Process and device for suppressing interferences in a picture composed of electronically generated image points

Claim 2

A process for suppressing interferences in the display of a picture composed of image points in the form of electronically generated luminous dots projected onto a viewing surface in a predetermined pattern of consecutive line scans, the brightness of each dot being determined by the level of a luminance signal, comprising the steps of: (a) comparing a given luminance signal S(i,j), pertaining to an image point P(i,j) where i indicates the order number of a scanning line and j indicates the dot position in said line, with a luminance signal S(i-k,j-p) pertaining to at least one adjacent image point P(i-k,j-p); and (b 1 ) upon the comparison in step (a) revealing a level difference between signals S(i,j) and S(i-k,j-p) whose absolute value does not exceed a predetermined threshold, using said luminance signal S(i,j) to control the brightness of image point P(i,j); (b 2 ) upon the comparison in step (a) revealing a positive level difference between signals S(i,j) and S(i-k,j-p) exceeding said predetermined threshold, incrementing said signal S(i-k,j-p) by a corrective signal Sc of predetermined magnitude +ΔLSM to produce a resulting signal Sc(i,j)=S(i-k,j-p)+Sc and using said resulting signal Sc(i,j) to control the brightness of image point P(i,j); (b 3 ) upon the comparison in step (a) revealing a negative level difference between signals S(i,j) and S(i-k,j-p) whose absolute value exceeds said predetermined threshold, decrementing said signal S(i-k,j-p) by a corrective signal Sc of predetermined magnitude -ΔLSm to produce a resulting signal Sc(i,j)=S(i-k,j-p)-|Sc| and using said resulting signal Sc(i,j) to control the brightness of image point P(i,j).

Claim 3

A process as defined in claim 1 wherein the magnitudes +ΔLSM and -ΔLSm of said corrective signal Sc are chosen in the vicinity of peaks of a histogram curve representing the frequency of occurrence of different brightness contrasts of adjacent image points.

Claim 4

A process as defined in claim 2 wherein said histogram curve is plotted from statistical measurements.

Claim 5

A process as defined in claim 2 wherein said picture is produced in recurrent frame sweeps, said histogram curve being quasi-instantaneously established by calculations based on the actual luminance signals of a frame.

Claim 6

A process as defined in claim 1, 2, 3 or 4 wherein the signal S(i-k,j-p) compared with signal S(i,j) in step (a) has a level calculated as the mean of the levels of a plurality of luminance signals pertaining to adjacent dots P(i-k,j-p) where k and p have any of the values +1, 0 and -1.

Claim 7

In a system for displaying a picture by the sweep of an electron beam in a succession of line scans across a receiving surface, the picture being composed of image points whose brightness is determined by intensity-control means in response to luminance signals emitted at discrete intervals by a source to produce a multiplicity of closely spaced luminous dots on said viewing surface, the combination therewith of a device for suppressing interferences in the form of spurious signals tending to impair the quality of the displayed picture, said device comprising: comparison means having inputs connected to said source for receiving therefrom a first luminance signal S(i,j), pertaining to a given image point P(i,j) where i indicates the order number of a scanning line and j indicates the dot position in said line, together with a second luminance signal S(i-k,j-p) pertaining to at least one adjacent image point P(i-k,j-p), said comparison means generating a corrective signal Sc upon detecting a level difference between said first and second luminance signals with an absolute value exceeding a predetermined threshold, said corrective signal having a predetermined magnitude +ΔLSM upon the level of said first luminance signal S(i,j) exceeding the level of said second luminance signal S(i-k,j-p) by more than said threshold but having a predetermined magnitude -ΔLSm upon the level of said second luminance signal S(i-k,j-p) exceeding the level of said first luminance signal S(i,j) by more than said threshold; adding means with inputs connected to said source and to said comparison means for algebraically summing said second luminance signal with said corrective signal to produce a resulting signal Sc(i,j)=S(i-k,j-p)±|Sc|; and switching means controlled by said comparison means for feeding to said intensity-control means said first luminance signal S(i,j) in the absence of said corrective signal Sc and said resulting signal Sc(i,j) in the presence of said corrective signal Sc.

Claim 8

In a system for displaying a picture by the sweep of an electron beam in a succession of line scans across a receiving surface, the picture being composed of image points whose brightness is determined by intensity-control means in response to luminance signals emitted at discrete intervals by a source to produce a multiplicity of closely spaced luminous dots on said viewing surface, the combination therewith of a device for suppressing interferences in the form of spurious signals tending to impair the quality of the displayed picture, said device comprising: comparison means having inputs connected to said source for receiving therefrom a first luminance signal S(i,j), pertaining to a given image point P(i,j) where i indicates the order number of a scanning line and j indicates the dot position in said line, together with a second luminance signal S(i-k,j-p) pertaining to at least one adjacent image point P(i-k,j-p), said comparison means generating a corrective signal Sc upon detecting a level difference between said first and second luminance signals with an absolute value exceeding a predetermined threshold, said corrective signal having a predetermined magnitude +ΔLSM upon the level of said first luminance signal S(i,j) exceeding the level of said second luminance signal S(i-k,j-p) by more than said threshold but having a predetermined magnitude -ΔLSm upon the level of said second luminance signal S(i-k,j-p) exceeding the level of said first luminance signal S(i,j) by more than said threshold; adding means with inputs connected to said source and to said comparison means for algebraically summing said second luminance signal with said corrective signal to produce a resulting signal Sc(i,j)=S(i-k,j-p)±|Sc|; and switching means controlled by said comparison means for feeding to said intensity-control means said first luminance signal S(i,j) in the absence of said corrective signal Sc and said resulting signal Sc(i,j) in the presence of said corrective signal Sc.

Claim 9

The combination defined in claim 6 wherein said comparison means is a differential amplifier receiving said first and second luminance signals for deriving therefrom a difference signal, a first threshold circuit connected to said differential amplifier for generating a corrective signal Sc of magnitude +ΔLSM in response to a difference signal of one polarity whose absolute value surpasses a predetermined level, a second threshold circuit connected to said differential amplifier for generating a corrective signal Sc of magnitude -ΔLSm in response to a difference signal of opposite polarity whose absolute value surpasses a predetermined level, and a summing amplifier with inputs connected to said threshold circuits for emitting the corrective signal so generated.

Claim 10

The combination defined in claim 7 wherein said comparison means further comprises a calculator having inputs connected in parallel with those of said differential amplifier for determining from a series of first and second luminance signals an optimum value for said corrective signal Sc, said threshold circuits having control inputs connected to said calculator for modifying said magnitudes +ΔLSM and -ΔLSm in accordance with said optimum value.

Claim 11

The combination defined in claim 6, 7 or 8 wherein said device further comprises arithmetic means for calculating the level of said second luminance signal as the mean of the levels of a plurality of luminance signals pertaining to adjacent dots P(i-k,j-p) where k and p have any of the values +1, 0 and -1.