Two-dimensional pyramid filter architecture

Details Two-dimensional pyramid filter architecture Two-dimensional pyramid filter architecture

2001-04-30

2004-04-20

Ngo, Chuong Dinh (Department: 2124)

Electrical computers: arithmetic processing and calculating

Electrical digital calculating computer

Particular function performed

C382S240000, C382S260000

Reexamination Certificate

active

06725247

ABSTRACT:

BACKGROUND
This disclosure is related to pyramid filters.
In image processing, it is often desirable to decompose an image, such as a scanned color image, into two or more separate image representations. For example, a color or gray-scale document image can be decomposed into background and foreground images for efficient image processing operations, such as enhancement, compression, etc., as are at times applied in a typical photocopying machine or scanner device. In this context, this operation is often referred to as a descreening operation. This descreening is also sometimes applied to remove halftone patterns that may exist in an original scanned image. For example, these halftone patterns may cause objectionable artifacts for human eyes if not properly removed. The traditional approach for this decomposition or descreening is to filter the color image in order to blur it. These blurred results are then used to assist in determining how much to blur and sharpen the image in order to produce the decomposition. Typically this blurring can be achieved using a “symmetric pyramid” filter. Symmetric pyramid finite impulse response (FIR) filters are well-known.
One disadvantage of this image processing technique, however, is that the complexity increases many fold when a number of pyramid filters of different sizes is applied in parallel in order to generate multiple blurred images, to apply the technique as just described. A brute force approach for this multiple pyramid filtering approach is to use multiple FIR filters in parallel, as illustrated in FIG.
1
. Such an approach demonstrates that the design and implementation of fast “symmetric pyramid filtering” architectures to generate different blurred images in parallel from a single source image may be desirable.
The numbers provided in parenthesis for each FIR block in
FIG. 1
represents the pyramid filter of corresponding length. For example, (1, 2, 1) are the filter coefficients for a symmetric pyramid finite impulse response (FIR) filter of order or length
3
. Likewise, (1, 2, 3, 2, 1) are the coefficients for an FIR pyramid filter of order
5
, (1, 2, 3, 4, 3, 2, 1) are the coefficients for an FIR pyramid filter of order
7
, (1, 2, 3, 4, 5, 4, 3, 2, 1) are the coefficients for an FIR pyramid filter of order
9
, (1, 2, 3, 4, 5, 6, 5, 4, 3, 2, 1) are the coefficients for an FIR pyramid filter of order
11
, and so forth.
Unfortunately, the approach demonstrated in
FIG. 1
has disadvantages. For example, inefficiency may result from redundant computations. Likewise, FIR implementations frequently employ multiplier circuits. While implementations exist to reduce or avoid the use of multipliers, such as with shifting and summing circuitry, that may then result in increased clocking and, hence, may reduce circuit throughput. A need, therefore, exists for improving pyramid filtering implementations or architectures.


REFERENCES:
patent: 5359674 (1994-10-01), van der Wal
patent: 5963675 (1999-10-01), van der Wal et al.
patent: 6018597 (2000-01-01), Maltsev et al.
1998 IEEE; “Simplified Design of Steerable Pyramid Filters”, K. Castleman, et al., pp.: V-329-V-332.
1997 IEEE, “A High-Speed Reconfigurable Integrated Architecture for DWT”, T. Acharya, p. 669-673.

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