Method of showing 16:9 pictures on 4:3 displays

DETAILED DESCRIPTION The method of the invention is characterised in that each line signal is compressed and/or expanded so that the ratio of the length of a segment of the unprocessed signal to the length of the segment of the resultant signal derived from it varies continuously along each line.
In a pre erred embodiment, the signal representing each line is compressed more adjacent the ends of each line than it is in the middle of the line, each line signal being compressed as though the line were disposed along an arc of a circle and projected onto the chord joining the ends of that arc along a direction perpendicular to that notional chord, the overall compression ratio of the line being given by sin (.
alpha.
)/.
alpha.
where 2.
alpha.
is the angle in radians subtended by the notional chord at the centre of a notional circle of which said arc is a part.
This technique may permit an increase in the active picture height but with less obvious geometric distortion than results from a simple vertical stretch in its preferred form, the technique involves squeezing the sides of the 16:9 picture while leaving the centre of the picture undisturbed using a process which will be referred to as "cylindrical" processing.
This squeezing produces a picture with all the original details but with an aspect ratio lower than 16:9, e.
c.
14:9 as shown in FIG.
2.
As a result, the active height of the picture is greater than that of a 432-line full letterbox display assuming that the picture occupies the full width of the 4:3 display in both cases.
Although cylindrical processing could be used to squeeze a 16:9 picture into a 4:3 aspect ratio, thus entirely eliminating the black borders on a 4:3 display, the resulting geometric distortion has been found to be unacceptable.
Hence, if cylindrical processing is to be employed, a compromise is required which results in a residual amount of border.
Following a number of initial tests, it was decided that subjective tests should be carried out to assess the acceptability of 16:9 pictures on a 4:3 display using (a) a 16:9 full letterbox format and (b) a 14:9 format achieved using a combination of cylindrical processing and simple vertical stretch; this combination will be referred to as "stretched cylinder" processing