by operation of control 20 the operator indicates 16 discrete levels of gray the maximum number of levels in the system which are to be included within the digital gray scale as will be seen in the more detailed discussion below the 16 levels are quantized by digitization of the video input signal thus actuation of control 20 causes the system upon analyzing the video input signal to quantize the video input signal in accordance with 16 discrete levels operation of control 21 permits the operator to select eight shades of gray as opposed to 16 to be included within the digital gray scale in the preferred embodiment this is accomplished by assigning the first two levels of the normal 16 level gray scale to the first level of the 8 level scale selected with subsequent pairs of levels in the 16 level scale being assigned as a single level in the 8 level scale thus shades 1 and 2 in the a scale the normal 16 level scale will be assigned as shade 1 in the b scale shades 3 and 4 in the a scale will be assigned as shade 2 in the b scale and so forth until shades 15 and 16 in the a scale are assigned as shade 8 in the b scale operation of control 22 permits the operator to select a 4 level c scale such that shades 1 through 4 in the a scale will be assigned as the first level in the c scale shades 5 through 8 in the a scale will be assigned as the.