An object of the present invention is to enable the detection of a mixture ratio indicating the mixture state of a plurality of objects, such as a background image and a moving object image. A normal-equation adder 541 extracts mixed pixel data according to a motion, and also extracts background pixel data corresponding to the mixed pixel data so as to generate relational expressions for a designated pixel. A normal-equation calculator 542 detects the mixture ratio indicating the mixture state of the objects based on the relational expressions. The normal-equation adder 541 generates the plurality of relational expressions based on a first approximation in which foreground object components change substantially linearly, and a second approximation in which the mixture ratio changes substantially linearly. The present invention is applicable to a signal processing apparatus for processing images.