Method and apparatus for decomposing an image stream into units of local contrast

• US 5,909,516 A
• Filed: 03/28/1997
• Issued: 06/01/1999
• Est. Priority Date: 03/29/1996
• Status: Expired due to Term

• Current Assignee: Asev Display Labs Inc. (AmTRAN Technology Co., Ltd.)
• Original Assignee: Sarnoff Corporation (SRI International, Inc.)
• Inventors: Lubin, Jeffrey
• Primary Examiner(s): Rogers, Scott
• Assistant Examiner(s): BILLINGS, CHAD
• Application Number:
  US08/829,540
• Time in Patent Office: 795 Days
• Field of Search: 382/260, 382/264, 382/302, 382/263, 382/254, 382/275, 382/303, 348/623, 348/25, 348/107, 348/153, 348/451
• US Class Current: 382/260
• CPC Class Codes: H04N 19/117 Filters, e.g. for pre-processing or post-processing sub-band filter banks H04N19/635
• CPC Class Codes: H04N 19/14 Coding unit complexity, e.g. amount of activity or edge presence estimation H04N19/146 takes precedence
• CPC Class Codes: H04N 19/154 Measured or subjectively estimated visual quality after decoding, e.g. measurement of distortion use of rate-distortion criteria H04N19/147
• CPC Class Codes: H04N 19/172 the region being a picture, frame or field
• CPC Class Codes: H04N 19/42 characterised by implementation details or hardware specially adapted for video compression or decompression, e.g. dedicated software implementation H04N19/635 takes precedence
• CPC Class Codes: H04N 19/60 using transform coding
• CPC Class Codes: H04N 19/85 using pre-processing or post-processing specially adapted for video compression

Abstract

An apparatus and concomitant method for decomposing an image stream into units of local contrast. A temporal contrast transform (pyramid), comprises a spatial filter, a cascade of lowpass temporal filters and a plurality of subtractors and dividers. The spatial filter is followed by a cascade of lowpass temporal filters, producing a set of temporally lowpass, spatially low pass images. Adjacent filter outputs are then subtracted, producing a set of temporally bandpass (Laplacian) images. Finally, each Laplacian image is divided by a lower level temporal lowpass image, to produce a set of temporally bandpass contrast images.

Claims

1. Apparatus for computing units of local contrast from an input sequence having a plurality of signals, said apparatus comprising:

a plurality of cascaded temporal filters for generating a plurality of temporal filtered signals from each of the signal of the input sequence;

at least one subtractor, coupled to at least two of said temporal filters, for generating a temporal bandpass signal; and

at least one divider, coupled to one of said subtractor and one of said temporal filter, for generating a temporal bandpass contrast signal.

2. The apparatus of claim 1, wherein said plurality of signals are images.

3. The apparatus of claim 1, further comprises:

a spatial filter, coupled to one of said temporal filter, for applying spatial filtering to the image of the input sequence to generate a spatial filtered image, where said spatial filtered image is used to generate said temporal filtered signals.

4. The apparatus of claim 1, wherein said temporal filters are lowpass filters.

5. The apparatus of claim 4, wherein each of said temporal filter is expressed as:

space="preserve" listing-type="equation">h(t)=a exp(-at) u(t)

where u(t) is the unit step function u(t)=0 for t<

0, else u(t)=1, and a is a fitted parameter.

6. The apparatus of claim 1, wherein said temporal filters are FIR filters.

7. The apparatus of claim 1, wherein said plurality of cascaded temporal filters, said subtractor, and said divider form a temporal contrast pyramid.

8. Method for computing units of local contrast from an input sequence having a plurality of signals, comprising the steps of:

(a) using a plurality of cascaded temporal filters to generate a plurality of temporal filtered signals from each of the signal of the input sequence;

(b) generating a temporal bandpass signal from adjacent set of said temporal filtered signals; and

(c) dividing said temporal bandpass signal by one of said temporal filtered signals to generate a temporal bandpass contrast signal.

9. The method of claim 8, wherein said plurality of signals are images.

10. The method of claim 8, further comprising the step of:

(a'"'"') spatial filtering the image of the input sequence to generate a spatial filtered image, where said spatial filtered image is said signal of the input sequence in step (a).

11. The method of claim 8, wherein said temporal filters are lowpass filters.

12. The method of claim 8, wherein each of said temporal filter is expressed as:

space="preserve" listing-type="equation">h(t)=a exp(-at) u(t)

where u(t) is the unit step function u(t)=0 for t<

0, else u(t)=1, and a is a fitted parameter.

13. The method of claim 8, wherein said temporal filters are FIR filters.

14. Method for computing units of local contrast from an input sequence having a plurality of signals, comprising the steps of:

(a) generate a plurality of temporal filtered signals from each of the signal of the input sequence;

(b) generating a temporal bandpass signal from adjacent set of said temporal filtered signals; and

(c) generating a temporal bandpass contrast signal from said temporal bandpass signal and said temporal filtered signals.

15. The method of claim 14, wherein said plurality of signals are images.

16. The method of claim 14, further comprising the step of:

(a'"'"') spatial filtering the image of the input sequence to generate a spatial filtered image, where said spatial filtered image is said signal of the input sequence in step (a).