In astronomical image processing, a method for comparing two similar but different images wherein a display is switched between the two images in rapid succession. Spatial differences appear to move back and forth, while intensity differences pulsate. When the switching rate, duty cycle and transfer functions of the displays are controllable by the user, blinking is a powerful tool for assessing subtle but systematic differences between images, e.g. those due to moving or variable objects in crowded fields, or to subtle artifacts in image formation.