WO2010123063A1 - 光学フィルタ及びディスプレイ評価システム - Google Patents
光学フィルタ及びディスプレイ評価システム Download PDFInfo
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- WO2010123063A1 WO2010123063A1 PCT/JP2010/057142 JP2010057142W WO2010123063A1 WO 2010123063 A1 WO2010123063 A1 WO 2010123063A1 JP 2010057142 W JP2010057142 W JP 2010057142W WO 2010123063 A1 WO2010123063 A1 WO 2010123063A1
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- 230000003287 optical effect Effects 0.000 title claims abstract description 83
- 238000011156 evaluation Methods 0.000 title claims abstract description 10
- 238000002834 transmittance Methods 0.000 claims abstract description 23
- 238000009826 distribution Methods 0.000 claims description 72
- 238000003384 imaging method Methods 0.000 claims description 19
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/42—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect
- G02B27/46—Systems using spatial filters
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
- G03B11/00—Filters or other obturators specially adapted for photographic purposes
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N17/00—Diagnosis, testing or measuring for television systems or their details
- H04N17/002—Diagnosis, testing or measuring for television systems or their details for television cameras
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/60—Noise processing, e.g. detecting, correcting, reducing or removing noise
- H04N25/67—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to fixed-pattern noise, e.g. non-uniformity of response
- H04N25/671—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to fixed-pattern noise, e.g. non-uniformity of response for non-uniformity detection or correction
- H04N25/673—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to fixed-pattern noise, e.g. non-uniformity of response for non-uniformity detection or correction by using reference sources
- H04N25/674—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to fixed-pattern noise, e.g. non-uniformity of response for non-uniformity detection or correction by using reference sources based on the scene itself, e.g. defocusing
Definitions
- the present invention relates to an optical filter and a display evaluation system used for evaluating the image quality of a display.
- the moire pattern is a pattern generated by interference of a lattice-like pattern (pixel lattice pattern) like a liquid crystal panel and a lattice of each pixel of the CCD.
- Patent Document 2 discloses a technique for removing moire components from image data used for image quality inspection in an image quality inspection apparatus that detects pixel defects in a flat panel display.
- a plurality of moire components are extracted from image data obtained by an imaging device, a period of the moire components is detected, and pixel values arranged for each period are connected to remove defective components.
- Find a smooth curve The difference between the pixel values located on the plurality of smooth curves and the original image data is obtained to obtain defect image data, and the average of the plurality of smooth curves is obtained to obtain smooth image data not including a moire pattern. .
- the smoothed image data and the defect image data are added, and the addition result is stored in the image memory as inspection image data.
- Patent Document 3 discloses a technique for reducing moire patterns and improving inspection accuracy in an LCD inspection apparatus.
- the LCD panel is passed between a camera that captures the LCD panel that is the object to be inspected and a monitor that is connected to the camera and displays an image of the LCD panel captured by the camera.
- An optical low-pass filter is provided to spread the emitted light to the black mask portion of the LCD panel.
- Patent Document 4 discloses a technique for obtaining a captured image without a moire pattern using only an optical member having a simpler structure without requiring processing by software.
- imaging is performed by inserting a scattering transmission plate that scatters light at any position between the camera and the inspection target screen.
- Japanese Patent No. 4109702 Japanese Patent Laid-Open No. 11-352011 (first page, FIG. 1) JP-A-8-327496 (1st page, FIG. 1) Japanese Patent Laid-Open No. 11-6786 (first page, FIG. 1)
- moire patterns are aliasing distortions in digital signal processing theory. It is a moire pattern that this folding distortion appears as a pattern.
- the aliasing distortion is a frequency in which a frequency equal to or higher than the Nyquist frequency appears on the low frequency side by sampling.
- FIG. 11 shows a general circular diaphragm 50 for adjusting the amount of light, and transmits light through the aperture region.
- FIG. 12 is an example of a blur shape (point spread function PSF: Point Spread Function) in a general circular stop 50, and
- FIG. 13 is a two-dimensional representation of this shape.
- a general optical low-pass filter is formed of a quartz plate and is installed immediately before the CCD.
- the quartz low-pass filter uses the double refraction (doubling) of quartz, it is fundamental to duplicate one point to two points slightly separated.
- two quartz plates are overlapped and this effect is used twice vertically and horizontally, so that one point is divided into four quadrant points and is copied onto the CCD. With such a low-pass filter, the moire pattern cannot be removed.
- the present invention has been made to solve the above-mentioned problems, and its purpose is to focus on this Nyquist frequency, to suppress a moire pattern, and to capture an image resolved in units of one pixel. It is to provide an optical filter and a display evaluation system.
- the present invention is an optical filter applied to a solid-state imaging device including a plurality of light-receiving pixels, and has a frequency equal to or higher than a Nyquist frequency determined based on the pitch of the light-receiving pixels in the solid-state imaging device.
- the gist of the present invention is to provide a transmittance distribution that generates a waveform with suppressed spatial frequency components.
- the present invention it is possible to sufficiently attenuate high frequency components. If the size of the PSF is set appropriately and the Nyquist frequency starts to drop, the ideal optical low-pass that sufficiently attenuates the frequency component above the Nyquist frequency and passes the frequency component below the Nyquist frequency well. A filter can be created.
- an opening having a normally distributed opening width is provided with respect to at least one transverse axis that traverses the optical filter.
- the high-frequency component can be attenuated by matching the transverse axis to a periodic pattern pattern to be imaged (for example, a lattice pattern such as a liquid crystal panel).
- the opening is constituted by two normal distribution curves arranged symmetrically with respect to the transverse axis.
- the transmittance distribution is configured using a density distribution of apertures formed in the plate.
- the density distribution of the apertures in 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 hole processing on the plate.
- the transmittance distribution is configured using a density distribution of dot patterns formed on a transparent plate. Thereby, the transmittance can be easily increased while maintaining the strength of the transparent plate.
- a distribution configured such that the light intensity on the light receiving surface of the solid-state imaging device has a normal distribution is used as the transmittance distribution.
- the present invention also provides a solid-state imaging device having a plurality of light-receiving pixels, an optical system member that focuses an image on a display to be evaluated, and a diaphragm position of the optical system member.
- the gist is provided with an optical filter provided with a transmittance distribution that generates a waveform in which a spatial frequency component at a frequency equal to or higher than the Nyquist frequency determined based on the pitch is suppressed.
- the present invention it is possible to accurately evaluate a display by suppressing the occurrence of a moire pattern due to a frequency component equal to or higher than the Nyquist frequency. According to the above-described present invention, it is possible to provide an optical filter and a display evaluation system for capturing an image that suppresses moire patterns and is resolved in units of pixels.
- Explanatory drawing of the display evaluation system of one Embodiment of this invention The light ray figure in a display evaluation system.
- Explanatory drawing of the light intensity distribution at the time of using the filter of this invention Explanatory drawing of light intensity distribution (two-dimensional) at the time of using the filter of this invention.
- Explanatory drawing of the frequency characteristic of the light intensity distribution at the time of using the filter of this invention It is explanatory drawing of the relationship between the defocus amount and the frequency characteristic of light intensity distribution, (a) is 2 times defocus amount, (b) is a reference
- the optical filter and display evaluation system of the present invention will be described below.
- the image quality of the display panel to be adjusted is evaluated using a CCD image sensor.
- a liquid crystal panel 10 is used as a display panel to be adjusted.
- the liquid crystal panel 10 forms an image with pixel elements arranged at a predetermined cycle (first pitch).
- the display evaluation system for evaluating the liquid crystal panel 10 includes an optical adjustment device 20, a photographing camera 30, and a measurement device 35. In addition, an image signal generation device 15 is connected to the liquid crystal panel 10.
- the imaging camera 30 as an imaging means (imaging device) captures an image acquired via the optical adjustment device 20 and supplies output image data to the measurement device 35.
- a monochrome camera provided with a CCD image sensor 31 as a solid-state image sensor is used as the photographing camera 30.
- the CCD image sensor 31 captures an image with a pixel sensor arranged at a predetermined cycle (a second pitch different from the first 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 response to the test pattern signal.
- the optical adjustment device 20 is a device that adjusts the focus of the image displayed on the liquid crystal panel 10.
- the optical adjusting device 20 includes an optical filter 21 and lenses (221, 222) as optical system members for focusing an image.
- the transmittance of the peripheral portion of the optical filter 21 to be inserted into the aperture portion needs to be substantially “0”.
- the lens (221, 222) is designed using a lens having a sufficiently bright F value, and the effective F value after the filter is inserted becomes a target value. To design.
- the PSF on the light receiving surface of the CCD image sensor 31 installed at the defocus position is set to a target shape.
- the optical filter 21 is provided with a transmittance distribution that generates a waveform that suppresses a spatial frequency component at a frequency equal to or higher than the Nyquist frequency determined based on the pixel pitch in the CCD image sensor 31. For this reason, in the optical adjustment device 20, an optical filter 21 having an optical density gradient is inserted as a low-pass filter at the aperture position of the lens (221, 222).
- the optical filter 21 used in the present embodiment is formed by processing a metal plate (plate) into a mesh shape, thereby giving the optical filter 21 a target optical density gradient. Specifically, an opening 211 is provided in the optical filter 21. The density distribution of the apertures 211 is changed depending on the position (21a, 21b, 21c) from the center of the optical filter 21. That is, the apertures 211 are provided in the optical filter 21 so that the distribution density of the apertures 211 changes (decreases) concentrically from the center of the optical filter 21 toward the radially outer side.
- This mesh shielding rate corresponds to the optical density distribution. Since the mesh pattern itself composed of the apertures 211 is a very fine pattern on the image plane, a gradation corresponding to the density distribution of the apertures 211 can be obtained without being resolved.
- the light emitted from the pixels of the liquid crystal panel 10 reaches the CCD image sensor 31 according to the optical path shown in FIG.
- the distance from the focal position of the optical adjustment device 20 to the CCD image sensor 31 is defined as a defocus amount (df).
- the aperture shape is projected onto the CCD image sensor 31 with a size proportional to the defocus amount (df). Accordingly, by adjusting the defocus amount (df), it is possible to create a defocused image (blurred) having any size. Note that the shape of the blur does not depend on the defocus amount (df).
- FIG. 3 shows the target blur shape of the present embodiment, that is, the light intensity distribution when a filter is used.
- the height direction indicates the light intensity
- the XY axis indicates the position on the surface of the CCD image sensor 31.
- FIG. 4 is a two-dimensional representation of this light intensity distribution.
- the scale of the horizontal axis is normalized so that the pitch length of the CCD image sensor 31 is just “1”.
- the vertical scale is normalized with the maximum light intensity.
- FIG. 5 shows the frequency characteristics of this shape.
- the unit of the horizontal axis is a frequency, and the Nyquist frequency determined by the pitch of the CCD image sensor 31 is normalized so as to be “1”.
- the unit of the vertical axis is displayed in dB as a response, and becomes “1/100” in the case of ⁇ 40 dB.
- the defocus amount (df) of the present embodiment is adjusted so that the size of the blur is as shown in FIG.
- the shape of the blur is determined by the optical filter 21 placed at the aperture position, and does not change even if the defocus amount is changed.
- FIG. 6 shows frequency characteristics in which the defocus amount is changed with reference to FIG.
- FIG. 6A shows frequency characteristics when the defocus amount is changed to twice the reference
- FIG. 6B is the same as the reference
- FIG. 6A shows frequency characteristics when the defocus amount is changed to twice the reference
- FIG. 6B is the same as the reference
- FIG. 6A shows frequency characteristics when the defocus amount is changed to twice the reference
- FIG. 6B is the same as the reference
- FIG. 6 When the defocus amount is increased, blurring increases, and instead of being attenuated from a low frequency, it is possible to surely attenuate frequencies above the Nyquist frequency. If the defocus amount is reduced, blurring is reduced, and instead of suppressing attenuation at a low frequency, a frequency higher than the Nyquist frequency cannot be attenuated and increases.
- a trade-off between the attenuation amount of the high frequency and the passing amount of the low frequency component can be taken.
- the light intensity “V (r)” at the defocus position is set to have a normal distribution, and is expressed by the following calculation formula.
- V (r) exp (-2 * r 2 )
- “r” is a distance from the origin (0, 0)
- a length equal to the pitch interval of the CCD image sensor 31 is “1” (unit).
- the transmittance distribution of the optical filter 21 of this 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 close to the normal distribution, but the occurrence of moire can be reduced even when there is a substantial deviation from the normal distribution.
- the optical filter 21 having a transmittance gradient (optical density gradient) is provided at the stop position.
- This filter blocks Nyquist frequency components and higher in the image.
- the frequency characteristic of the present embodiment (FIG. 5) is compared with the frequency characteristic of a normal diaphragm (FIG. 14).
- the magnitude of the blur is adjusted so that the responses at the Nyquist frequency are the same. Comparing the frequency characteristics in both figures, it can be seen that the high frequency is well attenuated in the target shape, but the high frequency is not attenuated in the general shape blur.
- the cause of the moire pattern is the lattice pattern of the display, which is concentrated at high frequencies. If this high frequency can be effectively attenuated, the generation of moire patterns can be suppressed. Accordingly, it is possible to accurately evaluate the display while suppressing the moire pattern.
- the metal plate is processed into a mesh shape in order to achieve the target optical density gradient in the optical filter 21. Even if the optical density distribution is precisely changed using a general neutral density filter (ND filter), it is difficult to control the optical density gradient.
- the shielding ratio of the mesh of the metal plate corresponds to the optical density distribution, and the optical density distribution can be accurately set with metal processing accuracy.
- the transmittance distribution is provided in the optical filter 21 by providing the apertures 211 in the optical filter 21 so that the distribution density thereof changes concentrically.
- an optical filter using an opening having a normally distributed opening width will be described.
- the optical filter 21 shown in FIG. 8B is used for the pixel 11 of the liquid crystal panel 10 shown in FIG.
- the optical filter 21 has an opening 213.
- the opening 213 is configured by an edge having a shape obtained by joining two normal distribution curves arranged symmetrically with respect to the transverse axis 214.
- the transverse axis 214 is disposed so as to pass through the center of the optical axis (optical filter 21).
- the transverse axis 214 is aligned with the direction in which the pixels 11 of RGB colors are arranged (the horizontal direction in FIG. 8A). According to this embodiment, the following effects can be obtained.
- the opening 213 has a shape in which two normal distribution curves arranged symmetrically with respect to the transverse axis 214 are joined.
- a vertical stripe luminance pattern (periodic pattern pattern) is generated.
- an opening 213 having a shape in which normal distribution curves having the same shape are joined symmetrically an opening having a “mountain” shape can be formed on an orthogonal axis (vertical direction in FIG. 8) perpendicular to the transverse axis. A width distribution can be obtained. Thereby, generation
- the transverse axis 214 of the opening 213 is configured to pass through the center of the optical axis (optical filter 21).
- production of the aberration of a lens can be suppressed.
- the present invention is applied to the suppression of the moire pattern of the liquid crystal panel 10, but the display panel to be adjusted is not limited to this.
- the present invention can also be applied to an image output device composed of periodic pixels such as a plasma display (PDP), an organic EL display, a projection projector, and the like.
- PDP plasma display
- organic EL display organic EL display
- projection projector and the like.
- an image is taken using the CCD image sensor 31 including pixel sensors arranged at a predetermined cycle, but the imaging device is not limited to this.
- the present invention can be applied to an image pickup device (for example, a CMOS image pickup device) including pixel sensors arranged at a cycle such that a moire pattern is generated due to the pixel arrangement cycle of the display.
- the optical filter 21 was created by processing a metal plate.
- the optical filter 21 can be created by printing a mesh pattern on a transparent plate (for example, a glass plate).
- a transparent plate for example, a glass plate.
- dot patterns having different dot distribution densities are formed.
- the dots are arranged such that the distribution density changes (increases) concentrically from the center of the optical filter 21 toward the radially outer side.
- the strength of the metal plate may decrease as the number of holes increases, but in the case of a glass plate, the transmittance can be easily increased.
- the lens used at this time it is desirable that the relationship between the light beam passage position at the aperture position and the arrival position on the image plane at the time of defocusing does not change over the entire imaging area. Therefore, this uses a lens with almost no aberration over the entire imaging area.
- the edge of the opening 213 is configured by a curve obtained by joining a normal distribution curve symmetrically with respect to the transverse axis 214.
- the shape of the edge is not limited to this, and it is sufficient that the opening width of the opening 213 has a normal distribution with respect to the transverse axis.
- an opening having a straight line and a normal distribution curve as edges can be used.
- an opening can be formed by setting an opening width of a normal distribution on a curve.
- the opening 213 it is only necessary that the distribution of the opening width on the transverse axis 214 is close to the normal distribution. In this case, it is possible to reduce the occurrence of moire even when the opening width is partially a normal distribution or a distribution close to the normal distribution.
- the transverse axis 214 of the opening 213 is configured to pass through the center of the optical axis (optical filter 21), but this position is not limited to the center.
- the transverse axis 214 is deviated from the center of the optical filter 21, the occurrence of moire can be reduced.
- DESCRIPTION OF SYMBOLS 10 Liquid crystal panel, 15 ... Image signal generator, 20 ... Optical adjustment apparatus, 21 ... Optical filter, 211 ... Opening, 213 ... Opening, 214 ... Transverse axis, 221, 222 ... Lens, 30 ... Shooting camera, 31 ... CCD image sensor, 35 ... Measuring device.
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Abstract
Description
例えば、特許文献2には、フラットパネル表示器の画素欠陥を検出する画質検査装置において、画質検査に供する画像データからモアレ成分を除去するための技術が開示されている。この文献に記載された技術では、撮像装置で得られる画像データからモアレ成分を抽出し、このモアレ成分の周期を検出して周期毎に配置される画素値を結んで欠陥成分を除去した複数の平滑曲線を求める。この複数の平滑曲線上に位置する画素値と、元の画像データとの差を求めて欠陥画像データを取得し、複数の平滑曲線の平均を求めてモアレ模様を含まない平滑画像データを取得する。そして、この平滑画像データと欠陥画像データとを加算し、この加算結果を検査用画像データとして画像メモリに格納する。
図12は、一般的な円形絞り50でのボケの形状(点像強度分布関数PSF:Point Spread Function)の例であり、図13はこの形状を2次元で表示したものである。
また、一般的な光学ローパスフィルタは、水晶板で構成されCCD直前に設置される。しかしながら、水晶ローパスフィルタは水晶の複屈折(ダブリング)を利用しているため、1つの点を僅かに分離した2つの点に2重に写すことが基本である。一般には水晶板を2枚重ねて、この効果を縦横2回使用することにより、1つの点を4つに分離した4重の点としてCCD上に写す。このようなローパスフィルタでは、モアレ模様を除去することはできない。
上記態様によれば、前記横断軸を、撮影対象の周期的パターン模様(例えば、液晶パネルのような格子状模様)に合わせることにより、高周波成分を減衰させることができる。
これにより、横断軸に対して直交する直交軸においても、「山」形状の開口部を得ることができるので、直交軸方向においても、高周波数成分の発生を抑制することができる。
これにより、プレートの開孔の密度分布が光学フィルタにおける透過率分布、言い換えれば光学濃度分布に対応し、プレートに対する孔加工で精密に光学濃度分布を設定することができる。
これにより、透明板の強度を維持しながら、透過率を容易に高くすることができる。
これにより、ナイキスト周波数以上の周波数を確実に減衰させることができる。
上記した本発明によれば、モアレ模様を抑制し、かつ1ピクセル単位で解像している画像を撮影するための光学フィルタ及びディスプレイ評価システムを提供することができる。
以下、本発明の光学フィルタ及びディスプレイ評価システムについて説明する。本実施形態では、CCDイメージセンサを用いて、調整対象の表示パネルの画質を評価する場合を想定する。ここでは、図1に示すように、調整対象の表示パネルとして、液晶パネル10を用いる。この液晶パネル10は、所定の周期(第1ピッチ)で配置された画素素子により画像を形成する。
画像信号生成装置15は、液晶パネル10に、画質評価のためのテストパターン信号を供給する。このテストパターン信号に応じて、液晶パネル10上にテストパターン画像が出力される。
本実施形態では、デフォーカス位置に設置されたCCDイメージセンサ31の受光面でのPSFを目的の形状に設定する。具体的には、CCDイメージセンサ31における画素のピッチに基づいて決まるナイキスト周波数以上の周波数における空間周波数成分を抑制した波形を生成する透過率分布を、光学フィルタ21に設ける。このため、光学調整装置20においては、レンズ(221,222)の絞り位置に、ローパスフィルタとして光学濃度勾配を持つ光学フィルタ21を挿入する。
開孔211からなる網目模様自体は、像面では極めて細かな模様となるために、解像されずに開孔211の密度分布に応じたグラデーションを得ることができる。
次に、デフォーカス量の決定について説明する。
液晶パネル10の画素から発せられた光は、図2に示す光路に従ってCCDイメージセンサ31に達する。ここで、光学調整装置20の焦点位置からCCDイメージセンサ31までの距離をデフォーカス量(df)とする。この場合、絞りの形状がデフォーカス量(df)に比例した大きさでCCDイメージセンサ31上に投影される。従って、デフォーカス量(df)を調整することにより、自由な大きさのデフォーカス画像(ボケ)を作ることができる。なお、ボケの形はデフォーカス量(df)に依存しない。
図4は、この光強度分布を2次元で表示したものである。横軸目盛はCCDイメージセンサ31のピッチの長さがちょうど「1」になるように正規化している。縦軸目盛は、最大光強度で正規化されている。
V(r)=exp(-2*r2)
ここで、「r」は原点(0,0)からの距離であり、CCDイメージセンサ31のピッチ間隔と等しい長さを「1」(単位)としている。本実施形態の光学フィルタ21の透過率分布も正規分布に近似しており、デフォーカス位置において光強度が正規分布になるように補正されている。なお、透過率分布は正規分布に近い方が望ましいが、実質的に正規分布からのズレがある場合にも、モアレの発生を低減することができる。
・本実施形態では、絞り位置において、透過率勾配(光学濃度勾配)を有する光学フィルタ21を設ける。このフィルタにより、画像においてナイキスト周波数成分以上を遮断する。ここで、本実施形態の周波数特性(図5)と通常の絞りの周波数特性(図14)とを比較する。図14と図5とにおいては、ボケの大きさを調整してナイキスト周波数でのレスポンスが同一になるようにしてある。両図の周波数特性を見比べると、目的の形状では高い周波数が良く減衰されているが、一般的な形状のボケでは高い周波数が減衰しないことが分かる。
上記第1実施形態においては、光学フィルタ21に開孔211をその分布密度が同心円的に変化するように設けることにより、光学フィルタ21に透過率分布を設けた。第2実施形態においては、正規分布の開口幅を有する開口部を用いた光学フィルタを説明する。
本実施形態によれば、以下のような効果を得ることができる。
また、上記実施形態は以下のように変更してもよい。
Claims (7)
- 複数の受光画素を備えた固体撮像素子に適用する光学フィルタであって、
前記固体撮像素子における受光画素のピッチに基づいて決まるナイキスト周波数以上の周波数における空間周波数成分を抑制した波形を生成する透過率分布を設けたことを特徴とする光学フィルタ。 - 前記透過率分布を設けるために、光学フィルタを横断する少なくとも一つの横断軸に対して、正規分布の開口幅を有する開口部を設けたことを特徴とする請求項1に記載の光学フィルタ。
- 前記開口部を、横断軸に対して対称に配置した2つの正規分布曲線により構成したことを特徴とする請求項2に記載の光学フィルタ。
- 前記透過率分布は、プレートに形成された開孔の密度分布を用いて構成することを特徴とする請求項1に記載の光学フィルタ。
- 前記透過率分布は、透明板に形成されたドットパターンの密度分布を用いて構成することを特徴とする請求項1に記載の光学フィルタ。
- 前記透過率分布として、固体撮像素子の受光面における光強度が正規分布になるように構成した分布を用いることを特徴とする請求項4又は5に記載の光学フィルタ。
- 複数の受光画素を備えた固体撮像素子と、
評価対象のディスプレイの画像をフォーカスする光学系部材と、
前記光学系部材の絞り位置に設置され、前記固体撮像素子における受光画素のピッチに基づいて決まるナイキスト周波数以上の周波数における空間周波数成分を抑制した波形を生成する透過率分布を設けた光学フィルタと
を備えたことを特徴とするディスプレイ評価システム。
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CN109708842B (zh) * | 2018-10-18 | 2022-07-26 | 北京航空航天大学 | 一种基于单像素成像的相机镜头点扩散函数测量方法 |
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