An image sensor acquires a preparatory image that is lighted for a predetermined preparatory duration by a strobe. The preparatory image data corresponding to the preparatory image from the image sensor is processed and an average preparatory image luminance is determined based on the preparatory image data and weighting at least a subset of the preparatory image data. A supplemental strobe duration is generated based on the average preparatory image luminance and luminance weightings. The electronic image sensor may be activated to acquire an image with supplemental light provided by the supplemental strobe duration.