Abstract: The dimensions and light output of a beam in a shadow mask cathode-ray tube are determined by means of an optical system 7 focussed on a phosphor dot to pick up and record the light generated by a ray 4 passing through a single aperture 6 in the shadow mask 2. The cathode-ray beam 1 is moved so that the whole cross-section of the beam passes the aperture 4. The detected light outputs are plotted to provide an accurate representation of the whole beam.

Abstract: Mixed color effects in a character graphics display system are achieved by providing font characters comprising several character cells with different patterns which can selectively be read simultaneously to different color registers, thereby determining the color in which each character cell is to be displayed. The system also provides characters comprising only a single character cell which can selectively be directed to any of the color registers. A control system interprets color bits in a control word in accordance with the type of character being accessed.

Abstract: An electromagnetic lateral convergence assembly includes a generally-annular, planar magnetic core (optionally found as a laminate) having integral pole pieces extending toward the center of the annulus. Electrical coils are mounted on selected pole pieces for producing a convergence-compensating magnetic field within the center of the annulus. The coils are secured to a printed circuit board to hold the core in spaced parallel relationship to the board. Optionally a purity assembly including a planar magnetic core having a number of electrical coils for producing a rotatable, variable, linear field is mounted on the other side of the printed circuit board.

Abstract: A method of convergence correction in a three beam color cathode ray tube dividing the screen into a plurality of discrete areas. Digital values for convergence factor signals are derived for a predetermined number of the discrete areas and a spreading algorithm is used to derive digital values for the remaining areas. The resulting digital values are stored in a digital store and used to provide convergence correction factor signals during operation of the tube.

Abstract: A three color gun cathode ray tube has convergence correction signals derived from digital signals stored in a digital data store. The screen of the tube is divided into a plurality of areas and a digital correction signal derived for each area. The system is arranged so that when the three beams are scanning a particular area the digital correction signal associated with that area is read out from the digital store, passed through a digital to analog converter and then applied to the convergence coils of the tube.