This invention relates to reducing bandwidth requirements for stereoscopic imagery and video signals. The invention comprises a method of producing two streams of images or signals for producing images, separately for the left eye and for the right eye. One image of each stereoscopic pair in the streams is of reduced quality relative to the other. On occurrence of a significant change in image content, or similar occurrence, the image quality of the two streams are switched or transposed, whereby the higher quality image is seen alternately by one eye and then the other. Intervals between switching are indeterminate, and such switching is continued for the duration of the streams of images or video signals.