Boots – shoes – and leggings
Patent
1997-06-24
1999-06-15
Ngo, Chuong Dinh
Boots, shoes, and leggings
364724014, 36472417, G06F 1710
Patent
active
059128267
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
This invention concerns methods and apparatus for processing data, particularly but not exclusively electrical signals, by filtering the data according to value and extent (duration). The invention is of particular application in the field of image analysis, pattern recognition and the like.
BACKGROUND OF THE INVENTION
A technique of data processing as aforesaid has been described inter alia in PCT/GB94/00080, in which a series of data values are subjected to a so-called Datasieve, in which the values are successively filtered using a progressively increasing size criterion and the output of each successive filtering stage supplies the input to the next.
The Datasieve as described in PCT/GB94/00080 employs ordinal value filtering in each stage, and a commonly used ordinal value filter is a median filter.
This type of processing often requires a root signal to be obtained from each filtering stage (ie a signal that is invariant to further processing if recycled through the filter which has produced it). Using conventional ordinal value filters and particularly median filters, has involved the recycling of the filtered values two or three times or more through the same stage before a root signal has been obtained, and where this has to occur a number of times at each stage, the computational complexity and buffer storage requirements have detracted from the advantages obtained from Datasieve.
It is an object of the present invention to provide a filtering technique and apparatus for use in the successive filtering stages of the Datasieve which does not suffer from this particular disadvantage.
It is another object of the present invention to provide a method of operating the Datasieve at a higher speed.
DEFINITIONS
An ordinal value operator, (also known as a rank order operator), of ordinal value p is a non-linear operator that takes as its input w data samples (w>=p) and outputs the p'th largest value (1<=p<=w) from the w input samples.
The normalised rank of the operator, r, is defined by r=(p-1)/(w-1) so o<=r<=1.
An ordinal value filter processes a signal by applying the ordinal value operator at each possible position along the input signal to form a filtered output signal. This corresponds to sliding a window containing w samples along the signal and applying the ordinal value operator to the contents of each window, to produce an output sample for each window position.
A Datasieve is a device for performing a method of filtering and analysing signals which applies ordinal value filters in a cascade such that the output of the n'th filter forms the input to the (n+1)'th filter in the succession, and in which the `scale` increases at each successive filtering stage.
The `scale` of a filter corresponds to the extent (ie width or duration) of the signal features that it removes, and this is related to the number of input samples to each ordinal value operator, ie. the extent of the window. For an ordinal value filter of a particular normalised rank, larger windows correspond to greater filtering scales. However, for different types of ordinal value filter, the window size corresponding to a particular filtering scale may be different.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, in a Datasieve (as aforesaid) at least one of the succession of filtering stages is constructed and operates as a recursive ordinal value filter, typically a recursive median filter.
The key difference between a non-recursive ordinal value filter and a recursive ordinal value filter, is that a non-recursive ordinal value filter operates on a group of data values all of which are taken from the input signal, whereas a recursive ordinal value filter operates on a group of values made up of future input values and past output values of the filter.
For illustrative purposes, consider a particular ordinal value filter--the median filter, which has normalised rank 1/2. For an input signal x(m) a median filter of scale n (also-known as the `order` of the median filt
REFERENCES:
patent: 4928258 (1990-05-01), May
patent: 5097433 (1992-03-01), Caraccilo
patent: 5319583 (1994-06-01), Wildes
Bangham James Andrew
Bragg Nigel Lawrence
Young Robert William
Cambridge Consultants Limited
Ngo Chuong Dinh
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