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Scaling Characters in a Character Generator

IP.com Disclosure Number: IPCOM000073494D
Original Publication Date: 1970-Dec-01
Included in the Prior Art Database: 2005-Feb-22
Document File: 3 page(s) / 67K

Publishing Venue

IBM

Related People

Bachman, DE: AUTHOR [+2]

Abstract

Shown is a system for scaling character size in a computer-controlled photoprinter. The printing operation is performed by cathode ray tube 10. The image on the screen of the tube is directed by reciprocating lens 12 onto photographic film 14. The film then serves as the master for the subsequent printing operation.

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Scaling Characters in a Character Generator

Shown is a system for scaling character size in a computer-controlled photoprinter. The printing operation is performed by cathode ray tube 10. The image on the screen of the tube is directed by reciprocating lens 12 onto photographic film 14. The film then serves as the master for the subsequent printing operation.

All of the commands for generation of characters and for position of characters are fed from computer 20. Cathode ray tube display controls 22 respond to commands from the computer to paint characters on the film. The cathode ray beam is only driven vertically to scan a single vertical line. Horizontal indexing of lines is achieved by reciprocating lens 12 which is moved across the face of the film. Each scan line will contain blank and unblank portions, depending upon whether that particular portion of a scan line is associated with a character or with background. The affect is to paint the character on film 14 by a series of vertical stripes.

To achieve scaling of characters, adjustments are required in the cathode ray tube sweep and clocking rate applied to display controls 22 the cathode ray tube gird bias, and reciprocating lens motor speed controls 24. More particularly, cathode ray tube display controls 22 must be adjusted for a higher unblank beam resolution, i.e., more black/white bits in each vertical scan of the cathode ray beam. Also the intensity of the cathode ray beam must be reduced to avoid over exposing the film. finally, the velocity of the reciprocating lens must be slowed during the scaling operation. This latter adjustment is necessary to increase scans per inch resolution capability at the reduced scan rate. Actual scans per inch resolution is controlled by the clocking rate.

To adjust beam resolution, the deflection velocity of the beam is reduced by a factor of "2," the number of data bits per inch of vertical deflection is varied with scale factor, and finally, the speed of the reciprocating lens as it moves across the film is reduced by a factor of "2." The speed of the reciprocating lens is changed by a command from the computer to reciprocating lens motor controls
24. Other commands are sent to motor controls 24 with regard to position of the lens and accelerating and decelerating lens 12.

Reducing the deflection velocity of the beam by a factor of 2 is accomplished by a scale/command which sets trigger 26. When trigger 26 is set, its output energizes relay 28. Relay 28 then reduces to half the normal reference voltage input to current source 29. This current source is utilized in the ramp generator of cathode ray tube deflection controls 22 to control beam velocity. When a scaling operation is not called for, a command from the computer resets trigger
26. Trigger 26 then activates relay 30 to pass the full reference voltage to current source 29 an...