1. A method of image processing comprising the steps of: estimating pixel motion values for pixels in blocks of a current image field; calculating a difference measure of a difference in pixel brightness or color values between corresponding blocks of the current image field and an adjacent image field; calculating a variability measure of a variability of pixel brightness or color values in respect of at least one of said corresponding blocks; determining whether the difference measure exceeds the variability measure; and if the difference measure exceeds the variability measure, overriding estimated pixel motion values to set respective inter-image mixing values for pixels in the corresponding block of the current image field to indicate that the current image field should not be mixed with the adjacent image field at that pixel position.