System and method for selectively compressing images
View Patent ↗A system and method for characterizing the sensitivity of image data to compression. After a video signal is transformed to the frequency domain, statistical data regarding a video signal or frame of a video signal can be calculated. In one alternate, a contour map of the original signal can be calculated and the parameters of the contour map can be recorded. The same signal can be compressed and then upscaled and a second contour map can be calculated and the parameters of the second contour map can be recorded. Based on the difference between the first and second contour maps, a sensitivity of the video to compression can be determined.
1. A method for characterizing and transcoding segments of a video, comprising:
acquiring a first picture from a video signal;
calculating a first spatial frequency transform of the first picture;
fitting a first line to the log magnitude of a main horizontal component of the first spatial frequency transform;
storing at least one of a first slope, a first intercept, and a first correlation coefficient of the first line;
acquiring a second picture from a video signal;
calculating a second spatial frequency transform of the second picture;
fitting a second line to the log magnitude of main horizontal component of the second spatial frequency transform;
storing at least one of a second slope, a second intercept, and a second correlation coefficient of the second line;
determining a first difference between at least one of the first slope and the second slope, the first intercept and the second intercept and the first correlation coefficient and the second correlation coefficient;
determining whether the first difference exceeds a first prescribed threshold;
signaling that the first prescribed threshold has been exceeded; and
calculating a compression level for transcoding based upon the first prescribed threshold when the threshold first prescribed threshold has been exceeded.
2. The method of claim 1 further comprising the steps of:
fitting a third line to the log magnitude of a main vertical component of the first spatial frequency transform;
storing at least one of a third slope, a third intercept, and a third correlation coefficient of the third line;
fitting a fourth line to the log magnitude of a main vertical component of the second spatial frequency transform;
storing at least one of a fourth slope, a fourth intercept, and a fourth correlation coefficient of the fourth line;
determining a second difference between at least one of the third slope and the fourth slope, the third intercept and the fourth intercept and the third correlation coefficient and the fourth correlation coefficient;
determining whether the second difference exceeds a second prescribed threshold; and
signaling that the second prescribed threshold has been exceeded.
3. The method of claim 2 wherein at least one of the first line, the second line, the third line and the fourth line is fitted using linear regression.
4. The method of claim 1 further comprising the steps of:
comparing at least one of the first slope, the second slope, the first intercept, the second intercept, the first correlation coefficient and the second correlation coefficient to a threshold; and
generating a segment-boundary indicator when the threshold is exceeded be a prescribed quantity.
5. The method of claim 1 further comprising the steps of:
comparing at least one of the first slope, the second slope, the first intercept, the second intercept, the first correlation coefficient and the second correlation coefficient to a threshold; and
generating a segment-boundary indicator when the threshold is exceeded be a prescribed percentage.
6. The method of claim 1 further comprising the steps of:
storing the first difference;
transmitting the difference when the difference exceeds a prescribed threshold; and
recording the transmitted difference value.
7. The method of claim 1 , wherein a compression level during transcoding transfers resolution from 4K to a lower resolution video when the threshold is exceeded.