JP2006091149A - Flicker measuring method and flicker measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flicker measuring method with which a flicker measuring cost is kept low and flicker in all dots of an imaging area on a screen, is measured at once. <P>SOLUTION: Projection light from a projector 1 is received by a light sensor 3 attached to a screen 2. A light signal L from the light sensor 3 is filtered by a bandpass filter 4 and a periodic wave F<SB>lc</SB>of liquid crystal flicker caused by an alternate voltage for driving a liquid crystal panel 12, is inputted to an imaging time detecting circuit 5. The imaging time detecting circuit 5 analyses F<SB>lc</SB>and detects two imaging time of a day, t1 and t2 and a video camera 6 images the screen 2. An image processing section 7 calculates the liquid crystal flicker in all dots at once in the imaging area on the screen 2 by performing differential processing of two imaged images. As one light sensor 3 is enough, the number of components is reduced and consequently the measuring cost is reduced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a flicker measuring method and a flicker measuring apparatus. Specifically, the present invention relates to a method and apparatus for measuring flicker of an image displayed on an image display surface.

Conventionally, for the purpose of adjusting an image display device such as a liquid crystal screen or a plasma display, flicker of an image displayed on an image display surface of the image display device is measured by an optical sensor. By adjusting the image display device while referring to the measurement result of the optical sensor, the flicker of the image can be suppressed below a predetermined allowable value, and the flicker of the image can be reduced.
Further, for the purpose of adjusting the image display device so that the size of the flicker is substantially constant over the entire image display surface, optical sensors are arranged at a plurality of points on the image display surface, and Measurement of flicker is also performed (see, for example, Patent Document 1). By adjusting the image display device while referring to the measurement results at each measurement point, the flicker at all the measurement points can be kept below the allowable value, and the difference between the flickers at any two measurement points can be set to a predetermined allowable value. Since the difference can be suppressed to less than the difference, the flicker size can be made substantially constant over the entire image display surface.
Hereinafter, in order to simplify the expression, the degree of flicker uniformity over the entire image display surface is expressed by the term “flicker balance”. When the flicker size is substantially constant over the entire image display surface and the degree of uniformity is high, it is expressed as “flicker balance is good”, and conversely, when the degree of uniformity is low, “flicker balance is I will say "bad". In addition, according to this expression, the method described in Patent Document 1 can be rephrased as a method of adjusting the flicker balance using the flicker measurement results at a plurality of points on the image display surface.

JP 2001-128090 A (2nd to 5th pages, FIGS. 1 and 4)

In the method described in Patent Document 1, the flicker balance is adjusted using the flicker measurement result at each measurement point on the image display surface. Therefore, in order to adjust the flicker balance with higher accuracy, it is necessary to increase the number of photosensors and increase the number of flicker measurement points on the image display surface. However, there is a problem that an extra measurement cost is generated for the increased number of optical sensors.
Conversely, if the number of optical sensors that measure flicker is reduced in order to reduce the measurement cost, there is a problem that the accuracy of flicker balance adjustment deteriorates.
Such a problem occurs not only when measuring the flicker of an image displayed on the liquid crystal screen or the like, but also when measuring the flicker of an image projected on a screen by a projector.

  An object of the present invention is to provide a flicker measurement method and apparatus that can keep flicker measurement costs low and can simultaneously measure flicker at a plurality of points on an image display surface.

  The flicker measurement method of the present invention is a method for measuring flicker of an image displayed on an image display surface, and receives flicker of image light for displaying the image, thereby detecting flicker at at least one point in the image. Flicker periodic waveform detection step for detecting a periodic waveform, and imaging for detecting a first imaging time for applying a predetermined first phase and a second imaging time for applying a predetermined second phase in the detected flicker periodic waveform. Based on the time detection step, the imaging step of capturing the image on the image display surface at the first and second imaging times, the two images captured, and the first and second phases. An arithmetic processing step of performing arithmetic processing and calculating flicker of the image on the image display surface.

In the flicker periodic waveform detection step, a flicker periodic waveform is detected at at least one point in the image. At this time, at least one optical sensor or the like for detecting the flicker periodic waveform is sufficient, and it is not necessary to provide a plurality of optical sensors as in Patent Document 1.
In the imaging time detection step, the flicker periodic waveform detected by the optical sensor or the like is analyzed to detect a first imaging time for giving the first phase and a second imaging time for giving the second phase. The first imaging time and the second imaging time specify timing for capturing an image on the image display surface in the subsequent imaging process. In the present invention, it is assumed that the first and second phases are set to appropriate values in advance so that the image capturing timing (first and second image capturing times) suitable for flicker measurement can be obtained.
In the arithmetic processing step, arithmetic processing is performed based on the two images captured in the imaging step, and flickers of all points within the imaging range on the image display surface are calculated at once. At this time, there are various methods for calculating the flicker, but the method including the difference processing of two images is the simplest. This method mainly includes a difference processing step for differentially processing two images, and a phase factor removal step for calculating flicker by removing a factor including the first and second phases from data obtained by the difference processing. . Data obtained by differential processing of two images is generally represented by the product of a flicker factor relating to flicker and a phase factor relating to the first and second phases. In the phase factor removal step, the difference processing is performed. The flicker factor is calculated by dividing the data by the phase factor.
Through the above steps, all flickers within the imaging range on the image display surface can be calculated at once.

Hereinafter, the case where the flicker periodic waveform in the image displayed on the image display surface is expressed by a sine function will be described in detail. Note that the present invention is not limited to the flicker periodic waveform in the following example, and can be applied to a flicker periodic waveform having an arbitrary function form.
In this example, the flicker period waveform F at each point in the image can be expressed as F = A · sin (2πft + φ) = A · sin θ (t). Here, A is the flicker amplitude, f is the flicker frequency, t is the time, φ is the initial phase when t = 0, and θ (t) = 2πft + φ is the flicker phase. Of these quantities, the frequency f, the initial phase φ, and the phase θ (t) including f and φ are almost determined according to the generation method of the image displayed on the image display surface. It may be considered as a common value at each point. On the other hand, the amplitude A is an amount determined for each point in the image. Therefore, if each point in the image is expressed by two-dimensional coordinates (X, Y), the amplitude A can be expressed as a function of (X, Y), A (X, Y). Further, since the flicker periodic waveform F includes A (X, Y) and θ (t), it is a function of X, Y, t and can be expressed as F (X, Y, t).
Now, since the flicker amplitude A (X, Y) indicates the size of the flicker at each point (X, Y) in the image, the above-described flicker balance can also be described. For example, when the flicker amplitude A (X, Y) is substantially constant over the entire XY plane representing the image display surface, it can be said that the flicker balance is good, and the flicker amplitude A (X, Y) is within the XY plane. It can be said that the flicker balance is bad when it fluctuates greatly.

Hereinafter, each process in the flicker measuring method of the present invention will be described.
<Flicker periodic waveform detection process>
Image light for displaying an image is received, and a flicker periodic waveform F is detected. If the intersection between the optical path of the received image light and the image display surface is (Xs, Ys), the detected flicker cycle waveform F is the flicker cycle waveform F (Xs at the point (Xs, Ys) on the image display surface. , Ys, t) = A (Xs, Ys) · sin θ (t). In this flicker periodic waveform detection step, it is sufficient to detect the flicker periodic waveform at at least one point (Xs, Ys) in the image. Therefore, one optical sensor or the like for detecting the flicker periodic waveform F is sufficient. It is not necessary to provide a plurality as in Patent Document 1.

<Imaging time detection process>
The detected flicker periodic waveform F (Xs, Ys, t) we analyzed, theta ₁ = theta first and capturing time _{t 1} satisfying _{(t 1)} for the _first predetermined first phase theta, a predetermined second phase for _{θ 2 θ 2 = θ (t} 2) for detecting a second capturing time _{t 2} satisfying. By solving θ _i = 2πft _i + φ (i = 1, 2) with respect to t _i , a specific expression of t ₁ and t ₂ , t _i = (θ _i −φ) / 2πf is obtained. It is done.
<Imaging process>
At the detected image capturing times t ₁ and t ₂ , an image within a predetermined image capturing range on the image display surface is captured.

<Calculation process>
The captured image constitutes data of the light amount L (X, Y, t) at an arbitrary point (X, Y) within the imaging range. In general, the light quantity L (X, Y, t) is expressed as L (X, Y, t) = L ₀ (X, Y) using the flicker periodic waveform F (X, Y, t) at the point (X, Y). ) + F (X, Y, t). Here, L ₀ (X, Y) is a non-flicker component and is an amount that does not vary with time.
In this calculation process, the light quantity data _L 1 based on the captured image at the time _{t 1 (X, Y, t} 1) = L 0 (X, Y) + F (X, Y, t 1) and, time _{t 2} Based on the light amount data L ₂ (X, Y, t ₂ ) = L ₀ (X, Y) + F (X, Y, t ₂ ) based on the image captured in the image, an arbitrary value within the imaging range on the image display surface Flicker at the point (X, Y) is calculated. One example of calculation will be shown below.

≪Calculation procedure 1 (difference processing step) ≫
The differential processing on the L ₁ and _{L 2,} calculates the L 1 -L _2. Since L ₁ and L ₂ both contain L ₀ (X, Y) that does not depend on time t (t ₁ , t ₂ ), this is erased and L ₁ −L ₂ = F (X, Y , T ₁ ) −F (X, Y, t ₂ ) = A (X, Y) · {sin θ (t ₁ ) −sin θ (t ₂ )} = A (X, Y) · (sin θ ₁ −sin θ ₂ ) .
≪Calculation procedure 2 (Phase factor removal process) ≫
Subsequently, by dividing both sides by a phase factor (sin θ ₁ −sin θ ₂ ) including the _first and second phases θ ₁ and θ ₂ , A (X, Y) = (L ₁ −L ₂ ) / (sin θ ₁ − sin θ ₂ ).
≪Calculation procedure 3≫
Finally, both sides are doubled to calculate the flicker FL (X, Y) (= twice the flicker amplitude A (X, Y)). That is, FL (X, Y) = 2 · A (X, Y) = 2 · (L ₁ −L ₂ ) / (sin θ ₁ −sin θ ₂ ).
From this equation, it is understood that the flicker FL (X, Y) is calculated based on the two captured images L ₁ and L ₂ and the first and second phases θ ₁ and θ _2. .

The FL (X, Y) calculated in this way is a flicker at an arbitrary point (X, Y) within the imaging range on the image display surface. In the arithmetic processing step, this calculation is performed for all the points in the imaging range at a time. Therefore, according to the flicker measurement method of the present invention, the flickers for all the points in the imaging range can be measured at a time.
In the present invention, the flicker periodic waveform detection process may be performed by detecting the flicker periodic waveform at at least one point in the image. At this time, only one optical sensor or the like for detecting the flicker periodic waveform is sufficient, and there is no need to provide a plurality of optical sensors as in Patent Document 1, so that the measurement cost can be reduced.
In addition, when the flicker measurement result obtained using the flicker measurement method of the present invention is used for adjusting the flicker balance in an image, the flicker balance can be adjusted while referring to the flicker at all points in the imaging range. Therefore, the flicker balance adjustment accuracy can be improved as compared with the method of Patent Document 1 in which the adjustment is performed with reference to only the flicker at the arrangement point of the optical sensor.

In the present invention, the first phase and the second phase differ by an odd multiple of π, and in the arithmetic processing step, a difference process is performed on the two images taken in the imaging step. Is preferred.
Since the first phase and the second phase are different by an odd multiple of π, it can be expressed as θ ₂ = θ ₁ + (2k + 1) · π (k: integer). In the arithmetic processing step, arithmetic processing including difference processing is performed based on this expression. The following << calculation procedures 1 to 3 >> are described so as to correspond to the above << calculation procedures 1 to 3 >>.

≪Calculation procedure 1 (difference processing step) ≫
The difference L ₁ −L ₂ between L ₁ and L ₂ is calculated. As described above, L ₁ −L ₂ = A (X, Y) · (sin θ ₁ −sin θ ₂ ), but sin θ ₂ = sin {θ ₁ + (2k + 1) · π} = − sin θ ₁ . L ₁ −L ₂ = 2 · A (X, Y) · sin θ ₁ .
≪Calculation procedure 2 (Phase factor removal process) ≫
Then, by dividing both sides by _{sinθ 1, 2 · A (X} , Y) = (L 1 -L 2) / sinθ 1, obtained. 2 · A (X, Y) calculated here is equal to flicker FL (X, Y).
≪Calculation procedure 3≫
Since the flicker FL (X, Y) has already been calculated in the calculation procedure 2, there is no need to perform the arithmetic processing corresponding to the above << calculation procedure 3 >>.

  Therefore, according to this flicker measurement method, the number of calculation procedures in the arithmetic processing step can be reduced, so that the configuration of the apparatus for performing the arithmetic processing can be simplified and the flicker measurement speed can be increased.

Also, in the present invention, in the imaging time detection step, the first imaging time is a time at which a positive peak in the flicker cycle waveform detected in the flicker cycle waveform detection step is given, and the second imaging time is It is preferable to set the time to give a negative peak.
When the flicker cycle waveform F detected in the flicker cycle waveform detection step is expressed as F = A · sin θ (t) as described above, the phase giving a positive / negative peak is θ = π / 2 (+ 2k ₁ π (k ₁ is an integer): hereinafter omitted), −π / 2 (+ 2k ₂ π (k ₂ is an integer): hereinafter omitted).
Since the first imaging time t ₁ is a time for giving a positive peak of F and the second imaging time t ₂ is a time for giving a negative peak of F, θ ₁ = π / 2, θ ₂ = −π / 2.

The arithmetic processing step will be described.
≪Calculation procedure 1 (difference processing step) ≫
To calculate the difference _L 1 -L ₂ of L ₁ and _{L 2.} As described above, L ₁ −L ₂ = 2 · A (X, Y) · sin θ ₁ , but sin θ ₁ = sin (π / 2) = 1, so L ₁ −L ₂ = 2 · A ( X, Y). 2 · A (X, Y) calculated here is equal to flicker FL (X, Y).
≪Calculation procedure 2, 3≫
Since the flicker FL (X, Y) has already been calculated in the calculation procedure 1, it is not necessary to perform the arithmetic processing corresponding to the above << calculation procedures 2, 3 >>.

  Therefore, according to this flicker measurement method, the number of calculation procedures in the calculation processing step can be further reduced, so that the configuration of the apparatus for performing the calculation processing can be simplified and the flicker measurement speed can be increased. .

In the present invention, the image displayed on the image display surface is generated based on AC power, and the flicker periodic waveform detection step detects only the AC flicker periodic waveform caused by the AC power. Is preferred.
There are various causes for the occurrence of flicker in an image, and one of them is that when the image is generated based on AC power, the AC power is not adjusted appropriately. Hereinafter, the flicker generated on the screen due to this is referred to as AC flicker.

  In this flicker measurement method, in the flicker periodic waveform detection step, only the periodic waveform of AC flicker can be detected without detecting the periodic waveform of flicker other than AC flicker. In the time detection process, it is possible to detect the first and second imaging times optimal for the measurement of AC flicker. Therefore, according to this flicker measurement method, the measurement accuracy of AC flicker in an image can be improved. Further, by adjusting the AC power for generating an image while referring to the measurement result, AC flicker in the image can be effectively reduced, and an image with less flicker can be provided.

In the present invention, the light source and an image pattern generation unit that generates an image pattern based on the applied AC power are configured to irradiate the image pattern with light from the light source and transmit the light. And an image generation means for generating an image displayed on the image display surface by at least one of reflected light, and in the flicker periodic waveform detection step, the periodic waveform of the light source flicker caused by the light source is removed, It is preferable to detect only the periodic waveform of the AC flicker.
In this case, the main flickers in the image are flicker derived from the light source (hereinafter referred to as light source flicker) and flicker derived from AC power applied to the image pattern generation means (AC flicker). .
In this flicker measurement method, since the periodic waveform of the light source flicker is removed in the flicker periodic waveform detection step and only the periodic waveform of the alternating current flicker can be detected, the alternating current flicker is detected regardless of the presence or absence of the light source flicker in the subsequent imaging step and arithmetic processing step. Only can be measured selectively. Since there is a direct causal relationship between the AC power applied to the image pattern generation means and the AC flicker in the image, if the selectively measured AC flicker is referred to, it is applied to the image pattern generation means. The AC power can be adjusted with high accuracy, and AC flicker can be reduced directly and effectively.

  Hereinafter, a flicker measuring apparatus having a configuration for implementing the flicker measuring method described so far will be described.

  The flicker measuring apparatus of the present invention is an apparatus for measuring flicker of an image displayed on an image display surface, and receives flickering light for displaying the image, thereby detecting flicker at at least one point in the image. Flicker periodic waveform detecting means for detecting a periodic waveform, and imaging for detecting a first imaging time for applying a predetermined first phase and a second imaging time for applying a predetermined second phase in the detected flicker periodic waveform. Based on time detection means, imaging means for capturing the image on the image display surface at the first and second imaging times, the two images captured, and the first and second phases. Arithmetic processing means for performing arithmetic processing and calculating the flicker of the image on the image display surface.

<Flicker periodic waveform detection process>
The image light is received by the flicker periodic waveform detecting means, and the flicker periodic waveform is detected. The flicker period waveform detected here is equal to the flicker period waveform F (Xs, Ys, t) at the point (Xs, Ys) on the image display surface.
<Imaging time detection process>
The imaging time detection means analyzes the detected flicker period waveform F (Xs, Ys, t), and the first imaging time t ₁ that satisfies θ ₁ = θ (t ₁ ) for the first phase θ ₁ , A second imaging time t ₂ that satisfies θ ₂ = θ (t ₂ ) for the two phases θ ₂ is detected.
<Imaging process>
The imaging means captures an image within a predetermined imaging range on the image display surface at the detected imaging times t ₁ and t ₂ .
<Calculation process>
Arithmetic processing means, the light quantity data L ₁ based on the captured image at time t _1, on the basis of the time t ₂ to the light quantity data L ₂ based on the captured image, any in the imaging range on the image display surface Flicker FL (X, Y) at the point (X, Y) is calculated. The calculation procedure is as described above.

FL (X, Y) calculated as described above is a flicker at an arbitrary point (X, Y) within the imaging range on the image display surface. In the arithmetic processing step, this calculation is performed at once for all the points in the imaging range. Therefore, according to the flicker measuring apparatus of the present invention, the flickers for all the points in the imaging range can be measured at a time.
Further, in the present invention, the flicker periodic waveform detecting means only needs to detect the flicker periodic waveform at at least one point in the image, so one is sufficient, and it is necessary to provide a plurality of optical sensors as in Patent Document 1. Therefore, the number of parts can be reduced, and a flicker measuring apparatus having a simple configuration can be manufactured at low cost.
In addition, when adjusting the flicker balance in an image with reference to the flicker measurement result obtained using this flicker measuring apparatus, the flicker balance can be adjusted while referring to the flicker at all points in the imaging range. Thus, the flicker balance adjustment accuracy can be improved.

  The present invention includes a light source and a liquid crystal panel that generates an image pattern based on the applied AC power. The liquid crystal panel is irradiated with light from the light source, and at least transmitted light and reflected light thereof are emitted. Image generating means for generating an image to be displayed on the image display surface is provided on one side, and the flicker periodic waveform detecting means does not pass the periodic waveform of the light source flicker caused by the light source and does not pass through the AC power. It is preferable to include a filter that passes only the periodic waveform of liquid crystal flicker generated due to this, and to detect only the liquid crystal flicker periodic waveform that has passed through this filter.

In this case, the main flickers in the image are the light source flicker derived from the light source and the AC flicker derived from the AC power applied to the liquid crystal panel (herein referred to as “liquid crystal flicker” in particular).
In this flicker measuring apparatus, the periodic waveform of the light source flicker is removed by the action of the filter, and only the periodic waveform of the liquid crystal flicker is detected by the flicker periodic waveform detecting means. The imaging time detection means detects the first and second imaging times that are optimal for liquid crystal flicker measurement based on the detected liquid crystal flicker periodic waveform. Therefore, in the subsequent imaging process and arithmetic processing process, almost only liquid crystal flicker can be selectively measured regardless of the presence or absence of light source flicker. Further, by adjusting the AC power applied to the liquid crystal panel while referring to the measurement result of the liquid crystal flicker, the liquid crystal flicker in the image can be effectively reduced, and an image with less flicker is provided. Can do.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The flicker measuring apparatus shown in FIG. 1 is an apparatus for measuring flicker of an image projected on a screen 2 as an image display surface by projection light emitted from a projector 1 as an image generating means.
The projector 1 includes a lamp 11 as a light source and a liquid crystal panel 12 as an image pattern generation unit. The liquid crystal panel 12 has a large number of minute liquid crystal pixels arranged in alignment over the entire surface thereof. The transmittance (transmissivity) of each liquid crystal pixel can be changed by an AC voltage applied from an AC power source (not shown), whereby an image pattern is generated on the surface of the liquid crystal panel 12. The lamp 11 illuminates this image pattern. This illumination light is transmitted according to the transmittance of each liquid crystal pixel constituting the image pattern, and is irradiated onto the screen 2 as projection light. This projection light is image light for displaying an image, and an image based on the image pattern on the liquid crystal panel 12 is projected on the screen 2.

In FIG. 1, the projector 1 is illustrated as a so-called single-plate liquid crystal projector including one liquid crystal panel 12, but this is for simplification of illustration, and actually, three sheets for each RGB color. This is configured as a so-called three-plate type liquid crystal projector provided with a liquid crystal panel. However, in the present invention, any type of projector can be used as the image projection means regardless of single plate type, three plate type, or the like. Further, the liquid crystal panel 12 is not limited to a transmission type liquid crystal panel that generates projection light by transmitting the light from the lamp 11 as shown in FIG. 1, but the projection is performed by reflecting the light from the lamp 11. It may be a reflective liquid crystal panel that generates light.
The screen 2 is a reflection type screen, and reflects the projection light emitted from the projector 1 to display an image. At this time, the light reflected from the screen 2 also functions as image light for displaying an image. Here, the screen 2 may be a transmissive screen. At this time, the transmitted light functions as image light. An arbitrary position on the surface of the screen 2 is represented by XY orthogonal coordinates (X, Y).

  Hereinafter, flicker measurement of an image will be described. It is assumed that the waveform of the AC voltage applied to the liquid crystal panel 12 is kept constant during flicker measurement. At this time, a predetermined inspection image is projected on the screen 2 from the projector 1.

<Flicker periodic waveform detection process>
An optical sensor 3 is provided at the center of the screen 2. The optical sensor 3 has a dot-shaped light receiving portion exposed at the center (X ₀ , Y ₀ ) on the surface of the screen 2. The light receiving portion receives projection light from the projector 1 and receives an optical signal. To detect.
This optical signal mainly includes two types of flicker, that is, lamp flicker (light source flicker) and liquid crystal flicker (AC flicker). The lamp flicker is flicker derived from the lamp 11, and the frequency thereof is approximately determined according to the type of the lamp 11. In this embodiment, a high-pressure mercury lamp is used as the lamp 11, and the lamp flicker has a frequency of about 200 to 500 Hz. The liquid crystal flicker is flicker derived from an AC voltage applied to the liquid crystal panel 12. The frequency is determined by the frequency of the AC voltage (AC frequency), and in most cases is a value near the AC frequency. In the present embodiment, the AC frequency is 50 to 60 Hz, and the liquid crystal flicker frequency is about 10 to 70 Hz.
Here, the optical signal L detected by the optical sensor 3 is approximately L = L ₀ + F _la as the sum of the non-vibration component L ₀ other than flicker, the lamp flicker periodic waveform F _la , and the liquid crystal flicker periodic waveform F _lc . + F _lc . Each of these amounts is detected at the light receiving portion of the optical sensor 3 exposed at the center (X ₀ , Y ₀ ) on the surface of the screen 2, and when this needs to be clearly shown Hereinafter, L (X ₀ , Y ₀ , t), F _lc (X ₀ , Y ₀ , t), and the like (t is time).

The optical signal L detected by the optical sensor 3 is then filtered by the band pass filter 4. The passable frequency band in the band pass filter 4 is set to 10 to 70 Hz in order to pass only the liquid crystal flicker periodic waveform F _lc in the optical signal L. As a result, the non-vibration component L ₀ (0 Hz) and the lamp flicker periodic waveform F _la (200 to 500 Hz) in the optical signal L are removed, and only the liquid crystal flicker periodic waveform F _lc (10 to 70 Hz) is passed. Are input to the imaging time detection circuit 5.
In the above configuration, the optical sensor 3 and the band-pass filter 4 receive the image light (projection light) from the projector 1 and the liquid crystal flicker periodic waveform F _lc ( ₁ ) at one point (X ₀ , Y ₀ ) in the image. The flicker periodic waveform detecting means of the present invention for detecting X ₀ , Y ₀ , t) is configured.

<Imaging time detection process>
FIG. 2 shows a liquid crystal flicker periodic waveform F _lc (X ₀ , Y ₀ , t) input to the imaging time detection circuit 5. F _lc (X ₀ , Y ₀ , t) can be approximated by a sine function. Hereinafter, F _lc (X ₀ , Y ₀ , t) = A (X ₀ , Y ₀ ) · sin (2πft + φ) = A (X ₀ , Y ₀ ) · sin θ (t). Here, A (X ₀ , Y ₀ ) is the liquid crystal flicker amplitude at the center (X ₀ , Y ₀ ) of the screen 2, f is the liquid crystal flicker frequency (10 to 70 Hz), and φ is the initial phase when t = 0. , Θ (t) = 2πft + φ is a liquid crystal flicker phase.
The imaging time detection circuit 5 as the imaging time detection means includes a first imaging time t ₁ that gives a positive peak P ₁ in the input liquid crystal flicker periodic waveform F _lc (X ₀ , Y ₀ , t), and a negative peak. detecting a second capturing time _{t 2} to give P _2. Here, t ₁ and t ₂ are times when the first and second phases θ ₁ and θ ₂ are given, and θ ₁ = θ (t ₁ ) = π / 2 + 2k ₁ π (k ₁ : integer), and θ ₂ = θ (t ₂ ) = − π / 2 + 2k ₂ π (k ₂ : integer) is satisfied. Specifically, θ _i = θ (t _i ) = 2πft _i + φ (i = 1, 2) is solved for t _i , and t ₁ = (1/2 + 2k ₁ −φ / π) / 2f, t ₂ = (− 1/2 + 2k ₂ −φ / π) / 2f.
In addition, since θ ₁ −θ ₂ = π + 2 · (k ₁ −k ₂ ) · π = {2 · (k ₁ −k ₂ ) +1} · π, the first phase θ ₁ and the second phase θ ₂ Is different from π by an odd multiple.

<Imaging process>
The video camera 6 as the imaging means takes a shutter image of the entire surface of the screen 2 on which the image is projected at the first and second imaging times t ₁ and t ₂ detected by the imaging time detection circuit 5. The video camera 6 has a large number of minute imaging pixels arranged in alignment over the entire light receiving surface. Therefore, the image on the screen 2 imaged by the video camera 6 is light amount data constituted by the amount of received light for each imaging pixel. Since the video camera 6 images the entire surface of the screen 2, the position of each imaging pixel in the video camera 6 can be described by XY coordinates representing the position on the surface of the screen 2. Therefore, hereinafter, the “imaging pixel that receives image light from the point (X, Y) on the screen 2” is expressed as “imaging pixel arranged at the point (X, Y)”, and the description is simplified. To do.

As described above, the two images captured by the video camera 6 are light amount data configured by the amount of light received by each imaging pixel arranged at each point (X, Y). In other words, this light quantity data is data of the light quantity L (X, Y, t) at each point (X, Y) on the surface of the screen 2. In general, the light quantity L (X, Y, t) is L = L ₀ as the sum of a constant non-flicker component L ₀ (X, Y) and a flicker component F (X, Y, t) regardless of time t. + F. As described above, the main flicker components F are the lamp flicker and the liquid crystal flicker, but in this embodiment, the optical signal L from the optical sensor 3 is filtered by the band-pass filter 4 and the lamp flicker periodic waveform is obtained. The imaging times t ₁ and t ₂ suitable for measuring the liquid crystal flicker are detected by analyzing the liquid crystal flicker periodic waveform F _lc (see FIG. 2) obtained by removing F _la . Therefore, in the data of the light amounts L ₁ and L ₂ based on the two images captured by the video camera 6 at t ₁ and t ₂ , the influence of lamp flicker is almost negligible, and only the liquid crystal flicker needs to be considered. Therefore, F (X, Y, t) = F _la (X, Y, t) + F _lc (X, Y, t) _{≈F lc} (X, Y, t).
The liquid crystal flicker component F _lc (X, Y, t) can be represented by F _lc (X, Y, t) = A (X, Y) · sin θ (t). Here, A (X, Y) is the amplitude of the liquid crystal flicker at an arbitrary point (X, Y) on the surface of the screen 2, and θ (t) is the phase of the liquid crystal flicker. Note that the phase θ (t) of the liquid crystal flicker is almost determined by the frequency of the AC voltage for driving the liquid crystal panel 12, so that it has a common phase over the entire surface of the screen 2 regardless of the position (X, Y) on the screen 2. is there. Therefore, this θ (t) is the above formula for the liquid crystal flicker periodic waveform F _lc (X ₀ , Y ₀ , t) at the center (X ₀ , Y ₀ ) of the screen 2: F _lc (X ₀ , Y ₀ , t) = A (X ₀ , Y ₀ ) · sin θ (t): It is the same as θ (t) appearing in: and satisfies θ (t) = 2πft + φ.

As described above, the light amount data L _i (i = 1, 2) based on the two images captured at t ₁ and t ₂ by the video camera 6 is expressed as L _i (X, Y) = L (X, Y, t _i ) = L ₀ (X, Y) + F (X, Y, t _i ) ≈L ₀ (X, Y) + F _lc (X, Y, t _i ) = L ₀ (X, Y) + A (X, Y ) · Sin θ (t _i ). Here, since θ (t ₁ ) = π / 2 + 2k ₁ π and θ (t ₂ ) = − π / 2 + 2k ₂ π, sin θ (t ₁ ) = 1 and sin θ (t ₂ ) = − 1. is there. _{Thus, L 1 (X, Y)} = L 0 (X, Y) + A (X, Y), L 2 = L 0 (X, Y) -A (X, Y), and it becomes.

<Calculation process>
The image processing unit 7 serving as an arithmetic processing unit performs a difference process on the light amount data L ₁ and L ₂ input from the video camera 6 to thereby obtain a liquid crystal flicker value FL (X, Y) (= 2 · A (X, Y)) to calculate _{a: L 1 (X, Y)} -L 2 (X, Y) = {L 0 (X, Y) + a (X, Y)} - {L 0 (X, Y) -A ( X, Y)} = 2.A (X, Y) = FL (X, Y). Specifically, the difference in the amount of received light for each imaging pixel in the video camera 6 arranged at each point (X, Y) is calculated, and the liquid crystal flicker value FL (X, Y) at each point (X, Y) is calculated. Will do.
FIG. 3 schematically shows the difference process. The positions on the light quantity data L ₁ and L ₂ are represented by XY coordinates corresponding to the positions on the screen 2, and the imaging pixels of the video camera 6 are arranged at each point (X, Y). In the arithmetic processing step, the difference between the received light amounts (L ₁ (X, Y) and L ₂ (X, Y)) of the imaging pixels arranged at the respective points (X, Y) on the light amount data L ₁ and L ₂ is calculated. The liquid crystal flicker value (FL (X, Y)) is calculated by calculation.

<Effect of embodiment>
The liquid crystal flicker value FL (X, Y) calculated as described above is a liquid crystal flicker value at an arbitrary point (X, Y) on the surface of the screen 2. In the arithmetic processing step, since this calculation is performed for all points on the surface of the screen 2 at once, according to the flicker measurement method of this embodiment, the liquid crystal flicker value on the surface of the screen 2 can be measured at a time.

In the present embodiment, the optical sensor 3 for receiving the projection light from the projector 1 is installed for the purpose of detecting the timing of image capturing by the video camera 6, so that the flicker periodic waveform is displayed over the entire surface of the image. There is no need to detect, and it is only necessary to detect the flicker cycle waveform at one point in the image (in this embodiment, the center (X ₀ , Y ₀ ) of the screen 2). Therefore, one optical sensor 3 is sufficient, and it is not necessary to provide a plurality of optical sensors 3 as in Patent Document 1. Therefore, the number of parts can be reduced, and a flicker measuring device having a simple configuration can be manufactured at low cost. Cost can also be reduced.

  Further, by using the liquid crystal flicker value data measured in the present embodiment, the AC voltage applied to the liquid crystal panel 12 is adjusted while referring to the liquid crystal flicker values at all points on the surface of the screen 2, and the liquid crystal flicker balance is adjusted. Since the adjustment is possible, the adjustment accuracy of the liquid crystal flicker balance can be improved as compared with the method of Patent Document 1 in which the adjustment is performed with reference to only the flicker at the arrangement point of the optical sensor.

In the present embodiment, the first and second imaging times t ₁ and t ₂ are represented by positive and negative peaks P ₁ and P 2 in the liquid crystal flicker periodic waveform F _lc (X ₀ , Y ₀ , t) shown in FIG. by detecting a time to give _2, so that is possible to calculate the crystal flicker value FL simply performing difference processing between the image processing section 7, L ₁ and L _2. Therefore, according to the present embodiment, the arithmetic processing in the image processing unit 7 can be remarkably simplified, and the liquid crystal flicker measurement speed can be increased.

Further, in the present embodiment, the optical signal L from the optical sensor 3 is filtered by the band-pass filter 4 to remove the non-flicker component L ₀ and the lamp flicker period waveform F _la and extract only the liquid crystal flicker period waveform F _lc. it can. Since the imaging time detection circuit 5 can detect the imaging times t ₁ and t ₂ that are optimal for the measurement of liquid crystal flicker based on this F _lc , the measurement accuracy of the liquid crystal flicker can be improved.

It should be noted that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.
For example, in the above embodiment, the light sensor 3 is attached to the screen 2 to receive the projection light from the projector 1 and the flicker periodic waveform is captured. However, in the present invention, the light sensor 3 is connected to the screen 2. The optical sensor 3 may be any sensor as long as it can receive at least one of projection light from the projector 1 and reflected light from the screen 2.
Even when the optical sensor 3 is attached to the screen 2, it is not necessary to arrange the light receiving portion at the center of the screen 2 as in this embodiment, and the light receiving portion is arranged at an arbitrary position on the surface of the screen 2. it can. The liquid crystal flicker periodic waveform F _lc can be acquired by the optical sensor 3 and the band pass filter 4 regardless of the arrangement position of the light receiving unit, so that there is no problem in the imaging time detection circuit 5 detecting an appropriate imaging time. Because.

  In the above embodiment, flicker measurement of an image projected on the screen 2 based on projection light from the projector 1 has been described. However, according to the flicker measurement method and apparatus of the present invention, flicker of other images is also possible. It can be measured. For example, the present invention can also be used for flicker measurement of images displayed on various image display surfaces such as a liquid crystal display, a CRT display, a plasma display, an LED display, and an organic EL display.

  In the above-described embodiment, the entire surface of the screen 2 is imaged by the video camera 6 in the imaging process, and the flicker over the entire surface of the screen 2 is measured at one time. In some cases, the video camera 6 may pick up this part. In this case as well, flicker at all points within the imaging range can be measured at once, so the number of measurement points can be easily increased compared to the conventional method where each point on the screen is measured by each optical sensor. Thus, the flicker balance adjustment accuracy can be improved.

In the embodiment, the imaging times t ₁ and t ₂ detected by the imaging time detection circuit 5 are input to the video camera 6. However, in the present invention, t ₁ and t ₂ are input to the image processing unit 7. May be. In this case, the video camera 6 is continuous images the screen on the screen 2, the image processing section 7 takes in the image of the video camera 6 at time t ₁ and t _2. The two images constitute the light quantity data L ₁ and L _2, the difference processing for the L ₁ and L ₂ as described above in the image processing section 7 is performed.

In the embodiment, the first imaging time t ₁ in the imaging time detection step is a time at which the positive peak P ₁ in the liquid crystal flicker cycle waveform F _lc detected in the flicker cycle waveform detection step is given, and the second imaging is performed. The time t ₂ is a time for giving the negative peak P ₂ , and the first phase θ ₁ = π / 2 and the second phase θ ₂ = −π / 2. In the present invention, θ ₁ And θ ₂ may be in any phase. At this time, the image processing unit 7 performs arithmetic processing based on the _two images L ₁ and L ₂ captured by the video camera 6 and θ ₁ and θ ₂ to calculate the flicker of the image. Specifically, FL (X, Y) = 2 · (L ₁ −L ₂ ) / (sin θ ₁ −sin θ ₂ ).
At this time, if the condition that “θ ₁ and θ ₂ differ by an odd multiple of π” is added, the arithmetic processing in the image processing unit 7 can be simplified. Specifically, since sin θ ₂ = −sin θ ₁ , FL (X, Y) = (L ₁ −L ₂ ) / sin θ ₁ .

In the embodiment, the image processing unit 7 calculates the flicker by performing the difference processing on the _two images L ₁ and L ₂ captured by the video camera 6. There is no need to perform differential processing. The image processing unit 7 only needs to calculate flicker based on the two images L ₁ and L ₂ and the first and second phases θ ₁ and θ ₂ . The calculation order and the like can be freely selected as appropriate.

  In the embodiment, in order to efficiently measure the liquid crystal flicker caused by the AC voltage applied to the liquid crystal panel 12, the bandpass filter 4 that passes only the liquid crystal flicker periodic waveform is provided. An imaging time suitable for liquid crystal flicker measurement is detected. However, the flicker as a measurement target of the flicker measurement method of the present invention is not limited to liquid crystal flicker (AC flicker). When the liquid crystal flicker is not measured, it is not necessary to provide the band pass filter 4. Further, when it is desired to measure a specific flicker other than the liquid crystal flicker (for example, light source flicker), a band pass filter that passes only the periodic waveform of the specific flicker and does not pass the liquid crystal flicker may be provided. Even when liquid crystal flicker is measured, it is not necessary to provide the band-pass filter 4 if there is no possibility that flicker other than liquid crystal flicker adversely affects the measurement of liquid crystal flicker. In particular, if a light source such as the lamp 11 in the present embodiment is not used to display an image on the image display surface, the light source flicker does not occur in the first place, and thus the bandpass filter 4 can be omitted.

  The present invention can be used for flicker measurement of images displayed on various image display surfaces such as a projection screen, a liquid crystal display, and a plasma display.

1 is a block diagram showing a flicker measuring apparatus according to an embodiment of the present invention. The figure which shows the liquid crystal flicker period waveform input into the imaging time detection circuit in the said embodiment. The figure which shows the mode of the difference process of two images performed in the image process part in the said embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Projector, 2 ... Screen, 3 ... Optical sensor, 4 ... Band pass filter, 5 ... Imaging time detection circuit, 6 ... Video camera, 7 ... Image processing part, 11 ... Lamp, 12 ... Liquid crystal panel, _Flc ... Liquid crystal Flicker periodic waveform, t ₁ ... first imaging time, t ₂ ... second imaging time.

Claims (7)

A method of measuring flicker of an image displayed on an image display surface,
A flicker periodic waveform detecting step of detecting a flicker periodic waveform at at least one point in the image by receiving image light for displaying the image;
An imaging time detection step of detecting a first imaging time for applying a predetermined first phase and a second imaging time for applying a predetermined second phase in the detected flicker periodic waveform;
An imaging step of imaging the image on the image display surface at the first and second imaging times;
An arithmetic processing step of performing arithmetic processing based on the two captured images and the first and second phases, and calculating flicker of the image on the image display surface;
A flicker measuring method comprising: The flicker measurement method according to claim 1,
The first phase and the second phase differ by an odd multiple of π,
In the arithmetic processing step, difference processing is performed on the two images captured in the imaging step.
The flicker measuring method characterized by the above-mentioned. The flicker measurement method according to claim 2,
In the imaging time detection step, the first imaging time is a time for giving a positive peak in the flicker cycle waveform detected in the flicker cycle waveform detection step, and the second imaging time is a time for giving a negative peak. And
The flicker measuring method characterized by the above-mentioned. In the flicker measurement method according to any one of claims 1 to 3,
The image displayed on the image display surface is generated based on AC power,
In the flicker periodic waveform detection step, only the periodic waveform of AC flicker generated due to the AC power is detected.
The flicker measuring method characterized by the above-mentioned. The flicker measurement method according to claim 4,
A light source and image pattern generation means for generating an image pattern based on the applied AC power, irradiating the image pattern with light from the light source, and transmitting at least one of the transmitted light and the reflected light An image generating means for generating an image displayed on the image display surface is provided by
In the flicker periodic waveform detection step, the periodic waveform of the light source flicker caused by the light source is removed, and only the periodic waveform of the AC flicker is detected.
The flicker measuring method characterized by the above-mentioned. An apparatus for measuring flicker of an image displayed on an image display surface,
Flicker periodic waveform detection means for detecting a flicker periodic waveform at at least one point in the image by receiving image light for displaying the image;
In the detected flicker periodic waveform, an imaging time detecting means for detecting a first imaging time for giving a predetermined first phase and a second imaging time for giving a predetermined second phase;
Imaging means for imaging the image on the image display surface at the first and second imaging times;
Arithmetic processing means for performing arithmetic processing based on the two captured images and the first and second phases and calculating flicker of the image on the image display surface;
A flicker measuring apparatus comprising: The flicker measuring apparatus according to claim 6,
A light source and a liquid crystal panel that generates an image pattern based on the applied AC power. The liquid crystal panel is irradiated with light from the light source, and the image is transmitted by at least one of transmitted light and reflected light. Image generating means for generating an image to be displayed on the display surface is provided;
The flicker periodic waveform detection means includes a filter that does not pass the periodic waveform of the light source flicker caused by the light source but passes only the periodic waveform of the liquid crystal flicker caused by the AC power. Detecting only the liquid crystal flicker periodic waveform that has passed through the filter;
Flicker measuring device characterized by the above.

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