Television – Video display – Projection device
Reexamination Certificate
1998-12-01
2001-02-20
Hsia, Sherrie (Department: 2714)
Television
Video display
Projection device
C348S747000, C348S806000, C348S807000
Reexamination Certificate
active
06191827
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to image processing for electronic devices having a visual display. In particular, this invention relates to a method of electronic Keystone correction for video and data projectors which exhibit optical distortion on the display screen, and for CAD/CAM applications.
A major problem of electronic devices having visual displays (e.g., video and data projectors, computers) operating with three liquid crystal display (LCD) panels is that when the projector is not properly aligned with the screen (i.e., the ray of the projected image is not perpendicular to the projection screen), the projected image on the screen undergoes optical trapezoidal distortion. Electronic or computer software correction of the optical trapezoidal distortion results in fractures of the projected image, due to limited resolution of the finite sized digital grid. In the present invention, a new way is shown to correct the optical trapezoidal distortion electronically or by the use of computer software, in way that eliminates fractures (i.e., Keystone correction using the following method eliminates optical trapezoidal distortion along with fractures of an image resulting from conventional optical correction).
Another distortion to the display of an image by an electronic device occurs during the drawing of a line diagonal to the x- and y-axes (i.e., parallel to neither axis). An example of this is computerized drawing or graphics, widely used, for example, in the field of computerized automated design/computerized automated manufacturing (CAD/CAM). Drawn lines appear fractured on the visual display, due to limited resolution of the finite sized digital grid. The above types of distortion of a displayed image are collectively referred to as the Keystone problem, and a solution to the Keystone problem is known as a Keystone correction or Keystone solution.
For processing and projection of full range color images, the three basic colors, red, green, and blue are typically used; other color sets which may be used include YUV, and YCrCb, as examples. Until recently, electronic devices with projection systems and visual displays, either had three separate LCD panels with three separate lenses, or a single LCD panel incorporating the three basic, or other set of, colors. In either of these image processing and projection systems, optical trapezoidal distortion, or the Keystone problem, is simple to solve by adjusting the mirror system, containing reflected data coming from each LCD.
New projectors have been developed which incorporate a single lamp, three LCDs, and a single lens, where the image data is split and collected by beam splitters and collectors. In such electronic devices, it is essentially impossible to solve the Keystone problem by changing angles of reflective mirrors, since the light originates and terminates within a single lamp and a single lens. Therefore, a sophisticated electronic solution to the Keystone problem is needed.
There is thus a need for, and it would be useful to have, a method of Keystone correction for electronic devices having a visual display, and for CAD/CAM software or any graphics application, which leads to the reduction or substantial elimination of optical distortion, and concurrent elimination of fracture lines appearing on the display screen. Moreover, it would be highly efficient and advantageous to have a method of electronic Keystone correction for electronic devices, which could operate as part of the mechanisms of standard electronic devices, for example, video and data projectors, televisions, computers. Furthermore, there is a need for such an electronic Keystone correction method which can operate in real time domain.
SUMMARY OF THE INVENTION
The present invention relates to a method of electronic Keystone correction for electronic devices having visual displays which exhibit optical distortion on the display screen. Examples of electronic devices which, are suitable for application of the Keystone correction include video and data projectors, cameras, computer displays for graphics applications, video games and televisions.
The method of electronic Keystone correction of the present invention is based on a unique combination of computation and electronic (i.e., physical) manipulation of images featuring individual pixels positioned in a grid located in a visual display screen. Hereinafter, in the present invention, the word ‘image’ refers to a digitally coded two-dimensional array of picture elements, known as pixels. Hereinafter, the word ‘pixel’ refers to a dynamic range that results in luminous radiance. The pixel is located within a digital grid characterized by a two-dimensional coordinate system. A pixel features two components, a position, and a value or magnitude. The position of a pixel is described by a two-dimensional function in grid space. The value, or magnitude, of a pixel represents the magnitude of illumination at a particular position in grid space of that component of the image identified by the pixel. Magnitude of illumination relates to a given set of three basic color components of each pixel (e.g., red, green, and blue; YUV; or YCrCb).
The method of electronic Keystone correction of the present invention features seven principle steps: 1) characterization of the size of the input image, 2) determination of the number of generated pixels in the output image, 3) determination of the real position of each pixel in the output image by performing an electronic distortion to the input image opposite to the optical distortion of the input image, 4) interpolation of the output value of all color components of each pixel of the input image, 5) correction of (non-uniform) edge effects at both ends of each line of pixels in a way that results in straight diagonal lines along each of the two sides of the output image, 6) transmission of the output image to a display device, pixel by pixel individually, or as a set of all output pixels collectively using a memory buffer, and 7) display of the perfected optical image.
The method of electronic Keystone correction for electronic devices having a visual display, of the present invention, leads to elimination of the appearance of optical distortion, and concurrent line fractures on the visual display screens, and is applicable to CAD/CAM and graphic software applications. The Keystone correction of the present invention is applicable to real time domain of operation of electronic devices with visual displays.
According to the present invention, there is provided a method for correcting an optical distortion of an image on a visual display screen, the steps of the method being performed by a data processor, the method comprising the steps of: (a) receiving an input image featuring pixels, (b) determining a distortion mode of the input image, (c) determining a number of the pixels in the input image, (d) determining a number of horizontal lines of the pixels in each group of the horizontal lines of the pixels in the input image, (e) determining a number of the groups of the horizontal lines of the pixels in the input image, (f) determining a number of output pixels of each horizontal line in a corrected output image, (g) determining a plurality of positions of the pixels of the input image, (h) performing an opposite electronic distortion to the optical distortion of the input image, (i) determining the plurality of positions of the output pixels of the opposite electronic distortion to the optical distortion of the input image, (j) determining a plurality of values of the output pixels of the opposite electronic distortion to the optical distortion of the input image to form the corrected output image, (k) correcting a plurality of edge effects in the horizontal lines of the plurality of the output pixels of the corrected output image to form a straight diagonal line along each of two sides of the corrected output image, (
1
) transmission of the plurality of the output pixels of the corrected output image to a visual display device, and (
Segman Yosef
Strominger Avy
Yearim Gady
Friedman Mark M.
Hsia Sherrie
Oplus Technologies Ltd.
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