Apparatus and method for exotic cadence detection
View Patent ↗Aspects of the invention are directed towards an apparatus and method for detecting conventional and exotic cadences in video sequences. The cadence detector includes a motion auto-correlation unit using the inter-frame/field motion information to detect the cadence and a motion cross-correlation unit using the inter-frame/field motion information and the detected cadence to determine the cadence phase. The cadence detector also may include a reset signal generator to generate a reset signal to control the motion auto-correlation unit and the motion cross-correlation unit. The exotic cadence detector is robust and may support many cadences with reduced cadence detection latency as compared to the prior art.
1. A film mode detecting apparatus, comprising:
an inter-frame/field motion detector;
a motion auto-correlation unit coupled to the inter-frame/field motion detector;
a motion cross-correlation unit coupled to the motion auto-correlation unit; and
a cadence pattern storage look-up-table coupled to the motion cross-correlation unit,
wherein the motion auto-correlation unit comprises:
an auto-correlation parameter initialization unit;
a plurality of auto-correlation and cadence length detectors coupled to the auto-correlation parameter initialization unit;
a cadence length analyzer coupled to the plurality of auto-correlation and cadence length detectors and a cadence patterns look-up-table; and
an auto-correlation analyzer coupled to the cadence length analyzer, the plurality of auto-correlation and cadence length detectors, and the cadence patterns look-up-table.
2. The apparatus of claim 1 , further comprising:
a reset signal generator coupled to the motion auto-correlation unit.
3. The apparatus of claim 2 , wherein the reset signal generator is configured to provide a reset signal to the motion auto-correlation unit and the motion cross-correlation unit.
4. The apparatus of claim 1 , wherein the inter-frame/field motion detector comprises:
a pre-filter;
an inter-field motion detector;
an inter-frame motion detector; and
a repeat field detector.
5. The apparatus of claim 4 , wherein the inter-frame/field motion detector comprises:
a plurality of field buffers;
a plurality of inter-frame motion detectors coupled to the plurality of field buffers having a plurality of outputs;
a max operator coupled to the plurality of outputs;
a field or block average unit; and
an array buffer to store the average inter-frame/field motion for a period of time.
6. The apparatus of claim 4 , wherein the repeat field detector comprises:
a sum unit configured to receive a plurality of average inter-frame motion inputs at predetermined time intervals;
a first multiplier;
an adder;
a second multiplier coupled to the adder;
a comparator configured to compare the average inter-frame motion at a specific time to a predetermined threshold parameter;
a multiplexer configured to select the parameter kr or knr in accordance to the result of the comparator; and
an array buffer.
7. The apparatus of claim 1 , wherein the auto-correlation parameter initialization unit is configured to receive the reset signal and provide a maximum detectable cadence length δ max , and an auto-correlation input length T A .
8. The apparatus of claim 7 , wherein the auto-correlation parameter initialization unit is configured to initialize the maximum detectable cadence length and the auto-correlation input length to support only conventional cadence detection when the time after the reset is less than a control parameter MinTLong, and support conventional and exotic cadence detection when the time after the reset is more than MinTLong.
9. The apparatus of claim 1 , wherein the auto-correlation and cadence length detector comprises:
an auto-correlation calculator;
a peaks detector; and
a harmonics remover.
10. The apparatus of claim 1 , wherein the motion cross-correlation unit comprises:
a cross-correlation parameter initialization unit;
a normalized cross-correlation calculator coupled to the cross-correlation parameter initialization unit and the cadence patterns look-up-table;
a peak detector coupled to the normalized cross-correlation calculator; and
a repeat field flag generator coupled to the peak detector and the cadence patterns look-up-table.
11. The apparatus of claim 10 , wherein the cross-correlation parameter initialization unit is configured to receive the reset signal and a phase break signal and provide a cross-correlation input length T C .
12. The apparatus of claim 10 , wherein the normalized cross-correlation calculator comprises:
a cross-correlation calculator;
a normalization unit coupled to the cross-correlation calculator;
a movement count unit coupled to the normalization unit.
13. The apparatus of claim 2 , wherein the reset signal generator comprises:
a scene change detector coupled to the inter-frame/field motion detector;
a cadence break detector;
a phase break detector coupled to the motion cross-correlation unit;
a cadence pattern look-up-table coupled to the phase break detector; and
a reset scenario analyzer coupled to the scene change detector, the cadence detector, and the phase break detector.
14. A cadence detection system for processing a sequence of video fields, comprising:
an inter-frame/field motion detector;
a motion auto-correlation unit coupled to the inter-frame/field motion detector;
a motion cross-correlation unit coupled to the motion auto-correlation unit;
a cadence pattern storage look-up-table coupled to the motion cross-correlation unit; and
a reset signal generator coupled to the motion auto-correlation unit configured to provide a reset signal based upon at least one of a scene change, cadence break, or phase break,
wherein the reset signal generator comprises:
a scene change detector coupled to the inter-frame/field motion detector;
a cadence break detector;
a phase break detector coupled to the motion cross-correlation unit;
a cadence pattern look-up-table coupled to the phase break detector; and
a reset scenario analyzer coupled to the scene change detector, the cadence detector, and the phase break detector.
15. The system of claim 14 , wherein the reset scenario analyzer is configured to provide a reset signal when at least one of a cadence break or phase break occurs at substantially the same time as a scene change.
16. The system of claim 15 , wherein the reset scenario analyzer is configured not to provide a reset signal when a scene change occurs without any cadence break or phase break.
17. The system of claim 14 , wherein the inter-frame motion detector comprises:
a prefilter;
an inter-field motion detector;
a repeat field detector, wherein the repeat field detector comprises:
a sum unit configured to receive a plurality of average inter-frame motion inputs at predetermined time intervals;
a first multiplier;
an adder;
a second multiplier;
a comparator configured to compare the average inter-frame motion at a specific time to a predetermined threshold parameter;
a multiplexer configured to select a parameter kr or knr in accordance with a result of the comparator; and
an array buffer.
18. The system of claim 14 , wherein the motion cross-correlation unit comprises:
a cross-correlation parameter initialization unit;
a normalized cross-correlation calculator coupled to the cross-correlation parameter initialization unit and the cadence patterns look-up-table;
a peak detector coupled to the normalized cross-correlation calculator; and
a repeat field flag generator coupled to the peak detector and the cadence pattern look-up-table.
19. The system of claim 14 , wherein the cadence pattern look-up-table comprises cadence patterns selected from the group consisting of 2:2 cadence, 3:2 cadence, 2:2:2:4 cadence, 2:3:3:2 cadence, 5:5 cadence, 6:4 cadence, 3:2:3:2:2 cadence, 8:7 cadence, and 2:2:2:2:2:2:2:2:2:2:2:3 cadence.
20. A method for detecting film mode, comprising:
receiving a video signal;
detecting a cadence by detecting the inter-frame/field motion and analyzing the motion auto-correlation;
determining a cadence phase by calculating the motion cross-correlation based on the detected cadence;
generating a reset signal with a reset generator; and
providing the reset signal to the motion auto-correlation detector and the motion cross-correlation unit,
wherein the reset generator is configured to generate a reset signal when a cadence break and/or phase break of the video signal occur at substantially the same time as the scene change signal.
21. The method of claim 20 , wherein detecting a cadence by analyzing the auto-correlation comprises:
receiving a plurality of average motion inputs;
initializing the auto-correlation parameters;
calculating the auto-correlation and detecting the cadence length;
analyzing the cadence length with reference to a cadence patterns look-up-table;
analyzing the auto-correlation characteristics with reference to the cadence patterns look-up-table; and
providing the detected cadence based on the detected cadence length and the auto-correlation characteristics.
22. The method of claim 21 , wherein calculating the auto-correlation and detecting the cadence length comprises:
calculating the auto-correlation of the average motion by using the equation
A
(
δ
)
=
∑
t
=
0
T
A
-
δ
max
m
(
t
)
·
m
(
t
+
δ
)
δ
∈
[
2
,
δ
max
]
detecting the first and second highest peaks of the auto-correlation; and
removing the harmonics and providing the fundamental period as the final cadence length.
23. The method of claim 21 , wherein removing the harmonics and providing the fundamental period as the final cadence length comprises:
initializing the cadence length variable δ to the minimum cadence length possible;
checking if δ is a fundamental period of d 1 and d 2 ; if yes
checking if A(n×δ) for all interger nε[1,└d 1 /2┘] are local peaks eg. if A(n×δ) >A(n×δ−1) & A(n×δ)>A(n×δ+1)∀nε[1└d 1 /2┘];
let the finally detected cadence length d be 8 if yes, and increment δ by 1 if no and
δ
≤
d
1
2
.
24. The method of claim 21 , wherein initializing the auto-correlation parameters comprises:
checking if the received reset signal bReset is true;
resetting the time after reset τ Reset if yes, incrementing τ Reset if no;
checking if τ Reset is larger than the minimum auto-correlation input length MinTShort;
let the auto-correlation input length T A be the maximum of τ Reset and MinTShort;
checking if τ Reset is larger than the duration control for conventional cadence detection period after the reset; and
supporting exotic cadence if yes, else supporting only convention cadence.
25. The method of claim 20 , wherein determining a cadence phase by calculating the motion cross-correlation comprises:
receiving a plurality of average inter-frame/field motions;
initializing cross-correlation parameters based on the reset signal and the phase break signal;
calculating the normalized cross-correlations; and
detecting the peak of the cross-correlation and providing the cadence phase.
26. The method of claim 21 , wherein initializing cross-correlation parameters comprises:
checking if the received reset signal bReset is true;
resetting the time after reset τ Reset to ‘0’ if yes, incrementing τ Reset by ‘1’ if no;
checking if τ Reset is larger than the minimum auto-correlation input length MinTShort;
let the cross-correlation input length T C be the maximum of τ Reset and MinTShort;
checking if the phase break signal bBreak is true;
resetting the time after the phase break τ Break to ‘0’ if yes, incrementing τ Break by ‘1’ if no; and
let the cross-correlation input length T C be τ Break if τ Break is smaller than itself.
27. The method of claim 25 , wherein calculating the normalized cross-correlation comprises:
calculating the cross-correlation between the average inter-frame/field motions and the cadence patterns by the equation
S
(
ρ
)
=
∑
t
=
0
T
C
-
d
(
m
12
(
t
)
·
r
12
(
(
t
+
ρ
)
%
L
)
+
m
13
d
(
t
)
·
r
13
d
(
(
t
+
ρ
)
%
L
)
)
accumulating the movement bits in the cadence patterns by the equation
U
(
ρ
)
=
∑
t
=
0
T
C
-
d
(
r
12
(
(
t
+
ρ
)
%
L
)
+
r
13
d
(
(
t
+
ρ
)
%
L
)
)
normalizing the cross-correlation with the movement bits by the equation
C
(
ρ
)
=
S
(
ρ
)
U
(
ρ
)
ρ
∈
[
0
,
d
)
.