JP2005049660A - Projector and focusing method for projector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projector accurately obtaining contrast characteristic so as to perform accurate focusing by processing a contrast value on a return-path and making it approximate to a contrast value on a outward-path. <P>SOLUTION: The projector 2 is equipped with a projection lens 8 for projecting an image on a screen 1, a lens moving means 23 for moving the lens 8 between preset positions in an optical axis direction, a passive sensor 21 for reading light from the image on the screen 1 and outputting an image signal, an arithmetic means 22 for calculating the contrast value in a specified cycle by processing the image signal, and a focus detection means 5. The detection means 5 is constituted in such a way that the position of the lens 8 where the contrast value becomes maximum may be a focusing position after correcting the contrast value from the arithmetic means 22 so that the detection levels in the outward-path and the return-path where the lens 8 moves may be the same. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a projector that projects a desired image on a screen. More specifically, the present invention relates to a projector having an automatic focus adjustment function (autofocus (AF) function).

  In order to enhance the convenience for the user, the projector is preferably an apparatus having an AF function capable of automatically adjusting the focus of the image projected on the screen. The sensors used for focus adjustment include an active sensor that uses light emitted by itself (active sensor) and a passive sensor that detects light received from the object to be measured (screen in the case of a projector) without emitting light by itself. There are two types of sensors (Passive Sensor). Of these, the passive sensor does not require a light source and can be downsized. In addition, since there is a merit that measurement can be performed at a plurality of points on the screen, it is desirable to use a passive sensor for the projector.

  Conventionally, a technique called a hill-climbing type is widely known as a technique for performing focus detection. For example, Patent Document 1 describes automatic focus adjustment using this hill-climbing formula. This patent document 1 discloses automatic focus adjustment of an imaging apparatus such as a video camera. This Patent Document 1 discloses an automatic focus imaging apparatus that performs focus adjustment by moving a focus lens back and forth in the optical axis direction with a stepping motor, measuring a high-frequency component of a luminance signal from an imaging circuit, detecting a focal position. is doing. In the automatic focus detection apparatus described in Patent Document 1, the focus lens is moved between the infinity focal position and the closest focal position in order to focus an image formed on the image sensor. Then, the focus evaluation value of the output luminance signal from the imaging circuit is measured, and the position where the focus evaluation value is maximized is set as the focus position.

  In this type of hill-climbing focus detection, when the image to be photographed is in focus, the resolution is the highest (the contrast is the highest), so the light and darkness of fine pixels is displayed and the high-frequency component of the image is the highest. Is focused on. That is, the focus evaluation value substantially evaluates the magnitude of the contrast value, and the point where the contrast value is the highest is set as the in-focus position.

  In the technique disclosed in Patent Document 1, the stepping motor is driven to continuously move the focus lens in the optical axis direction, and an operation for searching for a point having the maximum contrast value is performed. Specifically, the contrast value is calculated for each pulse for driving the focus motor, and when the contrast value decreases continuously from a certain contrast value for a predetermined pulse, the contrast value is set to the maximum value, and this is set as the in-focus position. .

Japanese Patent Laid-Open No. 8-186752

  When the hill-climbing focus detection is applied to a projector, the level of the contrast value may be different when the projection lens is reciprocated. FIG. 7 is a diagram showing an example of the relationship between the contrast value and the projection lens position in the forward path F and the backward path B of the projection lens. The waveforms shown in FIG. 7 indicate different levels in the forward path F and the return path B of the projection lens. Note that the method of detecting the in-focus position in Patent Document 1 determines the maximum contrast value when the contrast value decreases continuously for a predetermined pulse after a large contrast value is detected, so the projection lens does not necessarily reach the final position. Does not move. However, a similar problem occurs when the return is made after the maximum contrast value is determined. In this specification, a path from the initial position to the final position of the projection lens is referred to as an outward path, and the reverse is referred to as a return path. Further, the end position from the initial position is between the predetermined positions.

  As shown in FIG. 7, the reason why the contrast value level in the forward path F and the contrast value level in the return path B are different may be the noise at the place where the projector is installed or the influence of pulsating light from the fluorescent lamp. It is done. As an example, the influence of pulsating light from a fluorescent lamp will be described. When focus detection of the projector is performed, light (reflected light) from an image projected on the screen is received by a light receiving sensor, and a contrast value is calculated. However, the brightness of the fluorescent lamp changes at a predetermined cycle, while the light receiving sensor receives light from the image at a constant cycle. For example, when the light receiving period of the light receiving sensor coincides with the time when the fluorescent lamp emits intense light, the contrast value increases. On the contrary, when the period of the light receiving sensor coincides when the fluorescent lamp emits light weakly, the contrast value becomes small. Therefore, as shown in FIG. 7, a situation occurs in which a relatively high contrast value is calculated in the forward path F and a relatively low contrast value is calculated in the reverse path B. Naturally, on the contrary, a low contrast value may be calculated in the forward path F, and a high contrast value may be calculated in the return path B.

  In order to accurately detect the in-focus position, it is desirable to confirm the maximum contrast value at the predetermined lens position detected in the forward path F also in the return path B and finally determine the in-focus position. However, if the contrast level detection levels are different between the forward path F and the backward path B as described above, it is difficult to confirm the same maximum contrast value on the backward path B, which causes a problem that accurate focus adjustment cannot be performed.

  SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a projector that can solve the above-described conventional problems and can perform focus adjustment with high accuracy based on a contrast value with a constant level in a round trip without being affected by the surrounding environment. To do.

  The object is to project a projection lens for projecting an image on a screen, lens moving means for moving the projection lens between predetermined positions in the optical axis direction, and receiving an image on the screen and outputting an image signal at a predetermined cycle. An output passive sensor, an arithmetic means for processing the image signal to calculate a contrast value, and correcting the contrast value so that the level of the contrast value is the same in the forward path and the return path in which the projection lens moves, This can be achieved by a projector including a focus detection unit that sets the position of the projection lens where the contrast value is maximized as the in-focus position of the projection lens.

  According to the present invention, when a level difference occurs between the forward path and the backward path in the contrast value calculated by the calculation means, the focus detection means confirms the position of the projection lens where the contrast value is maximized after correcting the contrast value. Thus, the in-focus position is detected. Therefore, it is possible to cancel the influence from the external environment where the projector is installed and always perform focus detection with high accuracy.

  The focus detection unit compares the contrast value at the same position on the forward path and the return path on which the projection lens moves, sets a coefficient α that makes the level of the contrast value the same, and sets the focus position on the return path. It is possible to configure so as to perform detection. By setting the coefficient α, it is possible to easily confirm and correct the difference in contrast value in the round trip. Further, the focus detection means determines a focus position as a position where the position of the projection lens where the contrast value is maximum on the forward path and the position of the projection lens where the contrast value is maximum on the backward path are the same. It is further desirable to do so. In this way, the in-focus position can be determined with higher accuracy. A line sensor can be adopted as the passive sensor. When a passive line sensor is used, the configuration can be simplified and the cost can be reduced.

  Further, the object is to move the projection lens for projecting an image on the screen between predetermined positions in the optical axis direction, receive the image on the screen, and output an image signal at a predetermined cycle; A calculation step of calculating the contrast value by processing the image signal, a correction step of correcting the contrast value so that the level of the contrast value is the same in the forward path and the return path in which the projection lens moves, and This can also be achieved by a focus adjustment method for the projector, which includes a focus detection step in which the position of the projection lens with the maximum contrast value is the in-focus position.

  As described above, according to the present invention, it is possible to provide a projector capable of performing stable focus adjustment without being influenced by an installed environment.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best embodiment according to the present invention will be described in detail with reference to the accompanying drawings.

  As shown in FIG. 1, the projector 2 of this embodiment receives light (reflected light) from an image projected on the screen 1 via the projection lens 8 and outputs a contrast value for determining the focal position. An automatic focus detection device 20 is included. The projector 2 includes first and second line-type passive distance measuring devices 3 and 4 that accurately measure the relative inclination angle of the screen 1 in a horizontal plane and a vertical plane. The projection lens 8 may be configured as a projection lens optical system including a plurality of lenses.

  The control circuit 5 shown in FIG. 1 controls the automatic focus detection device 20 and the first and second line type passive distance measuring devices 3 and 4. The control circuit 5 controls a projection image generation unit 6 that inputs an image from a device such as a personal computer (not shown) and outputs image information, and a display drive unit 7 that outputs an image to the projection lens 8. Furthermore, the control circuit 5 moves the projection lens 8 along the optical axis by controlling the optical system driving unit 23 including a pulse motor and the like.

  That is, the control circuit 5 adjusts the focal length by moving the projection lens 8 via the optical system driving unit 23 based on the output from the first calculation unit 22 of the automatic focus detection device 20. Further, the control circuit 5 is configured to output the projector 2 based on outputs from the second calculation unit 32 of the first line type passive distance measuring device 3 and the third calculation unit 42 of the second line type passive distance measuring device 4. The relative tilt angles of the screen 1 with respect to the horizontal and vertical directions are calculated. Then, the control circuit 5 controls the projection image generation unit 6 and the display drive unit 7 so as to correct the trapezoidal distortion based on the calculated tilt angle, and enlarges the image projected on the top, bottom, left and right of the screen 1. , Reduce. Such a control circuit 5 can be constituted by a CPU, for example.

  The memory unit 10 stores data and commands necessary for the configuration of the projector 2, and data is stored as needed in the control circuit 5, the first calculation unit 22, the second calculation unit 32, the third calculation unit 42, and the like. And commands are received, and data of operation results are received from these units. The memory unit 10 has two types of memory devices such as a non-volatile flash memory and a volatile RAM, and stores necessary data and instructions and data used for a long time in the non-volatile memory device. Store data that is only used temporarily in a volatile memory device.

  The automatic focus detection apparatus 20 performs a predetermined calculation using a light receiving sensor 21 that receives light from an image projected on the screen 1 via the projection lens 8 and an image signal output from the light receiving sensor 21. And a first calculation unit 22 that outputs a contrast value at a predetermined cycle. As the light receiving sensor 21, for example, a passive sensor such as a CCD line sensor can be used. The structure can be simplified by using a line sensor.

  The first calculation unit 22 of the automatic focus detection apparatus 20 will be described with reference to FIG. As shown in FIG. 2, the first calculation unit 22 performs high-pass filter (HPF) 22 a that extracts a high-frequency component from the image signal input from the light receiving sensor 21, and amplitude detection of the luminance signal that includes only the high-frequency component. A detector 22b to perform, an A / D converter 22c for A / D converting the detection output of the detector 22b and converting it to a digital signal, and an integrator 22d for integrating the digital signal output from the A / D converter 22c And. A contrast (cont) value corresponding to the image signal is output from the integrator 22d. Note that the contrast value can be obtained as the sum of absolute values of output differences between adjacent pixels when, for example, a passive line sensor is used as the light receiving sensor.

  The contrast value has a characteristic that the contrast value becomes maximum at the in-focus position and decreases as the position deviates from the in-focus position. In this embodiment, using this characteristic, the contrast value of light received from the image projected on the screen 1 via the projection lens 8 is calculated, and the position of the projection lens 8 where the maximum contrast value is obtained is adjusted. Detect as the focal position.

  More specifically, first, an image pattern for autofocus is projected from the projection lens 8 onto the screen 1. The projection lens 8 is moved in the direction of the optical axis at a constant speed in the range from the initial position to the final position by the optical system driving unit 23. Here, the initial position is, for example, the position of the projection lens 8 at which the focus position of the image projected on the screen 1 is infinity. The final position is, for example, the position of the projection lens 8 at which the focus position of the image projected on the screen 1 is the closest point. Light from the image projected on the screen 1 via the moving projection lens 8 is received by the light receiving sensor 21, and the first arithmetic unit 22 calculates the contrast value of the image. Then, the control circuit 5 moves the projection lens 8 back and forth in the optical axis direction, confirms the position where the contrast value is maximized, and detects the in-focus position.

  However, as described above in the problem, the contrast detection level may differ between the forward path and the return path. The projector 2 has a configuration that can eliminate such a difference in contrast value in the round trip. This point will be described with reference to FIG. FIG. 3 is a diagram illustrating an example when different contrast values are detected in the forward path F from the initial position to the final position and the return path B from the final position to the initial position. FIG. 3 illustrates a case where the level of the contrast value in the forward path B is low.

  The correction when the level of the contrast value is different is executed by the control circuit 5. The contrast adjustment by the control circuit 5 will be described with reference to FIGS. The control circuit 5 moves the projection lens 8 between the initial position and the final position via the optical system driving unit 23. At the same time, the control circuit 5 calculates the contrast value by the first calculation unit 22 at a predetermined period T, and monitors this. In addition, the control circuit 5 stores the contrast value data in the round-trip path associated with the lens position of the projection lens 8 in the memory unit 10. Further, the control circuit 5 compares the contrast values calculated in the round-trip path, and corrects this if a level difference occurs in the contrast values. This point will be described in detail below with reference to FIG.

  The control circuit 5 confirms the contrast level immediately after starting the contrast detection on the return path B in which the projection lens 8 is moved from the final position toward the initial position. For example, the control circuit 5 compares the contrast values at the first time on the return path B (the time at which the contrast value was first calculated on the return path B), and determines the coefficient α for correction. The control circuit 5 moves the projection lens 8 at the same speed in the round-trip path, and causes the first calculation unit 22 to calculate at the same period T. Therefore, the contrast value F (T (E-1)) at the time T (E-1) immediately before the final time TE (time to reach the final position) in the forward path F and the first time T ( The contrast value B (T (1)) in 1) is substantially the same. Therefore, when the control circuit 5 confirms the contrast value B (T (1)) at the first time T (1) in the forward path B, the contrast value F (T (E-1)) in the forward path F from the memory unit 10. ) Is read and compared.

The control circuit 5 sets the coefficient α from, for example, the ratio expression [B (T (1)) / F (T (E-1))] = α. This coefficient α is a correction coefficient for the return path B with respect to the forward path F, or a weighting adjustment coefficient for making the contrast value identical. After setting the coefficient α, the control circuit 5 detects the in-focus position based on the corrected contrast value obtained by multiplying the contrast value calculated from the first calculation unit 22 in the return path B by the coefficient α. Since the corrected contrast value is corrected to the same level as that of the forward path F, the contrast value can be detected on the same path in the backward path B. Therefore, the projector 2 can detect the in-focus position with high accuracy by performing a hill-climbing operation of confirming the maximum contrast value detected in the forward path F on the return path B.

  An example of the focus detection operation executed by the control circuit 5 described above will be described in more detail with reference to the flowcharts shown in FIGS. For example, when the power switch of the projector 2 is turned on, the control circuit 5 takes out a pattern image stored in advance from the projection image generation unit 6, sends it to the display drive unit 7, and projects it onto the screen 1 through the projection lens 8. To do. Further, the control circuit 5 moves the step motor of the optical system driving unit 23 to move the projection lens 8 to the initial position (S11).

  Subsequently, the control circuit 5 starts to extend the projection lens 8 at the initial position, that is, to move to the forward path F (S12). At the same time, the control circuit 5 drives and controls the light receiving sensor 21 (S13). Then, the image signal (sensor data) detected by the light receiving sensor 21 is read by the first calculation unit 22 (S14). The first calculation unit 22 performs A / D conversion processing or the like (S15), and calculates a contrast value at a predetermined period T (S16). The contrast value output from the first calculation unit 22 is supplied to the control circuit 5.

  The control circuit 5 compares the contrast value calculated at a predetermined cycle from the first calculation unit 22 with the previously held trust value (S17), and updates Max_cont when a larger contrast value is detected. (S18). The detection of the contrast value is continued until the projection lens 8 reaches the final position (S19).

  When it is confirmed in step 19 that the projection lens 8 has reached the final position, the detection of the contrast value in the forward path F is terminated. At this time, the control circuit 5 stores the contrast value data in the forward path F in the memory unit 10. This data is formed so that the position of the projection lens 8 in the forward path F and the contrast value can be confirmed in association with each other. Therefore, the position of the projection lens 8 at which the maximum contrast value is confirmed, the contrast value F (T (E-1)) at the time immediately before the projection lens 8 reaches the final position (E-1), etc. are easily read out. Can be put out.

  Subsequently, the control circuit 5 retracts the projection lens 8 from the final position, that is, starts to move the projection lens 8 in the backward path B direction, and similarly executes the calculation of the contrast value by the first calculation unit 22 ( S21). Then, when the first contrast value B (T (1)) is calculated, the control circuit 5 obtains the contrast value F (T (E−) immediately before the final position (E−1) of the forward path F obtained previously. The coefficient α is set by comparison with 1)) (S22). Thereafter, in the return path B, the control circuit 5 calculates a corrected contrast value obtained by multiplying the contrast value calculated from the first calculation unit 22 by the coefficient α (S23). The control circuit 5 performs detection by moving the projection lens 8 toward the forward path until the corrected contrast value becomes substantially the same value as the maximum contrast value (Max_cont) confirmed in the forward path F (S24). When the corrected contrast value almost the same as the maximum contrast value is confirmed in step 24, the control circuit 5 confirms that the projection lens 8 is at the same position in the round trip (S25). Finally, the control circuit 5 detects this position as an in-focus position (S26), and ends the processing according to this flowchart in which the lens driving is stopped (S27).

  In the first embodiment described above, the control circuit 5 included in the projector 2 functions as a focus detection means, and when the contrast values are different in the round trip, the levels are adjusted so that they are the same, and then the in-focus position is set. Therefore, even when the light received by the light receiving sensor 21 changes due to the influence of the installed external environment, the in-focus position can be reliably detected. Theoretically, the coefficient α is 1 when there is no difference in the detection level of the contrast value between the forward path F and the backward path B. However, even when there is substantially no difference in the detection level, it is very rare that the coefficient α is 1. Therefore, if the coefficient α is close to 1 and the contrast detection level difference falls within a range of, for example, about ± 5%, it may be processed that there is no difference in contrast value. In this case, the control circuit 5 may be set so that the corrected contrast value is calculated with the coefficient α = 1 or the contrast value is confirmed in the forward path B without calculating the corrected contrast value. In the above example, the correction is performed by multiplying the coefficient α by the contrast value, but it is also possible to apply adding the coefficient α as an offset or adding the offset coefficient β by multiplying the coefficient α.

  In the above example, the initial position is the infinity side, but it may be the closest point side opposite to this. Further, in the above flowchart, in order to detect the in-focus position more reliably, it is confirmed in step 25 that the projection lens 8 is in the same position in the round-trip path, but this step can be omitted. In the above flowchart, the process is completed when a (corrected) contrast value corresponding to the maximum contrast value of the forward path F is confirmed on the return path B, but the focus position is finally detected after the contrast value is detected to the initial position. May be confirmed.

  In the first embodiment described above, the automatic focus detection device 20 that outputs a contrast value for determining the focus position of the projection light, and the first and second line types that measure the relative tilt angle of the screen 1 with respect to the projector 2. A configuration in which the passive distance measuring devices 3 and 4 are separately provided is shown. A second embodiment shown in FIG. 6 is a configuration example in which one of the first and second line type passive distance measuring devices 3 and 4 has the function of the automatic focus detection device 20 shown in the first embodiment. The same parts as those shown in FIG.

  In the present embodiment, line sensors are employed for the imaging units 31 and 41 of the first and second line type passive distance measuring devices 3 and 4. The output of either of the line sensors is calculated by the second calculation unit 32 or the third calculation unit 42, and the contrast value of the image is calculated. The control circuit 5 detects the position where the contrast value is maximized based on the contrast value output from one of the first and second line type passive distance measuring devices 3 and 4, and detects the position from the projection lens optical system 8. Alignment is performed so that the image is projected onto the screen 1. In the second embodiment, since the distance measuring device is used to measure the contrast value for detecting the focal position of the projection light, the number of parts of the projector having the tilt correction function as well as the AF function can be reduced. .

  The preferred embodiment of the present invention has been described in detail above. However, the present invention is not limited to the specific embodiment, and various modifications can be made within the scope of the gist of the present invention described in the claims. Deformation / change is possible.

1 is a block diagram illustrating an outline of a projector according to a first embodiment. It is a block diagram of the 1st calculating part of the automatic focus detection apparatus contained in the projector shown in FIG. It is the figure which showed an example when a different contrast value is detected by the outward path | route which goes to an end position from an initial position, and the return path | route which goes to an initial position from an end position. It is the figure which showed the flowchart performed by the operation | movement of the focus detection performed by the control circuit. It is the figure which showed the flowchart performed by the operation | movement of the focus detection performed by the control circuit. FIG. 6 is a block diagram schematically illustrating a projector according to a second embodiment. It is the figure which showed an example of the relationship between the contrast value in the outward path | route of a projection lens, and a projection lens position regarding a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Screen 2 Projector 3 1st line type passive distance measuring device 4 2nd line type passive distance measuring device 5 Control circuit 8 Projection lens 20 Automatic focus detection apparatus 21 Light receiving lens 22 1st calculating part 23 Optical system drive part 32 2nd Operation unit 42 Third operation unit

Claims (5)

A projection lens for projecting an image on the screen;
Lens moving means for moving the projection lens between predetermined positions in the optical axis direction;
A passive sensor that receives an image on the screen and outputs an image signal at a predetermined period;
Arithmetic means for processing the image signal to calculate a contrast value;
The contrast value is corrected so that the level of the contrast value is the same in the forward path and the return path in which the projection lens moves, and the position of the projection lens where the contrast value is maximized is the in-focus position of the projection lens. And a focus detection means. 2. The focus detection unit compares the contrast values at the same position on the forward path and the return path on which the projection lens moves, and sets a coefficient α that makes the level of the contrast value the same. The projector described. The focus detection means sets a position at which the position of the projection lens where the contrast value is maximized on the forward path and the position of the projection lens where the contrast value is maximized on the return path coincide as the in-focus position. The projector according to claim 1. The projector according to claim 1, wherein the passive sensor is a line sensor. An image light reading step of moving a projection lens that projects an image on a screen between predetermined positions in an optical axis direction, receiving an image on the screen and outputting an image signal at a predetermined period;
An arithmetic step of processing the image signal to calculate a contrast value;
A correction step of correcting the contrast value so that the level of the contrast value is the same in the forward path and the return path in which the projection lens moves;
And a focus detection step in which the position of the projection lens having the maximum corrected contrast value is the in-focus position.

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