Compression and decompression

The purpose of compression and decompression is to preserve the important essence of the information, but to use fewer bits to represent it for storage and transmission. There are several important concepts:

• to preserve the important essence of the information
• to transform the representation of the information to use fewer bits to represent it for storage and transmission

Let us start by exmining the concept of preserving the essence of the information

• It is implicit in this concept that some components of the information are more important that others
• One such element is that the background may be less important than the foreground
• An examble of another element may be that the size is more important than the exact colour
• It is also implicit that some information may be lost by compression
• There are loss-less methods of compression, but most methods are 'lossy', i.e. they lose some detailed elements of the information that are considered less important
• Loss-less compression means that the original can be restored exactly with the appropriate decompression
• From our perspective, the importance of an element of information is relevant to its impact on survival, on mating, and on other aspects of evolution
• If the information does not help, then it can be ignored or taken out in compression

Next, let us look at compression of visual information

• Typically 2D pixellated information is compressed within a single image or frame. One can get even better compression by compressing across a number of frames.
• Parts of the picture may not change from frame to frame, or change very slowly

Next, let us look at compression of action sequences

• We expect to deliver 1000 updates per second to each of the muscles, specifying each muscle twitch in detail
• It seems unlikely that there is much opportunity to compress across the muscle pairs during a single 1ms refresh transmission. Balancing pairs for a single plane of action (degree of freedom) for a single joint may complement each other. There may be other correlations that allow the tension on a single muscle to be predicted from the tension on one or more other muscles.
• It seems quite likely that we can compress over time for a given muscle pair for a joint and a bone. There may be no change, or the change may be linear or may follow some other standard progression.