White balance control system

Abstract

A white balance control system which has two amplifiers for red and blue video signals, two memory circuits for selecting the gains of the amplifiers in response to signals applied thereto, and two comparator circuits for comparing a green video signal with the red and blue video signals, respectively. The compared signals are respectively applied to the memory circuits selectively.

We claim as our invention: 
     
       1. A white balance control system comprising a first gain control circuit .[.,.]. .Iadd.and .Iaddend.means for applying a first color video signal to the first gain control circuit .[.,.]. .Iadd.; .Iaddend.a second gain control circuit .[.,.]. .Iadd.and .Iaddend.means for applying a second color video signal to the second gain control circuit .[., means for applying a third color video signal, means for producing a first color difference signal,.]..Iadd.; .Iaddend.means for producing .[.a.]. first .Iadd.and second .Iaddend.color difference .[.signal between the first color video signal as received from the first gain control circuit and the third color video signal, means for producing a second color difference signal between the second color video signal as received from the second gain control circuit and the third color video signal,.]. .Iadd.video signals and means for applying a third color video signal to said last-named means, said first and second gain control circuits being connected to said last-named means; .Iaddend.a first memory circuit connected to said first gain control circuit for controlling the first gain control circuit .[.,.]. .Iadd.; .Iaddend.a second memory circuit .Iadd.connected to said second gain control circuit .Iaddend.for controlling the second gain control circuit, .Iadd.said first and second memory circuits respectively comprising first and second capacitors connected to have signals derived from said first and second color difference signals, respectively, applied thereto, and field effect transistors having gate electrodes connected to said capacitors to memorize the signals applied to said capacitors; .Iaddend.and means for selectively applying the first and second color difference .Iadd.video .Iaddend.signals to the first and second memory circuits.Iadd., .Iaddend.respectively, the first and second memory circuits storing the color difference signals applied thereto for maintaining constant the gains of the first and second gain control circuits. .[.2. A white balance control system as claimed in claim 1 wherein the first and second memory circuits respectively comprise field effect transistors and memorize the color difference signals in capacitors connected to the gates of the 
     
     
        transistors..]. 3. A white balance control system as claimed in claim .[.2.]. .Iadd.1 .Iaddend.wherein the field effect transistors are .[.of the.]. .Iadd.connected as .Iaddend.source .[.follower connection.]. .Iadd.followers .Iaddend.and supply their source voltages to the 
     
     
        respective gain control circuits.Iadd.. .Iaddend. 4. A white balance control system as claimed in claim 1 wherein the first, second and third .[.color.]. video signals are each any one of red, blue and green signals. 
     
     
        . A white balance control system as claimed in claim 4 wherein the .[.first and second.]. color difference .Iadd.video .Iaddend.signal producing means are first and second subtraction circuits .[., 
     
     
        respectively.].. 6. A white balance control system .[.as claimed in claim 4 which is provided with.]. .Iadd.comprising a first gain control circuit and means for applying a first color video signal to the first gain control circuit; a second gain control circuit and means for applying a second color video signal to the second gain control circuit; .Iaddend.a matrix circuit for producing R-Y and B-Y .Iadd.color difference .Iaddend.signals .[.,.]. .Iadd.and means for applying a third color video signal to said matrix circuit, said first and second gain control circuits being connected to said matrix circuit; a first memory circuit connected to said first gain control circuit for controlling the first gain control circuit; a second memory circuit connected to said second gain control circuit for controlling the second gain control circuit; and means for selectively applying .Iaddend.the R-Y and B-Y signals .[.being supplied.]. to the first and second memory circuits.Iadd., respectively, the first and second memory circuits storing the color difference signals applied thereto for maintaining constant the gains of the first and second control 
     
     
        circuits. .Iaddend. 7. A white balance control system as claimed in claim 6 wherein the first and second memory circuits .[.are.]. each .[.provided with.]. .Iadd.comprises .Iaddend.a clamp circuit and an integration 
     
     
        circuit. 8. A white balance control system as claimed in claim 1 wherein the color difference .Iadd.video .Iaddend.signal applying means are actuated when .[.the image of a white object is picked up.]. .Iadd.said first, second, and third color video signals are related to each other in magnitude in correspondence with a predetermined white level ratio..Iaddend.