Abstract: The present invention relates to a camera (1) for generating a cut key signal (K) for a subject moving in front of a background on the basis of invisible frequencies originating from the said background. The camera comprises an optical separator (3), a detector (7) and a processing circuit (9). The optical separator (3) makes it possible to separate the beam, representing the subject and the background, into four separate beams, including three colour beams (FR, FV, FB) and a fourth beam consisting of the invisible frequencies originating from the background. The detector (7) makes it possible to convert the energy contained in the fourth beam to an electrical signal (PIR), and the processing circuit (9) makes it possible to generate the key signal (k) from the electrical signal originating from the detection of the invisible frequency beam. The invention applies to the cutting of subjects moving in front of coloured backgrounds so as to place these subjects in front of new coloured backgrounds.