image geometry refers to the # of planes and X/Y dimensions of the image, not the duration.
sounds like you are using a DSLR - first off a true bias frame is not possible with a DSLR so you should use the shortest exposure possible, not 1s. i think many canon cameras support 1/8192s exposures as the shortest.
second is that if it is a DSLR you have probably accidentally debayered the bias subexposures? you should be working with "raw cfa" for everything - lights, flats, darks, bias, until you've calibrated your lights; then you can debayer the calibrated lights.
rob