this part is understood

A stereogram consists of a pair of two-dimensional frames, one for each eye. The width and height of objects are common to both; Its depth is encoded in the differences between the right and left eye views. The geometric relationship between the third dimension of an object and these differences in position is presented below and depends on the location of the stereo camera lenses and the eyes of the observer. However, other factors contribute to the depth seen in a stereoscopic view and if it corresponds to that of the real object; The act of seeing a stereoscopic screen often alters the three-dimensional perception of observers.