Television – Mechanical optical scanning – Moving reflector
Reexamination Certificate
1999-04-12
2003-07-08
Harvey, David E. (Department: 2714)
Television
Mechanical optical scanning
Moving reflector
C348S745000
Reexamination Certificate
active
06590606
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention is directed to a method for the compensation of geometric image errors in video images with a plurality of lines, each line having a plurality of image points, wherein the image errors to be compensated influence the length of the lines and the ith line in geometric image errors that have not been compensated begins at a location x
ai
and ends at a location x
ei
on a projection surface. The invention is further directed to an arrangement for displaying video images on a projection surface in which image points in a plurality of lines are sequentially illuminated and geometric image errors are compensated in accordance with the method, wherein these image errors to be compensated influence the length of the lines and the ith line in geometric image errors that have not been compensated begins at a location x
ai
and ends at a location x
ei
on a projection surface. Moreover, the invention is directed to an arrangement for displaying video images on a projection surface in which the display is carried out on this projection surface at an inclination.
DESCRIPTION OF THE RELATED ART
Geometric image errors of the type mentioned above can occur, for example, when a transparency is projected at an angle. For an overhead projector, a mirror is provided for compensation according to WO 97/03380, wherein the image is projected onto the back of a projection surface by means of the mirror. The inclination of the mirror relative to the projection surface is arranged in such a way for compensating trapezoid distortions that the light paths from the projector to the projection surface are approximately identical in all areas of the image.
In a video projection according to DE 32 43 879 C2, mirrors are also used, as in the above-mentioned projection with the overhead projector, to compensate for the trapezoid distortions occurring through diagonal projection.
The above-mentioned compensation with mirrors requires very large mirrors for large-image projection. Therefore, it would take up much space and is substantially limited to rear projection so that the mirrors do not conceal the projection surface from view.
In the video technique disclosed in EP 0 756 425 A2, a liquid crystal matrix controlled with a video image is projected onto a screen. In this case, trapezoid distortions are compensated without mirrors in that all lines of the image are shortened with reference to the length of the shortest line. For this purpose, the picture is distorted on the liquid crystal matrix in a trapezoidal shape in such a way as to compensate precisely for this distortion due to diagonal projection. This type of distortion of the projected image is carried out in the case of LCD images in that image points are omitted in the shortened lines. At very large angles, however, it is to be expected that the loss of resolution will be so great that it will no longer be possible to display a high-quality pictures.
In diagonal projection of video images, trapezoid distortions of the type mentioned above change the line length, for example, when the orientation of the frame scanning is carried out at a small angle. This also changes the related density of image points in the line, so that these errors can essentially only be compensated through correction of the line information.
OBJECT AND SUMMARY OF THE INVENTION
It is the object of the invention to provide a method for compensation of image errors of the type mentioned above and an arrangement for carrying out this method in which, in the case of large angles, loss of information due to missing image points is reduced.
This object is met through a method of the type mentioned above in which a substantially parallel light bundle is deflected on the projection surface in two dimensions for sequential illumination of the image points of the video image, a light bundle for the image point at every location on which the light bundle is deflected is intensity-modulated at this location in accordance with the image point information of the undistorted video image, a value determining the start of the line of the compensated image is defined by x
ad
≧Max(x
ai
) and a value determining the end of the line of the compensated image is defined by x
ed
≦Min(x
ei
), where x
ed
>x
ad
, and the light bundle for each line is deflected in such a way that all image points of the line i are displayed sequentially within the area [x
ad
; x
ed
] on the projection surface. An arrangement according to the invention for carrying out the method comprises a source for the emission of a substantially parallel light bundle for a sequential illumination of image points of the video image, which source can be intensity-modulated, a deflection device for scanning the light bundle in two dimensions, a storage for the sequential storage of line information for the intensity modulation of the source for N image points, two values x
ad
and x
ed
, where x
ed
>x
ad
, wherein x
ad
describes the start of the line of the compensated image, where x
ad
≧Max(x
ai
) of all lines i, and x
ed
describes the end of the line of the compensated image, where x
ad
≧Min(x
ei
), and a control device for modulating the source and for controlling the deflection device in accordance with functions by which the light bundle is deflected and/or intensity-modulated in such a way that all image points of the line i for deflection can be displayed on the projection surface sequentially within the area [x
ad
; x
ed
]. Further, in accordance with the invention, there are provided in a special arrangement for the compensation of errors in diagonal projection a source for the emission of a substantially parallel light bundle for a sequential illumination of image points of the video image, which source can be intensity-modulated, a deflection device for scanning the light bundle in two dimensions, and a control device which controls the intensity modulation for the light bundle as well as the deflection of the light bundle in accordance with a function that is obtained through a calculated distortion correction of the image, at least with respect to the inclination.
Therefore, the technique employed in accordance with the invention is totally different from that used in EP 0 756 425 A2. That is, instead of a LCD matrix, substantially parallel light bundles which can be generated, for example, by a laser are used for sequential scanning of an image. Accordingly, there is no dependence on the matrix of an image. This technique has the advantage that the image is always sharp regardless of distance and even without special optics. The sharpness is limited practically only by the diameter of the light bundle. Therefore, by suitable control, an image can be distorted, also without loss of resolution, in such a way that a distortion expressing itself by a change in line length, for example, is compensated.
In particular, in the arrangement for displaying an image by diagonal projection, the image contents are calculated anew and the line density as well as the image point density in the recalculated image are displayed in a distorted manner such that the distortion causes, through the projection, a distortion correction of the video image. In this way, video images can be displayed practically as precisely as desired. Naturally, the accuracy of the calculation and display is substantially higher for CAD applications than for a television picture because the resolving capacity of the human eye is not as high. However, the principle is the same. Subsequent embodiment examples will provide more detailed information on the calculation of the distorted images which are then displayed in a rectified or distortion-corrected manner.
This calculation need not necessarily be carried out anew for every video image. For example, it is sufficient that the video images which are distorted for the purpose of distortion correction are stored on a videotape and then simply read out from the videotape in subsequent displaying of the video image.
Deter Christhard
Hiller Klaus
Vogel Wolfgang
Harvey David E.
LDT GmbH & Co. Laser-Display-Technology KG
Reed Smith LLP
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