Digital scan converter for image scanning and display system

Claim 1

In an imaging system for producing an image of an object wherein the imaging system includes: A. scanning means including at least one oscillating reflector positioned in an optical path between said object and an image field thereof for scanning the object along a bi-directional path at a sinusoidally varying speed, B. sensor means positioned in the image field derived from said object for measuring the radiance level of picture elements transferred thereto by said scanning means and for generating electrical representations of the picture elements, and C. display means having a constant rate scanned display monitor for receiving the electrical representations of the picture elements from said sensor means, an improved scan converter circuit for converting bi-directionally, sinusoidally rate generated representations of the picture elements into unidirectional, constant rate generated representations of the picture elements to be displayed in said display device, wherein the improvement comprises: A. constant rate clocking means for generating constant rate digital clocking signals coincident with the rate of display of picture elements displayed by said display device, B. sinusoidal rate clocking means for generating a sampling signal that enables said sensor means to produce electrical presentations of said picture elements at a substantially sinusoidally varying rate whereby said picture elements are sampled at equidistant positions along said path in each direction of said bi-directional sweep path, said sinusoidal rate clocking means being driven by said digital clocking signals from said constant rate clocking means, C. buffer means for temporarily storing said electrical representations of said picture elements during at least one of the bi-directional sweep directions of said oscillating reflector and for transmitting said stored representations in reverse order, D. zero crossing detector means for generating a zero crossing signal that indicates the zero crossings of said oscillating reflector about its center of oscillation, E. phase lock means for maintaining phase coherence between the periodic rate of change of said sampling signal from said sinusoidal rate clocking means and the occurrences of said zero crossing signal, and F. transfer means for alternately transferring said electrical representations of picture elements from said buffer means and said sensor means to said display device under control of said constant rate clocking means so that the positions of the picture elements of the object bear a one-to-one correspondence to the positions of picture elements displayed by said display means.