A method of compensating image signals for driving an OLED display having a plurality of light-emitting elements having outputs that change with time or use, comprising the steps of: a) obtaining a measured or estimated first value of the current used by individual light-emitting elements in response to known image signals at a first time; b) specifying multiple groups of light-emitting elements at a second time, wherein at least one of the specified groups contains at least one light-emitting element common to another specified group; c) measuring total currents used by each of the specified groups in response to known image signals at a second time; d) forming an estimated second value of the current used by individual light-emitting elements based on the measured total currents, e) calculating correction values for individual light-emitting elements based on the difference between the first and second current values, and f) employing the correction values to compensate image signals for the changes in the output of the light-emitting elements and produce compensated image signals.