Abstract: A television picture superimposing system comprises a video mixer including two variable gain amplifying circuits receiving two input picture signals having a given peak-to-peak amplitude, and an adding circuit for mixing the amplified picture signals into a resulting picture signal. The improvement resides in providing a circuit for deriving a single gain control signal based upon a linear combination of two signals derived respectively from the two input picture signals so that the resulting signal has the given peak-to-peak amplitude. The control signal is respectively applied, via an analog inverting circuit and directly, to gain control inputs of the variable gain amplifying circuits.