JP2011064859A - Projection type image display device and focus control circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten a processing time in an autofocus processing using a contrast detection method. <P>SOLUTION: A projection part 10 projects an image to a projection surface 200 through a lens 13. A lens driving part 20 moves the position of the lens 13. An imaging part 30 picks up an image projected to the projection surface 200. A control part 40 decides the position of the lens 13 based on definition of a plurality of images respectively picked up by the imaging part 30 at a plurality of lens positions. The control part 40 allows the lens driving part 20 to move the lens by a plurality of number of times in one frame period, and obtains the definition of a plurality of partial images exposed at the respective lens positions from one frame image. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a projection display apparatus equipped with an autofocus function, and a focus control circuit.

  2. Description of the Related Art In recent years, a projection display apparatus (hereinafter referred to as a projector as appropriate) equipped with an autofocus function has been put into practical use. For example, a distance measuring sensor (for example, composed of a pair of line sensors) is mounted on the projector main body, and a method of focusing by measuring the distance between the projector main body and the screen has been put into practical use (for example, Patent Document 1).

  In addition, a method has been proposed in which a camera is mounted on the projector body, the contrast of images captured at a plurality of lens positions is calculated, and the lens position at which the contrast is maximized is detected to thereby adjust the focus (for example, , See Patent Document 2). This method can be used even when the distance between the projector body and the screen is large. The method using the distance measuring sensor cannot cope with the distance between the projector main body and the screen exceeding a predetermined range. In that case, it is necessary to manually adjust the focus by visual observation of the user.

JP 2007-271760 A JP 2006-285016 A

  In the method using the camera described above, since it is necessary to calculate the contrast of images captured at a plurality of lens positions, a certain amount of time is required until the in-focus position is determined. In general, a digital camera is required to have a time of 1 second or less after the start of autofocus adjustment until the in-focus position is determined. Also in the projector, it is preferable that this time is shorter.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a technique for reducing processing time in autofocus processing using a contrast detection method.

  A projection display apparatus according to an aspect of the present invention includes a projection unit that projects an image on a projection surface via a lens, a lens driving unit that moves the position of the lens, and an image that captures an image projected on the projection surface. And a control unit that determines the position of the lens based on the sharpness of the plurality of images respectively captured by the imaging unit at the plurality of lens positions. The control unit moves the lens to the lens driving unit a plurality of times within one frame period, and acquires the definition of the plurality of partial images exposed at the respective lens positions from one frame image.

  Another aspect of the present invention is a focus control circuit. The focus control circuit is a focus control circuit to be mounted on a device including an image sensor, a lens, and a drive element for moving the lens, and each image is captured by the image sensor at a plurality of lens positions. An image processing unit that calculates the sharpness of the plurality of images, and a focus adjustment unit that determines the position of the lens based on the sharpness of the plurality of images calculated by the image processing unit. The focus adjustment unit causes the driving element to move the lens a plurality of times within one frame period, and causes the image processing unit to calculate the sharpness of the plurality of partial images exposed at the respective lens positions.

  According to the present invention, the processing time can be shortened by the autofocus processing using the contrast detection method.

It is a figure which shows the structure of the projection type video display apparatus concerning embodiment of this invention. It is a figure for demonstrating the determination process of the focus position of a focus lens. It is a timing chart for demonstrating the contrast detection method using the frame image imaged with a CMOS image sensor. 4 is a timing chart for explaining an application example 1 of the autofocus process using the contrast detection method shown in FIG. 3 to a digital camera. 4 is a timing chart for explaining an application example 2 of the autofocus process using the contrast detection method shown in FIG. 3 to a digital camera. It is a figure which shows an example of the pattern image projected on a projection surface. It is a figure which shows an example of the some partial image contained in a pattern image. It is a figure for demonstrating the operation example 1 of the projection type video display apparatus concerning embodiment of this invention. It is a figure for demonstrating the operation example 2 of the projection type video display apparatus concerning embodiment of this invention.

  FIG. 1 is a diagram showing a configuration of a projection display apparatus 100 according to an embodiment of the present invention. The projection display apparatus 100 includes a projection unit 10, a lens driving unit 20, an imaging unit 30, and a control unit 40.

  The projection unit 10 projects an image on a projection surface 200 such as a screen. During autofocus, a predetermined pattern image is projected. The projection unit 10 includes a light source 11, a light modulation unit 12, and a focus lens 13. As the light source 11, a halogen lamp having a filament-type electrode structure, a metal halide lamp having an electrode structure for generating arc discharge, a xenon short arc lamp, a high-pressure mercury lamp, an LED lamp, or the like can be employed.

  The light modulation unit 12 modulates light incident from the light source 11 in accordance with an image signal set by the control unit 40 (more specifically, an image signal setting unit 46 described later). For example, a DMD (Digital Micromirror Device) can be employed for the light modulator 12. The DMD includes a plurality of micromirrors corresponding to the number of pixels, and a desired image is formed by controlling the direction of each micromirror according to each pixel signal.

  The focus lens 13 adjusts the focal position of the light incident from the light modulation unit 12. The lens position of the focus lens 13 is moved on the optical axis by the lens driving unit 20.

  The lens driving unit 20 moves the position of the focus lens 13 in accordance with a driving signal set from the control unit 40 (more specifically, a driving signal setting unit 48 described later). For the lens driving unit 20, a stepping motor, a voice coil motor (VCM), a piezoelectric element, or the like can be employed.

  The imaging unit 30 captures an image projected on the projection plane 200. The pattern image is captured during autofocus. The imaging unit 30 includes a solid-state imaging device 31 and a signal processing circuit 32. A CMOS (Complementary Metal Oxide Semiconductor) image sensor or the like can be adopted as the solid-state imaging device 31. Any image sensor that can control shutter timing in units of scanning lines, such as a global shutter system, can be used. Note that a global shutter type CCD (Charge Coupled Devices) cannot be adopted. The signal processing circuit 32 performs various signal processing such as A / D conversion on the signal output from the solid-state imaging device 31 and outputs the signal to the control unit 40.

  The control unit 40 determines the position of the focus lens 13 based on the sharpnesses of the plurality of pattern images respectively captured by the imaging unit 30 at the plurality of lens positions. In the present embodiment, the control unit 40 causes the lens driving unit 20 to move the lens a plurality of times within one frame period, and from a single frame image, a plurality of partial images exposed at the respective lens positions. Get the definition.

  More specific description will be given below. The control unit 40 includes an image processing unit 41, an image memory 45, an image signal setting unit 46, a focus adjustment unit 47, and a drive signal setting unit 48. The image processing unit 41 includes an area setting unit 42, an HPF 43, and an integrating unit 44.

  The configuration of the control unit 40 can be realized by an arbitrary processor, memory, or other LSI in terms of hardware, and can be realized by a program loaded into the memory in terms of software. Draw functional blocks. Therefore, those skilled in the art will understand that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof.

  The image processing unit 41 processes the image signal supplied from the imaging unit 30. More specific description will be given below. The area setting unit 42 extracts an image signal of an area in which the pattern image is captured from an image of the projection plane 200 and passes the extracted image signal to the HPF 43. The HPF 43 extracts a high frequency component of the image signal in the area and passes the extracted high frequency component to the integrating unit 44. The integrating unit 44 integrates the high frequency components for each partial image included in the frame image of the area, and passes the integrated value to the focus adjusting unit 47.

  The image memory 45 holds image data to be projected on the projection plane 200. The image data is supplied from a PC or the like via an external interface (not shown). In the present embodiment, a pattern image projected during autofocus is also held. The image signal setting unit 46 sets an image signal based on the image data held in the image memory 45 in the light modulation unit 12.

  The focus adjustment unit 47 causes the image signal setting unit 46 to set the signal of the pattern image in the light modulation unit 12 and causes the pattern image to be projected onto the projection plane 200 during autofocus. At the same time, the focus adjustment unit 47 supplies a control signal for sequentially moving the focus lens 13 with a predetermined step width to the drive signal setting unit 48. Note that the integrated value is calculated by the image processing unit 41 for each movement of one step. The focus adjustment unit 47 determines the position of the focus lens 13 that takes the maximum value among the plurality of integration values delivered from the integration unit 44 as the in-focus position.

  FIG. 2 is a diagram for explaining the determination process of the focus position of the focus lens 13. When the autofocus function is enabled, the focus adjustment unit 47 instructs the image signal setting unit 46 to project a pattern image, and moves the focus lens 13 from the near side to the far side or from the far side to the near side. A control signal for sequentially moving in the step width is set in the drive signal setting unit 48. The image signal setting unit 46 sets a pattern image signal in the light modulation unit 12, and the drive signal setting unit 48 sets a drive signal corresponding to the control signal in the lens driving unit 20.

  The image processing unit 41 calculates the sharpness (the integrated value can be used) of the partial image included in the pattern image captured at each lens position of the focus lens 13. This sharpness increases as the focus lens 13 approaches the in-focus position. When the rise peaks and falls, the focus adjustment unit 47 determines the previous lens position as the focus position.

  Note that the conditions for enabling the above-described autofocus function include power-on of the projection display apparatus 100, user operation, periodic automatic activation, and the like.

  First, prior to the description of the autofocus process using the contrast detection method executed by the projection display apparatus 100 according to the present embodiment, a compact digital camera or a camera mounted on a mobile phone (hereinafter collectively referred to as digital). The autofocus process executed in (described as “camera”) will be described.

  FIG. 3 is a timing chart for explaining a contrast detection method using a frame image captured by a CMOS image sensor. Since the CMOS image sensor employs a rolling shutter system, the exposure start timing of each scanning line is sequentially shifted. FIG. 3 shows an example in which m (m is a natural number) scanning lines are included in one frame.

  When a vertical synchronization signal (VSYNC) indicating the start of one frame period is set, exposure is sequentially started from the first scanning line to the mth scanning line of the CMOS image sensor. Since the exposure periods of all the scanning lines are equal, the exposure is sequentially completed from the first scanning line toward the mth scanning line. When the exposure is completed, the pixel data of each scanning line is output from the CMOS image sensor to the image processing unit 41 via the signal processing circuit 32, and the high frequency components of each pixel data are sequentially calculated.

  When the exposure of the m-th scanning line and the calculation of the high-frequency component of the pixel data are completed, it is possible to calculate an evaluation value (for example, the above-described sharpness) indicating the sharpness of the entire frame image. .

  FIG. 4 is a timing chart for explaining an application example 1 of the autofocus process using the contrast detection method shown in FIG. 3 to a digital camera. In application example 1, the focus lens 13 is moved once every two frames. More specifically, the focus lens 13 is moved after the evaluation value calculation for odd frames (or even frames) is completed. In FIG. 4, the movement of the focus lens 13 is expressed by a drive signal to a motor mounted on the lens drive unit 20.

  As described above, in the CMOS image sensor adopting the rolling shutter system, the exposure start timing of each scanning line is not uniform. Therefore, a scanning line in which the focus lens 13 moves during the exposure period is also generated. In FIG. 4, the scanning line included in the second frame moves the lens during the exposure period. In this case, the component before movement of the focus lens 13 and the component after movement are mixed in the pixel data of one scanning line imaged in one exposure period.

  In this regard, by adopting the evaluation value of the frame image by skipping one frame as in Application Example 1, the frame image including the scanning line in which the component before moving the focus lens 13 and the component after moving is mixed is excluded. can do. In FIG. 4, the focus lens 13 does not move during the exposure period of the scanning lines included in the first frame and the third frame.

  FIG. 5 is a timing chart for explaining an application example 2 of the autofocus process using the contrast detection method shown in FIG. 3 to a digital camera. In Application Example 2, the focus lens 13 is moved for each frame. More specifically, the focus lens 13 is moved after the evaluation value calculation for each frame is completed.

  When the focus lens 13 is moved for each frame, the focus lens 13 is moved during the exposure period in some scanning lines included in each frame. In FIG. 5, of each exposure period, the period exposed at the lens position before the focus lens 13 is moved is drawn by a solid line, and the period exposed at the lens position after the movement is drawn by a dotted line. The ratio of the period exposed at the lens position before the movement is larger as the scanning line is closer to the first line, and the ratio of the period of exposure at the lens position after the movement is larger as the scanning line is closer to the m-th line.

  In Application Example 2, the control unit 40 calculates the ratio of the first period exposed at the lens position before movement and the second period exposed at the lens position after movement, which occupies the exposure period of a certain scanning line. One lens position corresponding to the exposure period of the scanning line is simulated. For example, when the ratio between the first period and the second period is 1: 1, the lens position to be counterfeited is just an intermediate point between the lens position before the movement and the lens position after the movement. When the ratio between the first period and the second period is 1: 3, the lens position to be counterfeited is a 3/4 point between the lens position before the movement and the lens position after the movement.

  As described above, in application example 2, a frame image including a scanning line in which the component before movement of the focus lens 13 and the component after movement are mixed can be the target of the evaluation value calculation. The time required to determine the focal position can be shortened.

  FIG. 6 is a diagram illustrating an example of a pattern image projected on the projection plane. The pattern image PI projected on the projection plane 200 is formed with a pattern, a character string, or the like. FIG. 6 illustrates an example in which a vertical stripe pattern is formed.

  FIG. 7 is a diagram illustrating an example of a plurality of partial images included in the pattern image. In FIG. 7, four partial images (first partial image Ip1, second partial image Ip2, third partial image Ip3, and fourth partial image Ip4) are extracted from one pattern image PI. Each of these partial images is an image picked up by n (n is a natural number) main scanning lines of the solid-state image sensor 31. For example, an image captured by four main scanning lines or an image captured by one main scanning line may be used.

  A plurality of partial images extracted from one pattern image PI need to have the same content. In FIG. 7, four partial images having the same horizontal width are extracted from the vertically striped pattern image PI, so the patterns of the four partial images are the same. If this condition is satisfied, the number, shape, and position of partial images extracted from one pattern image PI can be arbitrarily set. It is possible to arbitrarily set whether or not to provide a space between the extracted partial images. Simply, the pattern image PI may be divided into upper and lower parts, and the upper half of the pattern image PI may be used as the first partial image and the lower half thereof as the second partial image.

  Hereinafter, according to the present embodiment, the first partial image Ip1, the second partial image Ip2, the third partial image Ip3, and the fourth partial image Ip4 are extracted from the pattern image PI illustrated in FIG. An operation example of the projection display apparatus 100 will be described.

  FIG. 8 is a diagram for explaining an operation example 1 of the projection display apparatus 100 according to the embodiment of the present invention. The operation example 1 is an example in which the exposure timings of the corresponding partial areas of the solid-state imaging device 31 are set so that the exposure periods of the plurality of partial images extracted from one pattern image PI do not overlap each other. is there. In this example, the control unit 40 moves the focus lens 13 to the lens driving unit 20 in synchronization with the exposure timing.

  In FIG. 8, by shortening the exposure periods of the first partial image Ip1, the second partial image Ip2, the third partial image Ip3, and the fourth partial image Ip4, without overlapping the exposure periods, The exposure period is within one frame period. More specifically, the exposure period of the second partial image Ip2 starts with the end of the exposure period of the first partial image Ip1, and the exposure period of the third partial image Ip3 with the end of the exposure period of the second partial image Ip2. And the exposure period of the fourth partial image Ip4 is started together with the end of the exposure period of the third partial image Ip3.

  The focus adjustment unit 47 instructs the drive signal setting unit 48 to move the focus lens 13 in synchronization with the end of each exposure period. The drive signal setting unit 48 sets a drive signal synchronized with the end of each exposure period in the lens drive unit 20 in accordance with an instruction from the focus adjustment unit 47. The image processing unit 41 calculates the evaluation value for each of the first partial image Ip1, the second partial image Ip2, the third partial image Ip3, and the fourth partial image Ip4, and passes the evaluation value to the focus adjustment unit 47. The focus adjustment unit 47 selects the partial image with the highest evaluation value, and determines the lens position of the partial image as the in-focus position.

  FIG. 9 is a diagram for explaining an operation example 2 of the projection display apparatus 100 according to the embodiment of the present invention. In the second operation example, unlike the first operation example, the exposure period of the partial image is set longer than the period during which the lens position of the focus lens 13 is switched.

  As described in the operation example 1, if the exposure period of each partial image is shortened, the case where the focus lens 13 is moved during each exposure period can be avoided even if the update interval of the lens position is shortened. be able to. However, if the exposure period is shortened, necessary and sufficient information (that is, necessary and sufficient light amount) may not be obtained for calculating the evaluation value. For example, there is a case where the distance between the projection surface 200 and the solid-state imaging device 31 is large, or a case where the brightness of the pattern image PI projected on the projection surface 200 is low.

  The operation example 2 provides a technique capable of shortening the update interval of the lens position while ensuring the length of each exposure period. Based on the ratio of the first period exposed at the lens position before the movement of the focus lens 13 to the second period exposed at the lens position after the movement, the controller 40 occupies the exposure period of the partial image. One lens position corresponding to the exposure period of the partial image is simulated.

  FIG. 9 shows an example in which the focus lens 13 is moved at a half point of each exposure period. Therefore, the ratio between the first period and the second period in each exposure period is 1: 1, and the lens position to be imitated is just an intermediate point between the lens position before the movement and the lens position after the movement. It becomes. In FIG. 9, as in FIG. 5, the exposure period at the lens position before the movement of the focus lens 13 in each exposure period is indicated by a solid line, and the exposure period at the lens position after the movement is indicated by a dotted line.

  Since a blank period is inserted between the frame periods, when the lens position of the focus lens 13 is updated at equal intervals, in the exposure period of the first partial image Ip1 that is first exposed across the blank period, The lens position is not updated at the intermediate point.

  On the other hand, in the operation example 2, in order to always keep the ratio between the first period and the second period constant, the movement timing of the last lens position in a certain frame period and the first lens position in the next frame period Is set to a period obtained by adding the blank period to the period between the other movement timings. Thereby, the lens position is updated at the midpoint of the exposure period of the first partial image Ip1 in the next frame period.

  The focus adjustment unit 47 instructs the drive signal setting unit 48 to move the focus lens 13 at a specific point in each exposure period. The drive signal setting unit 48 sets a drive signal for moving the focus lens 13 at a specific point in each exposure period in the lens driving unit 20 in accordance with an instruction from the focus adjustment unit 47. The image processing unit 41 calculates the evaluation value for each of the first partial image Ip1, the second partial image Ip2, the third partial image Ip3, and the fourth partial image Ip4, and passes the evaluation value to the focus adjustment unit 47. The focus adjustment unit 47 selects the partial image having the highest evaluation value, and determines the forged lens position of the partial image as the in-focus position.

  As described above, according to the embodiment, a contrast detection method is obtained by shortening the lens position update interval of the focus lens 13 and acquiring the evaluation value from each of a plurality of partial images included in one frame image. Processing time can be shortened by auto-focus processing using the. In other words, shortening the lens position update interval leads to early acquisition of information necessary for focus determination, and shortens the processing time until the focus position is determined.

  In the first operation example, by shortening the exposure period of each partial image, the lens position does not change during each exposure period even if the update interval of the lens position is shortened. Therefore, the evaluation value of each partial image simply represents the evaluation value at one lens position, and the ratio calculation required in the operation example 2 is not necessary, and the amount of calculation is reduced compared to the operation example 2. be able to.

  In the operation example 2, even if the lens position is changed during one exposure period, one lens position corresponding to the exposure period is determined from the ratio of the first period and the second period in the exposure period. By falsifying by calculation, the update interval of the lens position can be shortened while ensuring the length of the exposure period. By ensuring the length of the exposure time, the solid-state imaging device 31 can sufficiently acquire the light amount of each partial image, and the deterioration of the calculation accuracy of the evaluation value can be suppressed.

  The method described in the operation example 1 and the operation example 2 is suitable for application to a projector. The autofocus of the projector has a characteristic that the depth of field is substantially constant over the entire imaging region, and a characteristic that a designer can designate an image that should be the basis of the evaluation value as a pattern image.

  Therefore, the subject depth of the plurality of partial images included in one frame image is substantially constant. In the case of a natural image, there are cases where the subject depth varies depending on the region of the frame image. For example, there is a case where the depth at which the main subject is reflected differs from the depth at which the background is reflected.

  Further, by projecting a pattern image having a regular pattern, it is possible to obtain a partial image having the same pattern no matter which region in the frame image is extracted. Therefore, a plurality of partial images having the same pattern can be extracted from one frame image.

  As described above, the method described in the operation example 1 and the operation example 2 is suitable for application to a projector having the above characteristics. However, the method is not limited to application to a projector, but can be applied to all cameras. This is particularly effective when some of the above characteristics are provided. For example, in studio photography, the distance to the main subject and the background is substantially fixed, and the composition is also substantially fixed. The same applies to the automatic shooting in the shooting box.

  Even when a natural image is taken with a digital camera, when a frame image is divided into left and right parts and two partial images are extracted, there is a high possibility that the left and right partial images have a certain depth of subject.

  In addition, when the operation example 1 and the operation example 2 are applied to the camera, the focus lens is provided in the front stage of the solid-state imaging device mounted on the imaging unit of the camera.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  For example, the focus adjustment unit 47 may adaptively change the size of the partial image according to the amount of light exposed by the solid-state imaging device 31. For example, when the amount of light falls below a predetermined threshold, the size of the partial image may be switched to a larger size. Thereby, the autofocus accuracy can be improved.

  DESCRIPTION OF SYMBOLS 10 Projection part, 11 Light source, 12 Light modulation part, 13 Focus lens, 20 Lens drive part, 30 Imaging part, 31 Solid-state image sensor, 32 Signal processing circuit, 40 Control part, 41 Image processing part, 42 Area setting part, 43 HPF, 44 integration unit, 45 image memory, 46 image signal setting unit, 47 focus adjustment unit, 48 drive signal setting unit, 100 projection display apparatus, 200 projection plane.

Claims (5)

A projection unit that projects an image onto a projection surface via a lens;
A lens driving unit that moves the position of the lens;
An imaging unit that captures the image projected on the projection plane;
A control unit for determining the position of the lens based on the definition of the plurality of images respectively captured by the imaging unit at a plurality of lens positions;
The control unit moves the lens to the lens driving unit a plurality of times within one frame period, and acquires the definition of a plurality of partial images exposed at each lens position from within one frame image. A projection display apparatus characterized by the above. The exposure timing of each corresponding partial region of the solid-state imaging device mounted on the imaging unit is set so that the exposure periods of the plurality of partial images do not overlap each other,
The projection display apparatus according to claim 1, wherein the control unit moves the lens to the lens driving unit in synchronization with the exposure timing. When the exposure period of the partial image is set to be longer than the period during which the lens position is switched,
The control unit is a lens corresponding to the exposure period of the partial image, based on a ratio of a period exposed at the lens position before the movement and a period exposed at the lens position after the movement in the exposure period. The projection display apparatus according to claim 1, wherein the position is simulated.   4. The partial image according to claim 1, wherein the partial image is an image picked up by n (n is a natural number) main scanning lines of a solid-state image pickup element mounted on the image pickup unit. Projection display device. A focus control circuit to be mounted on a device including an imaging element, a lens, and a driving element for moving the lens,
An image processing unit that calculates the sharpness of a plurality of images respectively captured by the imaging device at a plurality of lens positions;
A focus adjustment unit that determines the position of the lens based on the sharpness of the plurality of images calculated by the image processing unit,
The focus adjustment unit causes the driving element to move the lens a plurality of times within one frame period, and causes the image processing unit to calculate the definition of a plurality of partial images exposed at the respective lens positions. Focus control circuit.

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