Device and method for sub-band decomposition of image signals

1. A device that receives and processes an image signal for sub-band decomposition of an image, the device comprising:

a first median filter that receives the image signal and processes signal values of pixel locations (x 0 , y 0 ), (x 0 +1, y 0 ), (x+1, y 0 ), (x 0 , y 0 −1) and (x 0 , y 0 +1) of the image signal to provide a first median filter output signal;

a second median filter that receives the first median filter output signal and processes signal values at pixel locations (x 0 , y 0 ), (x 0 −2, y 0 ), (x 0 +2, y 0 ), (x 0 , y 0 −2) and (x 0 , y 0 +2) of the first median output signal to provide a second median filter output signal;

a third median filter that receives the second median filter output signal and processes signal values at pixel locations (x 0 , y 0 ), (x 0 −3, y 0 ), (x 0 +3, y 0 ), (x 0 , y 0 −3) and (x 0 , y 0 +3) of the second median filter output signal to provide a third median filter output signal;

a first subtractor that computes the difference between the image signal and the first median filter output signal to provide a first sub-band signal;

a second subtractor that computes the difference between the first median filter output signal and the second median filter output signal to provide a second sub-band signal; and

a third subtractor that computes the difference between the second median filter output signal and the third median filter output signal to provide a third sub-band signal;

where each of the median filters considers not only the signal value at the pixel location (x 0 ,y 0 ) but also the signal values of four other pixels (x 0 k,y 0 ), (x 0 −k,y 0 ), (x 0 ,y 0 +k), and (x 0 ,y 0 −k) which, in a cruciform arrangement, are at the same distance from pixel (x 0 ,y 0 ) in the horizontal and the vertical direction.

2. A device that receives and processes an image signal for sub-band decomposition of an image, the device comprising:

a first median filter that receives the image signal and processes signal values of pixel locations (x 0 , y 0 ), (x 0 −1, y 0 ), (x+1, y 0 ), (x 0 , y 0 −1) and (x 0 , y 0 +1) of the image signal to provide a first median filter output signal;

a second median filter that receives the first median filter output signal and processes signal values at pixel locations (x 0 , y 0 ), (x 0 −2, y 0 ), (x 0 +2, y 0 ), (x 0 , y 0 −2) and (x 0 , y 0 +2) of the first median output signal to provide a second median filter output signal;

a third median filter that receives the second median filter output signal and processes signal values at pixel locations (x 0 , y 0 ), (x 0 −3, y 0 ), (x 0 +3, y 0 ), (x 0 , y 0 −3) and (x 0 , y 0 +3) of the second median filter output signal to provide a third median filter output signal;

a first summer that computes the difference between the image signal and the first median filter output signal to provide a first sub-band signal;

a second summer that computes the difference between the first median filter output signal and the second median filter output signal to provide a second sub-band signal; and

a third summer that computes the difference between the second median filter output signal and the third median filter output signal to provide a third sub-band signal.

3. The device of claim 2 , comprising a summer that sums the first, second and third sub-band signals with the third median filter output signal to provide a filtered image signal.

4. The device of claim 2 , comprising:

a first deadband filter that receives the first sub-band signal and provides a first sub-band filtered signal;

a second deadband filter that receives the second sub-band signal and provides a second sub-band filtered signal;

a third deadband filter that receives the third sub-band signal and provides a third sub-band filtered signal; and

a summer that sums the first, second and third sub-band filtered signals and the third median filter output signal to provide a filtered image signal.

5. The device of claim 4 , wherein the first deadband filter has a response such that when the input signal value has an amplitude less than x c then the first sub-band filtered signal is set equal to zero.

6. A device that receives and processes an image signal for sub-band decomposition of an image, the device comprising:

a first median filter that receives the image signal and processes signal values of pixel locations (x 0 , y 0 ), (x 0 −1, y 0 ), (x+1, y 0 ), (x 0 , y 0 −1) and (x 0 , y 0 +1) of the image signal to provide a first median filter output signal;

a second median filter that receives the first median filter output signal and processes signal values at pixel locations (x 0 , y 0 ), (x 0 −2, y 0 ), (x 0 +2, y 0 ), (x 0 , y 0 −2) and (x 0 , y 0 +2) of the first median output signal to provide a second median filter output signal;

a third median filter that receives the second median filter output signal and processes signal values at pixel locations (x 0 , y 0 ), (x 0 −3, y 0 ), (x 0 +3, y 0 ), (x 0 , y 0 −3) and (x 0 , y 0 +3) of the second median filter output signal to provide a third median filter output signal;

means for computing the difference between the image signal and the first median filter output signal and for deadband filtering the resulting difference to provide a first sub-band signal;

means for computing the difference between the first median filter output signal and the second median filter output signal and for deadband filtering the resulting difference to provide a second sub-band signal;

means for processing the first and second sub-band filtered signals to provide a filtered image signal.

7. The device of claim 6 , further comprising:

a third median filter that receives the second median filter output signal and processes signal values at pixel locations (x 0 , y 0 ), (x 0 −3, y 0 ), (x 0 +3, y 0 ), (x 0 , y 0 −3) and (x 0 , y 0 +3) of the second median filter output signal to provide a third median filter output signal;

means for computing the difference between the second median filter output signal and the third median filter output signal and for deadband filtering the resulting difference to provide a third sub-band signal; and

wherein the means for processing comprises a summer that sums the first, second and third sub-band signal and the third median filter output signal to provide the filtered image signal.

8. A device that receives and processes an image signal for sub-band decomposition of an image, the device comprising:

a first median filter that receives the image signal and processes signal values of pixel locations (x 0 , y 0 ), (x 0 −1, y 0 ), (x+1, y 0 ), (x 0 , y 0 −1) and (x 0 , y 0 +1) of the image signal to provide a first median filter output signal;

a second median filter that receives the first median filter output signal and processes signal values at pixel locations (x 0 , y 0 ), (x 0 −2, y 0 ), (x 0 +2, y 0 ), (x 0 , y 0 −2) and (x 0 , y 0 +2) of the first median output signal to provide a second median filter output signal;

a third median filter that receives the second median filter output signal and processes signal values at pixel locations (x 0 , y 0 ), (x 0 −3, y 0 ), (x 0 +3, y 0 ), (x 0 , y 0 −3) and (x 0 , y 0 +3) of the second median filter output signal to provide a third median filter output signal;

a first summer that computes the difference between the image signal and the first median filter output signal to provide a first sub-band signal;

a second summer that computes the difference between the first median filter output signal and the second median filter output signal to provide a second sub-band signal; and

a third summer that computes the difference between the second median filter output signal and the third median filter output signal to provide a third sub-band signal.

9. A device that receives and processes an image signal for sub-band decomposition of an image, the device comprising:

a first median filter that receives the image signal and processes signal values of pixel locations (x 0 , y 0 ), (x 0 −A, y 0 −A), (x−A, y 0 +A), (x 0 +A, y 0 −A) and (x 0 +A, y 0 +A) of the image signal to provide a first median filter output signal;

a second median filter that receives the first median filter output signal and processes signal values at pixel locations (x 0 , y 0 ), (x 0 −B, y 0 −B), (x 0 −B, y 0 +B), (x 0 +B, y 0 −B) and (x 0 +B, y 0 +B) of the first median output signal to provide a second median filter output signal;

a third median filter that receives the second median filter output signal and processes signal values at pixel locations (x 0 , y 0 ), (x 0 −C, y 0 −C), (x 0 −C, y 0 +C), (x 0 +C, y 0 −C) and (x 0 +C, y 0 +C) of the second median filter output signal to provide a third median filter output signal, where A, B and C integers;

a first summer that computes the difference between the image signal and the first median filter output signal to provide a first sub-band signal;

a second summer that computes the difference between the first median filter output signal and the second median filter output signal to provide a second sub-band signal; and

a third summer that computes the difference between the second median filter output signal and the third median filter output signal to provide a third sub-band signal.

10. The device of claim 9 , wherein B is equal to (A+1) and C is equal to (A+2).

11. The device of claim 10 , comprising a summer that sums the first, second and third sub-band signals with the third median filter output signal to provide a filtered image signal.

12. The device of claim 11 , wherein the first deadband has a response such that when the input signal value has an amplitude less than x c then the first sub-band filtered signal is set equal to zero.

13. The device of claim 9 , where A is equal to one, B is equal to two and C is equal to three.

14. The device of claim 9 , comprising:

a first deadband that receives the first sub-band signal and provides a first sub-band filtered signal;

a second deadband that receives the second sub-band signal and provides a second sub-band filtered signal;

a third deadband that receives the third sub-band signal and provides a third sub-band filtered signal; and

a summer that sums the first, second and third sub-band filtered signals and the third median filter output signal to provide a filtered image signal.