Method and apparatus for enhancing images using helper signals

• US 5,818,972 A
• Filed: 06/07/1995
• Issued: 10/06/1998
• Est. Priority Date: 06/07/1995
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: RealNetworks, Inc.
• Inventors: Girod, Bernd, Adelson, Edward H.
• Primary Examiner(s): Couso, Jose L.
• Assistant Examiner(s): Bella, Matthew C.
• Application Number:
  US08/480,169
• Time in Patent Office: 1,217 Days
• Field of Search: 382/275, 382/260, 382/261, 382/274, 382/263, 382/264, 382/262, 382/266, 382/269, 382/254, 348/606, 348/625, 348/607, 348/610, 348/627, 348/242, 358/463, 358/447, 358/455, 358/518, 358/532, 358/462, 364/724.014
• US Class Current: 382/260
• CPC Class Codes: H04N 5/208 for compensating for attenuation of high frequency components, e.g. crispening, aperture distortion correction
• CPC Class Codes: H04N 5/21 Circuitry for suppressing or minimising disturbance, e.g. moiré or halo

Abstract

A system for, and method of, enhancing a digitized image signal according to a helper signal architecture are described. The architecture includes an analysis filter, responsive to a digitized image signal, for filtering the digitized image signal, corresponding to a first frequency band, to produce a first frequency band signal. The first frequency band signal is then applied to a point operator, which modifies the first frequency band signal in accordance with a non-linear characteristic. The non-linear characteristic includes a first region having a negative slope for low amplitude input signals. The non-linearity further includes a second region having a positive slope for informational components of an input signal so that informational components of the first frequency band signal cause the point operator to produce a modified signal having components that relate to the input signal according to the positive slope. The modified signal is then received by an synthesis filter, corresponding to the analysis filter, to produce a helper signal. The helper signal and the digitized image signal are then added to yield an enhanced digitized image signal.

Claims

1. A system for enhancing digitized image signals, comprising:

an analysis filter for filtering the digitized image signals to produce first frequency band signals;

a point operator responsive to first frequency band signals for generating noise reduction signals and image sharpening signals;

a synthesis filter that filters the noise reduction signals and image sharpening signals to produce noise reduction helper signals and image sharpening helper signals, the synthesis filter shaping artifacts introduced by nonlinearities associated with the point operator to a desired pattern, and the combination of analysis and synthesis filtering resulting in at least one of smoothing along the edge and sharpening orthogonal to the edge of the image signal; and

a summing node by which the noise reduction helper signals, the image signal enhancement signals and the digitized image signals are combined to yield enhanced digitized image signals.

2. The system of claim 1 wherein the point operator is responsive to first frequency band signals having absolute amplitudes less than a predetermined threshold for generating negative noise reduction signals and responsive to first frequency band signals having absolute amplitudes greater than the predetermined threshold for generating positive image signal enhancement signals.

4. The system of claim 1 further comprising:

at least one additional analysis filter that filters the digitized image signal to produce at least one additional corresponding frequency band signal;

at least one additional point operator, responsive to the additional corresponding frequency band signal, that provides at least one additional modified signal;

at least one additional synthesis filter that filters the additional modified signal to produce at least one additional helper signal; and

wherein the additional helper signal is summed at the summing node with the image signal and the helper signal to yield the enhanced digitized image signal.

5. The system of claim 1 wherein the image signal is a two dimensional signal and wherein the analysis filter and the synthesis filter have predetermined impulse responses, each impulse response having non-zero weight diagonal coefficients across a first diagonal and zero weight coefficients across a second diagonal of the impulse response.

6. The system of claim 1 wherein the point operator is determined in accordance with impulse responses of the analysis and synthesis filters, such that a combination of the analysis filter the point operator, and the synthesis filter suppresses white noise.

8. The system of claim 1 wherein the analysis filter, the point operator, the synthesis filter, and the summing node are implemented on a general purpose computer as software routines.

3. A system for enhancing a digitized image signal, comprising:

an analysis filter that filters the digitized image signal to produce a first frequency band signal;

a point operator, responsive to the first frequency band signal, that provides a modified signal, the point operator including a non-linear characteristic to produce the modified signal, the non-linear characteristic having a first region, corresponding to low amplitude first frequency band signals, with a first predetermined negative slope, and further having a second region, corresponding to higher amplitude first frequency band signals with an amplitude higher than the low amplitude first frequency band signals, the second region having a positive slope;

a synthesis filter that filters the modified signal to produce a helper signal, the synthesis filter shaping artifacts introduced by non-linearities associated with the point operator to a desired pattern, and the combination of analysis and synthesis filtering resulting in at least one of smoothing along the edge and sharpening orthogonal to the edge of the image signal; and

a summing node by which the helper signal and the digitized image signal are summed to yield an enhanced digitized image signal.

7. The system of claim 3 wherein the point operator includes a LUT for providing the modified signals in response to the frequency band signal, and wherein the nonlinear characteristic includes a third region for frequency band signals having an amplitude higher than said higher amplitude first frequency signals, wherein the third region has a second negative slope.

9. The system of claim 3 wherein the digitized input signal is a real-time video signal according to a predefined signal standard and wherein the enhanced digitized image signal is in the predefined signal standard.

10. The system of claim 3 wherein the first frequency band is a high frequency band.

11. A method of enhancing digitized image signals, the method comprising the steps of:

a) analysis filtering the digitized image signal, to produce first frequency band signals;

b) generating noise reduction signals and image sharpening signals in response to the first frequency band signals;

c) synthesis filtering the noise reduction signals and image sharpening signals to shape artifacts introduced by non-linearities associated with the point operator to a desired pattern and produce noise reduction helper signals and image sharpening helper signals. the combination of analysis and synthesis filtering resulting in at least one of smoothing along the edge and sharpening orthogonal to the edge of the image signal; and

d) combining the noise reduction helper signals, the image signal enhancement signals and the digitized image signals to yield enhanced digitized image signals.

13. The method of claim 11 further comprising the steps of:

e) analysis filtering the digitized image signal to produce at least one additional frequency band signal;

f) modifying the additional frequency band signal to produce at least one additional modified signal therefrom;

g) synthesis filtering the additional modified signal to produce at least one additional helper signal; and

wherein step D further includes the step of

d1) adding the additional helper signal to the image signal and to the helper signal to yield the enhanced digitized image signal.

14. The method of claim 11 wherein the image signal is a two dimensional signal and steps a and c perform filtering steps according to predetermined impulse responses, each impulse response having non-zero weight diagonal coefficients across a first diagonal and zero weight coefficients across a second diagonal of the impulse response.

17. The method of claim 13 wherein steps (a)-(d) are executed on a general purpose computer as software routines.

18. The method of claim 13 wherein the digitized input signal is a real-time video signal according to a predefined signal standard and wherein the enhanced digitized image signal is in the predefined signal standard.

19. The method of claim 13 wherein the first frequency band is a high frequency band.

12. A method for enhancing a digitized image signal, the method comprising the steps of:

a) analysis filtering the digitized image signal to produce a first frequency band signal;

b) modifying the first frequency band signal in accordance with a non-linear characteristic to produce a modified signal, the non-linear characteristic having a first region with a negative slope for low amplitude first frequency band signals and a second region with a positive slope for higher amplitude frequency band signals;

c) synthesis filtering the modified signal to shape artifacts introduced by nonlinearities associated with the point operator to a desired pattern and produce a helper signal, the combination of analysis and synthesis filtering resulting in at least one of smoothing along the edge and sharpening orthogonal to the edge of the image signal; and

d) adding the helper signal and the digitized image signal to yield an enhanced digitized image signal.

15. The method of claim 12 wherein the first predetermined negative slope is determined in accordance with the impulse responses of the analysis and synthesis filters, such that a combination of the analysis filter, the point operator, and the synthesis filter suppresses white noise.

16. The method of claim 12 wherein step b includes accessing a LUT that provides the modified signals in response to the frequency band signal, and wherein the non-linear characteristic includes a third region for frequency band signals having an amplitude higher than said higher amplitude first frequency signals, wherein the third region has a second negative slope.