Apparatus and method for controlling video display blanking...

Television – Monitoring – testing – or measuring – Testing of image reproducer

Reexamination Certificate

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C348S745000, C348S807000

Reexamination Certificate




This invention relates to video displays, and more particularly to the monitoring and controlling of video display blanking signals for the purpose of improved display performance.
In the field of video displays, the practice of “overscanning” to insure that the picture fills the screen is well known. To illustrate the practice of overscanning, the practice's application in rear projection color television is considered. In a typical rear projection color television, as in many types of video displays, pictures are formed on a screen by combining multiple beams of light. Usually, a set includes three cathode ray tubes (CRTs), one for each of the primary colors—red, blue and green. The set combines the three monochromatic beams emanating from the CRTs to produce full color television pictures.
FIG. 1
is a plan view of a typical rear projection television set. The components of the set are housed within a cabinet
, and they include: a CRT
, a lens
, a mirror
, and a screen
. In actuality, the model set includes three CRTs and multiple lenses for each CRT, although for clarity, only the single CRT and the single lens are shown in the figure. The light from the CRT passes through the lens and illuminates the mirror which, in turn, reflects the light onto the screen for observation by the viewer. The screen is secured within the cabinet with the aid of a frame.
FIG. 2
is an isometric view which shows the position of a frame
relative to the cabinet and screen.
FIG. 3
illustrates the relationship between the three CRTs of the typical set. As can be seen from the figure, CRTs
are matched respectively with lenses
, and the CRTs are aligned so that their beams converge. The practice of overscanning concerns what happens when the CRT beams are scanning toward the edge of the screen.
FIG. 4
is a diagram that shows what happens when a CRT scan reaches the edge of the screen. Notably, the scan does not stop but continues on so that light emitted from the CRT is incident on the frame. That portion of the television picture signal that corresponds to the overscanned CRT emissions, and the overscanned CRT emissions themselves, are commonly referred to as the “blanking signal”.
FIG. 5
illustrates overscanning from the viewer's perspective. The figure shows an exemplary relationship between an area scanned by the CRT
, the screen, and the frame. When the CRT beams are properly aligned with the center of the screen, the scanned area shown extends beyond the screen dimensions by a distance “d” in all directions, as shown. Thus, even if the beams were to become misaligned by an amount ≦d, the viewer would still see a full display screen.
It has been recognized that although overscanning insures a full display screen, the reflections it causes degrade the displayed picture.
Accordingly, it is an object of the present invention to provide a system and method for controlling a video display blanking signal so as to maintain a full display screen without interfering with the displayed picture.
To control the blanking signal, one or more photosensors are placed at the periphery of the display screen. When a CRT overscans the screen at a sensor's location, the overscanning light from the CRT is incident on the sensor and the sensor generates a signal proportional to the amount of incident light. The sensor signal is used to adjust the CRT scan such that the CRT scan covers the screen but does not unnecessarily overscan. Thereby, insuring a full display screen while minimizing the degradation due to overscanning.

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