JP2004264668A - Projector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projector whose dark picture does not become hard to see even in a bright room while suppressing black floating and which is free of flickering of a picture due to variation in light quantity of a lamp even when luminance variation of the picture is large. <P>SOLUTION: A luminance adaptation value is calculated by operating the mean luminance of a picture visualized by using a display device 13 with a time constant made to correspond to dark adaptation of an appreciator. When the luminance adaptation value decreases to a given threshold or below, the quantity of light of a light source lamp 15 is decreased to make black floating inconspicuous to the appreciator. Further, an illuminance sensor 2 provided nearby a screen 3 detects illuminance and when the illuminance is equal to or larger than a given value, the black floating is inconspicuous, so light quantity decreasing control is not performed so that the picture does not become hard to see. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a projector for projecting an image on a screen using a light source lamp and an optical system, and more particularly, to eliminating black floating where a dark portion of an image has luminance.
[0002]
[Prior art]
2. Description of the Related Art As an image reproducing apparatus that reproduces an image on a large screen, a projector that projects an image visualized by an image display element such as a liquid crystal shutter or an MMD (micro mirror device) onto a screen using a light source lamp or an optical system has been put to practical use. .
[0003]
In order to project a larger image and to improve the brightness and contrast of the projected image, it is necessary to increase the light amount of the lamp. However, since the light-shielding property of the image display element is not perfect, there is a problem that when the amount of light of the lamp is increased, so-called black floating appears that even a black portion of the image is projected slightly even in a black portion. That is, as shown in FIG. 3A, the image display element ideally has a light output characteristic (light transmission characteristic, light reflection characteristic) that is linear with respect to an input image signal (color signal). However, in the case of a liquid crystal shutter that is currently in practical use, a certain amount of light leaks even when the shutter is completely closed. Therefore, even when the input video signal is 0, the light output does not become 0 and a residual light amount occurs. The characteristic is as shown in FIG. The contrast ratio (dynamic range) between the brightest part and the darkest part of the liquid crystal shutter is about 500: 1 to 1000: 1, and the dark part of the image has only this luminance (1/500 to 1/1000 of the bright part). If it had, the viewer would have a black floating image in which the dark part would appear to be dimly raised when the eyes of the viewer were accustomed to the darkness. Also, the micromirror device reflects irregularly at the ends and fulcrums of the micromirrors, so that the contrast ratio is about 2000: 1.
[0004]
In order to solve this problem, there has been proposed a projector that detects the luminance of an image to be projected and, when the image is dark, reduces the amount of light of a lamp to prevent floating of black (for example, Patent Document 1).
[0005]
[Patent Document 1]
JP 2001-346219 A
[Problems to be solved by the invention]
However, the above-described conventional projector calculates the average luminance of one frame (or one field) and controls the light amount of the lamp using the result, but this method projects a moving image in which the luminance changes frequently. In this case, since the light amount control of the lamp is frequently increased and decreased in synchronization with this, there is a problem that the image flickers and it becomes rather difficult to see.
[0007]
In addition, black floating is conspicuous when the entire image is dark, but even when the image is dark, the black floating is almost conspicuous when the illuminance at the projection place is high, that is, when projecting in a bright room. In this case, if the light amount of the lamp is reduced as in the above-described conventional projector, there is a problem that a dark image becomes darker and more difficult to see.
[0008]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a projector in which a dark image is not difficult to see even in a bright room while suppressing the floating of black, and the image does not flicker due to a change in the amount of light of a lamp even when the luminance of the image changes greatly.
[0009]
[Means for Solving the Problems]
The present invention provides an image display element for visualizing an image input as a signal, a light source lamp for projecting the visualized image on a screen via an optical system, and a luminance measuring unit for measuring the luminance of the image. Means for controlling the amount of light of the lamp according to the measurement result of the luminance measuring means, wherein the luminance of the image is calculated by a predetermined time constant, and when the calculation result is equal to or less than a predetermined value, the lamp of the lamp is controlled. Light quantity control means for decreasing the light quantity and increasing the light quantity of the lamp when the luminance of the image subsequently rises above a predetermined value.
The present invention is characterized in that the predetermined time constant is made to correspond to a time constant of visual dark adaptation.
The present invention is characterized in that it comprises illuminance measuring means for measuring the illuminance near the screen, and wherein the light quantity control means controls the amount of decrease in the light quantity of the lamp in accordance with the illuminance near the screen.
[0010]
According to the present invention, when the luminance of the image is reduced, the light amount of the lamp is reduced to prevent the floating of black. This light amount reduction control is performed with a predetermined time constant (for example, a time constant of dark adaptation of human vision). I made it. As a result, the light amount control means does not react to an image in which the luminance of the image fluctuates frequently, and the light amount of the lamp does not fluctuate. In addition, in the case of such an image, the viewer's vision reacts to the bright image and the pupil is closed, so that even if the amount of light of the lamp is high and black floating occurs, the viewer does not notice the black floating. That is, by setting a time constant for controlling the light amount of the lamp when the viewer's vision has adjusted to the darkness (when the pupil is opened) after the dark image has continued for a predetermined time, the light amount of the lamp fluctuates. And the viewer can be prevented from seeing the black float.
[0011]
Further, in the present invention, the degree to which the light amount of the lamp is reduced is controlled according to the illuminance near the screen on which the image is projected. That is, when the illuminance near the screen is low, the amount of decrease in the amount of light of the lamp is increased when the luminance of the image is reduced, and when the illuminance near the screen is high, the amount of light of the lamp is reduced even when the luminance of the image is reduced. To reduce the amount of decrease. Thus, when a room to be projected is dark, emphasis is placed on preventing black floating, and when a room to be projected is bright, emphasis is placed on making a dark image visible to a viewer.
In the third aspect, "controlling the amount of decrease in the amount of light of the lamp in accordance with the illuminance near the screen" means changing the amount of decrease in the amount of lamp light continuously or stepwise so as to follow the illuminance near the screen. In addition, when the illuminance in the vicinity of the screen is equal to or more than a predetermined value, control is performed so as not to perform a process of reducing the light amount of the lamp.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
A projector according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram around an optical system of a projector (projection display device) according to an embodiment of the present invention.
This projector is a three-panel type including three display devices 13 for three primary colors of RGB, and combines the three primary colors of RGB visualized by the three display devices into a color video by combining mirrors. Although a liquid crystal shutter is used in this embodiment as a display device, a micromirror device may be used.
[0013]
A video signal reproduced by a reproduction unit (not shown) is input to the video signal processing unit 10. This video signal may be an NTSC composite signal or an RGB (Y, Cr, Cb) component signal. Further, it may be inputted as a data stream as it is as a DV digital video signal. In this embodiment, the video signal processing unit 10 is constituted by a DSP, and an input video signal is a digital video signal.
[0014]
Further, an illuminance sensor 2 that is installed near the screen 3 and detects illuminance near the screen 3 is connected to the video signal processing unit 10. The illuminance sensor 2 is for detecting the brightness of the environment near the screen 3 and is provided at a position where the image light projected by the projector 1 does not enter. This illuminance sensor includes, for example, a phototransistor, a photodiode, a CdS cell (a cadmium sulfide light variable resistance element), and the like, and is connected to the projector main body 1 (video signal processing unit 10) by a cable.
[0015]
The video signal processing unit 10 separates the input video signal into color signals of three primary colors of RGB and inputs the signal to the display device driver 11. The display device driver 11 visualizes the video signal by opening and closing each cell of the display device based on the color signal. The gradation of each cell is controlled in 256 steps from 0 to 255.
[0016]
Further, the video signal processing unit 10 calculates the average luminance Ya of the input video signal. This average luminance Ya is obtained by integrating the Y signals for one frame and dividing by the number of dots. This average luminance Ya also takes a value in the range of 0 to 255. The video signal processing unit 10 calculates the average luminance Ya once per second (once every 30 frames). Then, when the image having the low average luminance Ya continues for a predetermined period, an instruction to reduce the light amount of the light source lamp 15 to prevent the floating of black is output to the light source lamp driver 12.
[0017]
The video signal processing unit 10 calculates the average luminance Ya obtained by the above processing using a time constant corresponding to a time (dark adaptation time) until a person becomes used to darkness. This calculation can be equivalently represented by the integration circuit of FIG. 2, and the time constant τ is determined by CR. When the luminance adaptation value Ys calculated by this calculation becomes smaller than a predetermined threshold value Thd, in order to make the floating of black inconspicuous to a viewer, as shown in FIG. , The luminance of the image is reduced, and the substantial contrast ratio is improved.
[0018]
However, when the illuminance near the screen detected by the illuminance sensor 2 is equal to or more than a certain value, the floating of black is inconspicuous, and the dark part of the image becomes rather difficult to see. I try not to do it.
[0019]
When the average luminance Ya of the image rises above the threshold value Thu while the light amount is being reduced, the light amount reduction control of the light source lamp 15 is performed in order to project the bright portion of the brightened image vividly. It is released and the light source lamp 15 emits light with a high light quantity. In this way, when the image becomes brighter, increasing the light amount of the light source lamp without waiting for the result of the time constant calculation to exceed the threshold value is because the viewer's eyes are accustomed to the brightness. Is shorter than the dark adaptation, so that if the light amount of the light source lamp 15 is changed after the image becomes brighter, the amplitude of the luminance becomes too large, and also the image effect that the screen suddenly becomes brighter is enhanced. It is.
[0020]
FIG. 4 is a diagram illustrating an example of the light amount control. FIGS. 3A, 3B, and 3C are each composed of a two-stage graph, in which an upper graph shows a change in the average luminance Ya and a luminance adaptation value Ys obtained by calculating a time constant thereof, and a lower graph shows a light source. 6 is a graph showing light amount control of the lamp 15.
[0021]
In FIG. 7A, when a scene is changed from a bright scene to a dark scene in a movie or the like, the average luminance Ya changes discontinuously when the scene is changed, but the luminance adaptation value Ys gradually decreases after the scene is changed. Go on. Then, when the luminance adaptation value Ys becomes equal to or less than the threshold Thd after the dark scene continues, the light amount of the light source lamp 15 is controlled to L. Thereafter, when the scene changes to a bright scene again, the light amount of the light source lamp 15 is controlled to H by using the average luminance Ys having become larger than the threshold value Thu as a trigger. At this time, the luminance adaptation value Ys is made to match the average luminance Ya.
[0022]
Note that, when the scene is changed to a bright scene, the rising timing of the average luminance Ya and the rising timing of the luminance adaptation value Ys are simultaneous, but in this figure, they are slightly shifted so that both can be seen.
[0023]
FIG. 6B is a diagram showing a change in the luminance adaptation value Ys for an image in which the average luminance Ya changes frequently. Such images often appear in animations and games, but the average luminance Ya repeats high luminance and low luminance discontinuously in a short cycle. Even in such an image, the luminance adaptation value Ys does not react to a sudden change in the average luminance Ys. Since it only changes slowly, the light amount of the light source lamp 15 does not fluctuate between H / L.
[0024]
FIG. 3C shows an example of control for a video that gradually becomes brighter from a dark scene. Following the dark scene, the luminance adaptation value Ys is equal to or smaller than the threshold Thd, and the light amount of the light source lamp 15 is controlled to L. In this case, when the average luminance Ya gradually increases and exceeds the threshold value Thu, the down light control of the light amount of the light source lamp 15 is canceled without waiting for the increase of the luminance adaptation value Ys, and the light amount is set to the high luminance H. You. The luminance adaptation value Ys does not follow this change because the time constant is calculated, but at this time, the luminance adaptation value Ys is forcibly made to match the average luminance Ya by the calculation of “Ys ← Ya”. Start a new time constant calculation. As described above, when the average luminance Ya rises and exceeds the threshold value Thu, the luminance adaptation value Ys is forcibly made to match the average luminance Ya. The lamp control can be reset without subtracting the luminance change.
[0025]
FIG. 5 is a flowchart showing the procedure of the light amount control operation of the light source lamp 15. This operation is an operation repeatedly executed at appropriate intervals (for example, at one-second intervals). First, the illuminance sensor 2 is checked, and the brightness (illuminance) near the screen 3 is read (s1). If the illuminance is equal to or more than a predetermined value, it is determined that the brightness control of the light source lamp 15 should not be performed, and the light amount is set to H (normally set to H, in which case the operation is terminated). (S11).
[0026]
When the illuminance near the screen 3 is equal to or less than the predetermined value, the following operation is performed. First, the average luminance Ya of the video is calculated (s2). The average luminance Ya is a value in the range of 0 to 255 obtained by averaging the luminance signals for one frame of the video. Then, it is determined whether the current light amount setting value is H / L (s3).
[0027]
When the current light amount setting value is H, a time constant calculation is performed using the average luminance Ya calculated this time and Ya calculated and stored in the past operation to calculate a luminance adaptation value Ys (s4). ). It is determined whether the calculated luminance adaptation value Ys is equal to or smaller than the threshold Thd (s5). If the luminance adaptation value Ys is equal to or smaller than the threshold Thd, the light amount setting value of the light source lamp 15 is reduced to L. Control is performed (s6). The light amount setting value is output from the video signal processing unit 10 to the light source lamp driver 12, and the light amount of the light source lamp 15 is controlled by the light source lamp driver 12. The light amount control of the light source lamp 15 may be performed by any control method such as voltage control, phase control, and PWM control. Further, the specific value of H / L of the light amount setting value may be set to an optimum value based on the total light amount of the light source lamp 15, the size of the image to be projected, and the like.
[0028]
According to this process, when the luminance adaptation value Ys has decreased due to the continuation of a dark (low average luminance) image for a predetermined period of time, the luminance of the light source lamp 15 is controlled to be lower, and the viewer is blacked out. Float can be made inconspicuous.
[0029]
On the other hand, if the current light amount setting value is L, it is determined whether or not the average luminance Ya calculated this time is larger than the threshold value Thu (s7). When the average luminance Ya becomes larger than the threshold value Thu, control is performed to return the light amount of the light source lamp 15 to H, which is a regular set value, in order to correspond to a bright image (s8). Then, the luminance adaptation value Ys is rewritten to the current average luminance Ya, the stored past average luminance Ya is reset (s9), and the operation is terminated. If the average luminance Ya calculated this time is equal to or smaller than the threshold value Thu, the operation is terminated.
[0030]
When the time constant calculation is performed using the past average luminance Ya each time without using the recurrence formula, the average luminance Ya calculated in s2 is accumulated and stored.
[0031]
By the above processing, the degree of dark adaptation of the viewer's vision is estimated by calculating the time constant of the transition of the average luminance Ya of the image, and the light source lamp 15 is determined based on the luminance adaptation value Ys indicating the degree of dark adaptation. Can be controlled.
In addition, when the illuminance near the screen on which the image is projected is equal to or more than a predetermined value, the light amount control is not performed, thereby preventing a dark image from being blurred when projecting an image in a bright place. Can be.
[0032]
FIG. 6 is a block diagram showing a second embodiment of the present invention. This embodiment is different from the first embodiment shown in FIG. 1 in that an optical shutter 17 such as a liquid crystal shutter is provided on the front of the light source lamp 15 to control the light amount of the light source lamp 15. The point is that the amount of light transmitted to the optical system 14 is controlled by controlling the opening angle of the optical shutter 17 instead of controlling the amount of light itself.
[0033]
An optical shutter driver 18 is connected to the optical shutter 17. When controlling the light quantity of the light source lamp 15, the video signal processing unit 10 outputs a shutter opening angle control signal to the optical shutter driver 18. The optical shutter driver 18 controls the voltage applied to the optical shutter 17 based on the opening angle control signal, and controls the optical system 14 to transmit a predetermined amount of light.
[0034]
In this method, since the power applied to the light source lamp 15 may be constant, the lighting state of the light source lamp 15 is stabilized, and the life of the lamp can be extended. Furthermore, since the optical shutter 17 can control the amount of transmitted light in multiple steps or continuously, the light amount of the light source is not controlled in two steps of H / L, but is controlled according to the average luminance Ya or the luminance adaptation value Ys. Step or continuous control is also possible.
[0035]
In the above embodiment, when the illuminance in the vicinity of the screen 3 is equal to or more than the predetermined value, the light source light amount is not controlled. When the illuminance in the vicinity is high, the control can be variably controlled so as to increase the L level light amount. Note that this L-level variable control can also be performed by the configuration of FIG. 1 when the light source lamp 15 supports multi-step or continuous light amount control.
[0036]
【The invention's effect】
As described above, according to the present invention, it is possible to reduce the amount of lamp for an image having a low luminance so that the floating of black is not conspicuous to a viewer, and to increase or decrease the luminance of the image frequently. The light intensity does not fluctuate even for a perfect image.
Further, according to the present invention, by controlling the degree to which the light amount of the lamp is reduced according to the illuminance near the screen that projects the image, it is possible to prevent black floating when the room to be projected is dark, When the room to be projected is bright, the floating of black is inconspicuous, so that it is possible to perform control with an emphasis on making a dark image visible to a viewer.
[Brief description of the drawings]
FIG. 1 is a block diagram of a projector according to an embodiment of the present invention. FIG. 2 is a circuit diagram equivalently showing a time constant calculation performed by the projector. FIG. FIG. 4 is a diagram illustrating changes in average light amount Ya, luminance adaptation value Ys, and lamp light amount of an image. FIG. 5 is a flowchart illustrating the operation of the projector. FIG. Block diagram of a projector according to an embodiment of the present invention.
1. Projector (body), 2. Illuminance sensor, 3. Screen,
DESCRIPTION OF SYMBOLS 10 ... Video signal processing part, 11 ... Display device driver, 12 ... Light source lamp driver, 13 ... Display device, 14 ... Optical system, 15 ... Light source lamp, 16 ... Condenser lens, 17 ... Optical shutter, 18 ... Optical shutter driver

Claims (3)

A video display element for visualizing a video input as a signal,
A light source lamp for projecting the visualized image onto a screen via an optical system,
Brightness measurement means for measuring the brightness of the image,
Means for controlling the amount of light of the lamp according to the measurement result of the luminance measuring means, wherein the luminance of the image is calculated by a predetermined time constant, and the light amount of the lamp is determined when the calculation result becomes a predetermined value or less. And light amount control means for increasing the light amount of the lamp when the luminance of the image rises above a predetermined value,
Projector equipped with. The projector according to claim 1, wherein the predetermined time constant corresponds to a time constant of visual dark adaptation. An illuminance measurement unit that measures illuminance near the screen,
The projector according to claim 1, wherein the light amount control unit controls a decrease amount of the light amount of the lamp in accordance with illuminance near the screen.

Images