Method and system for enhancement of a digitized image

• US 4,941,190 A
• Filed: 07/15/1988
• Issued: 07/10/1990
• Est. Priority Date: 07/15/1988
• Status: Expired due to Term

• Current Assignee: Eastman Kodak Company
• Original Assignee: 3M Company
• Inventors: Joyce, Terrence H.
• Primary Examiner(s): Boudreau, Leo H.
• Assistant Examiner(s): COUSO, YON JUNG
• Application Number:
  US07/219,377
• Time in Patent Office: 725 Days
• Field of Search: 382/54, 382/27, 382/50, 382/41, 382/52, 382/22, 358/166, 358/167, 358/160, 358/284, 358/36, 358/447, 358/463, 358/464
• US Class Current: 382/264
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/75 Unsharp masking

Abstract

A system and method of modifying pixels supplied to the system that a multiple level signals for a digitized image wherein a moving pixel window with a center pixel, D_c, is used from which the annular means, m_a, of the center pixel (the mean of the 2^N pixel values of the window surrounding the center pixel, where N is an integer of 1 or more) is determined with the center pixel and selected pixels surrounding the center pixel, D_c, are used to determine a measure of deviation (center deviation, σ_c) of the center pixel relative to the center pixel that is used to obtain a modification gain, f(σ_c,C_g). The center pixel, D_c, its annular mean, m_a, and its modification gain, f(σ_c,C_g) or F'"'"'(σ_c,C_g) are used to obtain a modified center pixel value, D_c 40 , in accordance with one of the following equations that are of the form for an algorithm for determining the unsharp marking filter value for an image pixel:

D.sub.c '"'"'=[f(σ.sub.c,C.sub.g)×(D.sub.c -m.sub.a)]+m.sub.a ; or

##EQU1## where N is an integer of 0 or greater.

Claims

1. A system for modifying pixels supplied to the system that are multiple level signals for a digitized image including:

means providing a moving pixel window from pixels supplied to the system, said pixel window having a center pixel, D_c and at least 2^N pixels surrounding said center pixel, where N is an integer of 1 or more;

means receiving 2^N pixels of said pixels surrounding said center pixel for providing the annular mean, m_a, of said received 2^N pixels;

means receiving said center pixel and selected for providing an output based on the center deviation σ

_c, for said center pixel; and

means connected to said output for obtaining a modification gain, f(σ

_c, C_g); and

means receiving said center pixel, D_c, said annular means, m_a, and said modification gain, f(σ

_c,C_g) for providing a modified center pixel, D_c '"'"', in accordance with the following equation;

space="preserve" listing-type="equation">D.sub.c '"'"'=[f(σ

.sub.c, C.sub.g)×

(D.sub.c -m.sub.a)]+m.sub.a.

2. A system according with claim 1 wherein said means connected to said output is a memory containing modification gain look-up tables.

3. A system according to claim 1 wherein said output based on the center deviation is equal to the center deviation divided by the number of selected pixels.

4. A system according to claim 1 further including:

a background detection circuit portion receiving said annular mean for providing an output that is a measure of the background for said modified center pixel;

means connected to said output of said background detection circuit portion for obtaining a threshold value; and

a comparator receiving said threshold value at one input of said comparator and said modified center pixel at a second input of said comparator for which a measure of its background is provided by said background detection circuit, said comparator providing one output signal when said modified center pixel at said second input exceeds or is equal to said threshold value at said one input and providing a different output signal when said modified center pixel is less than said threshold value.

5. A system according to claim 4 wherein said means for obtaining a threshold value is a memory containing threshold value look-up tables.

6. A system according to claim 1 further including:

a memory containing look-up tables of half tone values; and

a comparator for receiving a half tone value from said memory at one input of said comparator and said modified center pixel at a second input of said comparator, said comparator providing one output signal when said modified center pixel at said input exceeds or is equal to said half tone value at said one input and providing a different output signal when said modified center pixel is less than said half tone value at said one input.

7. A system for modifying pixels supplied to the system that are multiple level signals for a digitized image including:

means providing a moving pixel window from pixels supplied to the system, said pixel window having a center pixel, D_c, and at least 2^N pixels surrounding said center pixel, wherein N is an integer of 1 or more;

means receiving 2^N of said pixels surrounding said center pixel for providing the annular mean, m_a, of said received 2^N pixels, said annular means being the single result obtained by repeating a process of addition of two sets of values and the division by two of each such additions, such process beginning with the addition of the values of each set of two pixels of said 2ⁿ pixels;

means receiving said center pixel, D_c, and selected pixels of said pixel window surrounding said center pixel for providing a modification gain, g, and receiving said annular means, m_a, for providing a modified center pixel, D_c '"'"', in accordance with the following equation;

space="preserve" listing-type="equation">D.sub.c '"'"'=]g×

(D.sub.c -m.sub.a)]+m.sub.a.

8. A system according to claim 7 further including:

a background detection circuit portion receiving said annular mean for providing an output that is a measure of the background for said modified center pixel;

means connected to said output of said background detection circuit portion for obtaining a threshold value;

a comparator receiving said threshold value at one input of said comparator and said modified center pixel at a second input of said comparator for which a measure of its background is provided by said background detection circuit, said comparator providing one output signal when said modified center pixel at said second input exceeds or is equal to said threshold value at said one input and providing a different output signal when said modified center pixel is less than said threshold value.

9. A system according to claim 8 wherein said means for obtaining a threshold value is a memory containing threshold value look-up tables.

10. A system according to claim 7 further including:

a memory containing look-up tables of half tone values; and

a comparator for receiving a half tone value from said memory at one input of said comparator and said modified center pixel at a second input of said comparator, said comparator providing one output signal when said modified center pixel at said input exceeds or is equal to said half tone value at said one input and providing a different output signal when said modified center pixel is less than said half tone values at said one input.

11. A method for modifying pixels that are multiple level signals for a digitized image including the steps of:

(a) establishing a moving pixel window from the pixels wherein said pixel window has a center pixel, D_c and at least 2^N pixels surrounding said center pixel, where N is an integer of 1 or more;

(b) determining the annular mean, m_a, of 2^N pixels of said pixels surrounding said center pixel for each established pixel window;

(c) determining the center deviation for the center pixel of each established pixel window using selected pixels of the pixel window surrounding the center pixel;

(d) establishing a modification gain, f(σ

_c,C_g), for each center pixel based on the center deviation; and

(e) processing the annular mean, m_a, the center pixel, D_c, and the modification gain, f(σ

_c, C_g), to produce a modified center pixel, Dc'"'"', in accordance with the following equation;

space="preserve" listing-type="equation">D.sub.c '"'"'=[F(σ

.sub.c,C.sub.g)×

(D.sub.c -m.sub.a)]+m.sub.a.

12. A method for modifying pixels that are multiple level signals for a digitized image according to claim 11 wherein the step of establishing a modification gain, f(σ

_c,C_g), includes providing a memory containing modification gain look-up tables and using said center deviation for addressing said memory to establish said modification gain.

13. A method for modifying pixels that are multiple level signals for a digitized image according to claim 11 wherein the step of establishing a modification gain, f(σ

_c, C_g), based on the center deviation includes division of the center deviation by number of selected pixels used to determine the center deviation and using the result for establishing said modification gain.

14. A method for modifying pixels that are multiple level signals for a digitized image according to claim 11 including the additional steps of

(f) using the annular mean, m_a, to provide a measure of the background for said modified center pixel;

(g) establishing a threshold value based on the said measure of the background;

(h) comparing said threshold value with said modified pixel and providing one signal if said modified pixel is greater or equal to the threshold value and providing a different signal if said modified pixel is less than said threshold value.

15. A method of modifying pixels that are multiple level signals for a digitized image according to claim 14 wherein step (g) includes providing a memory containing threshold value look-up tables and using said measure of the background for addressing said memory to establish said threshold value.

16. A method for modifying pixels that are multiple level signals for a digitized image according to claim 11 including the additional steps of

(f) providing a memory containing look-up tables of half tone values;

and

(g) comparing a half tone value obtained from said memory and providing one signal if said modified pixel is greater or equal to said half tone value and providing a different signal if said modified pixel is less than said half tone value.

17. A system for modifying pixels supplied to the system that are multiple level signals for a digitized image including:

means providing a moving pixel window from pixels supplied to the system, said pixel window having a center pixel, D_c nd at least 2^N pixels surrounding said center pixel, where N is an integer of 1 or more;

means receiving 2^N pixels of said pixels surrounding said center pixel for providing the annular mean, m_a, of said received 2^N pixels;

means receiving said center pixel and selected pixels of said pixel windows surrounding said center pixel for providing an output based on the center deviation σ

_c, for said center pixel; and

connected to said output for obtaining a modification gain, f'"'"'(σ

_c,C_g); and

means receiving said center pixel, D_c, sa1d annular means, m_a, and said modification gain, f(σ

_c,C_g 0 for providing a modified center pixel, D_c '"'"', in accordance with the following equation;

##EQU6## where N is an integer of 0 or more.

18. A system according to claim 17 wherein said means connected to said output is a memory containing modification gain look-up tables.

19. A system according to claim 17 further including:

a background detection circuit portion receiving said annular mean for providing an output that is a measure of the background for said modified center pixel;

means connected to said output of said background detection circuit portion for obtaining a threshold value; and

a comparator receiving said threshold value at one input of said comparator and said modified center pixel at a second input of said comparator for which a measure of its background is provided by said background detection circuit, said comparator providing one output signal when said modified center pixel at said second input exceeds or is equal to said threshold value at said one input and providing a different output signal when said modified center pixel is less than said threshold value.

20. A system according to claim 19 wherein said means for obtaining a threshold value is a memory containing threshold value look-up tables.

21. A system according to claim 17 further including:

a memory containing look-up tables of half tone values; and

a comparator for receiving a half tone value from said memory at one input of said comparator and said modified center pixel at a second input of said comparator, said comparator providing one output signal when said modified center pixel at said input exceeds or is equal to said half tone value at said one input and providing a different output signal when said modified center pixel is less than said half tone value at said one input.

22. A method for modifying pixels that are multiple level signals for a digitized image including the steps of:

(a) establishing a moving pixel window from the pixels wherein said pixel window has a center pixel, D_c and at least 2^N pixels surrounding said center pixel, where N is an integer of 1 or more;

(b) determining the annular mean, m_a, of 2^N pixels of said pixels surrounding said center pixel for each established pixel window;

(c) determining the center deviation for the center pixel of each established pixel windows using selected pixels of the pixel window surrounding the center pixel;

(d) establishing a modification gain, f'"'"'(σ

_c,C_g), for each center pixel based on the center deviation; and

(e) processing the annular means, m_a, the center pixel, _c, and the modification gain, f'"'"'(σ

_c,C_g) to produce a modified center pixel, D_c '"'"', in accordance with the following equation;

##EQU7## where N is an integer of 0 or greater.

23. A method for modifying pixels that are multiple level signals for a digitized image according to claim 22 wherein the step of establishing a modification gain, f'"'"'(σ

_c,C_g) includes providing a memory containing modification gain look-up tables and using said center deviation for addressing said memory to establish said modification gain.

24. A method for modifying pixels that are multiple level signals for a digitized image according to claim 22 including the additional steps of

(f) using the annular mean, m_a, to provide a measure of the background for said modified center pixel;

(g) establishing a threshold value based on the said measure of the background;

(h) comparing said threshold value with said modified pixel and providing one signal if said modified pixel is greater or equal to the threshold value and providing a different signal if said modified pixel is less than said threshold value.

25. A method of modifying pixels that are multiple level signals for a digitized image according to claim 24 wherein step (g) includes providing a memory containing threshold value look-up tables and using said measure of the background for addressing said memory to establish said threshold value.

26. A method for modifying pixels that are multiple level signals for a digitized image according to claim 22 including the additional steps of

(f) providing a memory containing look-up table of half tone values;

and

(g) comparing a half tone value obtained from said memory and providing one signal if said modified pixel is greater or equal to said half tone value and providing a different signal if said modified pixel is less than said half tone value.

27. A method for modifying pixels that are multiple level signals for a digitized image including the steps of:

(a) establishing a moving pixel window from the pixels wherein said pixel window has a center pixel, D_c and at least 2^N pixels surrounding said center pixel, where N is an integer of 1 or more;

(b) determining the annular means, m_a, of 2ⁿ pixels of said pixels surrounding said center pixel for each established pixel window by repeating a process of addition of two sets of values and the division by two of each such additions, such process beginning with the addition of the values of each set of two pixels of said 2^N pixels to create a single result which is said annular means;

(c) establishing a modification gain, g, from the center pixel, D_c, and selected pixels of said window surrounding said center pixel;

(d) processing the annular mean, m_a, the center pixel D_c, and the modification gain, g, to produce a modified center pixel, D_c '"'"', in accordance with the following equation;

space="preserve" listing-type="equation">Dc, =[g×

(D.sub.c -m.sub.a)]=m.sub.a.

28. A method for modifying pixels that are multiple level signals for a digitized image according to claim 27 including the additional steps of

(e) using the annular mean, m_a, to provide a measure of the background for said modified center pixel;

(f) establishing a threshold value based on the said measure of the background;

(g) comparing said threshold value with said modified pixel and providing one signal if said modified pixel is greater or equal to the threshold value and providing a different signal if said modified pixel is less than said threshold value.

29. A method of modifying pixels that are multiple level signals for a digitized image according to claim 28 wherein step (f) includes providing a memory containing threshold value look-up tables and using said measure of the background for addressing said memory to establish said threshold value.

30. A method for modifying pixels that are multiple level signals for a digitized image according to claim 27 including the additional steps of

(f) providing a memory containing look-up tables of half tone values;

and

(g) comparing a half tone value obtained from said memory and providing one signal if said modified pixel is greater or equal to said half tone value and providing a different signal if said modified pixel is less than said half tone value.

31. A background detection circuit for a system for modifying pixels supplied to the system that are multiple level signals for a digitized image wherein the system has means providing a moving pixel window from pixels supplied to the system, with the pixel Window having a center pixel, D_c, and at least 2^N pixels surrounding the center pixel, when N is an integer of 1 or more plus means receiving 2^N pixels of said pixels surrounding the center pixel for providing the annular mean, m_a, of the received 2ⁿ pixels, the background detection circuit including:

means accessing the annular mean for a number of non-overlapping pixel windows preceding a center pixel, D_c, and for a number of non-overlapping pixel windows following said center pixel, D_c, and

means for determining the average of the annular means accessed by said last-mentioned means, said average providing a measure of the background of the center pixel, D_c.