Computer graphics processing and selective visual display system – Data responsive crt display control – Data responsive intensity control
Reexamination Certificate
1998-03-30
2001-05-29
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Data responsive crt display control
Data responsive intensity control
C345S182000, C345S022000
Reexamination Certificate
active
06239773
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an image display device comprising an input for receiving information representing an image; drive means for generating a drive signal from the information; a cathode ray tube for displaying the image driven by the drive signal; and input means coupled to the drive means for receiving further information identifying a window of pixels in the image, the drive means being arranged to change a relation between the information and the drive signal in the window as compared to a further relation between the information and the drive signal in an area outside the window, so as to enhance a drive signal range in the window.
2. Description of the Related Art
Such a device is known from PCT Patent Application No. WO 96/17338, corresponding to U.S. Pat. No. 5,638,090. This device makes it possible to show an image which contains video and text and to enhance the luminosity range of the image in windows which contain video beyond the luminosity range of areas outside the windows which contain text. The increase in the luminosity range makes the video richer in contrast, but, on a CRT, it also increases the spot-size, which would be undesirable for text areas. By increasing the range of luminosity only locally where a window with video is shown, video with a richer contrast can be combined with text.
However, it has been found that by extending the luminosity range, one increases the risk of doming (deformation of the shadow mask due to heating by the electron beam) and overloading of the high voltage (EHT) power supply.
SUMMARY OF THE INVENTION
Among others, it is an object of the invention to combine the display of high luminosity video, photographs or graphics with high resolution text on a CRT, without problems due to EHT overloading. A further object is to avoid problems due to doming in such a device.
The device according to the invention is characterized in that the drive means is arranged to change said relation between the information and the drive signal in the window so as to reduce the drive signal range when an average luminosity on the cathode ray tube exceeds a threshold value. By locally reducing the range of drive signal values in the windows where it has been enhanced in case the luminosity (i.e., beam energy) range becomes too high, overloading problems can be prevented.
A further embodiment of the device according to the invention is characterized in that said drive means is arranged to determine said average luminosity averaged over said window from the information received for said window, the drive means controlling said relation so that said average luminosity remains below the threshold value. By measuring the average luminosity in the window, or in each one of a number of separate windows where the drive signal range is increased, and reducing the drive signal range selectively if the average luminosity is too high, local doming effects are prevented. At the same time, text windows retain their original drive signal range and, therefore, they retain the same level of readability.
In an embodiment of the device according to the invention, the drive signal range is adjusted by varying an amplification gain of an amplification circuit for the image signal (e.g., for each of the R, G and B components). This can be readily implemented by inserting an amplifier with adjustable gain in the video signal path of known monitors, or using gain control inputs of available video amplifier IC's. In another embodiment, the window or several windows are identified by coordinates of corner points of the window(s) and/or values of the width and height of the window. Thus, the further information can be received with very little bandwidth using existing bus protocols, e.g., between monitors and PC's.
In a further embodiment of the device according to the invention, the average luminosity in a window is averaged over time, and the average over time is used to control the drive signal range for the window. By averaging the average luminosity over time, sudden artificial changes in visible luminosity due to the invention are prevented. Doming effects occur only with a long time constant of typically several minutes. Short excesses in the luminosity can be tolerated without visible effect. As a result, the time range over which the average is taken may be typically one minute or more. This also means that the circuit which selects the drive signal range may be relatively slow.
In another embodiment of the device according to the invention, the window is selected on the basis of a spatial frequency content of the image in the window. This makes it possible to discriminate between text and video, photo or graphics information.
REFERENCES:
patent: 5283561 (1994-02-01), Lumelsky et al.
patent: 0762753 (1997-03-01), None
patent: 0 601 647 (1997-12-01), None
patent: 0 762 753 (1997-12-01), None
patent: WO 9617338 (1996-06-01), None
“Encoding of a priori Information in Active Contour Models” in III Transactions of Pattern Analysis and Machine Intelligence, vol. 18, No. 9, Sep. 1996.
Holtslag Antonius H. M.
Lammers Matheus J. G.
Goodman Edward W.
Nelson Alecia D.
Saras Steven
U.S. Philips Corporation
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