JP6527572B2 - Laser projection display - Google Patents

Description

The present invention relates to a laser projection display apparatus which performs image display by scanning light source light such as a semiconductor laser with a two-dimensional scanning mirror such as a MEMS (Micro Electro Mechanical Systems) mirror.

In recent years, small projection projectors using MEMS and a semiconductor laser light source are in widespread use. For example, Patent Documents 1 and 2 disclose a projector which projects an image by scanning a biaxial MEMS mirror or scanner in the horizontal and vertical directions and simultaneously modulating a laser light source.
In a small projection projector using a semiconductor laser as described above, the semiconductor laser used is known to have a problem that the white balance of the display screen changes because the amount of light and forward current characteristics change with temperature.

In Patent Document 2, a test signal is inserted in a blanking period which is a non-image display period, light modulation is performed on an optical modulator, and actual gradation characteristics and ideal characteristics calculated by a microprocessor are fed back. A tone correction device is disclosed that is stored in a storage device and that performs tone correction automatically while performing normal operation.

JP, 2006-343397, A Unexamined-Japanese-Patent No. 5-224166

However, in the technology described in Patent Document 2, the brightness of the projected image, that is, the light control operation for changing the light intensity is not considered. That is, since gradation correction corresponding to a plurality of light intensities is not taken into consideration, it can not cope with light adjustment operation. Further, a method of performing gradation correction by making the current control range in the display period different from the current control range in the return period as disclosed in the following embodiment is not described.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a laser projection display device in which white balance change of a display image due to change of temperature is reduced while maintaining the display gradation number at the time of light control operation. Do.

In order to solve the above problems, the present invention is a laser projection display device that projects laser light of a plurality of colors according to an image signal to display an image according to the image signal, and the laser of the plurality of colors A laser light source for generating light; a laser light source drive unit for driving the laser light source to generate a laser beam corresponding to the image signal; and a laser beam generated by the laser source according to a synchronization signal related to the image signal The scanning unit for scanning and projecting, an optical sensor for detecting the light quantity of the laser light generated by the laser light source, and processing the image signal based on the light quantity of the laser light detected by the optical sensor to drive the laser light source And an image processing unit for supplying the image data to the image processing unit;
When acquiring data for the light amount of the laser beam detected by the light sensor to become a predetermined value for a plurality of luminance levels in the retrace period of the image signal, and projecting and displaying the image signal It is characterized in that an image signal to be supplied to the laser light source drive unit is processed based on the data.

Further, in the laser projection display device, the image processing unit may set a plurality of luminances at a second luminance different from the first luminance which is the luminance of the display image currently displayed in the flyback period of the image signal. The data for obtaining the light intensity of the laser beam detected by the light sensor with respect to the level becomes each predetermined value, and the projection display of the image signal with the second luminance is performed based on the data It is characterized by processing an image signal supplied to a laser light source drive unit.

According to the present invention, it is possible to provide a laser projection display device in which the change in white balance of the display image due to the change in temperature is reduced while maintaining the number of display gradations during the light adjustment operation.

It is a block diagram which shows the basic composition of the laser projection display apparatus in a present Example. It is a block diagram which shows the signal processing part of a present Example. It is a characteristic view which shows an example of the light quantity-forward direction current characteristic of a semiconductor laser. It is a 1st characteristic view for demonstrating operation | movement of LUT of a present Example. It is a 2nd characteristic view for demonstrating operation | movement of LUT of a present Example. It is a block diagram which shows the image correction part of a present Example. It is a characteristic view explaining operation of LUT in case current control range is not changed. 7 is a flowchart showing the entire process of the first embodiment. 7 is a timing chart showing the entire process of the first embodiment. 15 is a flowchart showing the entire process of the second embodiment. FIG. 10 is a timing chart illustrating the entire process of the second embodiment. FIG. 16 is a timing chart showing an entire process of another form according to Example 2. FIG. 21 is a flowchart showing the entire process of the third embodiment. It is a characteristic view which shows an example of the light quantity-forward direction current characteristic of a semiconductor laser. FIG. 18 is a timing chart illustrating the entire process of the fourth embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description is for describing one embodiment of the present invention, and does not limit the scope of the present invention. Therefore, one skilled in the art can adopt an embodiment in which each or all of these elements are replaced with equivalent ones, and these embodiments are also included in the scope of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, the overall configuration of the laser projection display device according to the present invention and the output characteristics of the semiconductor laser will be described using FIGS. 1 to 3.

FIG. 1 is a block diagram showing a basic configuration of a laser projection display apparatus in the present embodiment. The laser projection display device 1 includes an image processing unit 2, a frame memory 3, a laser driver 4, and a laser light source 5.
, Reflection mirror 6, MEMS scanning mirror 7, MEMS driver 8, amplifier 9, light sensor 10, illuminance sensor 11
, CPU (Central Processing Unit) 12 and displays a display image 13.

The image processing unit 2 generates an image signal obtained by adding various corrections to an image signal input from the outside,
And the horizontal synchronization signal and the vertical synchronization signal synchronized with it are generated and supplied to the MEMS driver 8. Further, the image processing unit 2 controls a laser driver (hereinafter also referred to as a laser light source driving unit) 4 according to the information acquired from the CPU 12, and performs laser output adjustment to make the white balance constant. The details will be described later.

Here, the various corrections described above refer to image distortion correction due to scanning of the MEMS scanning mirror 7, LOO
This means that gradation adjustment of an image is performed by K UP TABLE (hereinafter referred to as LUT).
Note that the image distortion differs depending on the relative angle between the laser projection display 1 and the projection surface, the laser light source 5
And the optical axis deviation of the MEMS scanning mirror 7 or the like. The matters regarding the LUT will be described later.

The laser driver 4 receives the image signal output from the image processing unit 2 and modulates the laser light source 5 accordingly. The laser light source 5 is, for example, three semiconductor lasers (5a, 5b, 5c) for RGB.
And emits RGB laser light corresponding to the image signal for each of RGB of the image signal.

The three laser lights of RGB are combined by the reflection mirror 6 having three mirrors, and the MEMS
The light is irradiated to the scanning mirror 7. The reflection mirror 6 reflects light of a specific wavelength, and a special optical element that transmits light of other wavelengths is used. This optical element is generally called a dichroic mirror.

Specifically, the reflection mirror 6 reflects the laser beam (for example, R light) emitted from the semiconductor laser 5a and transmits a laser beam of another color, and the laser beam emitted from the semiconductor laser 5b ( For example, a dichroic mirror 6b that reflects G light and transmits laser light of another color, and a dichroic that reflects laser light (for example, B light) emitted from the semiconductor laser 5c and transmits laser light of another color The laser beam of R light, G light, and B light is combined into one laser light and supplied to the MEMS scanning mirror 7.

The MEMS scanning mirror 7 is a scanning unit of an image having a biaxial rotation mechanism, and can vibrate the central mirror unit in two directions, horizontal and vertical. The vibration control of the MEMS scanning mirror 7 is performed by the MEMS driver 8. The MEMS driver 8 generates a sine wave in synchronization with the horizontal synchronization signal from the image processing unit 2 and generates a sawtooth wave synchronized with the vertical synchronization signal to drive the MEMS scanning mirror 7.

The MEMS scanning mirror 7 receives a sinusoidal drive signal from the MEMS driver 8 and performs sinusoidal resonant movement in the horizontal direction. At the same time, in response to the sawtooth wave from the MEMS driver 8, constant velocity movement is performed in one direction in the vertical direction. As a result, the laser light is scanned along a locus as shown in the display image 13 of FIG. 1, and the scanning is synchronized with the modulation operation by the laser driver 4, whereby the input image is optically projected.

The light sensor 10 measures the light quantity of the projected laser light and outputs the light quantity to the amplifier 9. The amplifier 9 is
The output of the light sensor 10 is amplified according to the amplification factor set by the image processing unit 2 and then output to the image processing unit 2. In FIG. 1, the light sensor 10 is arranged to detect leak light of RGB laser light combined by the reflection mirror 6. That is, the optical sensor 10 is disposed on the opposite side of the semiconductor laser 5c with the reflection mirror 6c interposed therebetween. The reflection mirror 6c is a characteristic that transmits the laser light from the semiconductor lasers 5a and 5b and reflects the laser light from the semiconductor laser 5c, but since it can not be made to have the characteristic of 100% transmission or reflection, % Reflects (light of the semiconductor lasers 5a and 5b) or transmits (light of the semiconductor laser 5c). Therefore, by disposing the optical sensor 10 at the position shown in FIG. 1, the reflection mirror 6c transmits several percent of the laser beam from the semiconductor laser 5c and reflects several percent of the laser beam from the semiconductor lasers 5a and 5b. , And can be incident on the light sensor 10.

Further, the illuminance sensor 11 detects the illuminance around the laser projection display device 1 and outputs it to the CPU 12.
The CPU 12 receives a signal from the illuminance sensor 11 or a control signal from the outside, and supplies a light adjustment request signal for controlling the brightness of the display image 13 generated by the image processing unit 2 to the image processing unit 2.

  Next, the configuration of the embodiment of the present invention will be described using FIG.

FIG. 2 is a block diagram showing the signal processing unit of this embodiment, and is a diagram showing details of the internal configuration of the image processing unit 2 and the laser driver 4 of FIG. An image signal input from the outside of the image processing unit 2 is input to the image correction unit 20.

The image correction unit 20 performs image distortion correction caused by scanning of the MEMS scanning mirror 7 and gradation adjustment of the image by the LUT. The gradation adjustment of the image by the LUT performed by the image correction unit 20 is performed using the LUT from the light emission control unit 22.
The image adjustment is performed on the image signal input from the outside based on the selection signal 27 and the LUT update signal 28, and the corrected image signal 29 is sent to the timing adjustment unit 21.

The timing adjustment unit 21 generates a horizontal (hereinafter also described as H) synchronization signal and a vertical (hereinafter also described as V) synchronization signal from the corrected image signal 29 input from the image correction unit 20, and controls the MEMS driver 8 and the light emission control. Send to unit 22. The image signal is temporarily stored in the frame memory 3.
The image signal written to the frame memory 3 is read out as a read signal synchronized with the horizontal synchronization signal and the vertical synchronization signal generated by the timing adjustment unit 21. Further, the image signal in the frame memory 3 is read by being delayed by one frame with respect to the input image signal.

  The detailed operation of the light emission control unit 22 will be described later with reference to FIGS. 7 and 8.

The read image signal is input to the line memory 23. The line memory 23 takes in an image signal of one horizontal period, and sequentially reads out the image signal in the next horizontal period. The reason for relaying in the line memory 23 is as follows. Generally, the read clock frequency of the frame memory 3
The clock frequency may differ when transmitting the image signal to the laser driver 4 side. Therefore, after the image signal of one horizontal period is once taken in by the line memory 23 at the read clock frequency of the frame memory 3, the process of reading from the line memory 23 at the transmission clock frequency of the image signal is performed. If the read clock frequency of the frame memory 3 matches the transmission clock frequency of the image signal, the line memory 23 becomes unnecessary. The image signal read from the line memory 23 is supplied to the laser driver 4.

Next, the current gain circuit 24 and the threshold current adjustment circuit 25 in the laser driver 4 will be described. The threshold current adjustment circuit 25 adjusts the threshold current that determines the lower limit value at which the semiconductor lasers 5a to 5c emit light according to the threshold current value set by the light emission control unit 22, as described in detail later. In other words, the threshold current adjustment circuit 25 generates an offset component of the current value flowing to the semiconductor lasers 5a to 5c. The current gain circuit 24 also responds to the image signal input from the line memory 23
The laser 5 is multiplied by the current gain for converting the image signal value (voltage value) into a current value.
Control the current value flowing to the The current gain is determined by the light emission control unit 22 and set in the current gain circuit 24. That is, to increase or decrease the current gain means to increase or decrease the current value corresponding to the image signal. Therefore, the current values actually flowing through the semiconductor lasers 5a to 5c are the threshold current value set by the threshold current adjustment circuit 25, the current gain set by the current gain circuit 24, and the signal current value corresponding to the image signal. It becomes a total value.

The above is the basic operation of the image processing unit 2. Next, the operation of the LUT having the role of maintaining the number of display gradations during operation will be described with reference to FIGS. 3, 4A, and 4B.

FIG. 3 is a characteristic diagram showing an example of the light quantity-forward direction current characteristic of the semiconductor laser. As shown in FIG. 3, the semiconductor laser has a characteristic that the light quantity sharply increases at a threshold current Ith1. Also, the amount of change in light quantity with respect to current is not constant, and has a non-linear characteristic as depicted by R1. Here, it is preferable that the current control range used when forming a bright image is a range from the threshold current Ith1 to the current Im at which the light amount Lm is obtained. In other words, the image signal
Assuming that t (maximum 255), if the image signal is 0 or 1, the forward current is Ith1,
The current gain circuit 24 and the threshold current adjustment circuit 25 are controlled so that the maximum forward current when the image signal is 255 becomes Im. More specifically, the light emission control unit 22 controls the threshold current adjustment circuit 25 so that the current value becomes Ith1, and sets a current gain of (Im−Ith1) / 255 in the current gain circuit 24. In this way, when the image signal is 0, the current of Ith1 flows to the laser, and when the image signal is 255, the current of Im can flow to the semiconductor laser. That is, the current range which flows through the semiconductor laser when forming a bright image is the current control range 1 in FIG. When the image signal is 0, the laser may be turned off by setting the forward current to 0 so as to obtain contrast.

As described above, in the current control range 1 shown in FIG. 3, the amount of change of the light amount with respect to the current of the semiconductor laser is not constant, and has a non-linear characteristic drawn by R1. In order to obtain the display gradation number of the display image, it is desirable that the light amount has a predetermined change amount with respect to a constant change amount of the image. As a means for causing the light amount to have a predetermined amount of change, a procedure for performing gradation adjustment of an image by a LUT will be described. For the sake of simplicity, a procedure of creating a LUT in which the output light quantity changes linearly with respect to the input image signal will be described.

FIG. 4A is a first characteristic diagram for explaining the operation of the LUT of this embodiment, in which characteristics obtained by converting the characteristics R1 to obtain the target characteristics T1 described in FIG. 3 are described. This conversion will be described. In the case of the current value It in FIG.
The target light amount Lt is obtained from the point of intersection with However, since the actual laser characteristic is R1, the actual current value to be the target light amount Lt is It '. Therefore, the input image signal Pi corresponding to the current of It
Are converted to an output image signal Po corresponding to the current of It '. Thereby, the light quantity obtained for the input image signal Pi corresponding to the current of It becomes Lt of the target light quantity. It is the LUT in FIG. 4A that shows this conversion for all input image signals. Although FIG. 4A depicts analog characteristics, it goes without saying that discrete values are shown because the actual LUT is a numerical table.

FIG. 4B is a second characteristic diagram for explaining the operation of the LUT of this embodiment. As described above, by using the LUT of FIG. 4A, the relationship between the output light quantity and the input image signal changes linearly as shown in FIG. 4B. Although the description has been given of the LUT in which the output light amount changes linearly with respect to the input image signal, it is needless to say that the LUT may be formed to have general gamma characteristics.

FIG. 5 is a block diagram showing the image correction unit 20 of the present embodiment. Using this, the image correction unit 20
The operation of will be described. Note that the image correction unit 20 in FIG. 5 has three of LUT1 (50), LUT2 (51), and LUT3 (52).
Although there are various types of LUTs, the present invention is not limited to this configuration, and may have more than three types.
In addition, it is sufficient that the output image changes with respect to the input image. However, this embodiment can be realized by having at least two types of LUTs.

The image correction unit 20 inputs an input image signal to LUT1, LUT2, and LUT3, and obtains an output for the image signal as described in FIG. 4A from each LUT. The output from each LUT is input to the selector 53, and the selector 53 outputs an image signal 29 based on the LUT selection signal 27 from the light emission control unit 22. Further, the contents of each LUT are updated according to the LUT update signal 28 from the light emission control unit 22. This LU
The procedure for updating T will be described later.

In the first embodiment, one feature is to have at least two types of LUTs.
Here, the necessity of having at least two types of LUTs will be described. For example, when a laser projection display device is used as a vehicle-mounted display device, when the brightest image is projected using the light amount Lm shown in FIG. 3, that is, the maximum light amount that the laser projection display device can project. good. In this case, the control range of the current for driving the semiconductor laser may be the current control range 1 shown in FIG. However, in an environment where the vehicle surroundings are dark, such as in a tunnel, if the image is projected with the brightness as it is, the driver will give a dazzling impression. Therefore, the laser projection display device needs to be switched immediately so as to project an image of brightness matched to the environment around the vehicle body. That is, the light control operation of changing the light intensity of the display image of the laser projection display device according to the surrounding environment is required. As an example, bright images in normal operation
The case where the maximum light amount is Lm to the image with a brightness of 1/4 in the light control operation (the maximum light amount is Lm / 4) will be considered, in particular, the current control range shown in FIG.

FIG. 6 is a characteristic diagram for explaining the operation of the LUT when the current control range is not changed at any brightness. Assuming that the current control range is the above-described current control range 1, the LUT shown in FIG.
By changing the LUT of the characteristics shown in FIG. 6 to the LUT of the characteristics shown in FIG. 6, an image with the maximum light amount of Lm / 4 can be output. As described above, at least two types of LUTs are prepared, and the light adjustment operation can be performed by changing the used LUT. However, the LUT shown in FIG. 6 is 8 bits (256 gradations)
Is converted to a 6-bit (64 gradation) output signal. That is, when the LUT in FIG. 6 is used, although the light adjustment operation is performed, the number of gradations of the display image is reduced, and the quality of the display image is degraded.

In order to suppress the deterioration of the quality of the displayed image, the current control range is set to the current control range shown in FIG.
It is necessary to change from 1 to the current control range 2. That is, when the image signal is 0 or 1, the current gain circuit 24 and the threshold current adjustment circuit 25 are controlled to set the forward current to Ith1 and the maximum forward current to I1 when the image signal is 255. More specifically, the light emission control unit 22 controls the threshold current adjustment circuit 25 so that the current value becomes Ith1, and the current gain circuit 24 controls (I1-Ith1) / 255.
Set the current gain of By doing this, when the image signal is 0, the current of Ith1 flows to the semiconductor laser, and when the image signal is 255, the current of I1 flows to the semiconductor laser, and the number of gradations of the image signal You can change the brightness of the displayed image without losing

As apparent from FIG. 3, since the table shape is different between the LUT for the current control range 1 and the LUT for the current control range 2, a LUT for the current control range 2 is required separately from the LUT for the current control range 1 Become. However, as semiconductors become more advanced, preparing multiple LUTs is not particularly problematic.

For example, in the case of outputting a bright image (maximum light amount is Lm), an image with a brightness of 1/4 (maximum light amount is Lm / 4) using current control range 1 and LUT1 corresponding to current control range 1 When outputting the light control unit 22 instantaneously switches the image correction unit 20 so that the current control range 2 and the LUT 2 corresponding to the current control range 2 are used. As a result, it is possible to maintain the number of display gradations without impairing the number of gradations of the display image at the time of light adjustment operation. As described above, by having at least two types of LUTs corresponding to at least two types of current control ranges, it is possible to maintain the number of display gradations during light adjustment operation. In the above example, the current control range 1 in which the maximum light amount is Lm and the current control range 2 in which the maximum light amount is Lm / 4 has been described. However, the present invention is not limited thereto. It goes without saying that multiple LUTs may be prepared.

The above is the basic operation of the laser projection display apparatus in the present embodiment. In this embodiment, by using this, it is possible to reduce the white balance change of the display image due to the temperature change while maintaining the number of display gradations even during the light control operation. A specific operation example in this case will be described focusing on the operation of the light emission control unit 22.

FIG. 7 is a flowchart illustrating the entire process of the first embodiment. FIG. 7 shows the case where the current control range of the display image is the current control range 1 and the LUT 1 is used as an example.

After the power is turned on, the light emission control unit 22 resets the variable i (St100). The variable i operates as a frame number counter, and operates as a counter that controls the frequency of performing the normal operation process and the light adjustment operation process described later. After resetting the variable i, it is determined whether the display period has ended based on the vertical synchronization signal sent from the timing adjustment unit 21 (St101). After the display period ends and the flyback period starts, the light emission control unit 22 increments the variable i (St102). after that,
The frequency of performing the normal operation processing and the light adjustment operation processing is determined, which is compared with a predetermined number N (St 103),
If the variable i is not equal to the predetermined number N, the process proceeds to the normal operation processing according to St104 to St109. If the variable i is equal to the predetermined number N, the process proceeds to the light adjustment operation processing according to St110 to St120.

The normal operation process and the light control operation process, which will be described later, are performed during the blanking period while avoiding the display period so as not to affect the image to be projected and displayed. Also, the normal operation processing and the light adjustment operation processing pertain to the predetermined number N according to their respective priorities, and for example, the former is performed (N-1) times and the latter is performed once every N frames. N may be a constant or a variable.

Here, the normal operation processing according to St104 to St109 will be described. In general, a semiconductor laser has temperature characteristics, and as the temperature rises, the threshold current at which light emission starts is increased, and the inclination of the light amount to the current is reduced. Therefore, in order to make the emission intensity of the semiconductor laser constant over time, the laser emission intensity is detected by the optical sensor 10 and monitored through the amplifier 9,
The APC (A) that feeds back the obtained light emission intensity to the current gain circuit 24 and the threshold current adjustment circuit 25
You need to do uto Power Control). As one example, the light emission control unit 22 sends the maximum image signal as an image signal to the current gain circuit 24, and the light intensity is detected by the light sensor 10, and the amplifier
9 to obtain the obtained light intensity and the target light amount Lm in the current control range 1, and set the current gain circuit 24 so that the output light amount at the maximum image signal input becomes Lm. Feedback control.

Further, in order to determine the set value to be applied to the threshold current adjustment circuit 25, an image signal having a current value at or near the threshold current Ith1 is sent as an image signal to the current gain circuit 24, and the light intensity is detected by the light sensor 10. The current value set in the threshold current adjustment circuit 25 is feedback-controlled so as to obtain the output light quantity at the time of image signal input which becomes the current value of the threshold current Ith1 or its vicinity by acquiring via the amplifier 9. By doing this, although the current control range 1 changes temporally, the value of the output light quantity with respect to the input image signal becomes constant, and it is possible to prevent the user from recognizing changes in the characteristics due to the temperature of the semiconductor laser. . Here, the output light amount Lm
And the output light quantity at the time of the image signal input which becomes the current value of the threshold current Ith1 or its vicinity is held in the storage area (not shown). Further, the white balance can be made constant by holding the value of the light quantity corresponding to each color of RGB. In addition, in order to simplify the explanation, an optical sensor
Although the light intensity detected at 10 and obtained through the amplifier 9 is an image signal having a maximum image signal and a current value at or near the threshold current Ith1, the light intensity in a predetermined image signal is not limited to this. It goes without saying that it may be detected by the light sensor 10 and acquired via the amplifier 9.

In order to perform the above-described processing for normal operation, the semiconductor laser is caused to emit light at a predetermined light intensity in the current control range 1 during the retrace period, and the light intensity is detected by the optical sensor 10. To obtain (St104). Based on the acquired light intensity, it is determined whether or not the current control range 1 is to be changed, and processing according to this is performed (St 105). Note that the light emission control unit 22 may determine whether to change the current control range 1 based on the light intensity, or the light emission control unit 22 sends light intensity information to the CPU 12, and the CPU 12 determines It is good. In St106, it is determined whether the current control range 1 has been updated, that is, at least one set value of the current gain circuit 24 or the threshold current adjustment circuit 25 has been changed. If updated, the process proceeds to St107. If updated, the stored data for LUT1 acquired in the past frame is reset at St107, and the process proceeds to St108. Above, the process concerning the current control range 1 is completed, and, if necessary, the current control range 1 is changed.

In St108, light intensity corresponding to the image signal is acquired. Here, in St108, it is desirable to acquire light intensities corresponding to a plurality of image signals. The acquired light intensity may be stored in a storage area (not shown) as holding data for LUT1, or the light emission control unit 2 may transmit light intensity information to the CPU 12 and the CPU 12 may hold the information. Here, the retention data for LUT1 is LUT1.
Data for updating data. Since an image signal can be converted into a current value flowing through the semiconductor laser, it is possible to create the light amount-forward current characteristic of the semiconductor laser in the current control range 1 by acquiring the light intensity corresponding to the image signal. The light amount-forward direction current characteristic of this semiconductor laser is taken as holding data for LUT1.

The LUT1 is updated by performing the conversion described in FIG. 4A from the retention data for LUT1 (St1
09). The calculation for updating the LUT 1 may be performed by either the light emission control unit 22 or the CPU 12. Further, while the current control range 1 is not changed, a large amount of light intensity may be acquired over a plurality of frames in St108, and the LUT1 may be updated after a certain amount of retained data for LUT1 is accumulated. By appropriately updating the data of the LUT 1 during operation as described above, it is possible to cope with the deterioration with time of the laser.

The above is the description of the normal operation processing related to St104 to St109. That is, the LUT 1 in the current control range 1 of FIG. 3 is updated according to the light intensity detected in a predetermined image signal during the blanking period. At that time, at St104, a predetermined image signal, for example, the light intensity at gradation 0 and 255 is detected, based on which it is determined whether or not the current control range 1 is updated at St105.
At St 107, the previously held data on LUT 1 is reset. Next, light intensity is detected at a plurality of image signal levels in the current control range 1 at the current time in St108, converted as described in FIG. 4A to obtain new data for updating LUT1, and LUT1 is updated in St109. .
As described above, the flow from St104 to S109 is performed in a flyback period in which the variable i is different from the predetermined number N as a result of the determination in S103.

Next, in St103, when it is determined that the variable i is equal to the predetermined number N, the process proceeds from St110.
The light intensity control intensity changing process according to St120 will be described.

If the variable i and the variable N are equal at St103, the process proceeds to St110, and the variable i is reset. Next, the current control range is changed from the current control range 1 which is the current control range during the normal operation period, and the current control range 2 is set (St 111). By changing the current control range in this manner, as described above, the number of display gradations can be maintained even during light adjustment operation. Next, the light emission control unit 22 changes the amplification factor 1 corresponding to the current control range 1 which is the current control range during the normal operation period to the amplifier 9 for amplifying the output from the light sensor 10, Set the amplification factor 2 corresponding to 2 (St1
12). This amplification factor relates to the output from the light sensor, and it is desirable to set different amplification factors in the current control range 1 where the maximum light amount is Lm and the current control range 2 where the maximum light amount is Lm / 4.

For example, in the current control range 1 of the amplifier 9, the laser light quantity ranges from 0 to
0) which is the amount of laser light in the current control range 2 at the same amplification factor when outputting at maximum 1023)
When the range of Lm / 4 is detected, the light intensity can be acquired only with an accuracy of 8 bits. Therefore, by setting the amplification factor 2 corresponding to the current control range 2 to 1⁄4 of the amplification factor 1 corresponding to the current control range 1, the output of the amplifier 9 can be obtained with an accuracy of 10 bits. As described above, by setting the amplification factor corresponding to the set current control range in the amplifier 9, it is possible to make the acquired data of the light intensity more accurate.

After setting the amplification factor 2 at St112, the laser is emitted at a predetermined light intensity in the current control range 2, the light intensity is detected by the light sensor 10, and acquired via the amplifier 9 (St113). Based on the acquired light intensity, it is determined whether or not the current control range 2 is to be changed, and processing according to this is performed (St 11
Four). Note that the light emission control unit 22 may determine whether to change the current control range 2 based on the light intensity, or the light emission control unit 22 sends light intensity information to the CPU 12, and the CPU 12 determines It is good. At St114, it is determined whether the current control range 2 has been updated, that is, at least one set value of the current gain circuit 24 or the threshold current adjustment circuit 25 has been changed. If updated, the process proceeds to St116. If updated, the stored data for LUT2 acquired in the past frame is reset at St116, and the process proceeds to St117.

In St117, the light intensity corresponding to the image signal is acquired. Here, in St117, it is desirable to acquire light intensities corresponding to a plurality of image signals. The acquired light intensity may be stored in a storage area (not shown) as holding data for LUT2, or the light emission control unit 22 may transmit light intensity information to the CPU 12, and the CPU 12 may hold the light intensity information. Here, the retention data for LUT2 is data for updating the data of LUT2. Since the image signal can be converted to the current value flowing to the laser, it is possible to create the light amount-forward current characteristic of the semiconductor laser in the current control range 2 by acquiring the light intensity corresponding to the image signal. The light amount-forward direction current characteristic of the semiconductor laser is taken as holding data for LUT2.

The LUT2 is updated by performing the conversion described in FIG. 4A from the retention data for LUT2 (St1
18). The calculation for updating the LUT 2 may be performed by either the light emission control unit 22 or the CPU 12. In addition, while the current control range 2 is not changed, a large amount of light intensity may be acquired over a plurality of frames in St117, and the LUT2 may be updated after a certain amount of retained data for LUT2 is accumulated. By appropriately updating the data of the LUT 2 during the operation as described above, it is possible to cope with the deterioration with time of the laser.

Next, before the display period starts, the current control range is changed from the current control range 2 to set the current control range 1 (St119). In addition, the light emission control unit 22 is an amplifier that amplifies the output from the light sensor 10
9, change the amplification factor from amplification factor 2 corresponding to current control range 2, set amplification factor 1 corresponding to current control range 1 (St 120), return to the previous St 101, and repeat the above processing flow .

The above is the description of the light control operation intensity change process according to St110 to St120. That is, the LUT 2 in the current control range 2 of FIG. 3 is updated according to the light intensity detected in a predetermined image signal during the blanking period. At that time, the light intensity at a predetermined image signal, for example, gradation 0 and 255 is detected in St113, and it is determined based on this whether or not the current control range 2 is updated in St114. Reset the data held so far. Next, light intensity is detected at a plurality of image signal levels in the current control range 2 at the present time in St117, converted as described in FIG. 4A to obtain new data for updating LUT2, and LUT2 is updated in St118. . Then, it returns to St101 through St119 and St120. As described above, the flow from St110 to S120 is performed in the flyback period in which the variable i is equal to the predetermined number N as a result of the determination in S103.

As described above, the light adjustment operation processing sets the current control range and amplification factor of the amplifier 9 different from those in the normal operation period during the retrace period, and sets the current control range and the current control range set during light adjustment. It is a process of updating the corresponding LUT. By doing this, it is possible to create in advance a current control range to be applied during light adjustment and a LUT corresponding to the current control range, so that the laser projection display apparatus can maintain the number of display gradations while the image is being displayed. The brightness of can be switched instantly.

In FIG. 7, the current control range during the normal operation period is described as the current control range 1 and the current control range during the light adjustment operation period is the current control range 2, but the invention is not limited to the above two types.
A plurality of branches at St 103 may be prepared to provide a plurality of current control ranges. Moreover, after updating the current control range 2 in the light adjustment operation processing, time division is performed such that the same processing is performed on the current control range different from the current control range 2 in the light adjustment operation processing of the next frame and subsequent steps. It goes without saying that processing may be performed.

Next, a specific timing chart at the time of light control using the flowchart of FIG. 7 will be described using FIG.

FIG. 8 is a timing chart showing the entire process of the first embodiment, showing a vertical synchronization signal, a current control range, an amplification factor setting signal, an amplification factor, a laser emission, a dimming request signal, and a use LUT. The processing for light adjustment operation is performed during the flyback period of the frame f0, and the processing for normal operation is performed during the flyback periods of the frame f1 and the frame f2. Further, regardless of these, for example, a device with the illuminance sensor 11 of FIG. A dimming request signal generated by the CPU 12 in accordance with the detection result of the peripheral brightness enters into the frame f3. Here, the light adjustment request signal is a signal indicating a request to change from the current control range 1 to the current control range 2.

First, assuming that i = N at St103 in FIG. 7 after the display period of the frame f0 ends, the process shifts to light adjustment operation processing. Next, current control range 2 and amplification factor 2 are set (St 111
And St 112). Thereafter, the light emission control unit 22 causes the semiconductor laser to emit light at light intensities at a plurality of locations in the current control range 2, and the light intensity is detected by the light sensor 10 and acquired via the amplifier 9 (St
113 or St 117). After current control range 2 change processing (St 114) and LUT 2 update (St 118) not shown in FIG. 8, current control range 1 and amplification factor 1 are set (St 119 and St 120),
Transition to frame f1.

Next, after the display period of the frame f1 ends, i ≠ N at St103, and the process shifts to processing for normal operation. The light emission control unit 22 causes the semiconductor laser to emit light at light intensities at a plurality of locations in the current control range 1, and the light intensity is detected by the optical sensor 10 and acquired via the amplifier 9 (St104 or St108). Current control range 1 change processing (St 105) and update of LUT 1 (St 1 not shown in FIG. 8)
After performing step 09), the process moves to frame f2. In the flyback period of the frame f2, processing for normal operation similar to that of the frame f1 is performed.

Next, the case where the light adjustment request signal is input to the light emission control unit 22 during the frame f3 will be described. The dimming request signal is temporarily held in the light emission control unit 22. The light emission control unit 22 is a frame
During the flyback period of f3, the current control range 2 and the amplification factor 2 created in advance are set, and the LUT selection signal 27 is supplied to the image correction unit 20 so that the LUT 2 is selected. By changing the current control range during the blanking period in this way, it is possible to suppress the discomfort due to the part of the image becoming dark rapidly. Further, from the flyback period of the frame f3, the target of the processing for normal operation is the current control range 2, and the brightness of the display in the display period is the brightness of the light control operation. Thereby, it is possible to project an image of brightness matched to the surrounding environment.

Therefore, in FIG. 8, the normal operation processing for current control range 2 is performed in the flyback period of frame f3, and in the flyback period after frame f3 to any other than current control range 2 not shown at an arbitrary frequency. The intensity adjustment process for light adjustment operation is performed. As described above, according to the present embodiment, since the LUT corresponding to the current control range and the current control range to be applied at the time of light adjustment can be created in advance, the laser projection display device maintains the number of display gradations. The brightness of the image can be switched immediately after the dimming request signal is input.

That is, when the light adjustment request signal is input, the light adjustment operation processing is performed regardless of the value of i in the return line period, and the light adjustment operation is performed from the next frame in the display period. The dimming operation is performed using the current control range 2 and the LUT 2 in the dimming operation prepared in the retrace period of the normal operation. Note that the light adjustment request signal is not limited to being generated according to the detection result of the brightness by the illuminance sensor 11 as described above, and may be generated according to, for example, the user's request.

According to the present embodiment, it is possible to provide the laser projection display device in which the white balance change of the display image due to the temperature change is reduced while maintaining the display gradation number at the time of the light adjustment operation.

In this embodiment, in the light adjustment operation processing, the current control range and amplification factor of the amplifier 9 which are different from those in the display period are set during the retrace period, and the current control range and current control applied during light adjustment Although the LUT corresponding to the range is shown in advance for the configuration to be created, only one of the current control range and the amplification factor may be changed. For example, when St112 and St120 are deleted in FIG. 7, the accuracy of the acquired data of the light intensity in St113 and St117 is not improved, so the accuracy of LUT2 corresponding to the current control range 2 falls, but the light emission control unit 22 or C
A simplified LUT 2 may be created and updated by interpolating retention data for LUT 2 using PU 12 or the like (St 118). By doing this, there is an advantage that the configuration is simplified. Further, after light adjustment, the accuracy of the simplified LUT 2 is improved by St109 of the normal operation processing.

In the above-described first embodiment, in the light adjustment operation processing, the current control range and the current control range to be applied at the time of light adjustment are set by setting the current control range and the amplification factor of the amplifier 9 different from those in the display period. The configuration for creating in advance the LUT corresponding to the above has been described.

Other than this control method, after the light adjustment request signal is input, control may be performed to determine a current control range to be applied during light adjustment or a LUT corresponding to the current control range. In this case, although the light adjustment operation can not be performed immediately after the light adjustment request signal is input, the number of display gradations can be maintained before and after the light adjustment operation. Furthermore, in this control method, the number of LUTs required can be reduced since control is performed to determine the current control range to be applied during light adjustment and the LUT corresponding to the current control range after the request signal is input. The circuit scale can be reduced. In addition, it is not necessary to perform the intensity change processing for light adjustment operation until the light adjustment request signal is input, and the intensity change processing for each frame normal operation can be performed.

Hereinafter, after the light adjustment request signal is input, a configuration for determining a current control range to be applied during light adjustment and a LUT corresponding to the current control range will be referred to as Embodiment 2 of the present invention with reference to FIGS. While explaining. The components having the same configurations and functions as those of the first embodiment are denoted by the same reference numerals, and the detailed description thereof is omitted.

FIG. 9 is a flowchart showing the entire process of the second embodiment. In the flowchart of FIG. 9, the current control range of the display image is set to the current control range 1, and the use of the LUT 1 is shown as an example. The dimming request signal here is for changing from the current control range 1 to the current control range 2,
For example, the signal is generated by the CPU 12 in accordance with the detection result of the brightness around the device in the illuminance sensor 11 of FIG.

After the power is turned on, the light emission control unit 22 determines whether the display period has ended based on the vertical synchronization signal sent from the timing adjustment unit 21 (St101). After the display period ends and the blanking period starts, the light emission control unit 22 determines whether a light adjustment request signal is input (St200). When the light adjustment request signal is not input, as in the first embodiment, the process proceeds to the normal operation processing according to St104 to St109.

If it is determined at St200 that the light adjustment request signal has been input, the process proceeds to St111, the current control range is changed from the current control range 1 which is the current control range during the normal operation period, and the current control range 2 is set. (St 111). Thereafter, St112 to St118 are performed as in the first embodiment. Next, in St201, it is determined whether the light adjustment operation is to be performed. Here, whether or not the light adjustment operation is performed is determined by the light emission control unit 22, and the light adjustment operation is performed after the LUT 2 is updated after the simple update of the LUT 2 or a predetermined time elapses. The difference in the update of the LUT 2 will be described in the timing chart described later.

If it is determined that the light adjustment operation is to be performed in St201, the process proceeds to St202, and the LUT applied in the display period is set to L.
The LUT selection signal 27 is supplied to the image correction unit 20 so that the UT 2 is selected. After St202, the current control range 2 is subjected to the normal operation processing, and the normal operation intensity change processing according to St104 to St109 is performed during the retrace period until the next dimming request signal is input.

If it is determined that the light adjustment operation is not performed in St201, the current control range is changed from the current control range 2 before the display period starts, and the current control range 1 is set (St119). In addition, the light emission control unit 22
For the amplifier 9 that amplifies the output from the optical sensor 10, the amplification factor is changed from the amplification factor 2 corresponding to the current control range 2, and the amplification factor 1 corresponding to the current control range 1 is set (St120). Then St20
In step 3, based on the vertical synchronization signal sent from the timing adjustment unit 21, it is determined whether the display period has ended, and the display period ends. After entering the flyback period, the process moves to St111.

As described above, after the dimming request signal is input, the current control range and the amplification factor of the amplifier 9 which are different from those in the normal operation period are set during the retrace period. By performing the process of updating the LUT corresponding to the control range, it is possible to switch the brightness of the image while maintaining the number of display gradations. In addition, it is not necessary to perform the intensity change processing for light adjustment operation until the light adjustment request signal is input, and the intensity change processing for each frame normal operation can be performed.

Next, a specific timing chart at the time of light control using the flowchart of FIG. 9 will be described using FIGS. 10 and 11. FIG.

FIG. 10 is a timing chart showing the entire process of the second embodiment, and in St201, LUT2 is
It is a timing chart at the time of judging that light control operation is performed after performing a simple update of a.

FIG. 11 is a timing chart showing an entire process of another mode according to the second embodiment, which is St 20
FIG. 10 is a timing chart when it is determined that the light adjustment operation is to be performed after the LUT 2 is updated according to the elapse of a predetermined time in 1;

FIG. 10 shows the case where the dimming request signal enters in the frame f0. The light adjustment request signal here is a request to change from the current control range 1 to the current control range 2. First, frame f0
After the end of the display period, it is determined that the light adjustment request signal has been input (St 200), and the current control range 2
And an amplification factor of 2 is set (St111 and St112). Thereafter, the light emission control unit 22 causes the semiconductor laser to emit light at the light intensity at a plurality of locations in the current control range 2, causes the light intensity to be detected by the light sensor 10, and is acquired via the amplifier 9 (St113 or St117). After current control range 2 change processing (St 114) and LUT 2 update (St 118) not shown in FIG. 10 are performed, it is determined whether simplified update of LUT 2 has been performed and it is determined whether to execute the light adjustment operation. (St201).

Here, the simplified update of LUT2 is to acquire much light intensity over a plurality of frames in St117, and
This means that the LUT2 is updated after a certain amount of retained data for UT2 is accumulated. Here, it is desirable that the certain amount be 25% or more with respect to the total number of representable image signals.
That is, the simplified update of LUT2 means that when the image signal has 8 bits (maximum 255) gradation, light intensity corresponding to 64 gradations or more is acquired as holding data for LUT2, and then LUT2 is updated in St118. Do. It is preferable that light intensities corresponding to the gradations of the image signal be acquired without any difference by assigning the gradations of the image signal to be acquired to be equal intervals to the total number of expressible image signals. By doing this, it is possible to reduce the error of the interpolation processing for the gradation of the image signal that has not been acquired.

In the frame f0 of FIG. 10, it is determined that the simplified update of the LUT 2 is not performed, and the light adjustment operation is not performed, so the current control range 1 and the amplification factor 1 are set in St119 and St120, and transition to the frame f1 is performed. . Also in the flyback period of the frame f1, the processing of St111 to St120 is executed similarly to the frame f0.

Next, the case where the simplified update of the LUT 2 is completed at St 118 in the flyback period of the frame f 29 will be described. In frame f29, the light emission control unit 22 determines that the simplified update of the LUT 2 has been performed in St201, and determines that the light adjustment operation is to be performed. In other words, shift to St202, and use LUT from LUT1
After setting to change to LUT2, the process proceeds to St101. Therefore, the frame f which is the next frame
After 30, the current control range 2 is the target of the normal operation processing, and the normal operation processing is executed in the blanking period of each frame until the next dimming request signal is input.

That is, in FIG. 10, in the retrace period after receiving the light adjustment request signal, the current control range 2 is
The LUT 2 is simply updated by acquiring light intensity data at a plurality of locations in the middle using a plurality of frame periods even if it does not extend to all gradations. In the flyback period and the display period after the simple update is completed, the operation based on the current control range 2 is performed, and the light control operation is performed.

In FIG. 11, compared with FIG. 10, the update processing of the LUT 2 in St 118 is different during the flyback period of the frame f29. In FIG. 11, the time after the light adjustment request signal is input is measured by a frame counter (not shown), and it is determined to forcibly execute the light adjustment operation in St201 after a predetermined time has elapsed. That is, the process proceeds to St202, and after setting the use LUT from LUT1 to LUT2, the process proceeds to St101. Therefore, after the frame f30 which is the next frame, the current control range 2
Is the target of the normal operation processing, and the normal operation processing is executed in the blanking period of each frame until the next dimming request signal is input. Meanwhile, since LUT2 is updated as needed, in FIG. 11, for example, LUT2 'different from LUT2 is applied at the time of frame f60.

Here, since the LUT 2 in FIG. 11 is updated by data from the input of the light adjustment request signal to the lapse of a predetermined time, the accuracy is not high as compared with the simplified update of the LUT 2 described above. However, in order to shorten the time from the input of the light adjustment request signal to the execution of the light adjustment operation as much as possible, the light adjustment operation is executed after a predetermined time has elapsed. The predetermined time is preferably one second or less. If the time from the dimming request signal to the dimming operation is one second or more, the user may feel discomfort.

As described above, according to the present embodiment, after the light adjustment request signal is input, the current control range and the amplification factor of the amplifier 9 which are different from those in the normal operation period are set during the retrace period. By performing processing to update the LUT corresponding to the current control range to be set and the current control range, the brightness of the image can be switched while maintaining the number of display gradations, and the white balance change of the display image due to the temperature change Can be reduced.

In the above-described first and second embodiments, the configuration has been described in which the current control range to be applied during light adjustment and the LUT corresponding to the current control range are created. In addition to this control method, a plurality of fixed LUTs may be prepared in advance in a storage area (not shown), and control may be performed to determine the current control range to be applied during light adjustment. Even in this case, the light adjustment operation can be performed immediately after the light adjustment request signal is input, and the number of display gradations can be maintained before and after the light adjustment operation. Furthermore, in this control method, since it is not necessary to update the LUT during operation, the circuit scale can be reduced and the load on the CPU can be reduced.

Hereinafter, a configuration in which a plurality of fixed LUTs are prepared in advance in the storage area (not shown) and the current control range to be applied at the time of light adjustment is determined will be described as Example 3 of the present invention with reference to FIG.
The components having the same configurations and functions as those of the first embodiment are denoted by the same reference numerals, and the detailed description thereof is omitted.

Here, the output light quantity at the time of the image signal input which becomes the above-described output light quantity Lm and the threshold current Ith1 or a current value in the vicinity thereof is held in advance in a storage area not shown. Further, the white balance can be made constant by holding the value of the light quantity corresponding to each color of RGB.

FIG. 12 is a flowchart showing the entire process of the third embodiment. In FIG. 12, the current control range of the display image is set to the current control range 1, and the use of the LUT 1 is shown as an example. Further, in FIG. 12, St106 to St109 and St115 to St118 are removed from FIG. So, St100 ~ S
Regarding matters related to t105 and St110 to St120, many of the matters already described in the first embodiment will be briefly described.

In the third embodiment, as described above, a plurality of fixed LUTs are prepared in advance according to the information related to the output light quantity and the current control range, and according to the light intensity measured by the light sensor 10 during the retrace period. It is arranged to select one of the fixed LUTs. For this reason, since the process of updating the LUT according to the measured light intensity is unnecessary, St106 to St109 and St115 to St118 shown in FIG. 7 are removed.

When the change processing for normal operation is selected (Y in St 103), the light emission control unit 22 causes the semiconductor laser to emit light at the light intensities of a plurality of locations in the current control range 1 during the blanking period. Optical sensor 10
, And acquired via the amplifier 9 (St104). Based on the acquired light intensity, processing is performed to determine whether or not the current control range 1 is changed, and in the case of changing, a LUT corresponding to the new current control range
Are selected from the plurality of fixed LUTs (St105). Note that the light emission control unit 22 may determine whether to change the current control range 1 based on the light intensity, or the light emission control unit 22 sends light intensity information to the CPU 12, and the CPU 12 determines It is good.

When the light adjustment operation change process is selected (N in St 103), St 110 to St 112 are the same as in FIG.
The light emission control unit 22 causes the laser to emit light at a plurality of light intensities in the current control range 2 during the retrace period, causes the light sensor 10 to detect the light intensity, and acquires the light intensity through the amplifier 9 (St113). ). Based on the acquired light intensity, processing is performed to determine whether the current control range 2 is to be changed. When changing, a LUT corresponding to a new current control range is selected from the plurality of fixed LUTs (St 114). The light emission control unit 22 may determine whether to change the current control range 2 based on the light intensity.
Alternatively, light intensity information may be sent from the light emission control unit 22 to the CPU 12, and the CPU 12 may make a determination. Less than,
After passing St119 and St120 as in FIG. 7 described above, the process returns to St102 and the operation is repeated.

By doing this, since the LUT based on the current control range to be applied at the time of light control is created in advance, the laser projection display apparatus can switch the brightness of the image instantly while maintaining the number of display gradations. . Of course, as in the previous embodiments, it is possible to reduce the change in white balance of the display image due to the change in temperature.

The fourth embodiment is different from the first to third embodiments in the processing for normal operation. Specifically, in the fourth embodiment, also in the normal operation processing, one of the current control range different from that in the display period and the amplification factor of the amplifier 9 is set during the blanking period. By performing control in this manner, it is possible to correspond to the current control range in which the laser light emits extremely weak light that can not be acquired by the light sensor 10 in the normal operation processing. In addition, it is possible to accurately detect light emission near the threshold current where the laser light emits weak light near the detection limit of the light sensor 10.

Hereinafter, also in the processing for normal operation, a configuration in which any one of the current control range different from that in the display period and the amplification factor of the amplifier 9 is set during the blanking period is shown as FIG.
, FIG. 13 and FIG. 14 will be described. In addition, the same code | symbol shall be attached | subjected to what has the same structure as Example 1-3, and a function, and the detailed description shall be abbreviate | omitted.

FIG. 13 is a characteristic diagram showing an example of the light quantity-forward direction current characteristic of the semiconductor laser. As shown in FIG. 13, the semiconductor laser has a characteristic that the light quantity sharply increases at a threshold current Ith1. In addition, the amount of change in light quantity with respect to current is not constant, and has a non-linear characteristic described by R1. Here, it is assumed that the current control range in the display image is set to the current control range 3 used when forming a very dark image. The light amount La0 to the light amount La1 in the current control range 3 are
A very weak light quantity that can not be obtained by the light sensor 10 is used.

When the light amount La1 to the light amount La1 can not be acquired by the light sensor 10, the current control range and amplification factor of the amplifier 9 different during the display period are set and obtained during the retrace period also in the normal operation processing. Change the current control range during the display period based on the data. That is, in FIG. 13, in order to change the current control range 3 so that the light amount does not have temperature characteristics, data is obtained using the current control range 4 which can be obtained by the light sensor 10 and the light amount Lb1.

Hereinafter, a procedure for changing the current control range 3 by using the current control range 4 for the normal operation processing will be described. After the display period ends and the blanking period starts, the current control range is changed from the current control range 3 which is the current control range in the display period, and the current control range 4 is set. After changing the current control range, an image signal in which the current flowing to the laser from the light emission control unit 22 becomes Ib0 and Ib1 is sent as an image signal to the current gain circuit 24 and the light intensity is detected by the light sensor 10. It supplies to the light emission control part 22 via, and light intensity signal Lb0 and Lb1 are acquired. From obtained Lb0 and Lb1,
The light emission control unit 22 or the CPU 12 calculates the current value of the threshold current Ith1 using linear approximation. A fixed constant Ic such that Ic = Ith1-Ia1 is stored in advance in a storage area not shown. As described above, each time the threshold current Ith1 is calculated, the value of Ia1 can be determined using the fixed constant Ic. I
a0 is obtained by subtracting a predetermined number from Ia1. By doing this, the laser beam can
To make the light quantity not have a temperature characteristic based on the threshold current Ith1 calculated using the current control range 4 which is a different current control range, and the current control range 3 which emits extremely weak light which can not be acquired by It can be changed.

Next, with reference to FIGS. 3 and 14, the case where the laser light accurately detects light emission in the vicinity of the threshold current at which weak light emission in the vicinity of the detection limit of the optical sensor 10 will be described.

As described above, FIG. 3 is a characteristic diagram showing an example of the light quantity-forward direction current characteristic of the semiconductor laser. As shown in FIG. 3, the semiconductor laser has a characteristic that the light quantity sharply increases at a threshold current Ith1. Here, accurate detection of the current value of the threshold current Ith1 is important in determining the current control range 1. Therefore, in determining current control range 1, threshold current It
It is preferable to detect the weak light amount Ls using the current I2 that is near h1 and whose light amount is a current value near the detection limit of the light sensor 10. However, since the light amount Ls is weak, it is difficult to accurately detect the light amount Lm with the same amplification factor as the amplification factor of the amplifier 9 at the time of detecting the light amount Lm. Therefore, even in the normal operation processing, the weak light amount Ls can be detected by setting the amplification factor of the amplifier 9 different from that in the display period during the blanking period. Of course, this method is applicable not only to the fourth embodiment but also to the first to third embodiments.

Next, a specific timing chart in the normal operation processing will be described with reference to FIG.

FIG. 14 is a timing chart showing the entire process of the fourth embodiment, showing a vertical synchronization signal, an amplification factor setting signal, a current control range, an amplification factor, a laser emission, a dimming request signal, and a use LUT. Here, the timing chart of FIG.
It is the same as

In FIG. 14, when processing for light adjustment operation is performed during the flyback period of frame f 0, processing for normal operation is performed during the flyback periods of frame f 1 to frame f 4, and frame f 1 and frame f 3 are amplifiers 9.
Of the frame f2 and the frame f4 are set to the amplification factor of 3. The light adjustment operation process of the frame f0 and the normal operation process of the frame f1 are the same as in the first embodiment.

In the flyback period of the frame f2, after the display period of the frame f2 ends, the light emission control unit 22 controls the amplifier 9 that amplifies the output from the light sensor 10 to a current control range that is a current control range during the display period. The amplification factor 1 corresponding to 1 is changed, and the amplification factor 3 for detecting the weak light quantity Ls and the light quantity in the vicinity thereof is set. Thereafter, the laser is emitted with a weak light intensity in the current control range 1, and the light intensity is detected by the light sensor 10 and acquired through the amplifier 9. By changing the amplification degree in this manner, it is possible to detect the amount of light in the vicinity of the current I2.

Based on the acquired light intensity, processing is performed to determine whether the current control range 1 is changed, and before the display period starts, the amplification factor 3 for detecting the light quantity Ls having a weak amplification factor and the light quantity in the vicinity thereof
And set the amplification factor 1 corresponding to the current control range 1. As described above, by changing the amplification factor according to the amount of light to be acquired, it becomes possible to detect a weak amount of light with high accuracy. This means that the accuracy of the current control range and the accuracy of the LUT to be updated are improved.

As described above, according to the present embodiment, also in the normal operation intensity changing process, by setting one of the current control range different from that in the display period and the amplification factor of the amplifier 9 during the blanking period, In the processing for normal operation, the laser light can correspond to a current control range in which light emission is very weak, which can not be obtained by the light sensor 10. In addition, it is possible to accurately detect light emission near the threshold current where the laser light emits weak light near the detection limit of the light sensor 10.

DESCRIPTION OF SYMBOLS 1 ... Projector unit, 2 ... Image processing part, 3 ... Frame memory, 4 ... Laser driver, 5 ... Laser light source, 6 ... Reflection mirror, 7 ... MEMS scanning mirror, 8 ... MEMS driver, 9 .. 11: illuminance sensor 12: CPU 13: display image 20: image correction unit 21: timing adjustment unit 22: light emission control unit 23: line memory 24: current gain circuit 25: threshold current adjustment circuit , 26: current value actually flowing, 27: LUT selection signal,
28: LUT update signal, 29: corrected image signal, R1: amount of light of semiconductor laser-forward current characteristic, T1: target characteristic.

Claims (3)

A laser projection display apparatus which projects laser light of a plurality of colors according to an image signal to display an image according to the image signal,
A laser light source generating laser light of the plurality of colors;
A laser light source drive unit for current-driving the laser light source to generate a laser beam corresponding to the image signal;
A scanning unit that scans and projects laser light generated by the laser light source according to a synchronization signal related to the image signal;
An optical sensor for detecting an amount of laser light generated by the laser light source;
An image processing unit that processes the image signal based on the light amount of the laser light detected by the light sensor and supplies a control signal for determining the current amount of the laser light source to the laser light source drive unit;
The image processing unit outputs laser light in a second current control range different from the first current control range of the laser light source used in the drawing period during the retrace period of the image signal.
A threshold current value , which is a current value at which the light amount of the laser light source sharply increases, is calculated based on the light amount of the laser light detected by the light sensor ,
A control signal is supplied to the laser light source drive unit to drive the laser light source with a current value smaller than the calculated threshold current value, and a dark image is formed by a weak light amount. In the laser projection display device according to claim 1,
In the calculation of the threshold current value, the light intensity of laser light at current values at two points in the second current control range is detected by the light sensor, and the light intensities at the two detected points are linearly approximated. A laser projection display apparatus characterized by calculating the threshold current value . The laser projection display device according to claim 1 or 2
The image processing unit drives the laser light source such that, when the laser light source is driven at a current value less than the threshold current value, the image processing unit is driven with a current value obtained by subtracting a predetermined value from the threshold current value as an upper limit. Processing the image signal supplied to the
What is claimed is:

Images