A Theory of Scanning and Its Relation to the Characteristics of the Transmitted Signal in Telephotography and Television

TN the usual telephotographic or television systems the image field is scanned by moving a spot or elementary area along some recurring geometrical path over this field. In the more common arrangement this path consists simply of a series of successive parallel strips. Imagining the path developed or straightened out (or in the more common case, the strips joined end to end), this method of scanning is equivalent to transmitting the image in the form of a long narrow strip. The theoretical treatment of such transmission has usually been developed by completely ignoring variations in brightness across the image strip, assuming the brightness to have a uniform distribution across this strip. This permits the'image to be analyzed as an ordinary one-dimensional or single Fourier series (or integral) along the length of the strip; and the theory is then developed in terms of the 464 A THEORY OF SCANNING 465 one-dimensional steady state Fourier components. Such a method of treatment naturally gives no information in regard to the reproduction or distortion of the detail in the original image across the direction of scanning, nor, as will appear below, does it give any detailed information in regard to the fine-structure distribution of energy over the frequency range occupied by the signal. The need of a more detailed theoretical treatment originally arose in connection with studies of the reproduction of detail in telephotographic systems, especially in comparisons of distortion occurring along the direction of scanning with that across this direction.