Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1983-06-16
1985-11-05
Britton, Howard W.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358140, 358160, H04N 533, H04N 308
Patent
active
045517525
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention refers to a method to correct distortion in an image recorded electronically and built up of picture elements along lines, the distortion consisting therein that in a field of view scanned along lines, the picture elements situated vertically under each other will be displaced horizontally relative to each other when reproduced on parallel straight lines.
BACKGROUND ART
When producing an electronic image by scanning the field of view by, for example, infra-red detectors and converting the signals sensed by the detectors to electronic picture elements for reproduction on a video-screen, an inevitable distortion arises in certain types of scanning devices. This distortion occurs due to the fact that the scanning lines associated with a certain elevation are longer than scanning lines associated with a smaller elevation while the sampling frequency is the same. Consequently when the sensed picture elements are reproduced in a rectangular electronic picture on a video-screen, the picture points which in reality are situated above each other, will be displaced laterally, the points having smaller elevation lying nearer to the center of the picture than the points having greater elevation. Consequently vertical objects will be reproduced as inclined and in the case the picture is built up of a number of band-shaped partial pictures, a long vertical object will be reproduced as a number of inclined parts forming a saw-tooth profile. Such devices are previously known. See British Pat. Nos. 1,361,145 and 1,361,144, for example.
Theoretically it would be possible to solve the problem by supplying the picture elements on the different lines to the TV-monitor with different frequencies for each line. This is however difficult as it is difficult to obtain sufficiently constant and exact frequencies. Another possibility is to omit certain samples with definite serial number on the long lines. The drawback in this case is that information will be lost.
DISCLOSURE OF INVENTION
An object of the invention is to provide a solution of the above mentioned problems without having the drawbacks of the solution which are theoretically possible.
SUMMARY OF THE INVENTION
Briefly the invention contemplates correcting distortion in an image recorded electronically and built up of picture elements along lines, the distortion being that in a field of view scanned along lines, the picture elements situated vertically below each other will be mutually horizontally displaced when reproduced on parallel straight lines. The correction is accomplished by storing in a memory the picture elements arising by scanning the field of view. These stored elements are then supplied line for line to a picture screen, the picture elements associated with the shortest reproduction line being fed from the memory unchanged while into lines corresponding to longer scanning lines additional picture elements and parts of elements respectively are inserted at definite distance from each other. The distance is selected in such a manner that the number per line of inserted picture elements and parts of picture elements respectively is proportional to the difference between the length of the respective line and of the shortest line.
BRIEF DESCRIPTION OF DRAWINGS
The invention will be described more in detail by means of an embodiment with reference to the enclosed drawing in which
FIG. 1 shows diagramatically a scanning device comprising a rotating polygonal mirror,
FIG. 2 shows the shape of a picture field which is sensed along parallel curved lines,
FIG. 3 shows the shape of the picture after having been represented in a video-screen,
FIGS. 4a-4d are diagrams which diagramatically show two scanning lines of different length and show different methods for compensating for the distortion occurring in the presentation,
FIG. 5 shows diagramatically apparatus for carrying out the method according to the invention and
FIG. 6 is a diagram showing that the invention also can be used for eliminating distortion which ari
REFERENCES:
patent: 4399458 (1983-08-01), Berry
patent: 4402009 (1983-08-01), Rathjens
patent: 4419692 (1983-12-01), Modisette
Jonsson John E.
Wall Lars E.
Britton Howard W.
Telefonaktiebolaget LM Ericsson
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