Browse Prior Art Database

Automatic Correction of TV Raster

IP.com Disclosure Number: IPCOM000080244D
Original Publication Date: 1973-Nov-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 3 page(s) / 60K

Publishing Venue

IBM

Related People

Eisenstadt, BM: AUTHOR

Abstract

A means is described for correcting rotation and skewing errors in the raster of a TV camera. Skew and rotation errors can arise due to maladjusted focus current, deflection fields or the existence of extraneous magnetic fields. The apparatus described compensates for the resulting raster distortion.

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Automatic Correction of TV Raster

A means is described for correcting rotation and skewing errors in the raster of a TV camera. Skew and rotation errors can arise due to maladjusted focus current, deflection fields or the existence of extraneous magnetic fields. The apparatus described compensates for the resulting raster distortion.

The apparatus for correcting the rotation and skew of a TV raster is shown in Fig. 1. An illustration of the TV raster before and after correction, is shown in Fig.
2. The image of a five point light source 1 is focused by lens 2 onto the photosensitive surface of a TV camera tube 3. The video output from this tube 3 is directed on line 5 to the threshold detector 4 for analysis by the system.

Initially, the starting point of each TV line is adjusted to its desired position. Thereafter, the system automatically corrects for horizontal and vertical drift. The raster is corrected horizontally by introducing a small component of the vertical sweep into the horizontal deflection coils 6. The addition of this vertical component is the equivalent to changing the centering of the horizontal sweep, so that it is always aligned with the desired axis of the vertical sweep.

The raster is corrected vertically by introducing a small component of the horizontal sweep into the vertical deflection coils 7. The addition of the horizontal component is the equivalent to tilting the position of each TV line so that it is parallel to the horizontal axis. The correction currents required are small, being only a few percent of the peak current required for the full raster deflection.

The apparatus shown in Fig. 1 analyses the position of the five light sources 1 in the video output signal on line 5, and makes the above-described compensation correction in the horizontal 6 and vertical 7 deflection coils. As the raster sweeps over the bright images of the light sources 1, the video output signals will exceed a threshold determined by the threshold detector 4. The detector 4 produces pulses which are sent to the rotation and skew computation logic 8. A crystal clock 9 sends timing pulses to the horizontal position counter 10 which, in turn, sends timing pulses to the vertical line counter 11.

When the raster rotation and skew computation logic 8 receives the pulses from the threshold detector 4, both horizontal position and vertical line...