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Low latency architecture for spatial filtration
| Details |
Inventors: Anderson, Mark A.;
Assignee: Hewlett-Packard Company (Palo Alto, CA)
Primary Examiner: Rogers; Scott
Assistant Examiner:
Attorney, Agent or Firm:
A spatial filter having coefficients selected and distributed within an array, so that when the array is divided non-diagonally into four equal quadrants, (1) the coefficients are of constant sign within each quadrant; (2) coefficients in diagonally opposed quadrants have like sign; and (3) coefficients in non-diagonally neighboring quadrants have unlike sign. In a preferred embodiment, coefficients cause the array to form a "saddle" shape when the coefficient values are representative of the local slope on a surface described by the array. This "saddle" shape enables improved filtration properties. The inventive spatial filter is further advantageously embodied in architecture comprising an array of individual calculation modules corresponding to the filter array. Rows of modules are coupled together in parallel. The input signal is fed to each row concurrently via FIFO buffers, enabling concurrent calculation operations. After calculation, output values for each module are accumulated and summed, the result being placed into an output stream. The FIFO buffers then present the next input values in the input stream to the calculation modules, and so on. The result is a low-latency "streaming" filtration that is further economical on hardware, requiring only FIFO storage resources. Advantageously, the entire inventive filter may be conveniently deployed as a digital signal processor ("DSP") on a unitary integrated circuit chip. |
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DETAILED DESCRIPTION These and other objects, features and technical advantages are achieved by a spatial filter in which coefficients are selected to have a numerical value and distribution so as to improve performance in key areas such as contrast enhancement, dynamic range compression, signal to noise discernability and offset cancellation.
The inventive spatial filter is further advantageously embodied on architecture enabling the desired "streaming" processing.
According to the present invention, a spatial filter is provided wherein coefficients are selected and distributed within a filter array so that when the filter array is divided non-diagonally into four equal quadrants, (1) the coefficients are of constant sign within each quadrant; (2) coefficients in diagonally opposed quadrants have like sign; and (3) coefficients in non-diagonally neighboring quadrants have unlike sign.
In a preferred embodiment, coefficients selected and distributed as set forth above within the filter array are arranged within the array to form a "saddle" shape when the coefficient values are representative of the local slope on a surface described by the filter array.
Examples of spatial filters with coefficients according to the invention are shown on FIGS.
3A through 3G and are described in more detail below.
This "saddle" shape exhibited by a preferred embodiment of the inventive spatial filter enables the filter to display improved characteristics.
First, the inventive spatial filter provides excellent contrast differentiation and edge detection in images where there is a gradual change in shade rather than a sharp edge.
Second, dynamic range compression is enabled, since input values to the exemplary inventive filters shown on FIGS.
3A through 3G will generally be 8 bits wide, while output (filtered) results will only be 4 bits wide.
The inventive spatial filter further shows improved signal to noise properties, having 16 non-zero elements in the filter of FIG.
3A, for example, as opposed to only 5 in the current art filter of FIG
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Image Analysis 
