Method and arrangement for compensating for stray light effects in television cameras

Claim 2

In a television camera having an optical system, a storage electrode accumulating charge varying in part as a function of stray light in said optical system, and an electron beam for discharging said storage electrode thereby generating a TV signal, having a first portion within a desired signal range and a second portion in an overdrive signal range and wherein said electron beam discharges said storage electrode to charges corresponding to said desired signal range during blanking intervals, said television camera further having clamping circuit means for clamping the black level of said television signal to a determined level, a method for compensating for stray light in said optical system, comprising, in combination, the steps of creating a first compensation signal varying as a function of a determined characteristic of said first portion of said television signal; creating a second compensation signal varying as a function of a determined characteristic of said second portion of said television signal; and applying said first and second compensation signals to said clamping circuit means for varying said determined level as a function thereof and in a direction opposing changes in said television signal caused by said stray light.

Claim 3

A method as set forth in claim 1, wherein said first and second compensation signals are first and second compensation voltages.

Claim 4

A method as set forth in claim 1, wherein said step of creating said first compensation signal comprises separating said first and second portions of said television signal from each other; and creating said first compensation signal as a function of the average value of said first portions.

Claim 5

A method as set forth in claim 1, wherein said step of creating said first compensation signal comprises amplifying and integrating said first portion of said television signal; and wherein said step of creating said second compensation signals comprises amplifying and integrating said second portion of said television signal.

Claim 6

A method as set forth in claim 1, wherein said television camera further has a variable gain amplifier; and wherein said method further comprises the step of applying said first and second compensation signals to said variable gain amplifier in such a manner that the gain of said variable gain amplifier varies as a function thereof.

Claim 7

In a television camera having a signal electrode furnishing television signals having first portions within a desired signal range and second portions in an overdrive signal range, in combination, amplitude discriminator circuit means having an input connected to said signal electrode and having a first output for furnishing first signals corresponding to said first portions of said television signals and a second output for furnishing second signals corresponding to said second portions of said television signals; first preamplifier means having an input connected to said first output of said amplitude discriminator means and having a first preamplifier output, for amplifying said first signals and furnishing amplified first signals at said first preamplifier output; clamping circuit means having a signal input connected to said first preamplifier output, a control input, and a clamping circuit output, for clamping said first signals to a level varying as a function of signals applied at said control input; first compensation signal furnishing means having an input connected to said first prEamplifier output, for furnishing first compensation signals varying as a function of said first signals at a first compensation output; second compensation signal furnishing means having an input connected to said second output of said amplitude discriminator means, for furnishing second compensation signals varying as a function of said second signals at a second compensation output; and connecting means for connecting said first and second compensation outputs to said control input of said clamping circuit means.

Claim 8

In a television camera having a signal electrode furnishing television signals having first portions within a desired signal range and second portions in an overdrive signal range, in combination, amplitude discriminator circuit means having an input connected to said signal electrode and having a first output for furnishing first signals corresponding to said first portions of said television signals and a second output for furnishing second signals corresponding to said second portions of said television signals; first preamplifier means having an input connected to said first output of said amplitude discriminator means and having a first preamplifier output, for amplifying said first signals and furnishing amplified first signals at said first preamplifier output; clamping circuit means having a signal input connected to said first preamplifier output, a control input, and a clamping circuit output, for clamping said first signals to a level varying as a function of signals applied at said control input; first compensation signal furnishing means having an input connected to said first prEamplifier output, for furnishing first compensation signals varying as a function of said first signals at a first compensation output; second compensation signal furnishing means having an input connected to said second output of said amplitude discriminator means, for furnishing second compensation signals varying as a function of said second signals at a second compensation output; and connecting means for connecting said first and second compensation outputs to said control input of said clamping circuit means.

Claim 9

A television camera as set forth in claim 6, wherein said clamping circuit means comprise a first and second clamping circuit, each having a control input; and wherein said connecting means comprise first connecting means for connecting said first compensation output to said control input of said first clamping circuit and second connecting means for connecting said second compensation output to said control input of said second clamping circuit.

Claim 10

A television camera as set forth in claim 6, wherein said first compensation signal furnishing means comprise an amplifier, and an integrating circuit connected to the output of said amplifier.

Claim 11

A television camera as set forth in claim 6, wherein said second compensation signal furnishing means comprise an amplifier, and an integrator circuit connected to the output of said amplifier.

Claim 12

A television camera as set forth in claim 6, wherein said television camera further comprises a variable gain amplifier having a gain control input; further comprising additional connecting means for connecting said first and second compensating outputs to said gain control input of said variable amplifier.