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Method, device and microprocessor for selectively compressing video frames of a motion compensated prediction-based video codec
| Details |
Inventors: Banham, Mark R.; Brailean, James C.; Levine, Stephen N.; Katsaggelos, Aggelos K.; Schuster, Guido M.;
Assignee: Motorola (Schaumburg, IL); Northwestern University (Evanston, IL)
Primary Examiner: Voeltz; Emanuel T.
Assistant Examiner: Peeso; Thomas
Attorney, Agent or Firm: Stockley; Darleen J.
A method (100, 200), device (300) and microprocessor (400) are provided for selectively compressing video frames of a motion compensated prediction-based video codec based on a predetermined set of compression techniques. An energy estimate of the current displaced frame difference, DFD, is used to compute a ratio between the estimate and a historical mean of energy estimates. The ratio is iteratively compared to a predetermined set of thresholds which are associated with the predetermined set of compression techniques. The comparisons are used to choose a technique based on the thresholds, and a technique is selected to be used for encoding the current DFD. |
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DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT A video sequence consists of individual images, or frames, of video data which are two dimensional representations of a three dimensional scene.
A frame of video at time instant k is represented by the two dimensional signal, f.
sub.
k (i,j).
These frames appear at regularly spaced intervals in time.
The displaced frame difference, or DFD, is obtained by taking the difference in intensity values at each pixel in a frame between the current frame, f.
sub.
k (i,j), and a motion compensated version of the previous frame, f.
sub.
k-1 (i-dx(i,j),j-dy(i,j)), where dx(i,j) and dy(i,j) are the estimated displacements in the x and y directions at pixel (i,j), obtained from a predetermined motion estimation technique.
The DFD, which is a prediction error image, may be encoded using a variety of compression techniques, as mentioned above.
The present invention provides a method which selects an appropriate coding technique from a predetermined set of candidates for each incoming DFD frame of a video sequence in the encoder.
This method leads to the efficient use of the multiple coding techniques to compress video sequences having variations in the amount and type of motion between frames in the scene.
FIG.
1, numeral 100, is a flow diagram of a preferred embodiment of a method for selectively compressing video frames of a motion compensated prediction-based video codec in accordance with the present invention.
The first step consists of using the current displaced frame difference, DFD, to compute a current estimate of an energy for the DFD (102).
The next step consists of computing a ratio of this energy estimate to a historical mean of energy estimates of previous DFDs (104).
The current predetermined threshold is then specified as the first predetermined threshold from a list of thresholds (106).
The ratio is then compared to a predetermined threshold according to a predetermined iterative scheme (108).
The predetermined iterative scheme consists of repeating a comparison of the ratio to the next current predetermined threshold which is related to a predetermined DFD coding technique
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I/O Systems 
