Control of frame types in video compression
View Patent ↗A method of controlling frame types in a video compression system having I, P and B frames calculates activity figures of the video signal in vertical, vertical temporal and horizontal directions. Video sequences with low complexity in which the vertical activity within a field is less than the vertical-temporal activity within a frame are encoded without using B frames whereas sequences with high complexity, i.e. spatial detail, are encoded using B frames by the use of the invention, disadvantages associated with B frames are reduced by the selected use of B frames.
1. A method of controlling frame types in a video compression system having Intra-encoded (I), Predictive (P) and Bi-directional (B) frames including the steps of:
determining from a video input signal an activity figure:
in a vertical direction within a field (1),
in a vertical-temporal direction within a frame (2),
determining an intra-field spatial activity figure in a horizontal direction along a TV line and in a vertical direction along lines in a field (3),
evaluating:
if (1) is less than (2)
and (3) is less than a predetermined threshold then increase a counter by a count of one, otherwise reset the counter to zero, if the count in the counter is greater than predetermined number N then do not use B frames, otherwise use B frames.
2. A method of controlling frame types in a video compression system having Intra-encoded (I), Predictive (P) and Bi-directional (B) frames including the steps of:
providing samples a, b, c, d, e of an interlaced video signal where
sample a is undelayed,
sample b is delayed by one line,
sample c is delayed by one field plus one line,
sample d is delayed by one field plus two lines,
sample e is delayed by one field plus one line plus a further delay along the line,
applying the samples to differencing means to determine |b-a|, |c-a|, |c-b|, |c-e|, and |c-d|,
accumulating the resultant output of the differencing means to provide
(i) (|b-a|+|c-d|) over a field (1)
(ii) (|c-a|+|c-b|) over a field (2)
(iii) (|c-e|+|c-d|) over a field (3)
evaluating:
if (1) is less than (2),
(3) is less than a predetermined threshold
then increase a counter by one, otherwise reset the counter to zero
if the count in the counter is greater than a predetermined number N then do not use B frames, otherwise use B frames in a frame switch signal.
3. An apparatus for controlling frame types in a video compression system having Intra-encoded (I), Predictive (P) and Bi-directional (B) frames including:
means for determining from a video input signal an activity figure:
in a vertical direction within a field of view (1),
in a vertical temporal direction within a frame (2),
means for determining an intra-field spatial activity figure in a horizontal direction along a TV line and in a vertical direction along the TV line in a field (3)
means for evaluating:
if (1) is less than (2)
and (3) is less than a predetermined threshold,
then if the foregoing condition is satisfied, means for increasing the count of a counter by one, otherwise resetting the counter to zero,
and if the count in the counter is greater-than a predetermined number then means for producing a switch signal to not use B frames, otherwise use B frames.
4. An apparatus for controlling frame types in a video compression system having Intra-encoded (I), Predictive (P) and Bi-directional (B) frames including:
providing samples a, b, c, d, e of an interlaced video signal where
means for providing sample where a is undelayed,
means for providing sample where b is delayed by one line,
means for providing sample where c is delayed by one field plus one line,
means for providing sample where d is delayed by one field plus two lines,
means for providing sample where e is delayed by one field plus one line plus a further delay along the line,
means for applying the samples to differencing means to determine |b-a|, |c-a|, |c-b|, |c-e|, and |c-d|,
means for accumulating the resultant output of the differencing means to provide
(i) (|b-a|+|c-d|) over a field (1)
(ii) (|c-a|+|c-b|) over a field (2)
(iii) (|c-e|+|c-d|) over a field (3)
means for evaluating:
if (1) is less than (2),
(3) is less than a predetermined threshold then increase a counter by one, otherwise reset the counter to zero, and means for evaluating if the count in the counter is greater than a predetermined number N then said evaluating means does not use B frames, otherwise use B frames in a frame switch signal.