KR20120016215A - Optical filter and display evaluation system - Google Patents

Abstract

The display evaluation system for evaluating the liquid crystal panel 10 is composed of the optical adjusting device 20, the photographing camera 30, and the measuring device 35. In addition, an image signal generation device 15 is connected to the liquid crystal panel 10. The imaging camera 30 has a CCD image sensor 31. The optical adjusting device 20 is composed of lenses 221 and 222. In the optical adjusting device 20, the metal plate is processed into a mesh, and the optical filter 21 which has a transmittance gradient is arrange | positioned at a tightening position. In the CCD image sensor 31 provided at the defocus position, the response of the Nyquist frequency or more is suppressed. As a result, the rippled pattern can be suppressed and the image resolved in units of one pixel can be photographed.

Description

Optical filter and display evaluation system {OPTICAL FILTER AND DISPLAY EVALUATION SYSTEM}

The present invention relates to an optical filter and a display evaluation system for use in evaluating the image quality of a display.

In recent years, manufacturing lines of displays, such as a liquid crystal panel, are constructed so that uniform quality may be implement | achieved. However, even in such a manufacturing line, manufacturing nonuniformity arises in an individual display. Therefore, various examinations are made in order to adjust the display which outputs a better image (for example, refer patent document 1). In the technique described in Patent Document 1, the image quality of the adjustment target device is adjusted to approximate the image quality of the target device.

However, when photographing an object having a periodic pattern using a camera using various imaging devices, a moire pattern may occur in the photographed image, but in reality, there is no such ripple pattern on the screen. . The rippled shape is a shape caused by the lattice shape (pixel lattice shape) such as a liquid crystal panel and the lattice of each pixel of the CCD interfere with each other.

Therefore, examination for removing the rippled shape is made (for example, refer patent document 2-4).

For example, Patent Document 2 discloses a technique for removing a ripple component from image data provided for image quality inspection in an image quality inspection apparatus for detecting pixel defects of a flat panel display. In the technique described in this document, a ripple component is extracted from the image data obtained by the imaging device, a period of the ripple component is detected, and a plurality of smooth curves obtained by removing a defective component having a pixel value arranged for each cycle are obtained. Defective image data is obtained by obtaining a difference between pixel values positioned on the plurality of smooth curves and the original image data, and averages of the plurality of smooth curves are obtained to obtain smooth image data that does not include a rippled shape. Then, the smooth image data and the defect image data are added, and the addition result is stored in the image memory as image data for inspection.

In addition, Patent Document 3 discloses a technique for reducing the rippled shape and improving the inspection accuracy in the LCD inspection apparatus. In the technique described in this document, the light passing through the LCD panel is interposed between the camera photographing the LCD panel to be inspected and the monitor connected to the camera and illuminating an image of the LCD panel photographed by the camera. Install an optical lowpass filter that extends to the black mask portion of the.

In addition, Patent Document 4 discloses a technique for obtaining a captured image without a ripple pattern using only an optical member having a simpler structure without requiring a process by software. In the technique described in this document, imaging is performed by inserting a scattering transmitting plate that scatters light at several positions between a camera and an inspection target screen.

Japanese Patent No. 41,9702 (first page, FIG. 1) Japanese Patent Laid-Open No. 1999-352011 (1 page, Fig. 1) Japanese Patent Publication No. 1996-327496 (Page 1, Fig. 1) Japanese Patent Laid-Open No. 1999-6786 (No. 1 page, Fig. 1)

In all of the prior arts, there is a problem that it is difficult to observe or detect a change in size or a defect at the same level as the pattern period existing in the object, with a significant unsharpening of the image.

In the case of performing the spot correction of the liquid crystal panel, when the rippled image is photographed, it becomes a problem that it is not distinguished from the original spot pattern. In addition, in order to photograph the minute unevenness, an image cannot be blurred unnecessarily.

Here, the rippled shape is a distortion in the digital signal processing theory. This distortion was seen as a ripple. The distortion is that frequencies above the Nyquist frequency appear on the low frequency side by sampling.

11 shows a general circular tightening 50 for adjusting the amount of light and transmits light by the aperture area.

FIG. 12 is an example of the shape of a blur (point spread function PSF: Point Spread Function) in a general circular tightening 50, and FIG. 13 shows this shape in two dimensions.

When such circular tightening 50 is used, the frequency characteristic is as shown in FIG. It can be seen that the high frequency component is not sufficiently attenuated.

In addition, a general optical low pass filter is composed of a quartz plate and installed just before the CCD. However, since the crystal lowpass filter uses crystal birefringence (doubling), it is basic to double-tap one point to two slightly separated points. Generally, two sheets of quartz plates are stacked and this effect is used two times in the vertical and horizontal directions, so that one point is divided into four and the image is taken on the CCD. In such lowpass filters, ripples cannot be removed.

This invention is made | formed in order to solve the said subject, The objective is to pay attention to this Nyquist frequency, to suppress a ripple shape, and to photograph the image which is resolving by one pixel unit, and It is to provide a display evaluation system.

MEANS TO SOLVE THE PROBLEM In order to solve the said problem, this invention is an optical filter applied to the solid-state image sensor which has a some light-receiving pixel, Nyquist determined based on the pitch of the light-receiving pixel in the said solid-state image sensor. It is a summary that the transmittance distribution which produces the waveform which suppressed the spatial frequency component in the frequency more than frequency is provided.

According to the present invention, it is possible to sufficiently attenuate the high frequency components. Then, if the size of the PSF is appropriately set and the Nyquist frequency is set to the start point of dropping, an ideal optical low pass through which the frequency component above the Nyquist frequency is sufficiently attenuated and the frequency component below the Nyquist frequency passes well. It becomes possible to manufacture a filter.

In a preferred aspect of the present invention, an opening having an opening width of a normal distribution is provided for at least one transverse axis traversing the optical filter to provide the transmittance distribution.

According to this aspect, the high frequency component can be attenuated by fitting the transverse axis to a periodic pattern shape (for example, a lattice shape such as a liquid crystal panel) of a photographing object.

Moreover, in the said aspect, it is preferable to comprise the said opening part with two normal distribution curves arrange | positioned symmetrically with respect to a transverse axis.

Thereby, since the opening part of a "mountain" shape can be obtained also in the orthogonal axis orthogonal to a transverse axis, generation | occurrence | production of a high frequency component can also be suppressed also in an orthogonal axis direction.

In the preferable aspect of this invention, the said transmittance | permeability distribution is comprised using the density distribution of the opening formed in the plate.

Thereby, the density distribution of the opening of the plate corresponds to the transmittance distribution in the optical filter, in other words, the optical density distribution, and the optical density distribution can be accurately set by the hole processing for the plate.

In another aspect of the present invention, the transmittance distribution is configured using a density distribution of a dot pattern formed on the transparent plate.

As a result, the transmittance can be easily increased while maintaining the strength of the transparent plate.

In a preferable aspect of the present invention, a distribution configured such that the light intensity on the light receiving surface of the solid-state imaging device is a normal distribution is used as the transmittance distribution.

This makes it possible to reliably attenuate frequencies above the Nyquist frequency.

The present invention further provides a solid-state imaging device having a plurality of light-receiving pixels, an optical system member that focuses an image of a display to be evaluated, and a tightening position of the optical system member, and receives light in the solid-state imaging device. The summary is provided with the optical filter provided with the transmittance distribution which produces | generates the waveform which suppressed the spatial frequency component in the frequency more than the Nyquist frequency determined based on the pitch of a pixel.

According to the present invention, it is possible to suppress the occurrence of ripples caused by frequency components above the Nyquist frequency and to accurately evaluate the display.

According to the present invention described above, it is possible to provide an optical filter and a display evaluation system for suppressing a moire pattern and capturing an image that is resolved in units of one pixel.

BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing of the display evaluation system of one Embodiment of this invention.
2 is a light diagram in a display evaluation system.
3 is an explanatory view of the light intensity distribution in the case of using the filter of the present invention.
4 is an explanatory diagram of light intensity distribution (two-dimensional) when the filter of the present invention is used.
5 is an explanatory diagram of frequency characteristics of light intensity distribution in the case of using the filter of the present invention.
6 is an explanatory diagram of the relationship between the defocus quantity and the frequency characteristic of the light intensity distribution, in which (a) represents twice the defocus quantity, (b) represents the reference, and (c) represents half the reference. Frequency characteristics when changed to
7 is an explanatory diagram of a filter in one embodiment of the present invention.
8 is an explanatory diagram of a filter of a second embodiment of the present invention, (a) is a pixel to be photographed, and (b) is an explanatory diagram of a filter structure.
9 is an explanatory diagram of a filter of another embodiment of the present invention, wherein (a) is an opening using one normal distribution curve, and (b) is an opening using a normal distribution curve on the curve.
It is explanatory drawing of the filter of other embodiment of this invention.
11 is an explanatory diagram of a conventional tightening.
12 is an explanatory diagram of light intensity distribution in the case of using a conventional tightening.
13 is an explanatory diagram of light intensity distribution (two-dimensional) in the case of using a conventional tightening.
14 is an explanatory view of the frequency characteristics of the light intensity distribution in the case of using a conventional tightening.

    (1st embodiment)

EMBODIMENT OF THE INVENTION Hereinafter, the optical filter and display evaluation system of this invention are demonstrated. In this embodiment, the case where the image quality of the display panel of adjustment object is evaluated using a CCD image sensor is assumed. Here, as shown in FIG. 1, the liquid crystal panel 10 is used as a display panel of adjustment object. The liquid crystal panel 10 forms an image by pixel elements arranged at a predetermined period (first pitch).

And the display evaluation system for evaluating this liquid crystal panel 10 is comprised with the optical adjusting device 20, the imaging camera 30, and the measuring device 35. As shown in FIG. In addition, an image signal generation device 15 is connected to the liquid crystal panel 10.

Here, the imaging camera 30 as an imaging means (imaging apparatus) photographs the image acquired via the optical adjustment apparatus 20, and supplies the output image data to the measuring apparatus 35. As shown in FIG. In this embodiment, the imaging camera 30 uses the monochrome camera provided with the CCD image sensor 31 as a solid-state image sensor. The CCD image sensor 31 picks up an image by the pixel sensor arrange | positioned by predetermined period (2nd pitch different from a 1st pitch).

The measuring device 35 evaluates the image quality of the image acquired from the CCD image sensor 31.

The image signal generation device 15 supplies a test pattern signal for image quality evaluation to the liquid crystal panel 10. A test pattern image is output on the liquid crystal panel 10 in accordance with this test pattern signal.

The optical adjusting device 20 is a device for adjusting the focus of an image displayed on the liquid crystal panel 10. The optical adjustment apparatus 20 is comprised with the optical filter 21 and the lenses 221 and 222 as an optical system member which focuses an image. In order to make a PSF shape into a smooth "mountain" shape as mentioned later, it is necessary to make the transmittance | permeability of the peripheral part of the optical filter 21 put in a fastening part nearly "0". Since a filter having a low transmittance is inserted in this manner, the lenses 221 and 222 are designed using a lens having a sufficiently bright F value, and are designed so that the effective F value after inserting the filter becomes a target value.

    (Optical filter)

In this embodiment, the PSF on the light receiving surface of the CCD image sensor 31 provided at the defocus position is set to the desired shape. Specifically, the optical filter 21 has a transmittance distribution that generates a waveform in which a spatial frequency component is suppressed at a frequency equal to or greater than the Nyquist frequency determined based on the pitch of the pixel in the CCD image sensor 31. do. For this reason, in the optical adjustment apparatus 20, the optical filter 21 which has an optical density gradient as a lowpass filter is inserted in the tightening position of the lens 221,222.

As shown in FIG. 7, the optical filter 21 used by this embodiment is formed by processing a metal plate (plate) in mesh shape, and, thereby, makes the optical filter 21 have the objective optical density gradient. Specifically, the opening 211 is provided in the optical filter 21. The density distribution of this opening 211 is changed by the positions 21a, 21b, 21c from the center of the optical filter 21. FIG. That is, the opening 211 is provided in the optical filter 21 so that the distribution density of the opening 211 may change (reduce) concentrically from the center of the optical filter 21 toward the radially outer side.

In this way, it becomes possible to set the optical density distribution precisely with the processing precision of a metal plate. The shielding ratio of this mesh corresponds to the optical density distribution.

Since the mesh itself consisting of the openings 211 becomes a very delicate shape in the image plane, it is not resolved and a gradation according to the density distribution of the openings 211 can be obtained.

    (Determination of the defocus amount)

Next, determination of the defocus amount will be described.

Light emitted from the pixels of the liquid crystal panel 10 reaches the CCD image sensor 31 in accordance with the optical path shown in FIG. 2. Here, the distance from the focus position of the optical adjusting device 20 to the CCD image sensor 31 is set as the defocus amount df. In this case, the shape of the tightening is projected onto the CCD image sensor 31 in a size proportional to the defocus amount df. Therefore, by adjusting the defocus amount df, a free size defocus image (blur) can be produced. Also, the form of blurring does not depend on the defocus amount df.

3 shows the blurring shape for the purpose of the present embodiment, that is, the light intensity distribution when a filter is used. The height direction indicates the intensity of light, and the XY axis indicates a position on the CCD image sensor 31 surface.

4 shows this light intensity distribution in two dimensions. The horizontal scale is normalized so that the length of the pitch of the CCD image sensor 31 becomes exactly "1". The vertical scale is normalized to maximum light intensity.

5 shows the frequency characteristics of this shape. The unit of the horizontal axis is normalized so that the Nyquist frequency determined by the pitch of the CCD image sensor 31 in frequency is "1". The unit of the vertical axis is expressed in dB in response, and becomes -1/100 in the case of -40dB.

The defocus amount df of this embodiment is adjusted so that the magnitude of blur will be FIG. The form of clouding is determined by the optical filter 21 placed in the tightening position, and does not change even if the amount of defocus is changed.

6 shows frequency characteristics in which the defocus amount is changed with reference to FIG. Here, Fig. 6 (a) is twice the defocus amount, (b) is the same as the reference, and (c) is the frequency characteristic when it is changed to half of the reference. Increasing the defocus amount increases blurring, and instead of attenuating from low frequencies, it is possible to reliably attenuate frequencies above the Nyquist frequency. If the defocus amount is made small, the blur becomes small, and instead of suppressing attenuation at low frequencies, the defocus amount increases without attenuating frequencies above the Nyquist frequency. By changing the defocus amount in this way, a trade-off between the attenuation amount of the high frequency frequency and the passage amount of the low frequency component is taken.

Here, with respect to the point light source on the liquid crystal panel 10, intensity | strength "V (r)" of the light in a defocus position is set so that it may become normal distribution, and is represented by the following calculation formula.

V (r) = exp (-2 * r ² )

Here, "r" is the distance from the origin (0, 0), and length equal to the pitch interval of the CCD image sensor 31 is set to "1" (unit). The transmittance distribution of the optical filter 21 of the present embodiment is also approximated to a normal distribution, and is corrected so that the light intensity becomes a normal distribution at the defocus position. The transmittance distribution is preferably closer to the normal distribution, but the occurrence of ripples can be reduced even when there is a deviation from the normal distribution.

In the above calculation formula, even if " r " is not increased to " 0 ", the existence range of light is strictly infinite. Since this is impossible to manufacture, it will be stopped in a suitable range. The optimum shape when this interruption is taken into account is different from the common sense, but consequently becomes a form similar to the above calculation formula.

According to this embodiment, the following effects can be acquired.

  -In this embodiment, the optical filter 21 which has a transmittance gradient (optical density gradient) in a tightening position is provided. This filter cuts off abnormal Nyquist frequency components in the image. Here, the frequency characteristic (FIG. 5) of this embodiment is compared with the frequency characteristic (FIG. 14) of normal fastening. In FIG. 14 and FIG. 5, the magnitude of the blur is adjusted so that the response at the Nyquist frequency is the same. Comparing the frequency characteristics of the two figures shows that the high frequency is attenuated well in the target shape, but the high frequency does not attenuate in the general shape blur.

The cause of the ripples is the lattice of the display, which concentrates on high frequencies. If the high frequency can be attenuated effectively, the occurrence of ripples can be suppressed. Therefore, the rippled shape can be suppressed and the display can be evaluated accurately.

  -In this embodiment, in order to realize the objective optical density gradient in the optical filter 21, a metal plate is processed to mesh. It is difficult to control this optical density gradient even if the optical density distribution is changed precisely using a general photosensitive filter (ND filter). In this embodiment, the shielding ratio of the mesh of a metal plate corresponds to optical density distribution, and an optical density distribution can be set precisely with metal processing precision.

    (2nd embodiment)

In the first embodiment, the transmittance distribution is provided in the optical filter 21 by providing the opening 211 in the optical filter 21 so that the distribution density thereof changes concentrically. In 2nd Embodiment, the optical filter using the opening part which has an aperture width of a normal distribution is demonstrated.

Here, the optical filter 21 shown to FIG. 8 (b) is used with respect to the pixel 11 of the liquid crystal panel 10 shown to FIG. 8 (a). This optical filter 21 has an opening 213. This opening part 213 is comprised by the edge of the shape which joined two normal distribution curves arrange | positioned symmetrically with respect to the transverse axis 214. As shown in FIG. In this embodiment, this transverse axis | shaft 214 is arrange | positioned so that the center of an optical axis (optical filter 21) may pass.

When using this optical filter 21, the transverse axis | shaft 214 is matched to the arrangement | positioning direction (horizontal direction with respect to FIG. 8 (a)) of the pixel 11 of each RGB color.

According to this embodiment, the following effects can be acquired.

  In the present embodiment, the opening 213 has a shape in which two normal distribution curves are symmetrically arranged with respect to the transverse axis 214. In the liquid crystal panel 10, since the relative luminance of the pixels 11 of the respective RGB colors is different, the luminance pattern (periodic pattern shape) of vertical stripes is generated. By providing an opening made of a normal distribution curve in accordance with the generation direction of the periodic pattern shape (here, the horizontal direction), it is possible to suppress the rippled shape and to accurately evaluate the display.

  -In this embodiment, the opening width of a "mountain" shape also exists in the orthogonal axis (vertical direction in FIG. 8) orthogonal to a transverse axis | shaft by providing the opening part 213 of the shape which symmetrically joined the normal distribution curve of the same shape. Distribution can be obtained. Thereby, generation | occurrence | production of the high frequency component in a perpendicular axis can be suppressed.

  In this embodiment, the transverse axis 214 of the opening 213 is configured to pass through the center of the optical axis (optical filter 21). Thereby, generation | occurrence | production of aberration of a lens can be suppressed.

In addition, you may change the said embodiment as follows.

  In the said embodiment, although it applied to the suppression of the rippled shape of the liquid crystal panel 10, the display panel of adjustment object is not limited to this. It is also possible to apply to an output device of an image constituted by periodic pixels such as a plasma display (PDP), an organic EL display, a projection projector, or the like.

  In the above embodiment, the image was taken using the CCD image sensor 31 having the pixel sensors arranged at predetermined cycles, but the imaging device is not limited to this. It can be applied to an image pickup device (for example, a CMOS image pickup device) having a pixel sensor arranged at a period where a ripple pattern occurs due to a cycle of pixel arrangement of a display.

  In the said embodiment, the metal plate was processed and the optical filter 21 was produced. Instead, the optical filter 21 can be produced by printing a mesh on a transparent plate (for example, a glass plate). Dot patterns with different distribution densities of dots are formed on the glass plate. The dots are arranged, for example, so that their distribution density changes concentrically (increase) from the center of the optical filter 21 toward the radially outer side. In the case of processing a metal plate, when the number of openings increases, the strength of a metal plate may fall, but in the case of a glass plate, a transmittance | permeability can be made easy easily.

However, in the case of using a glass plate, a lens design including the glass plate is required. Moreover, in order to suppress unnecessary reflection on the glass surface, it is necessary to apply low reflection coating like a lens.

For the lens used at this time, it is preferable that the relationship between the passage position of the light beam at the tightening position and the arrival position to the image plane at the time of defocusing does not change throughout the imaging area. Therefore, it uses a lens of almost aberration throughout the imaging area.

  In the said 2nd Embodiment, the edge of the opening part 213 was comprised by the curve which joined the normal distribution curve symmetrically about the transverse axis 214. As shown in FIG. The shape of this edge is not limited to this, The opening width of the opening part 213 should just be normal distribution with respect to a transverse axis. For example, as shown in Fig. 9 (a), it is also possible to use an opening portion whose edge is a straight line and a normal distribution curve. In addition, as shown in Fig. 9B, the openings can be formed by setting the opening widths of the normal distribution on the curve.

In the opening 213, the distribution of the opening width on the transverse axis 214 may be close to the normal distribution. In this case, the occurrence of ripples can be reduced even when the opening width is partially distributed in the normal distribution or the distribution close to the normal distribution.

  In the said 2nd Embodiment, although the transverse axis 214 of the opening part 213 was comprised so that the center of the optical axis (optical filter 21) may be passed, this position is not limited to the center. For example, as shown in FIG. 10, even when the transverse axis 214 is shift | deviated from the center of the optical filter 21, generation | occurrence | production of a ripple can be reduced.

10 Liquid Crystal Panel 15 Image Signal Generator
20 Optical regulator 21 Optical filter
211 opening 213 opening
214 transverse axis
221, 222 lens
30 shooting camera
31 CCD image sensor 35 Measuring device

Claims (7)

An optical filter applied to a solid-state imaging device having a plurality of light receiving pixels,
The transmittance distribution which produces | generates the waveform which suppressed the spatial frequency component in the frequency more than the Nyquist frequency determined based on the pitch of the light receiving pixel in the said solid-state image sensor, The optical filter characterized by the above-mentioned. The method of claim 1,
And an opening having an opening width of a normal distribution with respect to at least one transverse axis traversing the optical filter for providing the transmittance distribution. The method of claim 2,
The said opening part was comprised by the two normal distribution curve arrange | positioned symmetrically with respect to a transverse axis | shaft. The optical filter characterized by the above-mentioned. The method of claim 1,
The transmittance distribution is configured by using the density distribution of the pores formed in the plate. The method of claim 1,
The transmittance distribution is configured by using the density distribution of the dot pattern formed on the transparent plate. The method according to claim 4 or 5,
As the transmittance distribution, a distribution configured such that the light intensity on the light receiving surface of the solid-state imaging element becomes a normal distribution is used. A solid-state imaging device having a plurality of light receiving pixels,
An optical system member that focuses an image of a display to be evaluated,
It is provided at the tightening position of the said optical system member, and the transmittance distribution which produces the wave form which suppressed the spatial frequency component in the frequency above the Nyquist frequency determined based on the pitch of the light receiving pixel in the said solid-state image sensor is provided. Display evaluation system characterized by including an optical filter.

Images