A projection type video display device such as a liquid crystal projector receives a plurality of kinds of input videos with different aspect ratios, as videos to be displayed, through video signals. The aspect ratio refers to a width-to-height ratio of a video to be displayed or a video signal, or a width-to-height ratio of a display screen on a display element or a display terminal. Hereinafter, regarding an aspect ratio, a width-to-height ratio of a video signal or a display area of a display element will be displayed as “long side (horizontal direction):short side (vertical direction)” in the specification.
For example, an aspect ratio of a video in current TV broadcasting or a video in a general personal computer is 4:3, an aspect ratio of a high-quality video in high-definition broadcasting or the like is 16:9, and an aspect ratio of a CinemaScope movie video is 2.35:1.
On the other hand, in the projection type video display device, a display element such as a liquid crystal panel used as a light valve forming an optical image to be projected has a display area as an area capable of displaying a display video. Needless to say, the aspect ratio of the display area is physically constant for such an element, irrespective of the aspect ratio of an input video.
In recent years, the use of a liquid crystal projector for a home theater, through which a family can enjoy movies and the like, is increasing, since the liquid crystal projector can utilize a large screen easily. As a liquid crystal panel that is a display element of such a liquid crystal projector, those having a display area with an aspect ratio of 16:9 compatible with a high-quality video are used generally. Further, it is preferred that a screen displaying a projected video projected from a liquid crystal projector is fixed to a wall surface so as to ensure video quality. As a screen used in this case, those having the 2.35:1 aspect ratio of a Cinemascope movie video, which is an aspect ratio of the most horizontally oriented video among the videos projected for a home theater, are used often.
Under the above-mentioned circumstances, there is a demand that a plurality of kinds of projected videos with different aspect ratios are displayed on a specific screen, for example, with an aspect ratio of 2.35:1 properly, that is, without extending off the screen and in such a manner that a large projected video is displayed making the most use of the screen.
As one method for solving the above-mentioned problem, a technology is known, in which an input video is electrically converted from an original aspect ratio to be compressed or expanded so as to be fitted to an aspect ratio of a display area of a liquid crystal panel, a video is displayed making the most use of the display area of the liquid crystal panel, the converted aspect ratio is returned to the original aspect ratio of the input video optically by an anamorphic lens, and the input video is projected on a screen (see Patent Document 1).
The projection method in a conventional liquid crystal projector using the anamorphic lens will be described with reference to FIG. 12.
FIG. 12 shows views illustrating how three kinds of input videos with different aspect ratios are displayed by the conventional liquid crystal projector respectively on a liquid crystal panel and a screen. Herein, the case where the aspect ratio of a display area 51 of a liquid crystal panel is 16:9, and the aspect ratio of a screen 52 is 2.35:1 will be described.
FIG. 12A shows an input video a1 in which a video signal is an ordinary TV broadcasting signal, and the aspect ratio of an input video in the video signal is 4:3. In this case, the input video is expanded electrically in a horizontal direction so that the aspect ratio thereof becomes the aspect ratio of 16:9 of the display area 51 of the liquid crystal panel, and displayed on the liquid crystal panel as a display video a2. The display video a2 is expanded optically in a vertical direction by an anamorphic lens and displayed on the screen 52 as a video with the original aspect ratio of 4:3 as shown in a projected video a3. At this time, the right and left sides of the screen 52 are non-display areas 53.
FIG. 12B shows an input video b1 in which a video signal is a high-definition broadcasting signal and the aspect ratio of an input video in the video signal is 16:9. In this case, the aspect ratio of the display area 51 of the liquid crystal panel is the same as that of the input video b1, and the input video b1 is displayed on the display area 51 of the liquid crystal panel as a display video b2 while keeping the width-to-height ratio of the input video b1. Then, the display video b2 is expanded optically in the vertical direction by the anamorphic lens and displayed on the screen 52 as a video with the original aspect ratio of 16:9 as shown in a projected video b3. Even at this time, the right and left sides of the screen 52 are the non-display areas 53.
FIG. 12C shows an input video c1 with an aspect ratio of 2.35:1 in which a video in a video signal is a CinemaScope movie video. In this case, the input video c1 is reduced electrically in the horizontal direction so that the aspect ratio thereof becomes the aspect ratio of 16:9 of the display area 51 of the liquid crystal panel, and displayed on the liquid crystal panel as a display video c2. Then, the display video c2 is expanded and demodulated optically in the horizontal direction by the anamorphic lens and projected on the screen 52 and displayed on the screen 52 as a video with the original aspect ratio of 2.35:1 as shown in a projected video c3.
Thus, in the conventional liquid crystal projector using the anamorphic lens, even with input videos having different aspect ratios, display videos are displayed using the entire display area of the liquid crystal panel. Therefore, the use of the light of the lamp as a light source can be maximized, and a light projected video of high quality can be obtained. Further, according to a projection method in the conventional liquid crystal projector, it is not necessary to adjust the position of a projection lens at a time of switching input videos in switching and projecting input videos with different aspect ratios. Therefore, there also is an advantage that the projection lens of the liquid crystal projector need be set only once when the liquid crystal projector is set.
Prior Art Document
Patent Document
Patent document 1: JP 2005-72887 A