1. In an imaging system, apparatus for reducing extraneous image signals in a processed image signal of an object representing a desired parameter derived from a plurality of measurements comprising: first processing means for processing said plurality of measurements and producing a first processed image signal representing said desired parameter, second processing means for processing said plurality of measurements and producing a second processed image signal having a greater signal-to-noise ratio from said first processed image signal, third processing means interconnected with said first processing means and said second processing means for receiving and combining said first processed image signal and said second processed image signal and producing a third processed image signal, means for determining the spatial location of edges of extraneous images in said second processed image signal, and means for switching from said third processed image signal to a signal based on said first processed image signal when edges of extraneous images are detected.