light beam is 60 μm, it can be seen from FIG. 18 that the light beam has an intensity at a point 60 μm or more away from the center point.

Further, the stronger the intensity of the light beam is, the deeper the image is recorded on the sample 9.
The intensity of the light beam at the time of recording an image on the sample 9 can be obtained by back calculation from Equation 2. In Equation 2, γ is the sensitivity characteristic of the film of Sample 9, and E is the intensity of the light beam when recording an image on Sample 9.

[0076]

D = γ · log E At the time of image recording on the sample 9, for example, the light beam shown in FIG. 9 is moved in the vertical direction to record an image by the next one scanning line.

FIG. 19 shows the light beam intensity distribution obtained by inversely calculating Equation 2 using the density distribution of FIG.

In FIG. 19, the curve shown by the solid line corresponds to FIG.
Is a light beam intensity distribution obtained by back-calculating Equation 2 using the density distribution described above. On the other hand, a curve shown by a dashed line is a light beam waveform used when an image is recorded on the sample 9.
Because the waveform of the light beam has a Gaussian distribution as shown in FIG. 18, the intensities of the adjacent light beams are superimposed, and the intensity at the peak of the solid line curve and the peak of the chain line curve are indicated. It can be seen that the intensities do not match.

The light beam intensity to be obtained in step (F-9) in FIG. 3 is not the light beam intensity at the peak of the solid curve in FIG. Desirably the light beam intensity at the apex. Therefore, based on the solid curve in FIG. 19, the light beam intensity at the peak of the mountain of the one-dot chain line curve in FIG. 19 is obtained.

In FIG. 19, P _(n) is the intensity at the vertex of the n-th peak of the solid curve, and B _(n) is the right side of the n-th peak of the solid curve. The intensity at the lowest point of the valley, Pt _(n) is the distance (scanning line pitch) between the center position of the n-th peak and the center position of the (n + 1) -th peak, and R _n and What is present is the intensity at the vertex of the n-th mountain of the dashed line curve. Here, the number of peaks in the solid line is k
The description proceeds as if there are (in other words, n = 1, 2,
..., k-1, k).

First, the average value P _AVE of P _(n) is obtained by _Equation 3, the average value B _AVE of B _(n) is obtained by _Equation 4, and P _{t (n)}
The average value P _{t AVE of} is obtained by _Expression 5.

[0082]

(Equation 3)

[0083]

(Equation 4)

[0084]

(Equation 5) Next, the beam diameter (4σy) is calculated by regarding the waveform of the light beam as a Gaussian distribution. If the light beam has a Gaussian distribution, the beam diameter of the light beam (4σy) is calculated using the existing formula.
Is represented by equation (6).

[0085]

(Equation 6) Here, the average value R _AVE of R _(n) can be expressed by Expression 7. Here, BD is the radius of the light beam.

[0086]

(Equation 7) Subsequently, for ease of calculation, P _(n) is divided by R _AVE and the result is set to P _{R (n)} . This P _{R (n)} is the ratio of the light beam intensity at the peak of the peak of the solid curve in FIG. 19 when R _{AVE is set} to 1.

Next, P _{R (n)} is corrected according to equation 8 to
_{Find AD (n)} . This correction is intended to remove the effect of unevenness in the interval (scanning line pitch) between the n-th peak and its adjacent peak.

[0088]

(Equation 8) Finally, P _{AD (n)} is corrected according to equation 9 to obtain R _{AD (n)} (= R
_(n) / R _AVE ). This correction removes the influence of the light beam intensity unevenness of the adjacent mountain.

[0089]

(Equation 9) By plotting R _{AD (n)} obtained in the above description, the light beam intensity uneven distribution can be obtained. Note that the light beam intensity unevenness distribution obtained by this method is more than the light beam intensity unevenness distribution (more precisely, the density unevenness distribution corresponding to the light beam intensity) obtained in the description of step (F-9) in FIG. It is accurate and has few errors.

In this embodiment, the density of the sample 9 is detected by the transmitted light of the sample 9. However, the present invention is not limited to this, and is applicable to the case of detecting the density of the sample by the reflected light of the sample. Of course you can.

In this embodiment, the cylinder 3 is provided along the optical path of the laser beam 2 as shown in FIG.
The laser light 2 is made to pass through the inside. here,
The effect of the cylinder 3 will be described.

FIG. 20 is a diagram showing the amount of light transmitted through the sample 9 when the cylinder 3 is not provided.

FIG. 21 is a diagram showing the amount of light transmitted through the sample 9 when the cylinder 3 is provided.

In FIG. 20 and FIG. 21, the vertical axis represents FIG.
, The horizontal axis represents the light amount voltage of the laser beam 2 detected by the photodiode 10, and the horizontal axis represents the time elapsed since the power-on of the He-Ne laser 1 as 0 for a predetermined time, and the elapsed time from the predetermined time. is there. In FIG. 20, it can be seen that the transmitted light voltage is considerably scattered, whereas in FIG. 21, the scatter is extremely small.

As described above, the cylinder 3 prevents the laser beam 2 from being refracted by the influence of air fluctuation and changing the optical path.

Next, the sample holder 8 shown in FIG. 1 will be described.

FIG. 22 is a sectional view of the sample holder 8.

The sample holder 8 is provided with a transparent support 8a made of glass, for example, together with the outer frame 8b, and the sample 9 is fixed between the transparent supports 8a. By doing so, when the laser beam 2 is incident on the sample 8, the sample 8 can be prevented from being slightly deformed or moved by the heat.

FIGS. 23 to 26 show the effect of the transparent support 8a. FIG. 23 is a diagram showing the fluctuation range of the density measured when the transparent support 8a is not provided.

In FIG. 23, the vertical axis indicates the fluctuation range of the concentration (difference between the maximum value and the minimum value in 25 measurements) when the concentration of the sample 9 was measured 25 times without moving the uniaxial mechanical stage 7. Yes, horizontal axis is uniaxial mechanical stage 7
(That is, the concentration measurement position on the sample 9).

FIG. 24 is a diagram showing the density measured when the transparent support 8a is not provided.

In FIG. 24, the vertical axis represents the average value of the density of the sample 9 measured 25 times without moving the single-axis mechanical stage 7, and the horizontal axis represents the moving distance of the single-axis mechanical stage 7 (that is, the sample 9). Upper density measurement position).

Looking at FIG. 23 and FIG.
It can be seen that the density fluctuation width is large in the portion where the density changes greatly (the portion where the slope of the curve in FIG. 24 is large).

FIG. 25 is a diagram showing the fluctuation width of the density measured when the transparent support 8a is provided.

In FIG. 25, the vertical axis represents the fluctuation range of the concentration (difference between the maximum value and the minimum value in 25 measurements) when the concentration of the sample 9 was measured 25 times without moving the uniaxial mechanical stage 7. Yes, horizontal axis is uniaxial mechanical stage 7
(That is, the concentration measurement position on the sample 9).

FIG. 26 is a diagram showing the density measured when the transparent support 8a is provided.

In FIG. 26, the vertical axis represents the average value of the density of the sample 9 measured 25 times without moving the single-axis mechanical stage 7, and the horizontal axis represents the moving distance of the single-axis mechanical stage 7 (that is, the sample 9). Upper density measurement position).

When FIG. 23 and FIG. 25 are compared, FIG.
5 clearly shows that the density fluctuation width is smaller, and the effect of providing the transparent support 8a on the sample holder 8 is clear. By firmly fixing the sample 9 with the transparent support 8a so that the sample 9 does not move or vibrate due to the influence of the heat of the laser beam or the like, particularly, the sample 9 has a concentration gradient that greatly affects the displacement of the sample 9. In some portions, the maximum density fluctuation range can be reduced from 0.0042 to 0.0025, which is about 60%.

Further, since the transparent support 8a needs to be fixed firmly so that the sample 9 does not move, it is desired that the transparent support 8a be made of a material having sufficient hardness such as glass. Further, it is preferable that the transparent support 8a is thin. This is because the laser light 2 is diffused by the sample 9 when the amount of the laser light 2 transmitted through the sample 9 is detected.
Is required to be as close to the sample 9 as possible.

Even when the sample holder 8 is not provided with a transparent support, the window through which the sample 9 is exposed when the sample 9 is fixed to the sample holder 8 is reduced, so that the sample 9
Is fixed, the same effect as that of providing the transparent support 8a can be obtained.

In this embodiment, the sample 9 is moved to perform the micro trace of the concentration. However, by moving the optical path of the laser beam 2 to change the position on the sample 9 where the laser beam 2 is irradiated. A micro trace of the concentration may be performed.

Further, the “density measuring device” filed on the same day as the present application has a laser beam 2
Although the technique for correcting the light source light quantity I ₀ when the light quantity fluctuates has been disclosed, it is needless to say that this technique can be applied to the present invention.

Furthermore, in the present embodiment, the density of the sample 9 was measured by the transmitted light of the laser beam 2 shown in FIG. 1, but the present invention is not limited to this, and the density of the sample 9 was measured using the light of a lamp. You may make it measure.

[0114]

As described above, according to the present invention,
The output of an image recording device, such as a laser imager or laser printer, that scans a light beam to record an image, is measured with high accuracy by associating uneven density with its causes (uneven scanning line pitch, uneven light beam intensity). Can be evaluated.

That is, high-precision density unevenness evaluation (corresponding to density unevenness that can be visually recognized) can be performed, and
It is possible to quantitatively determine what causes the density unevenness (whether it is caused by uneven scanning line pitch or uneven light beam intensity, or if uneven scanning line pitch is caused by polygon effect). become. This is an effect of obtaining the density unevenness distribution, the scanning line pitch unevenness distribution, the light beam intensity unevenness distribution, and the like from one measurement result of the density distribution.

As described above, the density non-uniformity distribution, the scanning line pitch non-uniformity distribution, the light beam intensity non-uniformity distribution, and the like can be obtained by measuring the density non-uniformity distribution only once. The density distribution is measured in order to obtain the density distribution, and the density distribution is measured twice and three times in order to obtain the distribution of other unevenness (scanning line pitch unevenness distribution, light beam intensity unevenness distribution, etc.). This means that the distribution of each unevenness can be compared with each other and evaluated with high accuracy, and the number of times of measuring the concentration distribution is small, so that the time required for the evaluation is short.

In addition, since high-precision and quantitative evaluation of density unevenness can be performed, a quality standard of an image recording apparatus can be created.

Further, when there is density unevenness in the recording result of the image recording apparatus, the cause of the density unevenness can be understood, so that the accuracy in improving the image recording apparatus and the time required for the improvement are shortened. be able to.

[Brief description of the drawings]

FIG. 1 is a block diagram of an image density unevenness measuring apparatus according to the present invention.

FIG. 2 is a concentration distribution of a sample.

FIG. 3 is a flowchart of a process for analyzing a density distribution shown in FIG. 2;

FIG. 4 is a part of the flowchart of the process of analyzing the concentration distribution shown in FIG. 2 that follows FIG. 4;

FIG. 5 is an explanatory diagram of a method for obtaining a center position of a mountain.

FIG. 6 is an explanatory diagram of a method of calculating a cycle average of a concentration distribution.

FIG. 7 is an uneven density distribution.

FIG. 8 is a frequency distribution of uneven density.

FIG. 9 is a scan line pitch uneven distribution.

FIG. 10 is a frequency distribution of scanning line pitch unevenness.

FIG. 11 shows scanning line pitch unevenness due to polygons.

FIG. 12 is a scan line pitch uneven distribution other than polygons.

FIG. 13 is a scanning line pitch uneven frequency distribution other than polygons.

FIG. 14 is an explanatory diagram of a method for obtaining a density corresponding to the intensity of a light beam.

FIG. 15 is a light beam intensity uneven distribution.

FIG. 16 is a frequency distribution of light beam intensity unevenness.

FIG. 17 is a diagram showing a distribution of levels of visibility limit unevenness.

FIG. 18 is a diagram showing a waveform of the intensity of a light beam of a laser imager used when recording an image on a sample.

19 is a light beam intensity distribution obtained by back-calculating Equation 2 using the density distribution of FIG.

FIG. 20 is a diagram showing the amount of light transmitted through a sample when no cylinder is provided.

FIG. 21 is a diagram showing the amount of light transmitted through a sample when a cylinder is provided.

FIG. 22 is a sectional view of a sample holder.

FIG. 23 is a diagram showing a fluctuation range of density measured without using a transparent support.

FIG. 24 is a diagram showing a density measured without using a transparent support.

FIG. 25 is a diagram showing a fluctuation range of density measured using a transparent support.

FIG. 26 is a diagram showing the density measured using a transparent support.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 He-Ne laser 2 Laser beam 3 Cylinder 4 Beam expander 5 Cylindrical lens 6 Slit 7 Uniaxial mechanical stage 8 Sample holder 8a Transparent support 8b Outer frame 9 Sample 10 Photodiode 11 Laser length measuring device 12 Stage controller 13 Amplifier 14 A / D converter 15 CPU 16 Display device 17 Goniometer stage

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-284771 (JP, A) JP-A-4-335363 (JP, A) JP-A-3-282684 (JP, A) JP-A-4-284 229287 (JP, A) JP-A-1-91040 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 1/00 G06T 1/00

Claims (10)

(57) [Claims] 1. Recorded by scanning a light beam.
In the scanning line of the image sample, where the density of each scanning line may vary.
The density unevenness in the direction perpendicular tomeasurementAn apparatus having a finer width than a pitch of the scanning lines of the image sample.
Density measuring means for measuring the density of the image sample;
Moving means moving to the position; a position measuring means for measuring the concentration measuring position; a concentration measuring position measured by the position measuring means;
And the density measured by the density measuring means at the degree measurement position
Density distribution creating a density distribution of the image sample based on
Means for spatially filtering the density distribution to obtain density unevenness.
Density unevenness distribution creating means for creating a cloth; determining a scanning line pitch from the density distribution;
Scan line pitch to create scan line pitch uneven distribution
Unevenness distribution creating means for obtaining a value corresponding to the intensity of the light beam from the density distribution;
Create light beam intensity distribution from values
Distribution creation means, The density distribution created by the density distribution creating means;
Density unevenness distribution created by the
Scan line pitch unevenness created by the scanning line pitch unevenness distribution creating means
And the light beam intensity unevenness distribution creating means
At least one of the created light beam intensity distributions
Display means capable of displaying Characterized by having
Image density unevennessmeasurementapparatus. 2. The image density unevenness measuring apparatus according to claim 1, wherein the spatial filtering process is a filtering process based on a visual spatial frequency characteristic for a spatial sine wave pattern. 3. The light beam intensity non-uniformity distribution creating unit includes: a light beam intensity distribution creating unit that creates a light beam intensity distribution based on the density distribution and a sensitivity characteristic of the image sample; Beam diameter calculating means for calculating the beam diameter of the light beam based on the first scanning line pitch unevenness distribution creating means for the light beam intensity at the highest point of the peak of the curve of the light beam intensity distribution. A first correction unit that corrects so as to eliminate the influence of the overlapping component of the light beam intensities of adjacent scanning lines that fluctuates according to the scanning line pitch, using the scanning line pitch and the beam diameter; With respect to the light beam intensity corrected by the means, the light beam intensity at the highest point of the adjacent peak corrected by the first correction means and the scanning light intensity determined by the first scanning line pitch unevenness distribution creating means. Using said beam diameter a line pitch,
The second correction is performed so as to remove the influence of the overlapping component of the light beam intensity of the adjacent scanning lines which fluctuates according to the light beam intensity.
3. An image density unevenness according to claim 1 or 2, wherein the light beam intensity unevenness distribution is created from the light beam intensity corrected by the second correction means. Measuring device. 4. The light beam is deflected by a rotating polygon mirror.
Between the surfaces of the rotating polygon mirror from the scanning line pitch uneven distribution.
Second scan for creating scan line pitch unevenness distribution by period
Line pitch unevenness distribution creating means, and the scan created by the second scanning line pitch unevenness distribution creating means
The influence of the line pitch non-uniformity distribution is determined by the first scanning line pitch
From the scan line pitch unevenness distribution created by the
Scanning line pitches other than the period between the surfaces of the rotating polygon mirror.
Creating the third scan line pitch unevenness distribution for creating the unevenness distribution
And means., The display means generates the second scanning line pitch unevenness distribution.
Scanning line pitch unevenness distribution created by the means, and
The scanning line pitches created by the scanning line pitch unevenness distribution creating means 3
Displaying at least one of the spotty distributions
it can Claim 1, Claim 2, or Claim
Item 3. Image density unevenness according to item 3.measurementapparatus. 5. The density unevenness distribution is subjected to a Fourier transform to obtain a density
Density uneven frequency distribution creation means for creating uneven frequency distribution
Created by the first scanning line pitch unevenness distribution creating means.
Fourier transform is applied to the scanning line pitch
1st scan line pitch for creating a frequency distribution
Means for creating a wave number distribution, and performing a Fourier transform on the light beam
Deformation frequency distribution Creates a frequency distribution
Further comprising cloth making means, The display means is provided by the density unevenness frequency distribution creating means.
Density unevenness frequency distribution and first scanning line pitch
Scan line pitch uneven frequency created by the frequency distribution creating means
Number distribution and frequency distribution of light beam intensity unevenness
Of the frequency distribution of the light beam
At least one can be displayed Characterized by
The image density according to claim 1, 2, or 3
Lameasurementapparatus. 6. The density unevenness distribution is subjected to a Fourier transform to obtain a density
Density uneven frequency distribution creation means for creating uneven frequency distribution
Created by the first scanning line pitch unevenness distribution creating means.
Fourier transform is applied to the scanning line pitch
1st scan line pitch for creating a frequency distribution
Wave number distribution creating means, and the third scanning line pitch unevenness distribution creating means.
Fourier transform of the irregular scanning line pitch distribution and a rotating polygon mirror
2nd to create scan line pitch uneven frequency distribution by other than
Scanning line pitch non-uniformity frequency distribution creating means; and
Deformation frequency distribution Creates a frequency distribution
A cloth making means; and, The display means is provided by the density unevenness frequency distribution creating means.
Density unevenness frequency distribution and first scanning line pitch
Scan line pitch uneven frequency created by the frequency distribution creating means
Number distribution, the second scanning line pitch uneven frequency distribution
Scan line pitch unevenness frequency distribution created by the step
Optical beam intensity unevenness
Display at least one of the frequency distributions
To do Can The image according to claim 4, characterized in that:
Uneven image densitymeasurementapparatus. 7. The concentration measuring means includes: a light irradiating means; a light shaping means for shaping light from the light irradiating means into a slit shape; Irradiation position adjusting means for adjusting the irradiation position of the slit-shaped light on the sample so that the length direction is parallel to the sample; and the transmitted light or the slit-shaped light transmitted by the slit-shaped light transmitted through the image sample. And a density calculating means for calculating the density of the image sample based on the light reflected by the image sample. The image density unevenness measuring device according to claim 6. 8. The density measuring unit includes: a light irradiating unit; and a light transmitted from the light irradiating unit and transmitted light transmitted through the image sample or light reflected from the image sample reflected from the image sample. 5. The image processing apparatus according to claim 1, further comprising: a density calculation unit that calculates a density of the image sample based on the image data; and a cylinder that encloses an optical path of light from the light irradiation unit. An image density unevenness measuring apparatus according to claim 5 or claim 6. 9. The image density unevenness measuring apparatus according to claim 7, wherein the density measuring unit has a cylinder enclosing an optical path of the light from the light irradiating unit. 10. The image sample, wherein a density measurement surface of the image sample is covered with a transparent support and is held by scissors. 10. The image density unevenness measuring apparatus according to claim 6, claim 7, claim 8, or claim 9.