Method and apparatus for automatically controlling highlight effects
AssigneeAmpex Corporation
InventorJohn O. Ryan
Life of this patent
Estimating the term…
Abstract
During the horizontal retrace scan period of a scanning beam in a television pickup tube, the beam current is increased to the maximum possible value to recharge the target layer, and the cathode voltage is raised by a few volts to prevent readout of normal video. Also, the scanning beam path may be modified to insure that every area of the image is scanned by the retrace scan prior to being scanned by the active picture scan.
Claims11
A circuit for suppressing highlight effects, comprising;
- an image tube having a single control grid, a cathode and a target;
- current source transistor means coupled to the single control grid;
- a main beam control source coupled to the transistor means;
- a horizontal pulse source for generating a superimposed grid pulse also coupled to the transistor means;
- resistive means coupled to the cathode and responsive to the superimposed horizontal grid pulse for sufficiently raising the cathode voltage during the retrace scan to prevent readout of the normal video portions while allowing discharge of the highlight portions of the target;
- and
- means coupled to the tube for insuring that the retrace scan arrives at given areas of the target prior to the arrival at the area of the active picture scan.
A circuit for suppressing highlight effects comprising:
- an image tube having a single control grid, a cathode and a target having stored therein charged portions of normal video and highlights;
- means integral with the tube for generating horizontal active picture and retrace scans;
- grid control means including means for superimposing a horizontal grid pulse to increase the current to the single control grid to a preselected maximum of the order of five milliamps during the retrace scan;
- and
- resistive means coupled to the cathode and responsive to the superimposed horizontal grid pulse for sufficiently raising the cathode voltage during the retrace scan to prevent readout of the normal video portions while allowing discharge of the highlight portions of the target.
A method for controlling highlight effects in a standard television camera tube having a single control grid, a cathode for generating an electron beam and a target which is scanned by the electron beam during the successive horizontal active picture scan periods and respective alternate horizontal retrace scan periods, comprising;
- supplying the single control grid with grid control current during the horizontal active picture scan periods;
- superimposing a current pulse on the single grid control current during the horizontal retrace scan periods;
- applying a voltage to the cathode during the horizontal active picture scan periods to readout normally charged portions of the target;
- and
- applying a raised voltage to the cathode in response to the superimposed current pulse on the grid, of a value sufficient to prevent the electron beam landing on the normally charged portions of the target during the horizontal retrace scan periods.
A circuit for suppressing highlight effects in a standard image tube having a single control grid, a cathode for providing an electron beam, and a target having over-charged portions due to the highlights as well as normally charged portions and which are scanned by the electron beam during active picture scans and retrace scans, comprising;
- means coupled to the single control grid for increasing the grid current thereof to a maximum during the retrace scans;
- and
- means coupled to the cathode and responsive to the increase in grid current for raising the cathode voltage to a value sufficient to prevent the electron beam from landing on the normally charged portions of the target while allowing the beam to land on the highlight portions thereof during the retrace scans.
Dependencies are inferred from the claim text.