Adaptive security camera image compression apparatus and method of operation
A lossy compression method optimizes bandwidth and storage for a security surveillance network. An appliance on a local network attached to event capture terminals transforms image files into a key frame and at least one subsequent frame. Decompression combines a subsequent frame with its key frame to provide an image with graduated resolution/noise clutter. A camera records, and forwards a plurality of image files compatible with JPEG. Key frames are selected from among the plurality of image files. A configurable low pass filter is reset for each train of a key frame and its subsequent frames. Each low pass filter is selectively applied to each pixel block within a subsequent frame. The transformation operates on coefficients of frequency bins. Meta data enables decompression of a single subsequent frame by reversing some of the transformations to provide a JPEG compatible file having selectively reduced resolution or noise clutter.
1. An apparatus for conservation of bandwidth and storage in a security surveillance system comprising:
a circuit to receive JPEG codec compatible files and to reverse Huffman encoding to obtain frequency coefficients for each pixel block;
a circuit to distinguish key frames from subsequent frames;
a circuit to set a configurable low pass filter for each train of a key frame and its subsequent frame or frames;
a circuit to determine delta coefficients for each frequency bin of each pixel block;
a circuit to selectively zero insignificant delta coefficients; and
a circuit to apply the configurable low pass filter to selected pixel blocks;
wherein the circuit to set a configurable low pass filter determines the minimum number of high frequency coefficients to mask out to achieve a target compression size.
2. The apparatus of claim 1 wherein the circuit to apply the configurable low pass filter is controlled by the magnitude of the delta coefficients in certain low frequency bins.
3. The apparatus of claim 1 further comprising: a circuit to Huffman encode delta coefficients into a JPEG codec compatible file and store meta data to relate a subsequent frame to its key frame.