JP2008102442A - Image projector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively reduce power consumption, while restraining a change in the color of a projected image. <P>SOLUTION: The image projector includes a light source unit 2, having a plurality of LEDs 2a, 2b, and 2c that generate illuminating light rays of different colors; a transmission-type liquid crystal display panel 4 with which illuminating light rays, emitted by the light source unit 2, are modulated on the basis of input video signals; and a control device 10 for controlling the drive of each of the LEDs 2a, 2b, and 2c of the light source unit 2. The control device 10 has a first control mode for variably controlling the magnitude of the drive currents of the LEDs 2a, 2b and 2c, and a second control mode for variably controlling the duty ratio of the drive currents of the LEDs 2a, 2b, and 2c. Characteristic quantity of a display image is detected from a video signal corresponding to one or more of frames, on the basis of the quantity of the characteristic, the first and/or second control mode is selected, and the drive of the LEDs 2a, 2b, and 2c is controlled in the selected control mode. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image projection apparatus.

Conventionally, in an image projection apparatus such as a projector, as a method of adjusting the brightness of a projected image, a method of controlling the magnitude of a drive current applied to a light source, and a pulsed drive current applied to the light source and its duty ratio Is known (for example, see Patent Document 1).
JP-A-2005-70443

By the way, when an LED (light emitting diode) is used as a light source, if the light amount is adjusted by increasing or decreasing the driving current of the LED, the color of the emitted color changes, and the color of the projected image changes. there were.
Further, when the light amount is adjusted by controlling the duty ratio of the driving current applied to the light source, there is a disadvantage that the power consumption cannot be effectively reduced as compared with the method of increasing or decreasing the driving current.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an image projection apparatus capable of effectively reducing power consumption while suppressing a change in color of a projection image.

In order to achieve the above object, the present invention provides the following means.
The present invention includes a light source unit having a plurality of light sources that generate illumination lights of different colors, a light modulation unit that modulates illumination light emitted from the light source unit based on an input video signal, and the light source unit. A first control mode for variably controlling the magnitude of the drive current of the light source, and a first control mode for variably controlling the duty ratio of the drive current of the light source. A feature amount of a display image is detected from the video signal corresponding to one or a plurality of frames, and one of the first control mode and the second control mode is detected based on the feature amount. Alternatively, there is provided an image projection apparatus that selects both and performs drive control of the light source in the selected control mode.

  According to such a configuration, illumination lights of different colors emitted from the light source unit are guided to the light modulation unit, and the display image is superimposed by performing light modulation based on the video signal. In this case, each light source of the light source unit has a control mode corresponding to the feature amount of the video signal, specifically, a first control mode for adjusting the light amount by variably controlling the magnitude of the drive current of the light source, and Then, drive control is performed in one of the second control modes in which the light amount is adjusted by variably controlling the duty ratio of the drive current of the light source, or in a control mode in which both are combined. Therefore, the light quantity of each light source can be adjusted by an appropriate control mode corresponding to the feature amount of the display image.

  In the image projection apparatus, the control unit may detect the feature amount for each color of the illumination light and select a control mode for each color of the illumination light.

  According to such a configuration, the feature amount of the display image is detected for each color, and the light source of each color is driven and controlled in the control mode selected according to the feature amount. The amount of light can be adjusted according to an appropriate control mode every time.

  In the image projection apparatus, the control unit detects luminance as a feature amount of the display image, selects the second control mode when the luminance is equal to or greater than a predetermined value, and the luminance is less than the predetermined value. In this case, the first control mode may be selected.

  According to such a configuration, when the brightness of the display image is bright and the change in the color tone is easy to understand, the change in the color tone can be avoided because the second control mode in which the magnitude of the drive current is not changed is selected. . Further, when the brightness of the display image is dark and the change in color tone is difficult to understand, the power consumption can be reduced while allowing a slight change in color tone by selecting the second control mode.

  In the image projection apparatus, the control means detects the luminance of the image for each color of the illumination light, and when the luminance is equal to or higher than a predetermined value, sets the light source corresponding to the color to the second control mode. When the luminance is less than a predetermined value, the light source corresponding to the color may be driven and controlled in the first control mode.

  According to such a configuration, the brightness of the display image is detected for each color, and the light source control mode corresponding to each color is selected depending on whether the brightness is equal to or higher than a predetermined value. It can be performed.

  In the image projection apparatus, the control unit may detect a deviation of a color component as the feature amount of the image and may select a control mode according to the deviation of the color component.

  As described above, since the bias of the color component is detected as the feature amount of the image and the control mode is selected according to the bias of the color component, the bias of the color component can be reflected in the drive control of the light source. For example, when displaying an image having a color component bias that causes a significant change in color tone, the color tone is more important than a reduction in power consumption by driving and controlling each light source in the second control mode. . On the other hand, when displaying an image having a color component bias that does not cause a significant change in color tone, the power consumption of each light source is controlled by driving the light source in the first control mode while allowing a slight color tone change. Is effectively reduced.

  In the image projection apparatus, the control unit may select a color of illumination light whose color tone change due to increase / decrease in drive current is greater than a predetermined value as a color component of the display image, than the color of other illumination light or a predetermined value. When many are included, at least the light source corresponding to the color may be driven and controlled in the second control mode.

According to such a configuration, when displaying an image including a color of illumination light whose color tone change due to increase / decrease in driving current is larger than a predetermined value, other colors or more than a predetermined value, at least this color is displayed. For the corresponding light source, a change in color tone can be prevented by selecting the second control mode that does not increase or decrease the drive current. In this case, for the light sources corresponding to the other colors, the power consumption can be reduced by selecting the first control mode.
Further, when displaying an image that includes a color of illumination light whose color tone change due to increase / decrease of drive current is larger than a predetermined value, or less than a predetermined value, all light sources are driven in the first control mode. It is good also as controlling. As a result, power consumption can be effectively reduced while allowing some color change.

  In the image projection apparatus, the control unit may detect the number of colors in the image and select a control mode according to the number of colors.

  As described above, the number of colors is detected as the feature amount of the image, and the control mode is selected according to the number of colors. Therefore, the number of colors can be reflected in the drive control of the light source. For example, when displaying an image having the number of colors that cause a significant change in color tone, the color tone is more important than a reduction in power consumption by driving and controlling each light source in the second control mode. On the other hand, when displaying an image with the number of colors such that the color tone change is not so noticeable, driving of each light source is controlled in the first control mode to allow further power consumption while allowing a slight color tone change. Reduction can be achieved.

  In the image projection apparatus, the control unit may drive and control all the light sources in the first control mode when the number of colors in the image is less than a predetermined number.

  According to such a configuration, for example, when the number of colors in the display image is smaller than a predetermined number, such as a presentation image, the visual influence due to the color change is small. By adopting, power consumption can be effectively reduced.

  The present invention includes a light source unit having a plurality of light sources that generate illumination lights of different colors, a light modulation unit that modulates illumination light emitted from the light source unit based on an input video signal, and the light source unit. A first control mode in which the control means variably controls the magnitude of the drive current applied to each light source, and the duty of the drive current applied to each light source. A second control mode in which the ratio is variably controlled, and the light source whose color change due to the change in the magnitude of the drive current is larger than a predetermined value is driven and controlled in the second control mode, and the color change is predetermined. Provided is an image projection device that controls driving of the light source that is equal to or less than a value in the first control mode.

For a light source corresponding to a color having a large color change due to increase / decrease in drive current, if the first control mode for increasing / decreasing drive current is adopted, the color tone will change. Accordingly, the light amount of such a light source is adjusted by controlling driving in the second control mode. Thereby, the color tone change accompanying increase / decrease in drive current can be suppressed. On the other hand, for a light source corresponding to a color whose color tone change due to increase / decrease in drive current is small, the light amount is adjusted by performing drive control in the first control mode. This makes it possible to reduce power consumption while suppressing color changes.
For example, when an LED is used as the light source, the LED that emits red illumination light and the LED that emits blue illumination light have a color change due to increase / decrease in drive current smaller than a predetermined value. The amount of light is adjusted in one control mode. Further, for the LED that emits green illumination light, the change in color tone due to increase / decrease in drive current is larger than that of the other light sources, and thus the light amount is adjusted in the second control mode.
Moreover, the aspect mentioned above can be utilized combining in the possible range.

  The image projection apparatus according to the present invention has an effect that the power consumption can be effectively reduced while suppressing a change in the color of the projection image.

An image projection apparatus according to an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the image projection apparatus 1 according to this embodiment includes a light source unit 2, a light guide unit 3 that guides illumination light emitted from the light source unit 2, and illumination guided by the light guide unit 3. A transmissive liquid crystal display panel (light modulating means) 4 that modulates light and a projection optical unit 5 that projects illumination light modulated by the transmissive liquid crystal display panel 4 onto a screen S are provided. For the sake of simplicity, illustration of the polarizing plate and the like is omitted.

The light source unit 2 includes a plurality of light sources that emit illumination lights of different colors and a color composition element 6 that guides the illumination light emitted from each light source to a common optical path.
In the present embodiment, the light source includes an LED 2a that emits red illumination light, an LED 2b that emits green illumination light, and an LED 2c that emits blue illumination light.
The light guide unit 3 has various optical systems such as a tapered rod that appropriately adjusts the parallelism and the like.

  In the image projection apparatus having such a configuration, the LEDs 2a, 2b, and 2c are sequentially turned on in a time-sharing manner, and the illumination light is guided to the common light guide unit 3 by the color composition element 6, and the light guide unit 3 Is led to the transmissive liquid crystal display panel 4. The illumination light on which the display image is superimposed by passing through the transmissive liquid crystal display panel 4 is enlarged by the projection optical unit 5 and projected onto the screen S. Thereby, the display image is projected on the screen S.

  In this case, the transmissive liquid crystal display panel 4 is driven and controlled in synchronization with the lighting timing of the LEDs 2a, 2b, and 2c. Specifically, during the period in which the LED 2a emits light, the LED 2c emits light based on the red video signal, and in the period in which the LED 2b emits light, based on the green video signal. The transmissive liquid crystal display panel 4 is driven and controlled based on the blue video signal. Since the light emission period of each LED 2a, 2b, 2c is set to be very short, it is possible to give the observer a visual effect that is almost the same as when white illumination light is irradiated.

The LEDs 2a, 2b, 2c and the transmissive liquid crystal display panel 4 are controlled by a control device (control means) 10.
The control device 10 includes an image processing circuit 11, a panel drive circuit 12, a CPU 13, and a light source drive circuit 14 as main components.

A video signal is input to the image processing circuit 11. The image processing circuit 11 performs known image processing such as interpolation processing and gradation correction processing on the input video signal and detects the feature amount of the display image based on the video signal corresponding to one frame. .
For example, as shown in FIG. 2, the image processing circuit 11 includes a γ correction circuit 15, a feature amount detection circuit 16, and a gain adjustment circuit 17 as main components. The γ correction circuit 15 generates a linear video signal by performing γ correction on the video signal. The feature amount detection circuit 16 detects the feature amount of the display image based on the video signal corresponding to one frame input from the γ correction circuit 15, outputs the detected feature amount to the CPU 13, and outputs it to the gain adjustment circuit 17. The feature amount and the video signal are output.
For example, the feature amount detection circuit 16 detects feature amounts relating to the luminance of each color from the video signal corresponding to one frame, specifically, the maximum gradation values Rmax, Gmax, Bmax, and these maximum gradation values Rmax, Gmax. , Bmax are output to the CPU 13, and the maximum gradation values Rmax, Gmax, Bmax and the video signal are output to the gain adjustment circuit 17.

  The gain adjustment circuit 17 adjusts the level of each light quantity of red, green, and blue, outputs the adjusted video signal to the panel drive circuit 12, and outputs the adjustment state to the CPU 13. Specifically, when the maximum gradation values Rmax, Gmax, and Bmax of each color in the display image are input from the feature amount detection circuit 16 to the gain adjustment circuit 17, the maximum gradation values Rmax, Gmax, and Bmax are image projected. The gradation value of each pixel of the video signal is corrected so that the maximum display gradation value (for example, 255) of the apparatus is obtained, and the corrected video signal is output to the panel drive circuit 12. For example, when the maximum display gradation value of the image projection apparatus is 255, the gain adjustment circuit 17 applies 255 / Rmax to the gradation value of each pixel of the video signal as shown in FIG. The video signal related to the transmittance is corrected, and the corrected video signal is output to the panel drive circuit 12.

The gain adjustment circuit 17 outputs to the CPU 13 a value obtained by correcting the gradation value of the video signal output to the panel drive circuit 12 to be higher. Specifically, as described above, when 255 / Rmax is applied to the gradation value of each pixel, this coefficient 255 / Rmax is output to the CPU 13. The CPU 13 corrects the light quantity by multiplying the light quantity of each color by the inverse Rmax / 255 of this coefficient.
Thus, while increasing the transmittance of the transmissive liquid crystal display panel 4, the amount of light is reduced by an amount corresponding to this increase, so that without changing the brightness of the projected image finally displayed on the screen, It is possible to effectively reduce the light emission amount of the LEDs 2a, 2b, 2c. Thereby, power consumption can be reduced. Although the above description has been made with respect to red as an example, the same applies to green and blue.

  Returning to FIG. 1, the panel drive circuit 12 changes the transmittance of the transmissive liquid crystal display panel 4 for each pixel based on the gradation value of the video signal from the image processing circuit 11. Thereby, the transmittance of each pixel of the transmissive liquid crystal panel 4 is adjusted according to the video signal. As a result, the illumination light incident on the transmissive liquid crystal display panel 4 is based on the video signal as described above. The display image is superimposed.

Further, the CPU 13 generates a control signal for driving and controlling each of the LEDs 2 a, 2 b and 2 c based on the feature amount and the video signal from the image processing circuit 11, and outputs the generated control signal to the light source driving circuit 14. To do. Specifically, the CPU 13 variably controls the drive currents of the LEDs 2a, 2b, and 2c, thereby adjusting the amount of light emitted from the LEDs 2a, 2b, and 2c, and the LEDs 2a. , 2b, 2c by controlling the duty ratios of the drive currents, respectively, to provide a second control mode for adjusting the amount of light emitted from each LED 2a, 2b, 2c.
Then, the CPU 13 selects one or both of the first control mode and the second control mode according to the feature amount, and sends control signals for the LEDs 2a, 2b, 2c based on the selected control mode, respectively. These are generated and output to the light source drive circuit 14.

  The light source drive circuit 14 applies a drive current to each LED 2a, 2b, 2c based on each control signal from the CPU 13. Thereby, the light emission amounts of the LEDs 2a, 2b, and 2c are controlled based on the video signal.

  Further, the CPU 13 receives a mode instruction signal from the user I / F 18 and a power signal from the power circuit 19. When the user designates a mode, the user I / F 18 outputs a signal corresponding to the designated mode to the CPU 13 as a mode instruction signal. The power supply circuit 19 determines whether power is supplied from an AC adapter (not shown) or power is supplied from a battery (not shown), and this determination result is used as a power source. It outputs to CPU13 as a signal.

Next, the first control mode and the second control mode will be described in detail.
As shown in FIG. 5, the first control mode is a control mode in which the amount of light of each LED 2a, 2b, 2c is adjusted by increasing or decreasing the magnitude of the drive current of each LED 2a, 2b, 2c. In FIG. 5, the maximum current Imax is set to, for example, the maximum value that can be applied to the LEDs 2a, 2b, and 2c in a normal state. The maximum current Imax is a value that can be individually set for each LED 2a, 2b, 2c.
Thus, in the first control mode, the amount of light emitted from each LED 2a, 2b, 2c is adjusted by changing the magnitude of the drive current applied to each LED 2a, 2b, 2c.

  As shown in FIG. 6, the second control mode is a control mode in which the light quantity of each LED 2a, 2b, 2c is adjusted by variably controlling the duty ratio of the drive current of each LED 2a, 2b, 2c. As shown in FIG. 6, in the second control mode, the magnitude of the drive current applied to each LED 2a, 2b, 2c is not changed, for example, it is constant at the maximum current Imax, and the current application time is adjusted, The amount of light emitted from each LED 2a, 2b, 2c is adjusted.

Here, FIG. 7 shows general characteristics of the light amount and the power consumption with respect to the drive current of each LED 2a, 2b, 2c.
In FIG. 7, the horizontal axis indicates relative drive current, and the vertical axis indicates relative light quantity or power consumption.
As shown in FIG. 7, the light quantity of each LED 2a, 2b, 2c tends to saturate when the drive current increases to some extent. Further, the power consumption of each LED 2a, 2b, 2c increases as the drive current increases, but the increase width ΔP gradually increases as the applied current increases (ΔP1 <ΔP2 in FIG. 7). This is because the forward effect voltage of the LEDs 2a, 2b, and 2c slightly increases as the drive current increases.

Because of such characteristics, for example, when the light quantity of the LEDs 2a, 2b, and 2c is reduced, the power consumption is effectively reduced by reducing the magnitude of the drive current instead of changing the duty ratio. I understand that I can do it. For example, in FIG. 7, taking LED 2b as an example, when the light amount is reduced from 4 to 2, the drive current is reduced from about 9 to about 2.7, and the power consumption at this time Will drop from about 20 to about 4. For this reason, when the amount of light is reduced by 50%, the drive current can be reduced by about 70% and the power consumption can be reduced by about 83%. On the other hand, even if the duty ratio is reduced to ½ in the pulse drive, the power consumption is only 50%.
For this reason, the first control mode can effectively reduce power consumption compared to the second control mode.

  Next, FIG. 8 is a diagram showing a color expression area by red, green, and blue light from the LEDs 2a, 2b, and 2c on an xy color diagram. When the drive current of each LED 2a, 2b, 2c is small, it has a wide color gamut as shown by the broken line in the figure, but when the drive current of each LED 2a, 2b, 2c is large, the color tone of red, green, blue Each change as indicated by a solid line in the figure, and the color expression range tends to narrow. Further, as can be seen from this figure, in particular, in the LED 2b that emits green illumination light, it can be seen that the color tone of the illumination light changes greatly as the drive current increases and decreases. On the other hand, regarding the LED 2a that emits red illumination light and the LED 2c that emits blue illumination light, the change in color tone due to increase / decrease in drive current is small and is hardly affected by the drive current.

  Therefore, as shown in FIG. 5, the first control mode in which the magnitude of the drive current of the LEDs 2a, 2b, and 2c is variably controlled is highly effective in reducing the power consumption. On the other hand, as shown in FIG. Thus, it has the characteristic that the color tone of green illumination light changes.

  Therefore, in the image projection apparatus according to the present embodiment, the following light source control is performed in order to effectively reduce power consumption while suppressing color change while focusing on the above points.

  First, when a video signal is input to the image processing circuit 11 of the control device 10, γ correction is performed on the video signal by the γ correction circuit 15 shown in FIG. A detection process is performed. Specifically, the feature amount detection circuit 16 detects a feature amount related to the brightness of the display image, for example, the maximum gradation values Rmax, Gmax, Bmax of each color from the video signal corresponding to one frame, and these maximum gradations. The values Rmax, Gmax, Bmax are output to the CPU 13, and the maximum gradation values Rmax, Gmax, Bmax and the video signal are output to the gain adjustment circuit 17.

  The gain adjustment circuit 17 adjusts the level of the video signal of each color based on the maximum gradation values Rmax, Gmax, and Bmax, thereby generating a video signal related to the panel transmittance and a video signal related to the amount of light, and relates to the panel transmittance. The video signal is output to the panel drive circuit 12 and the video signal related to the light amount is output to the CPU 13.

  When the maximum gradation values Rmax, Gmax, Bmax and the value for correcting the light amount are input, the CPU 13 determines whether the maximum gradation values Rmax, Gmax, Bmax are equal to or greater than a preset threshold value. For the LED corresponding to the color for which the maximum gradation values Rmax, Gmax, and Bmax are determined to be greater than or equal to the threshold value, control according to the second control mode is selected, and the color for which the maximum gradation value is determined to be less than the threshold value The first control mode is selected for the LEDs corresponding to.

  For example, when the maximum gradation value Rmax of red is a maximum value (for example, 255), as shown in a of FIG. 9, the CPU 13 applies the maximum current Irmax to the LED 2a for a period of one frame. The control signal is generated and output to the light source drive circuit 14.

  If the maximum red gradation value Rmax is less than the maximum value and greater than or equal to the threshold value, the CPU 13 determines the duty ratio corresponding to the maximum gradation value Rmax to the LED 2a as shown in FIG. Is generated and output to the light source drive circuit 14. Here, the larger the maximum gradation value Rmax, the longer the current application time is set. Note that an optimal value can be selected for the pulse driving period depending on design matters.

On the other hand, when the maximum red gradation value Rmax is less than the threshold, the CPU 13 has a predetermined duty ratio with respect to the LED 2a as shown in c of FIG. A pulse-shaped control signal of current corresponding to the adjustment value Rmax is generated and output to the light source driving circuit 14. Here, the predetermined duty ratio employs the duty ratio when the maximum gradation value Rmax matches the threshold value.
Note that the CPU 13 does not increase or decrease the current value in the pulse-like waveform as shown in FIG. 9c, but supplies the current corresponding to the maximum gradation value Rmax in one frame period as shown in FIG. It is good also as producing | generating the control signal which applies continuously over.
The CPU 13 similarly generates control signals for the LEDs 2 b and 2 c and outputs them to the light source drive circuit 14.

When the light source drive circuit 14 receives the control signal generated in this manner, the light source drive circuit 14 applies a drive current based on each control signal to each LED 2a, 2b, 2c.
As a result, the LEDs 2a, 2b, 2c of the respective colors sequentially emit light with a light amount corresponding to the maximum gradation values Rmax, Gmax, Bmax, and each illuminating light is transmitted through the color composition unit 6 and the light guide unit 7 in a transmissive liquid crystal display. After being guided to the panel 4 and subjected to light modulation based on the video signal, the light is projected onto the screen S by the projection optical unit 5. Thereby, a projection image is displayed on the screen S.

As described above, according to the image projection apparatus according to the present embodiment, the feature amount related to the luminance of the display image is detected from the video signal corresponding to one frame, and the control mode is selected based on the detection result. The LEDs 2a, 2b, and 2c can be driven and controlled in an optimal control mode corresponding to the brightness of the display image.
Specifically, when the brightness of the displayed image is bright and the color tone changes significantly, the color tone is more important than the power consumption reduction by selecting the second control mode that does not change the magnitude of the drive current. To do.
Further, when the brightness of the display image is dark and the change in color tone is difficult to understand, the reduction of power consumption is more important than the change in color tone by selecting the first control mode.
This makes it possible to adjust the amount of light according to the characteristics of each frame image, and to effectively reduce power consumption while suppressing changes in color tone.
Further, according to the image projection apparatus according to the present embodiment, the brightness of the display image is detected for each color, and each LED 2a, 2b, 2c is driven and controlled in the control mode corresponding to the brightness, so all the LEDs 2a, 2b are controlled. , 2c can be controlled more finely than in the same control mode.

  In the present embodiment, the threshold value used by the CPU 13 is preferably set individually for each color. For example, as shown in FIG. 8, for red and blue, since the change in color tone due to increase / decrease in drive current is small, the power consumption can be effectively reduced by setting the threshold value higher. In the case of green, the change in color tone due to increase / decrease in drive current is large compared to other colors, so by setting the threshold value lower than other colors, The balance between the change in color tone and the reduction in power consumption is adjusted. Thereby, power consumption can be reduced more effectively.

  In the present embodiment, the maximum gradation value is detected from the video signal corresponding to one frame, and the control mode can be switched in one frame cycle. Instead, this corresponds to a plurality of frames. By detecting the maximum gradation value from the video signal, the control mode may be switched in a cycle of a plurality of frames.

  In the present embodiment, the maximum gradation value of each color of the display image formed based on the video signal is detected, and the control mode to be adopted is determined depending on whether or not the maximum gradation value is equal to or greater than a threshold value. However, instead of this, the average gradation value in the display image is obtained for each color, and when the average gradation value is equal to or greater than the threshold value, the second control mode (see FIG. 6) is adopted, and the average gradation value is determined. When the value is less than the threshold, the first control mode (see FIG. 5) or a control mode (see c in FIG. 9) based on a combination of the second control mode and the first control mode may be employed.

  Further, when determining whether or not the display image is bright, instead of the above method, pixels having a gradation value equal to or higher than the threshold value are detected for each color in the display image, and the number of detected pixels is preset. When the number of pixels is equal to or greater than the reference pixel number, the second control mode (see FIG. 6) is adopted, and when the number of pixels is less than the reference pixel number, the first control mode (see FIG. 5) or the second control mode is selected. A control mode (see c in FIG. 9) based on a combination of the control mode and the first control mode may be employed.

  Further, the method for determining whether the display image is bright or dark is not limited to the method described above. The point is that a determination criterion for determining whether or not the display image is bright is set as appropriate, and when it is determined that the display image is bright based on this determination criterion, the second control mode that does not change the color tone is set. When it is determined that the display image is dark, a first control mode that is accompanied by a change in color tone but has a high power consumption reduction effect, or a control mode that is a combination of the second control mode and the first control mode is selected. Adopt it.

In the present embodiment, the maximum luminance value is detected for each color, and the control mode of each LED 2a, 2b, 2c is selected based on the maximum luminance value. Instead of this, red, green All LEDs 2a, 2b, 2c may be controlled in the same control mode according to the overall brightness of the display image including blue.
A method for determining whether or not the display image is bright can be arbitrarily determined. For example, pixels having a gradation value equal to or larger than a predetermined value are extracted from a video signal in one frame, and the number of pixels is determined. If the number of pixels is equal to or greater than the preset reference pixel number, it is determined that the display image is bright and all the LEDs 2a, 2b, 2c are driven and controlled in the second control mode, and the pixel number is the reference pixel number. If it is less, the display image may be determined to be dark and all the LEDs 2a, 2b, 2c may be driven and controlled in the first control mode. Alternatively, an average gradation value in one frame may be obtained, and it may be determined whether or not the display image is bright based on whether or not the average gradation value is equal to or greater than a threshold value.

In the present embodiment, when the CPU 13 receives a mode designation signal from the user I / F 18, the control mode designated by the user may be preferentially adopted. For example, when the CPU 13 receives a signal for designating the first control mode from the user I / F 18, the LEDs 13a, 2b, and 2c are driven and controlled in the first control mode. Thus, by adopting the control mode desired by the user preferentially, the user's intention can be reflected in the drive control of the LEDs 2a, 2b, 2c.
The user may select a control mode for each color. Thereby, a user's intention can be reflected in detail. In addition to the control mode, for example, a determination criterion for determining whether the display screen is bright or dark, for example, the threshold value and the number of reference pixels may be set by the user.

In the present embodiment, the CPU 13 may switch the control mode based on the power signal from the power circuit 19. For example, during a period in which a power supply signal indicating a state in which power is supplied from the AC adapter is input, the power that can be consumed is not limited. Therefore, the CPU 13 adopts the second control mode, thereby reducing the power consumption. Emphasize color rather than color. On the other hand, during the period when the power supply signal indicating the state in which power is supplied from the battery is input, the usable power is limited. Therefore, the CPU 13 performs the first control mode or the first control described above. By adopting a control mode consisting of a combination of the mode and the second control mode, the effect of reducing power consumption is enhanced while allowing a change in color tone. Thus, the control mode may be switched according to the power supply state. Further, when power is supplied from the battery, the control mode may be switched according to the remaining capacity of the battery.
In addition, it is possible to apply each aspect mentioned above combining in the possible range.

[Second Embodiment]
Next, an image projection apparatus according to a second embodiment of the present invention will be described.
In the image projection apparatus according to the present embodiment, the first control mode is adopted for colors having a small color change due to increase / decrease in drive current, i.e., red and blue, that is, colors having a large color change due to increase / decrease in drive current, i.e. For green, the second control mode is adopted.
As described above, according to the image projection apparatus of this embodiment, the control mode is properly used for each color, so that the processing load on the image processing circuit 11 and the CPU 13 can be greatly reduced.

[Third Embodiment]
Next, an image projection apparatus according to a third embodiment of the present invention will be described.
The image projection apparatus according to the present embodiment is the same as the image projection apparatus according to the first embodiment described above in that the control mode is selected according to the bias of the color component of the display image formed based on the video signal. Different.
Hereinafter, the difference between the image projection apparatus according to the present embodiment and the first embodiment will be mainly described.

10 and 11 are diagrams in which the color tone of each pixel of the display image formed based on the video signal is plotted in the xy space with reference to the three primary colors of sRGB. FIG. 10 is an example of a flower image. Yes, FIG. 11 is an example of a sunset image.
In FIG. 10, since the color tone plot of the pixel is spread over the triangular color expression range surrounded by the three primary colors of RGB, it can be seen that this display image includes various color components. On the other hand, in FIG. 11, since the tone plot of pixels is biased to a range close to the primary color of R in the triangular color expression range surrounded by the three primary colors of RGB, this display image includes G (green) and B It can be seen that the component close to the primary color of (blue) is hardly included.

In the control device 10 of the image projection apparatus according to the present embodiment, the feature amount extraction circuit 16 detects the color tone bias of the display image from the video signal corresponding to one frame, and the control mode adopted by the CPU 13 based on the detection result. To decide. Here, the color tone of each pixel can be easily obtained by performing a matrix calculation process using a known method, for example, using the RGB signal level of each pixel in the video signal and the matrix of each tristimulus value XYZ of the RGB primary colors. Can be sought.
When there is no color tone bias, the CPU 13 adopts the second control mode to suppress the color change due to the change in the magnitude of the drive current. Further, the CPU 13 adopts the second control mode for a large number of colors (for example, red in the display image shown in FIG. 11) when the color tone is biased, thereby increasing the magnitude of the drive current. On the other hand, the color change due to the change is suppressed, and for the colors that are hardly included (for example, green and blue in FIG. 11), the first control mode is adopted to effectively reduce the power consumption.

As described above, according to the image projecting apparatus according to the present embodiment, the control mode is selected based on the color deviation of the display image formed based on the video signal, so that the color tone change of the projected image is allowed. Power consumption can be effectively reduced while keeping the range.
In the present embodiment, the first control mode is always adopted for red and blue that are not affected by the color due to the current magnitude, regardless of the color tone deviation, and the color changes according to the current magnitude change. Only for the green color that is easy to do, the control mode may be selected according to the color tone deviation. As described above, the power consumption of the LEDs 2a and 2c can be further reduced by always adopting the first control mode.

  Further, in the present embodiment, as shown in FIG. 12, when the plots on the tone map are linearly arranged, it is difficult to notice the change in the tone, so that the LEDs 2a, 2b, 2c are set in the first control mode. It is good also as controlling. For example, in the case of an image having many pixels represented by the same color, such as a presentation image, the color tone of each pixel of the display image formed based on the video signal is plotted in the xy space using the three primary colors of sRGB as a reference. Then, as shown in FIG. 12, there is a strong tendency for the plot to appear linearly, and the number of points representing the color tone (number of colors) is smaller than the natural images shown in FIGS. In such a case, it is preferable to adopt the first control mode in which it is determined that the change in color tone is not a concern and the power consumption can be effectively reduced.

[First Modification]
In each of the above embodiments, the light source unit 2 has three LEDs 2a, 2b, and 2c that emit illumination lights of different colors. Instead, as shown in FIG. It is good also as using LED group 2a ', 2b', 2c 'which has arrange | positioned several LED which radiate | emits this illumination light on the same surface at the array form. In this case, the light quantity control method for each LED is the same as described above.

[Second Modification]
Further, instead of the light source unit 2 according to each of the above embodiments, a light source unit 2 ′ as shown in FIGS. 14 to 16 may be used. 14 is a plan view of the light source unit 2 ′ when viewed from the illumination light exit end side, FIG. 15 is a longitudinal sectional view of the light source unit 2 ′, and FIG. 16 is a diagram illustrating the rotation state and light of the rotating rod 20 provided in the light source unit 2 ′. It is a figure for demonstrating the transmission efficiency of.
As shown in FIGS. 14 and 15, in the light source unit 2 ′, a plurality of LEDs 2a, a plurality of LEDs 2b, and a plurality of LEDs 2c are arranged on the same circumference. At the center of this array, there is provided a rotating rod 20 that can rotate around the center axis of the array.
An incident end 20a for taking in illumination light emitted from each LED is provided at the free end of the rotating rod 20, and is synchronized with the lighting timing of each LED 2a, 2b, 2c arranged on the same circumference. Then, when the rotating rod 20 is rotated around the arrangement center axis, the illumination light emitted from the LEDs 2a, 2b, 2c facing the incident end 20a of the rotating rod 20 is taken into the rotating rod 20 from the incident end 20a. Thus, the light is guided to the incident end of the fixed rod 23 through the rotating rod 20.

In such a light source unit 2 ′, the maximum drive current of each LED 2a, 2b, 2c is such that the combined light of the illumination light when all the LEDs 2a, 2b, 2c are turned on has a desired color (for example, white). To decide. For example, as shown in FIG. 17, the maximum drive current Irmax of the LED 2a, the maximum drive current Igmax of the LED 2b, and the maximum drive current Ibmax of the LED 2c are set as follows.
Ibmax <Irmax <Igmax
Then, as shown in FIG. 18, the second control mode is adopted for green with a large color change due to increase / decrease in drive current, and the first control mode for red and blue with small color change due to increase / decrease in drive current. To reduce power consumption.

  In addition, when the brightness | luminance concerning the green of a display image is below a preset threshold value (for example, brightness | luminance corresponding to the light quantity obtained by LED2b whole when one LED2b is made into a completely extinguished state) As shown in FIG. 19, one LED 2b may be completely turned off, and the other LED 2b may be controlled with a duty ratio corresponding to the luminance.

  In the light source unit 2 ′, when the rotating rod 20 is rotated around the central axis of the LEDs 2 a, 2 b, 2 c, when the rotation angle θ of the rotating rod 20 changes as shown in FIG. The coupling state between the exit end 20b and the entrance end 23a of the fixed rod 23 disposed to face the exit end 20b changes, and the light transmission efficiency varies. The exit end 20b of the rotating rod 20 and the entrance end 23a of the fixed rod 23 have the same shape, for example, a square. Here, when the rotation angle of the rotating rod 20 in the state where the four sides coincide is 0 °, the light transmission efficiency is maximum when the rotation angles are 0 ° and 90 °, as shown in FIG. It is expressed as a sine wave that takes a value and takes the minimum value at rotation angles of 45 ° and 135 °. As described above, the light transmission efficiency shows a periodic change depending on the rotation angle θ. Therefore, when the light amount is reduced, the light amount is preferentially given from the LEDs 2a, 2b, and 2c arranged at positions where the light transmission efficiency is low. Is preferably reduced. Thus, by adjusting the light amount, even when the same brightness is obtained, the power consumption can be efficiently reduced.

[Third Modification]
Moreover, in each embodiment mentioned above, although the illumination light inject | emitted from each LED2a, 2b, 2c was led to the common transmissive liquid crystal display panel 4 via the common light guide unit 3, it changes to this. As shown in FIG. 21, light guide units 3a, 3b, 3c and transmissive liquid crystal display panels 4a, 4b, 4c may be provided for the LEDs 2a, 2b, 2c, respectively. In this case, the illumination lights transmitted through the transmissive liquid crystal display panels 4a, 4b, and 4c are guided to the same light combining element 8, combined here, and then guided to the projection optical unit 5.

As mentioned above, although embodiment of this invention was explained in full detail with reference to drawings, the specific structure is not restricted to this embodiment, The design change etc. of the range which does not deviate from the summary of this invention are included.
For example, in each of the above-described embodiments, a reflective liquid crystal display panel or DMD (Digital Micro Mirror) may be employed instead of the transmissive liquid crystal display panel 4.

1 is a side view showing a schematic configuration of an image projection apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a schematic internal configuration of the image processing apparatus illustrated in FIG. 1. It is a figure for demonstrating the effect | action of the gain adjustment circuit shown in FIG. It is a figure for demonstrating the effect | action of the gain adjustment circuit shown in FIG. It is a figure for demonstrating the 1st control mode. It is a figure for demonstrating the 2nd control mode. It is the figure which showed the drive current-light quantity characteristic and drive current-power consumption characteristic of LED. It is the figure which showed the change of the color tone when drive current is increased / decreased. It is a figure for demonstrating light quantity control of the image projector which concerns on one Embodiment of this invention. It is the figure which plotted the color tone of each pixel of the display image formed based on a video signal on xy space on the basis of three primary colors of sRGB, and is the figure which showed the example of the image of a flower. It is the figure which plotted the color tone of each pixel of the display image formed based on a video signal on xy space on the basis of three primary colors of sRGB, and is the figure which showed an example of the image of a sunset. It is the figure which plotted the tone of each pixel of the display image formed based on a video signal in xy space on the basis of three primary colors of sRGB, and is a figure showing an example of a presentation image. It is the figure which showed the 1st modification of the light source unit shown in FIG. It is the figure which showed the 2nd modification of the light source unit shown in FIG. 1, and is a top view when seeing a light source unit from the emission end side of illumination light. It is a longitudinal cross-sectional view of the light source unit shown in FIG. It is a figure for demonstrating the rotation state of a rotating rod with which the light source unit shown in FIG. 14 is provided, and the transmission efficiency of light. It is the figure which showed the magnitude relationship of the maximum electric current value of the drive current of LED of each color with which the light source unit which concerns on a 2nd modification is provided. It is the figure which showed an example of the light quantity control of LED of each color with which the light source unit which concerns on a 2nd modification is provided. It is the figure which showed an example of the light quantity control of LED of each color with which the light source unit which concerns on a 2nd modification is provided. It is the figure which showed the relationship between the angle of the rotating rod which concerns on a 2nd modification, and the transmission efficiency of light. It is the figure which showed schematic structure of the image projector which concerns on a 3rd modification.

Explanation of symbols

1 Image Projector 2 Light Source Unit 2a, 2b, 2c LED
DESCRIPTION OF SYMBOLS 3 Light guide unit 4 Transmission-type liquid crystal display panel 6 Photosynthesis element 10 Control apparatus 11 Image processing circuit 12 Panel drive circuit 13 CPU
14 Light source drive circuit 18 User I / F
19 Power supply circuit S Screen

Claims (9)

A light source unit having a plurality of light sources for generating illumination lights of different colors;
A light modulation means for modulating the illumination light emitted from the light source unit based on an input video signal;
Control means for driving and controlling each of the light sources of the light source unit,
The control means is
A first control mode for variably controlling the magnitude of the drive current of the light source;
A second control mode for variably controlling the duty ratio of the driving current of the light source, detecting a feature amount of a display image from the video signal corresponding to one or a plurality of frames, and based on the feature amount, An image projection apparatus that selects one or both of a first control mode and a second control mode, and performs drive control of the light source in the selected control mode.   The image projection apparatus according to claim 1, wherein the control unit detects the feature amount for each color of the illumination light and selects a control mode for each color of the illumination light.   The control means detects luminance as a feature amount of the display image, selects the second control mode when the luminance is a predetermined value or more, and selects the second control mode when the luminance is less than a predetermined value. The image projection apparatus according to claim 1, wherein one control mode is selected.   The control means detects the luminance of the image for each color of the illumination light, and when the luminance is a predetermined value or more, drives and controls the light source corresponding to the color in the second control mode, The image projection apparatus according to claim 3, wherein when the luminance is less than a predetermined value, the light source corresponding to the color is driven and controlled in the first control mode.   The image projecting apparatus according to claim 1, wherein the control unit detects a bias of a color component as a feature amount of the display image, and selects a control mode according to the bias of the color component.   The control means includes, as the color component of the display image, at least when the color change of the illumination due to increase / decrease of the drive current includes a color of illumination light that is larger than a predetermined value, more than the color of other illumination light or a predetermined value The image projection apparatus according to claim 5, wherein the light source corresponding to the color is driven and controlled in the second control mode.   The image projection apparatus according to claim 1, wherein the control unit detects the number of colors in the display image and selects a control mode according to the number of colors.   The image projection device according to claim 7, wherein the control unit drives and controls all the light sources in the first control mode when the number of colors in the display image is less than a predetermined number. A light source unit having a plurality of light sources for generating illumination lights of different colors;
A light modulation means for modulating the illumination light emitted from the light source unit based on an input video signal;
Control means for driving and controlling each of the light sources of the light source unit,
The control means is
A first control mode for variably controlling the magnitude of the drive current applied to each light source;
A second control mode for variably controlling the duty ratio of the drive current applied to each of the light sources, and the light source having a color change larger than a predetermined value due to a change in the magnitude of the drive current in the second control mode. An image projection apparatus that controls driving and controls the light source whose color change is a predetermined value or less in the first control mode.

Images