Methods for converting a video signal into a black/white signal

Claim 2

An arrangement for converting a video signal into a bilevel black/white recording signal in facsimile reproduction, comprising a scanning member for obtaining a video signal by scanning an original having white, black, and tinted (grey or colored) areas, a threshold circuit following said scanning member and arranged to form a first dynamic threshold signal, a comparator to which said video signal and said dynamic threshold signal are applied, for generating a bilevel black/white signal, a device connected to said scanning member for generating a modified videosignal by suppressing the DC component of said video signal, a further threshold circuit following said device, arranged to form a second dynamic threshold signal, a further comparator to which said modified video signal and said second dynamic threshold signal are applied, for generating a modified bilevel black/white signal, and means for switching said bilevel black/white signal, if previously black, from black to white for a short interval of time and then back to black, in the region of each transition on the original from tinted to black, and for switching said bilevel black/white signal, if previously white, from white to black for a short interval of time and then back to white, in the region of each transition on the original from tinted to white, to obtain a black/white facsimile recording signal which produces a facsimile having a contrasting boundary at each such transition, said means comprising a pulse generating stage, connected to said further comparator, for generating control signals from the modified video signal, and a logic switching circuit connected to said comparator and said pulse generating stage.

Claim 3

An arrangement according to claim 1, wherein said device for suppressing the DC component of said video signal comprising a high-pass filter.

Claim 4

An arrangement according to claim 1, wherein said pulse generating stage consists of differentiating means and series-connected pulse former stages.

Claim 5

An arrangement according to claim 1, wherein a delay stage for the black/white signal is arranged between said comparator and said logic circuit.

Claim 6

An arrangement according to claim 4, wherein said delay stage comprising a shift register.

Claim 7

In facsimile reproduction, a method for converting a video signal, generated by scanning an original dot by dot and line by line, into a bilevel black/white recording signal, said original having white, black and tinted (grey or coloured) areas, said method comprising the steps of: a. generating a first dynamic threshold signal from said video signal following said video signal dynamically; b. converting said video signal into a bilevel black/white signal by comparing said video signal and said first dynamic threshold signal, said black/white signal having signal steps at each transition from white to tinted and from black to tinted areas in the original; c. suppressing the DC component of said video signal to obtain a modified video signal; d. generating a second dynamic threshold signal from said modified video signal following said modified video signal dynamically; e. converting said modified video signal into a bilevel modified black/white signal by comparing said modified video signal and said second dynamic threshold signal, said modified black/white signal having signal steps at each transition from tinted to black and from tinted to white areas of the original; f. switching said black/white signal in the region of a tinted to black transition of said modified black/white signal for a first time interval to "white" ("black") if previously the signal level of said black/white signal has changed from "white" ("black") to "black" ("white"), whereby a first "white" ("black") boundary line running transversely with respect to the scanning direction is produced at the transition from a tinted to an adjacent black (white) area in the original, said first time interval determining the width of said first boundary line; and g. switching said black/white signal in the region of a tinted to white transition of said modified black/white signal for a second time interval to "black" ("white") if previously the signal level of said black/white signal has changed from "black" ("white") to "white" ("black"), whereby a second "black" ("white") boundary line is produced at the transition from a tinted to an adjacent white (black) area in the original, said second time interval determining the width of said second boundary line, said switched black/white signal representing said black/white recording signal for facsimile reproduction.

Claim 8

In facsimile reproduction, a method for converting a video signal, generated by scanning an original dot by dot and line by line, into a bilevel black/white recording signal, said original having white, black and tinted (grey or coloured) areas, said method comprising the steps of: a. generating a first dynamic threshold signal from said video signal following said video signal dynamically; b. converting said video signal into a bilevel black/white signal by comparing said video signal and said first dynamic threshold signal, said black/white signal having signal steps at each transition from white to tinted and from black to tinted areas in the original; c. suppressing the DC component of said video signal to obtain a modified video signal; d. generating a second dynamic threshold signal from said modified video signal following said modified video signal dynamically; e. converting said modified video signal into a bilevel modified black/white signal by comparing said modified video signal and said second dynamic threshold signal, said modified black/white signal having signal steps at each transition from tinted to black and from tinted to white areas of the original; f. switching said black/white signal in the region of a tinted to black transition of said modified black/white signal for a first time interval to "white" ("black") if previously the signal level of said black/white signal has changed from "white" ("black") to "black" ("white"), whereby a first "white" ("black") boundary line running transversely with respect to the scanning direction is produced at the transition from a tinted to an adjacent black (white) area in the original, said first time interval determining the width of said first boundary line; and g. switching said black/white signal in the region of a tinted to white transition of said modified black/white signal for a second time interval to "black" ("white") if previously the signal level of said black/white signal has changed from "black" ("white") to "white" ("black"), whereby a second "black" ("white") boundary line is produced at the transition from a tinted to an adjacent white (black) area in the original, said second time interval determining the width of said second boundary line, said switched black/white signal representing said black/white recording signal for facsimile reproduction.

Claim 9

A method according to claim 6, further comprising the steps of: a. producing first and second control signals from said modified black/white signal occuring at the corresponding signal steps, the pulse duration of said first and second control signals determining said first and second time intervals; and b. switching said black/white signal by said first and second control signals.

Claim 10

A method according to claim 6, wherein the DC component of said video signal is suppressed by means of a high-pass filter.

Claim 11

A method according to claim 6, wherein, in the process of scanning the original dot by dot and line by line, each image dot is associated with one cycle of a scanning clock and wherein said first and second time intervals is associated in each case with a defined number of cycles or image dots respectively.

Claim 12

A method according to claim 9, wherein said defined number is between 1 and 5.

Claim 13

A method according to claim 6, wherein the black/white signal is delayed before said switching operation by the amount of the first time interval.

Claim 14

A method according to claim 11, wherein the black/white signal is delayed by means of a shift register controlled by said scanning clock.