TABLE OF CONTENTS Analog video samples in the time domain and vertically down the screen so a two-dimensional vertical/temporal sampling spectrum will result. In a progressively scanned system there is a rectangular matrix of sampling sites vertically and temporally. The rectangular sampling structure of progressive scan is separable which means that, for example, a vertical manipulation can be performed on frame data without affecting the time axis. The sampling spectrum will be obtained according to section 2.6 and consists of the baseband spectrum repeated as sidebands above and below harmonics of the two-dimensional sampling frequencies. The corresponding spectrum is shown in Figure 5.14. The baseband spectrum is in the centre of the diagram, and the repeating sampling sideband spectrum extends vertically and horizontally. The vertical aspects of the star-shaped spectrum result from vertical spatial frequencies in the image. The horizontal aspect is due to image movement. Note that the star shape is rather hypothetical; the actual shape depends heavily on the source material. On a still picture the horizontal dimensions collapse to a line structure. In order to return a progressive scan video signal to a continuous moving picture, a two-dimensional low-pass filter having a rectangular response is required. This is quite feasible as persistence of vision acts as a temporal filter and by sitting far enough away from the screen the finite acuity of the eye acts as a spatial reconstruction filter.
Interlace is actually...
