JP2007171430A - Automatic focus camera, projection display device and dlp projector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic focus camera that is free of generation of striped images, which result from flickers of a fluorescent lamp or changes in the color light of projection light. <P>SOLUTION: In the automatic focus camera 30 that images a projection image in order to detect the focused state of the projection image, exposure time for an imaging element 37 is made longer than a predetermined time, and light quantity decrease means 35 and 36, which make the quantity of light entering the imaging element 37 decrease, are disposed in front of the imaging element 37. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an autofocus camera.

  2. Description of the Related Art Some projection display devices such as liquid crystal projector devices include an autofocus camera (hereinafter referred to as an AF camera) that uses an image sensor such as a CCD (Charge Coupled Devices) as an imaging unit. For example, Patent Documents 1 to 3 disclose a projection display device that performs a focusing operation of a projection lens by a so-called contrast method based on a captured image captured by the AF camera. With this contrast method, the state in which the contrast of the projected image is the highest is regarded as being projected in a focused state, and the focus of the projection lens is set at the position where the contrast of the captured image of the AF camera is the highest. The lens is moved back and forth in the optical axis direction.

Japanese Patent Laying-Open No. 2005-70687 (see abstract, etc.) Japanese Unexamined Patent Application Publication No. 2004-109346 (refer to abstract, etc.) Japanese Patent Laid-Open No. 6-3577 (see abstract, etc.)

  However, when the projection display device is used under the illumination light of a fluorescent lamp, a phenomenon occurs in which a striped pattern is generated in the captured image of the AF camera due to the influence of flicker of the fluorescent lamp. Also, a projection display apparatus called a so-called DLP (Digital Light Processing: registered trademark of Texas Instruments Incorporated) projector using DMD (Digital Micromirror Device: registered trademark of Texas Instruments Incorporated) as a light modulation means is also used. The color light of the projection light to be formed is affected by the time-division change caused by the rotation of the color wheel, resulting in a phenomenon that a striped pattern is generated in the captured image of the AF camera.

  As described above, when a striped pattern occurs in the captured image due to flicker of fluorescent lamps or changes in the color light of the projection light, the contrast of the captured image differs from the original contrast, and there is a problem that the in-focus state cannot be accurately detected. .

  As a means for solving such a problem, it is conceivable to adopt a so-called flickerless method in which a CCD imaging cycle is set so that a striped pattern due to flickering of a fluorescent lamp does not occur in a captured image. However, when such a means is adopted, there is a problem that the circuit for driving the CCD becomes complicated and the cost of the CCD increases. In addition, according to such means, it is possible to eliminate the occurrence of a stripe pattern due to flickering of a fluorescent lamp, but as in a DLP projector, the color light of the projection light forming the projection image changes in a time-sharing manner to the captured image. There is a problem that the generated stripe pattern cannot be suppressed.

  Therefore, the present invention suppresses the occurrence of a stripe pattern in a captured image even when a projection image of a projection display device is captured under illumination light of a fluorescent lamp or a projection image of a DLP projector. An object of the present invention is to provide an AF camera that can be used. It is another object of the present invention to provide a projection display device and a DLP projector provided with such an AF camera.

  In order to solve the above-described problems, the present invention provides an autofocus camera that captures a projected image in order to detect the in-focus state of the projected image. It is assumed that a light amount reducing means for reducing the amount of light incident on the image sensor is provided in front. When configured in this way, even if there is flicker of a fluorescent lamp, or even if the color light of the projected light changes in a time-sharing manner, it is possible to obtain a captured image in which the occurrence of a striped pattern is suppressed, and the in-focus state The accuracy of detection can be increased.

  In another aspect of the invention, the light amount reducing means of the autofocus camera is one or both of an aperture and a neutral density filter. In this way, the amount of light can be effectively reduced by using one or both of the diaphragm device and the neutral density filter.

  In another aspect of the invention, the projection display device includes the autofocus camera. When configured in this way, even if there is flicker of a fluorescent lamp, it is possible to suppress a decrease in the accuracy of the projection image focusing operation.

  In another aspect of the invention, a DLP projector is provided with the above autofocus camera. When configured in this way, it is possible to suppress a decrease in the accuracy of the projection image focusing operation even though the color light of the projection light is changed by the color wheel.

  The AF camera according to the present invention generates a striped pattern even if a projection image of a projection display device is captured under illumination light of a fluorescent lamp or a projection image of a DLP projector is captured. Can be suppressed.

(First embodiment)
Embodiments of an AF camera according to the present invention will be described below with reference to FIGS. First, a first embodiment will be described with reference to FIGS. As a projection type display device incorporating an AF camera, two examples of a liquid crystal projector using the liquid crystal display device (first embodiment) and a DLP projector (second embodiment) will be described. However, the present invention can be applied to other types of projection display devices.

  FIG. 1 is a diagram illustrating a use state when performing a focusing operation of the liquid crystal projector 10 according to the first embodiment, and represents a state in which a test pattern T for detecting a focusing state is projected onto the screen S. Yes. The liquid crystal projector 10 includes a projection lens 20 and an AF camera 30.

  When the liquid crystal projector 10 performs a focusing operation, as shown in FIG. 1, a test pattern T in which a plurality of strip-like black stripes that are long in the vertical direction are arranged at regular intervals in the horizontal direction is projected from the projection lens 20. Project. Then, a focus lens (not shown) provided in the projection lens 20 is moved back and forth in the optical axis direction of the projection lens 20 to change the focus state of the test pattern T. The test pattern T is imaged by the AF camera 30, and a change in contrast of the captured image is evaluated by a control circuit unit not shown. Then, when the focus lens (not shown) moves to a position where the contrast of the captured image is the highest, it is determined that the test pattern T is projected in a focused state, and the focus lens (other than the figure) is determined at this position. ) Stop moving. In the present embodiment, the AF camera 30 is set to capture a rectangular area t centered on the center of the test pattern T, and evaluates the contrast of the captured image in the rectangular area t.

  A control circuit unit (not shown) evaluates the contrast level as follows. Regarding the captured image captured by the CCD 37 of the AF camera 30 which will be described in detail later, the luminance difference between the pixels arrayed in the horizontal direction for one line or several lines in the horizontal direction (black stripe arrangement direction). The values are detected and the difference values are summed. The closer the test pattern T is to the in-focus state, the higher the contrast of the test pattern T and the clearer the edge of the stripe. Therefore, as the contrast increases, the value of the luminance difference between the bright and dark pixels at the edge of the stripe increases, and the total difference value also increases as the test pattern T approaches the in-focus state. That is, the contrast level is evaluated based on the total value of the luminance difference values between the pixels, and the test pattern T is projected in the focused state when the total luminance difference value between the pixels is the largest. Judge.

  For example, as shown in FIG. 4A, for the test pattern T, for example, the value of the luminance difference between pixels arranged in one horizontal line L is as shown in FIG. That is, for the predetermined line L, the luminance difference between the edge portions E1 and E2 on both sides of the black stripe increases. At the edge portion E1, which is a portion that changes from a white background to a black stripe, the luminance drops sharply, and thereafter, the black stripe continues, so the luminance difference settles to zero. Thereafter, the brightness at the edge portion E2, which is a portion that changes from a black stripe to a white background, rapidly increases, and after that, the white background continues, so the brightness difference settles down to zero. Such a phenomenon is repeated, and a luminance difference graph as shown in FIG. 4B is obtained. When the focus lens (not shown) moves to a position where the sum of the brightness difference values is the highest, it is determined that the test pattern T is projected onto the screen S in a focused state.

  Next, the configuration of the AF camera 30 will be described with reference to FIGS. FIG. 2 is a front view of the AF camera 30 as viewed from the screen S side. FIG. 3 is a right side sectional view taken along a cutting line AA in FIG. In the following description, the screen S side as viewed from the AF camera 30 is described as the front (front side).

  As shown in FIG. 3, the AF camera 30 includes a lens barrel 31 and a substrate board 32, and the lens barrel 31 is attached to the substrate board 32 via a barrel holding cylinder 33. The lens barrel 31 includes, in order from the front, an imaging lens 34 having a convex lens and a concave lens, a diaphragm plate 35 serving as a diaphragm having a diaphragm aperture 35A in the center, and an ND (Neutral Density) filter 36 serving as a neutral density filter. Is incorporated. The substrate board 32 includes a CCD 37, a CCD drive circuit for driving the CCD 37, and a connector portion 37A for connecting the AF camera 30 and a control circuit portion (not shown).

  The lens barrel 31 has an imaging lens holding unit 31A that holds the imaging lens 34 on the front side, and a light amount reduction means holding unit 31B that holds the diaphragm plate 35 and the ND filter 36 on the rear side. The imaging lens holding portion 31A is formed with a step portion 31C having a step surface facing forward along the inner peripheral surface. The imaging lens 34 is fitted into the imaging lens holding portion 31A in a state where the outer peripheral portion of the rear surface is in contact with the stepped portion 31C. The imaging lens 34 is fitted in the imaging lens holding portion 31 </ b> A, and its front surface slightly protrudes from the front end portion of the lens barrel 31.

  A lens pressing ring 38 is attached to the front side of the lens barrel 31. The lens pressing ring 38 includes a flange-shaped lens pressing portion 38A that protrudes toward the inner peripheral side at the front end, and a female screw 38b is formed on the inner peripheral surface of the cylindrical portion 38B on the rear side of the lens pressing portion 38A. On the outer peripheral surface on the front end side of the lens barrel 31, a male screw 31D that is screwed to the female screw 38b of the lens pressing ring 38 is formed. The lens pressing ring 38 is attached to the lens barrel 31 by screwing the female screw 38b to the male screw 31D of the lens barrel 31. The lens pressing portion 38A of the lens pressing ring 38 attached to the lens barrel 31 is in contact with the front surface of the imaging lens 34 protruding from the front end portion of the lens barrel 31. Therefore, when the lens pressing ring 38 is tightened rearward, the imaging lens 34 is fixed and held on the imaging lens holding portion 31A so as to be sandwiched between the lens pressing portion 38A and the stepped portion 31C.

  The light quantity reducing means holding portion 31B is formed with a step portion 31E having a step surface directed rearward along the inner peripheral surface. The diaphragm plate 35 is fitted in the light amount reducing means holding portion 31B with the step portion 31E in contact with the outer peripheral portion of the front surface thereof, and the ND filter 36 is disposed on the rear side of the diaphragm plate 35. The diaphragm plate 35 is fitted into the diaphragm plate 35 in contact therewith.

  In the light quantity reduction means holding part 31B, a light quantity reduction means presser ring 38 is fitted from the rear side of the diaphragm plate 35 and the ND filter 36. The light amount reducing means presser ring 38 has a male screw 38A formed on the outer peripheral surface, and a female screw 31F screwed to the male screw 38A is formed on the inner peripheral surface of the light quantity reducing means holding portion 31B. Therefore, the light quantity reduction means presser ring 38 is screwed and fitted into the light quantity reduction means holding portion 31B. Then, by tightening the light quantity reduction means holding ring 38 forward, the diaphragm plate 35 and the ND filter 36 are sandwiched between the step portion 31E and the front face portion of the light quantity reduction means holding ring 38, and the light quantity reduction means holding section. It will be fixed in 31B. The light amount reducing means presser ring 38 is an annular body in which a hole 38B, which is a hole penetrating along the optical axis in the front-rear direction, is formed at the center, passes through the aperture opening 35A of the aperture plate 35, and then ND The filter 36 allows the subject light whose light amount is further reduced to pass through.

  On the outer peripheral surface of the lens barrel 31 and the inner peripheral surface of the lens barrel holding cylinder 33, a male screw 31G and a female screw 33A that are screw-coupled to each other are formed. The lens barrel 31 is screw-coupled to the barrel holding cylinder 33 by a male screw 31G and a female screw 33A. At the rear end of the lens barrel holding cylinder 33, a flange portion 33B having a rectangular shape as viewed from the front is provided. In the lens barrel holding cylinder 33, the flange portion 33B is attached to the substrate board 32 with screws 33C. Therefore, the lens barrel 31 is attached to the substrate board 32 via the barrel holding cylinder 33. An infrared cut filter 39 is held behind the lens barrel 31 on the inner periphery of the barrel holding cylinder 33.

  By passing screws (not shown) through screw holes 32A formed at the four corners of the board board 32 and screwing these screws to a camera mounting portion (not shown) provided in the liquid crystal projector 10, the AF camera 30 is It is attached to a camera attachment part (not shown).

  For example, the imaging lens 34 is configured to have a so-called pan focus that focuses on the imaging surface of the CCD 37 with respect to a subject at a distance from 1.5 meters ahead of the imaging lens 34 to infinity. Therefore, by disposing the liquid crystal projector 10 and the screen S so that the screen S and the imaging lens 34 are separated from each other by 1.5 meters or more, the captured image of the projection image of the rectangular region t is in focus on the imaging surface of the CCD 37. In this case, the image is formed. The amount of screw coupling between the lens barrel 31 and the barrel holding barrel 33 is adjusted so that the projected image of the rectangular area t is pan-focused with respect to the imaging surface of the CCD 37. The lens barrel 31 and the barrel holding cylinder 33 are fixed to each other with an adhesive or the like so that this adjustment state is maintained.

  The inventor of the present invention, while searching for means for solving the above-described problem, includes a light amount reducing means such as a diaphragm plate 35 and an ND filter 36 provided in the AF camera 30 of the present embodiment. Using a non-AF camera, that is, an AF camera composed only of an imaging lens and a CCD, a projected image is captured in an environment where there is flickering of a fluorescent lamp, and the exposure time of the CCD is shortened. An experiment was conducted to check for the occurrence of stripes. As a result, in the case of the liquid crystal projector, when the exposure time of the CCD is lengthened, it is possible to suppress the occurrence of the stripe pattern due to the flicker of the fluorescent lamp.

  On the other hand, when the exposure time of the CCD is lengthened, a so-called overexposure state occurs in which the captured image is overexposed. Therefore, the inventor has provided a diaphragm plate or ND filter in front of the CCD in a state where the exposure time of the CCD is long enough to prevent the occurrence of a striped pattern, thereby reducing the amount of light incident on the CCD. As a result, the occurrence of overexposure was suppressed without the occurrence of stripes.

  Based on the above experimental results, in the AF camera 30 of the present embodiment, the predetermined exposure time of the CCD 37 is rectangular in an environment where there is flickering of a fluorescent light with the diaphragm plate 35 and the ND filter 36 removed. Even when the region t is imaged, the length is set so long that a striped pattern due to flicker does not occur in the captured image. On the other hand, an aperture plate 35 and an ND filter 36 are provided between the projection lens 31 and the CCD 37 so as to prevent overexposure in the captured image, and the amount of subject light incident on the CCD 37 is suppressed. The specific exposure time of the CCD 37, the diameter of the aperture 35A of the aperture plate 35, and the light reduction amount of the ND filter 36 are set as appropriate based on the brightness of the fluorescent lamp, the brightness of the projected image, the sensitivity of the CCD 37, and the like.

  A position at which the contrast of the captured image is the highest when the control circuit unit (not shown) evaluates the contrast of the captured image captured with the occurrence of the stripe pattern suppressed by the AF camera 30 configured as described above. In addition, the focus lens is moved back and forth in the optical axis direction to perform the focusing operation of the projection lens 20.

  That is, when a striped pattern is generated on a line (one horizontal line or several lines) for detecting the luminance difference value of the test pattern T, an accurate luminance difference value cannot be detected. There is a possibility that the focusing operation cannot be performed properly. However, as described above, by evaluating the contrast based on the captured image captured with the occurrence of the striped pattern suppressed, it is possible to detect an accurate value of the luminance difference of the test pattern T, and to obtain an appropriate match. A focusing operation can be performed.

  By setting the exposure time of the CCD 37 of the AF camera 30, the aperture diameter of the aperture opening 35A of the aperture plate 35, and the amount of light reduction of the ND filter 36 as described above, the projection lens 20 can be used even under flicker of a fluorescent lamp. The projected image can be projected in a state where the projected image is reliably focused on the screen S.

  Next, a DLP projector 10A according to a second embodiment will be described. The AF camera 30 of the DLP projector 10A has the same configuration as the AF camera 30 of the liquid crystal projector 10, and the same members will be described using the same numbers.

  By the way, as described in the background section above, even in a DLP projector, a striped pattern is generated in the captured image of the AF camera due to the time-division change in the color light of the projection light forming the projection image. A phenomenon occurs.

  Therefore, the inventor, from the search for the countermeasure against the flicker of the fluorescent lamp, only from the CCD and the imaging lens not provided with the light amount reduction means such as the diaphragm plate 35 and the ND filter 36 provided in the AF camera 30. Using a configured AF camera, an image of the rectangular area t of the test pattern T projected by the DLP projector is imaged, and an experiment is conducted to check the exposure time of the CCD and the presence or absence of stripes in the captured image. It was. As a result, as in the case where an image is taken in an environment where there is flicker of a fluorescent lamp, when the exposure time of the CCD is lengthened, the generation of a striped pattern due to the change in the color light of the projection light can be suppressed.

  On the other hand, when the exposure time of the CCD is lengthened, a so-called overexposure state occurs in which the captured image is overexposed. Therefore, when the exposure time of the CCD is increased to such an extent that no stripe pattern is generated, an aperture plate or ND filter is disposed in front of the CCD to reduce the amount of light incident on the CCD. As in the case of taking an image in an environment with flicker of a fluorescent lamp, the result of suppressing the occurrence of overexposure was obtained without the occurrence of a stripe pattern.

  Therefore, even when the liquid crystal projector 10 is the DLP projector 10A, the test pattern which is a projection image by the DLP projector with the predetermined exposure time of the CCD 37 of the AF camera 30 with the diaphragm plate 35 and the ND filter 36 removed. Even if T is imaged, the exposure time of the CCD 37 is set to be long enough to prevent the occurrence of a stripe pattern due to the change in the color light of the projection light. Then, the aperture diameter of the aperture opening 35A of the aperture plate 35 and the light reduction amount of the ND filter 36 are set so that the overexposed image of the CCD 37 whose exposure time has become longer does not occur. As a result, it is possible to capture a captured image in which the occurrence of a striped pattern is suppressed even for the projection image of the DLP projector 10A. Also in the DLP projector 10A, it is possible to project the projection image by the projection lens 20 in a state where the projection image is reliably focused on the screen S.

  The specific exposure time of the CCD 37, the stop diameter of the stop opening 35A of the stop plate 35, and the light reduction amount of the ND filter 36 are set as appropriate based on the brightness of the projection light, the sensitivity of the CCD 37, and the like. Further, when capturing a projected image of the DLP projector 10A projected under an environment affected by flicker of a fluorescent lamp, the exposure time of the CCD 37 is set so as not to generate a striped pattern, and overexposure occurs in the captured image. By setting the aperture diameter of the aperture plate 35 and the light reduction amount of the ND filter 36 so that the projection image is projected on the screen S even when the DLP projector is used under the illumination light of a fluorescent lamp. The projection can be performed in a surely focused state.

(Modification)
In each of the embodiments described above, the diaphragm plate 35 and the two ND filters 36 are used as the light quantity reduction means. However, as shown in FIG. Alternatively, only the diaphragm plate 35 may be used as shown in FIG. 5A and 5B schematically show the optical system from the imaging lens 34 of the AF camera 30 to the CCD 37 in order to explain the first modified example.

  In each of the above-described embodiments and modifications thereof, the diaphragm plate 35 and the ND filter have an action of suppressing overexposure regardless of the location in front of the CCD 37. If the principal ray of the subject light is provided at a position where it intersects the optical axis of the optical system of the AF camera 30, the influence on the shooting angle of view is reduced and the amount of the subject light incident on the CCD 37 is effectively reduced. be able to.

  The neutral density filter may use a polarizing plate instead of the ND filter to reduce the amount of light. In addition to the CCD 37, for example, a C-MOS (Complementary Metal Oxide Semiconductor) sensor may be used as the image sensor.

It is a figure which shows the use condition at the time of performing the focusing operation | movement of a liquid crystal projector (DLP projector) provided with the camera for autofocus concerning this invention. 1 is a front view of an autofocus camera according to the present invention. It is sectional drawing cut | disconnected by AA in FIG. It is a figure explaining the evaluation method of the contrast of the captured image in the liquid crystal projector and DLP projector which concern on embodiment of this invention. It is a figure which shows the modification of the camera for autofocus shown in FIG.

Explanation of symbols

10 ... Liquid crystal projector (projection type display device)
10A ... DLP projector (projection type display device)
30 ... AF camera (autofocus camera)
35 ... Diaphragm plate (diaphragm)
36 ... ND filter (Density filter)
37 ... CCD (imaging device)

Claims (4)

In an autofocus camera that captures the projection image in order to detect the in-focus state of the projection image,
While making the exposure time of the image sensor longer than a predetermined time,
An autofocus camera comprising a light amount reduction means for reducing the amount of light incident on the image pickup device in front of the image pickup device.   2. The autofocus camera according to claim 1, wherein the light amount reducing means is one or both of a diaphragm and a neutral density filter.   A projection display device comprising the autofocus camera according to claim 1 or 2, wherein a projection image focusing operation is performed based on a captured image captured by the autofocus camera.   A DLP projector comprising the autofocus camera according to claim 1 or 2, wherein a projection image focusing operation is performed based on a captured image captured by the autofocus camera.

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