JP2005181731A - Video projection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain projection video in an optimum lightness display state even if it is dark in the circumference. <P>SOLUTION: The analog video signal from a video input circuit 11 is supplied to a video input mean value detecting circuit 17 to calculate a mean value of luminance, and the level of the inputted video signal is used to detect, for example, dark video, standard video, or light video. Based upon this detection information, a reference switching circuit 18 switches a reference level of lightness to be the reference for classifying the video lightness into a plurality of pieces such as dark video, standard video, and light video. According to the indication, the reference level value is inputted from a reference data storage part 19 to a comparator 21. Further, illuminance information on ambient light is inputted from an OPC 20 and the comparator 21 compares those input values to select an optimum gamma table. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a video projection apparatus that enlarges and projects a video on a screen.

  As a device that can display a large screen image, there is a video projection device that enlarges and projects the image on a screen. Examples of the video projection apparatus include a CRT projector apparatus that projects an image on a phosphor screen and a liquid crystal projector apparatus that projects an image on a liquid crystal panel.

  In these video projectors, the larger the screen, the lower the brightness of the screen. Therefore, it is necessary to view the video in a dark environment. However, it is not always used in an environment where the surrounding is dark, and the color and brightness of the image may change due to the influence of ambient light (illumination light, sunlight, etc.). Therefore, there has been proposed one that corrects a video signal in accordance with ambient light.

  Patent Document 1 discloses a video projection device that changes the contrast and brightness of a video signal according to the brightness of ambient light.

Patent Document 2 discloses performing gamma correction for expressing a video signal, particularly a black signal, with a good contrast according to the brightness of ambient light. When the surroundings are not dark, the black portion of the projected image does not become less than the illuminance of the screen, so that the color and brightness of the image change and sufficient display is not performed. Therefore, the image signal on the black side is improved by performing gamma correction.
JP-A-7-162791 JP 2001-51652 A

  However, the technique disclosed in Patent Document 1 changes uniformly over all gradations of the video signal. Since the influence of the brightness of the ambient light on the gradation of the image differs for each gradation, the display state cannot be sufficiently improved. In Patent Document 2, gamma correction is performed on the black-side signal, but no other part is taken into consideration.

  In view of such circumstances, an object of the present invention is to provide a video projection device capable of setting the brightness of a projected video to an optimum display state even if the surroundings are not dark.

  The present invention includes a video luminance detecting means for detecting video brightness from an input video signal, an illuminance detecting means for detecting ambient brightness by ambient light, and a projected video from the brightness of the video and the ambient brightness. Select multiple gamma tables for performing gamma correction on each input video signal for each gradation and the optimal gamma table by comparing the brightness of the video with the surrounding brightness so that it can be displayed optimally. And a comparison / selection unit.

  The present invention further includes reference level switching means for switching a reference level indicating a plurality of video brightness based on a detection result of the luminance detection means, and the comparator includes the switched reference level and the surroundings. The optimum gamma table is selected by comparing the brightness.

  In the present invention, the gamma table is selected based on the brightness of the image and the brightness of the ambient light, and the brightness of the projected image is controlled over all gradations. Display is possible.

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

  FIG. 1 is an explanatory diagram showing a use state of a video projection apparatus according to the present invention, and FIG. 2 is a block diagram showing an embodiment of the video projection apparatus.

  As shown in FIG. 1, this video projection device is a liquid crystal projector device 10 and projects a video on a screen 30. Here, the screen 30 and the liquid crystal projector device 10 are provided with an OPC (organic photoconductor) 20 for detecting the illuminance of ambient light.

  The liquid crystal projector 10 includes a video input circuit 11, a video processing circuit 12, a gamma table circuit 13, a DA converter 14, a liquid crystal driver 15, a liquid crystal panel 16, a video input average value detection circuit (video brightness detection means) 17, a reference. The switching circuit 18, a reference data storage unit 19, an OPC (illuminance detection means) 20, and a comparator (comparison selection means) 21 are included.

  A digital video signal is input to the video input circuit 11 from a video tape, DVD, or the like, and digital processing such as frequency conversion is performed in the video processing circuit 12. The digitally processed video signal is subjected to gamma correction in the gamma table circuit 13 and converted to an analog signal by the DA converter 14. The analog video signal is time-divided by the liquid crystal driver 15 and supplied to the liquid crystal panel 16, and the video is displayed on the liquid crystal panel 16.

  Also, the analog video signal from the video input circuit 11 is calculated by the video input average value detection circuit 17 with the average value of luminance, and the level of the input video signal is, for example, dark video, standard video, Detects whether the image is bright. Based on this detection information, the reference switching circuit 18 switches the reference level of the reference brightness for dividing the image brightness into a plurality of images such as a dark image, a standard image, and a bright image. Based on this instruction, the reference level value is input from the reference data storage unit 19 to the comparator 21. Also, the illuminance information of the ambient light is input from the OPC 20, and the comparator 21 compares these input values and selects an optimal gamma table.

Next, this gamma correction will be described in detail.
The gamma table provided in the gamma table circuit 13 performs gamma correction in each gradation based on the reference level indicating the brightness of the video and the brightness of the room (ambient environment) by the OPC 20. By performing gamma correction on the video signal using this gamma table, the projected video can be adjusted to an optimum state over all gradations.

  3 to 5 are diagrams illustrating gamma correction with respect to the reference in the relationship between the brightness of the video and the brightness of the room. In these figures, the dotted line is the gamma characteristic with γ = 1, and the solid line is the gamma correction characteristic for it. The gamma correction in each case will be described in detail.

FIG. 3 shows gamma correction for a dark room, a standard brightness room, and a bright room for a bright image.
In the case of a dark room with respect to a bright image, the screen looks brighter than the standard image, so that the brightness of the entire image displayed on the liquid crystal panel 16 is greatly suppressed.
In the case of a room having a standard brightness for a bright image, the brightness of the entire image displayed on the liquid crystal panel 16 is suppressed.
In the case of a bright room for a bright image, the entire image displayed on the liquid crystal panel 16 is slightly brightened, and since it is a bright image, the brightness is slightly increased compared to the standard image.

FIG. 4 shows gamma correction of a dark room, a standard brightness room, and a bright room for a standard brightness image.
In the case of a dark room with a standard brightness image, the brightness of the image displayed on the liquid crystal panel 16 is suppressed to prevent the screen from appearing bright and damaging eyes.
In the case of a room having a standard brightness with respect to a standard brightness image, the video is expressed with the standard brightness.
In the case of a bright room for a standard brightness image, the brightness of the image displayed on the liquid crystal panel 16 is increased so as not to lose the brightness of the room.

FIG. 5 shows gamma correction of a dark room, a standard brightness room, and a bright room for dark images.
In the case of a dark room with respect to a dark image, since the image is dark in the dark room, the black reproducibility is improved and the intermediate gradation of the image displayed on the liquid crystal panel 16 is slightly brightened.
In the case of a room having a standard brightness with respect to a dark image, the tone reproducibility of a dark scene of the image displayed on the liquid crystal panel 16 is enhanced.
In the case of a bright room for dark images, a gamma from black to middle of the image displayed on the liquid crystal panel 16 is set so that a dark image can be reproduced even in a bright room.

Thus, the comparator 21 selects a gamma table that can perform the above gamma correction based on the brightness of the video and the brightness of the room.
The comparator 21 compares the room brightness by the OPC 20 with the reference brightness reference, and switches the gamma table according to the room brightness. In this way, by detecting dark video, standard video, and bright video at the level of the input video signal and switching the reference level, the optimal gamma table is selected according to the room brightness and video signal, so projection The video can be displayed in an optimal state.

  In this description, the video signal is described in three levels: dark video, standard video, and bright video, and the room brightness is described in three levels: dark room, standard room, and bright room. It is also effective to divide the brightness of the room and the brightness of the video into optimum stages for smooth switching of images.

It is explanatory drawing which shows the use condition of the video projection apparatus which concerns on this invention. It is a block diagram which shows one Embodiment of the video projector which concerns on this invention. It is explanatory drawing which shows the gamma correction of the dark room with respect to a bright image, the room of standard brightness, and the bright room. It is explanatory drawing which shows the gamma correction of the dark room, the room of a standard brightness, and the bright room with respect to the image | video of standard brightness. It is explanatory drawing which shows the gamma correction of the dark room with respect to a dark image | video, the room of a standard brightness, and a bright room.

Explanation of symbols

10 projector 11 video input circuit 12 video processing circuit 13 gamma table 14 DA converter 15 driver,
16 Liquid crystal panel 17 Video input average value detection circuit 18 Reference switching circuit 19 Reference data storage unit 20 OPC
21 Comparator

Claims (2)

Video brightness detection means for detecting the brightness of the video from the input video signal;
Illuminance detection means for detecting ambient brightness by ambient light,
A plurality of gamma tables for performing gamma correction for each gradation on the input video signal so that the projected video is optimally displayed from the brightness of the video and the ambient brightness;
An image projection apparatus comprising: a comparison / selection unit that compares the brightness of the image with the brightness of the surroundings to select an optimal gamma table. Reference level switching means for switching a reference level indicating a plurality of video brightness based on the detection result of the video brightness detection means,
2. The video projection apparatus according to claim 1, wherein the comparator compares the switched reference level with the ambient brightness to select an optimal gamma table.

Images