JP2019040042A - Image projection device - Google Patents

Abstract

To reduce a scroll noise potentially occurring according to an image signal when rotating a wavelength conversion element.SOLUTION: An image projection device projects an image through converting illumination light by optical modulation means 105 according to an image signal. The device includes: a wavelength conversion element 108 configured to convert at least part of first light from a light source 111 to second light with a wavelength different from the first light to generate illumination light; rotation means 112 configured to rotate the wavelength conversion element; and control means 106 configured to control a rotation speed of the rotation means according to the image signal.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image projection apparatus such as a liquid crystal projector.

  In an image projection apparatus (hereinafter, referred to as a projector), when a light modulation element such as a liquid crystal panel that modulates illumination light is driven by a digital drive method, that is, a pulse width modulation (PWM) method, band-like luminance unevenness is generated in a projection image. Moving scroll noise may occur. Some projectors use a wavelength conversion element such as a phosphor that converts the wavelength of a part of excitation light emitted from a solid-state light source such as a laser to generate illumination light including excitation light and wavelength conversion light. is there. The wavelength conversion element is rotated so that excitation light does not continuously enter only a part of the wavelength conversion element. Patent Document 1 discloses a method of reducing scroll noise generated by the relationship between the modulation frequency of the light modulation element and the rotation speed of the phosphor by controlling the rotation speed of the phosphor.

JP 2012-103398 A

  However, Patent Document 1 does not mention that the scroll noise is also generated depending on the gradation and color of the video signal input to the projector.

  The present invention provides an image projection apparatus capable of reducing scroll noise that may be generated according to a video signal when a wavelength conversion element is rotated.

  An image projection apparatus according to an aspect of the present invention projects an image by modulating illumination light by a light modulation unit based on a video signal. The apparatus converts at least part of the first light from the light source into second light having a wavelength different from that of the first light to generate illumination light, and rotates the wavelength conversion element. Rotating means and control means for controlling the rotation speed of the rotating means in accordance with the video signal.

  The control method according to another aspect of the present invention generates illumination light by converting at least part of the first light from the light source into second light having a wavelength different from that of the first light. The present invention is applied to an image projection apparatus that includes a wavelength conversion element and a rotation unit that rotates the wavelength conversion element, and modulates the illumination light by a light modulation unit based on a video signal to project an image. The control method includes a step of acquiring a video signal and a step of controlling the rotation speed of the rotating means in accordance with the video signal.

  Note that a computer program that causes the computer of the image projection apparatus to execute the control method also constitutes another aspect of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the scroll noise which may generate | occur | produce according to a video signal can be reduced in the image projection apparatus which rotates a wavelength conversion element.

1 is a block diagram illustrating a configuration of a projector that is Embodiment 1 of the present invention. FIG. 3 is a flowchart showing phosphor rotation speed control processing in Embodiment 1. 3 is a diagram illustrating an example of a video signal output from a video signal processing unit in Embodiment 1. FIG. The figure which shows frequency distribution of the gradation in the said video signal. FIG. 5 is a diagram illustrating a table for determining the rotation speed of the phosphor in the first embodiment. The flowchart which shows the fluorescent substance rotational speed control process in Example 2 of this invention. The time table which shows the fluorescent substance rotational speed control process in Example 3 of this invention. The figure which shows the change of the target rotational speed and the actual setting rotational speed in fluorescent substance rotational speed control in Example 3. FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a projector as an image projection apparatus that is an embodiment of the present invention. A video signal (hereinafter referred to as an input video signal) 101 supplied from a video supply device such as a personal computer (not shown) is input to the signal processing unit 100. The signal processing unit 100 includes a video signal processing unit 102, a PWM drive unit 103, a phosphor rotation control unit 106, and a CPU 109.

  The video signal processing unit 102 performs, for the input video signal 101, resolution conversion processing, keystone processing, other geometric deformation processing, hue conversion processing, gamma processing, color unevenness correction processing, and other gradation conversion processing. Perform video signal processing. Thus, a video signal for driving a liquid crystal panel (to be described later) (hereinafter referred to as a panel driving video signal) is generated. The panel drive video signal indicates each gradation of the R (red) component, the G (green) component, and the B (blue) component as 12-bit digital data.

  The PWM drive unit 103 generates R, G, and B panel drive signals as pulse width modulation (PWM) signals according to the respective gradations of the R, G, and B components of the panel drive video signal, The data is output to a panel driver 104 for R, G, and B (only one is shown in the figure). Each of the R, G, and B panel drivers (modulation element driving means) 104 is a liquid crystal panel (only one in the figure) as an R, G, and B light modulation element according to the input panel drive signal. 105) is driven by a pulse width modulation method, that is, a digital drive method.

  Specifically, the panel driver 104 divides one frame period (or one field period) of the video signal into a plurality of subframe periods. Then, in accordance with the panel drive signal (that is, the gradation of the panel drive video signal), the voltage applied to each pixel of the liquid crystal panel 105 in each subframe period is lower than the first voltage and the first voltage. Control to the second voltage. In other words, application and non-application of a predetermined voltage to each pixel are controlled. The longer the time during which the first voltage or the predetermined voltage is applied to the pixel (the number of subframe periods is larger), the higher the gradation that the pixel forms. In this way, various gradations can be formed (displayed) on each pixel of the liquid crystal panel 105.

  The R, G, and B liquid crystal panels 105 modulate the incident R illumination light, G illumination light, and B illumination light in accordance with the gradation for each pixel, respectively, thereby R image light, G image light, and B image light. 5 is generated. The R image light, the G image light, and the B image light 5 are synthesized by a color synthesis optical system (not shown) and projected onto a projection surface such as a screen via a projection optical system (not shown). Thereby, a full-color image is displayed on the projection surface.

  In the projector of this embodiment, the phosphor 108 as a wavelength conversion element is used to generate illumination light modulated by the liquid crystal panel 105. When the B light as the first light from the blue laser as the solid light source 111 is irradiated to the phosphor 108 as excitation light, a part of the wavelength is converted by the fluorescence (phosphorescence) action of the phosphor 108, and the B light Is converted into Y (yellow) light as fluorescence which is second light having a different wavelength. W (white) illumination light in which B light and Y light (G light + R light) are mixed is separated into R light, G light, and B light by a color separation optical system (not shown) and is used for R, G, and B light. Guided to the liquid crystal panel 105.

  In addition, the wavelength conversion element should just wavelength-convert at least one part of the light from a light source, and may generate the illumination light by wavelength-converting all.

  The CPU 109 controls light emission and light emission intensity of the solid light source 111 through the light source driver (light source driving means) 110. The emission intensity is controlled by changing the duty ratio in the PWM driving of the solid state light source 111 by the light source driver 110.

  The phosphor 108 has a characteristic that the luminous efficiency of fluorescent light decreases as the temperature rises. For this reason, the fluorescent substance 108 is rotated by the motor 112 so that the same region of the fluorescent substance 108 is not continuously irradiated with the excitation light, and the temperature rise of the fluorescent substance 108 is suppressed. The motor 112 is driven by the rotating phosphor driver 107. The rotating phosphor driver 107 and the motor 112 constitute rotating means.

  The phosphor rotation control unit (control means) 106 acquires the panel driving video signal output from the video signal processing circuit 102, and in response to the panel driving video signal, the motor 112, that is, the motor 112 through the rotating phosphor driver 107. Controls the rotational speed (number of revolutions) of the phosphor 108. Specifically, the phosphor rotation control unit 106 sets the rotation speed of the phosphor 108 according to the gradation and color of one frame image constituting the panel driving video signal. The phosphor rotation control unit 106 instructs the rotating phosphor driver 107 to rotate the phosphor 108 at the set rotation speed, and the rotating phosphor driver 107 rotates the motor 112 so that the phosphor 108 rotates at the instructed rotation speed. Drive.

  The flowchart of FIG. 2 shows the rotational speed control processing of the phosphor 108 performed by the phosphor rotation control unit (hereinafter simply referred to as the control unit) 106. The control unit 106 executes this process according to a control program as a computer program.

  In step 301, the control unit 106 calculates the frequency for each gradation of R, G, and B in one frame image of the panel drive video signal (hereinafter simply referred to as video signal) obtained from the video signal processing unit 102. Create a histogram to show. An example of the one-frame image is shown in FIG. FIG. 3 shows a lamp image of WUXG (1600 × 1200 pixels). A histogram created from this ramp image is shown in FIG.

  As shown in FIG. 4, the histogram class is composed of colors (R, G, and B) and gradations. 4096 gradations from 0 to 4095 are divided into predetermined gradation ranges, here, every 256 gradations. In this example, the width (class width) of all gradation ranges is set to be equal, but the width of all gradation ranges may not necessarily be equal.

  The detection frequency indicates the frequency of the gradation counted (detected) in each class. In FIG. 4, the detection frequencies of all the classes are the same, but in practice, various values are obtained depending on the video signal.

  In step 302, the control unit 106 weights the detection frequency for each class counted in step 301. Specifically, the detection frequency is multiplied by a weight according to the color (hereinafter referred to as color weight) and a weight according to the gradation (hereinafter referred to as gradation weight). In FIG. 4, the result obtained by multiplying the detection frequency by the composite weight which is a value of color weight × gradation weight is shown as the weighted frequency. Note that the detection frequency may be weighted according to elements other than color and gradation, and the weight is not limited to an integer value but may be a decimal value.

  The color weight indicates the degree that the person who sees this feels unnatural with respect to the scroll noise. In particular, in G where the person feels brightness, the color weight is set larger than the other colors. Similarly, the gradation weight is increased as the gradation at which scroll noise is conspicuous is higher. In FIG. 4, the gradation weights in R, G, and B are the same value, but they may be different from each other.

  In step 303, the control unit 106 sums up the weighting frequencies of a plurality of classes to which the same speed index is assigned among the weighting frequencies for each class calculated in step 302. The speed index is an index (index) that is given to the rotation speed of the phosphor 108, in which the scroll noise is most inconspicuous for each class (gradation range) or the scroll noise can be suppressed within an allowable range. In FIG. 4, a common speed index is set for the same class in R, G, and B, but different speed indexes may be set for the same class in R, G, and B.

  The processing result of step 303 is shown in FIG. For example, in FIG. 4, the sum of the weighting frequencies (120,000, 120,000, 120,000, 360,000, 360,000, 130000, 120000, 120,000, 120,000) of each of the three classes R, G, and B to which the velocity index 0 is assigned is 180,000. It is. Similarly, the sum of the weighting frequencies of a plurality of classes of R, G, and B to which the speed indexes 1 and 2 are assigned is a total frequency of 11400,000 and 6000000.

  In step 304, the control unit 106 selects the largest total frequency (maximum total frequency) among the total frequencies calculated in step 303. In the example shown in FIGS. 4 and 5, the total frequency of 11400,000 to which the speed index 1 is assigned is selected. Next, as shown in FIG. 5, the control unit 106 sets the rotation set for the speed index for which the maximum total frequency is obtained among the rotation speed candidates (7000, 9000, 12000 RPM) set in advance for each speed index. A speed candidate (here, 9000 RPM) is selected. Then, the selected rotation speed candidate is set as the rotation speed for actually rotating the phosphor 108.

  When the total frequency for each speed index is the same, the control unit 106 may select the rotation speed candidate set for any speed index. The rotation speed candidate set for the smaller value of the speed index may be preferentially selected.

  In step 305, the control unit 106 instructs the phosphor rotation driver 107 about the rotation speed set in step 304. As a result, the control unit 106 controls the motor 112 to rotate the phosphor 108 at a rotation speed set according to the gradation of the video signal.

  According to the present embodiment, by controlling the rotation speed of the phosphor 108 to a rotation speed that can reduce the scroll noise set according to the gradation and color of the video signal, the scroll noise in the projected image is not noticeable. Can be realized.

  In this embodiment, the rotation speed calculated in the process shown in FIG. However, in order to suppress sudden fluctuations in the rotational speed of the phosphor 108, the rotational speed set in step 304 is set as a target value, and the actual rotational speed of the phosphor 108 is gradually changed toward the target value. May be. This will be described in detail later as a third embodiment.

  The flowchart of FIG. 6 shows the rotational speed control process of the phosphor 108 performed by the control unit 106 in the second embodiment of the present invention. The control unit 106 executes this process according to a control program as a computer program. In the present embodiment, the control unit 106 is as described in the first embodiment (FIG. 2) only when the video signal from the video signal processing unit 102 is a video signal of a still image (hereinafter referred to as a still image signal). Then, the rotation speed control process according to the gradation of the video signal is performed. In other words, in the case of a video signal of a moving image (hereinafter referred to as a moving image signal), the rotation speed control process according to the gradation of the video signal is not performed. This is because scroll noise is not noticeable in moving images.

  In step 701, the control unit 106 determines whether or not the video signal is a still image signal by using a plurality of frame images constituting the video signal from the video signal processing unit 102. For example, the control unit 106 sequentially obtains a difference between pixel values corresponding to each other between two temporally continuous frame images in the plurality of frame images. Then, when the number of times that the difference is within the predetermined range exceeds the predetermined number, it is determined that the video signal is a still image signal. When the number of times the difference is within the predetermined range is equal to or less than the predetermined number, it is determined that the video signal is a video signal. Since a series of video signals may change between a moving image signal and a still image signal, this determination is repeated at a predetermined cycle.

  After determining that the video signal is a still image signal in step 701, the control unit 106 performs the processing in steps 301 to 305 described in the first embodiment and sets (changes or maintains) the rotation speed of the phosphor 108. Then, the determination in step 701 is performed again.

  On the other hand, the control unit 106 that has determined in step 701 that the video signal is a moving image signal proceeds to step 702 without performing the processing in steps 301 to 305 and instructs the phosphor rotation driver 107 to perform a predetermined rotation speed. Thereby, the control unit 106 controls the motor 112 to rotate the phosphor 108 at a predetermined rotation speed regardless of the gradation of the video signal.

  The above-described method for determining whether the video signal is a still image signal or a moving image signal is an example, and any other determination method may be used. For example, the video signal may be determined as a still image signal when the change amount of the total value or the maximum value of all the pixel values for each frame image is within a predetermined range. Further, when the amount of change in the histogram of the video signal created in step 301 is within a predetermined range, it may be determined that the video signal is a still image signal.

  According to the present embodiment, the above control is performed by controlling the rotation speed of the phosphor 108 according to the gradation and color of the video signal only when the video signal in which scroll noise is conspicuous is a still image signal. The increase in power consumption due to can be suppressed.

  Next, Embodiment 3 of the present invention will be described with reference to FIGS. In Example 1 and Example 2, the rotational speed selected in Step 304 is instructed to the rotating phosphor driver 107 as it is. On the other hand, in the present embodiment, the rotational speed selected in step 304 is set as a target value (hereinafter referred to as target rotational speed) and the actual set rotational speed (hereinafter, actual set rotational speed) of the phosphor 108 is directed toward this. Are gradually changed, that is, gradually accelerate or decelerate.

  FIG. 7 is a time table showing an example of phosphor rotation speed control in the present embodiment. This phosphor rotation speed control method is a method generally called P control (proportional control). In the present embodiment, the control method described is merely an example, and other control methods may be used.

  The first line in FIG. 7 shows the meaning of numerical values arranged vertically. From left, time (seconds), target rotation speed, error, P, speed change amount_min, speed change amount_max, actual speed change amount, and actual set rotation speed. The time (seconds) indicates the timing at which the target rotational speed and the actual set rotational speed are updated in the present embodiment, and the control unit 106 performs processing for bringing the actual set rotational speed closer to the target rotational speed every second. The target rotation speed is a rotation speed that finally rotates the phosphor 108 and is the rotation speed selected in step 304 of the first embodiment or the second embodiment as described above.

  The error is a value obtained by subtracting the current actual set rotational speed from the target rotational speed. For example, when the time (second) is 10, the target rotation speed is 12000, and the actual setting rotation speed one second before is 7000, so the error is 5000. P is a value obtained by multiplying the error by a fixed parameter KP, and is a candidate for an actual speed change amount described later.

  The speed change amount_min indicates a lower limit value of the actual speed change amount, and a fixed value −300 is set here. The speed change amount_max indicates the upper limit value of the actual speed change amount, and a fixed value 300 is set here.

  The actual speed change amount is used to derive a new actual set rotational speed (after one second) by adding this to the current actual set rotational speed. When P is not less than the speed change amount_min and not more than the speed change amount_max, P is set as the actual speed change amount. When P is smaller than the speed change amount_min, the speed change amount_min is used as the actual speed change amount. When P is larger than the speed change_max, the speed change amount_max is used as the actual speed change amount.

  FIG. 8 shows changes in the actually set rotational speed by phosphor rotational speed control according to the time table shown in FIG. The dotted line in the figure indicates the change in the target rotation speed, and the solid line indicates the change in the actual set rotation speed. As shown in the figure, the actual set rotational speed changes so as to follow gently with respect to the rapidly changing target rotational speed. As a result, it is possible to suppress sudden fluctuations in the rotational speed of the phosphor 108 while controlling the rotational speed of the phosphor 108 to a rotational speed at which scroll noise can be reduced.

  In the present embodiment, the case where the phosphor rotation speed control is performed by feedforward control has been described. However, the actual rotation speed of the phosphor 108 may be detected to perform feedback control.

(Other examples)
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

  Each embodiment described above is only a representative example, and various modifications and changes can be made to each embodiment in carrying out the present invention.

111 Excitation light source 108 Phosphor 105 Liquid crystal panel (light modulation element)
103 PWM drive unit 106 phosphor rotation control unit 107 phosphor rotation driver 112 motor

Claims (11)

An image projection apparatus for projecting an image by modulating illumination light by a light modulation means based on a video signal,
A wavelength conversion element that generates illumination light by converting at least part of the first light from the light source into second light having a wavelength different from that of the first light;
Rotating means for rotating the wavelength conversion element;
An image projection apparatus comprising: a control unit that controls a rotation speed of the rotation unit according to the video signal.   The image projection apparatus according to claim 1, wherein the control unit controls the rotation speed in accordance with a gradation of the video signal.   The image projection apparatus according to claim 1, wherein the control unit controls the rotation speed according to a color of the video signal. Light source driving means for driving the light source by a pulse width modulation method;
4. The image projection apparatus according to claim 1, further comprising: a modulation element driving unit that drives the light modulation element by a pulse width modulation method based on the video signal. 5.   The image projection apparatus according to claim 2, wherein the control unit detects a frequency of gradation for each predetermined gradation range in the video signal, and sets the rotation speed using the frequency.   The image projecting apparatus according to claim 5, wherein the control unit sets the rotation speed using the frequency weighted according to a gradation or a color.   7. The control unit according to claim 5, wherein the control unit sets, as the rotation speed, a rotation speed candidate for the gradation range having the highest frequency among rotation speed candidates set for each of the gradation ranges. The image projection apparatus described.   The said control means controls the said rotational speed according to the said video signal, when it determines with the said video signal being a video signal of a still image, The any one of Claim 1 to 7 characterized by the above-mentioned. The image projection apparatus described.   9. The image projection apparatus according to claim 1, wherein the control unit gradually accelerates or gradually decelerates the rotation of the rotation unit toward the rotation speed set as a target value. 10. . A wavelength conversion element that converts at least part of the first light from the light source into second light having a wavelength different from that of the first light to generate illumination light, and a rotating unit that rotates the wavelength conversion element. A method for controlling an image projection apparatus for projecting an image by modulating the illumination light by a light modulation means based on a video signal,
Obtaining the video signal;
And a step of controlling the rotation speed of the rotating means in accordance with the video signal. A wavelength conversion element that converts at least part of the first light from the light source into second light having a wavelength different from that of the first light to generate illumination light, and a rotating unit that rotates the wavelength conversion element. A computer program for causing a computer of an image projection apparatus to project an image by modulating the illumination light by a light modulation unit based on a video signal,
The control process is
Processing for obtaining the video signal;
And a process for controlling the rotational speed of the rotating means in accordance with the video signal.