An apparatus (IP) and a method to generate temporally-aligned image frames for image-streams (LS, RS) in a multi-channel channel (CR, CL) imaging system (100). The apparatus (IP) allows reducing or removing temporal distance artifacts that occur when processing the frames into combined image material. The apparatus can also be used to improve signal-to-noise ratio of the frames. The multi-channel imaging system (100) may be a stereoscopic imager.