Method and apparatus for performing a contrast based dynamic range management algorithm

• US 6,766,064 B1
• Filed: 03/10/2000
• Issued: 07/20/2004
• Est. Priority Date: 03/10/2000
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Langan, David Allen, Nevin, Robert Leland, Lienard, Jean, Hopple, Michael Robert
• Primary Examiner(s): Boudreau, Leo
• Assistant Examiner(s): Dang, Duy M.
• Application Number:
  US09/522,384
• Time in Patent Office: 1,593 Days
• Field of Search: 382/274, 382/272, 382/275, 382/266, 382/268, 382/260, 382/261, 382/232, 382/128, 382/132, 382/131, 382/282, 378/62, 378/98.7, 378/98.11, 378/98.12
• US Class Current: 382/274
• CPC Class Codes: G06T 2207/10116 X-ray image
• CPC Class Codes: G06T 5/94 based on local image properties, e.g. for local contrast enhancement

Abstract

A method and apparatus are provided for performing a contrast-based dynamic range management (C-DRM) algorithm. The apparatus comprises an C-DRM processor that performs the C-DRM algorithm of the invention in order to compress an image input to the C-DRM processor down to a desired gray scale range for observation on a display. The C-DRM processor decouples adjustment of image mean values (low frequency) and image contrast values (high frequency), and manages mean and contrast separately. The use of separate mean and contrast modification functions improve on other known compression techniques by providing a more deterministic behavior and reduced complexity, allowing, for example, independent management of negative and positive contrasts. The C-DRM processor can also automatically adapt to the dynamic range of an input image so that the input image thereby applying the minimal compression needed to display the image.

Claims

1. A method of compressing an intensity dynamic range of an input image to a reduced intensity dynamic range of an image display signal, comprising:

a) defining plural units of each frame of the input image, each input image unit having a corresponding intensity;

b) determining a local mean estimate of the intensity of each of the plural units of the input image;

c) processing each local mean estimate, separately and directly, in accordance with;

i) a mean modification function to produce a corresponding mean modification processing result, and

ii) a contrast function, comprising a contrast modification function, to produce a corresponding contrast modification processing result, wherein the contrast function further multiplies an output of the contrast modification function by a contrast estimate to produce the contrast modification processing result; and

d) combining the corresponding mean modification function result and contrast modification function result to produce, for each input image unit intensity, a respective output intensity, within the reduced intensity range, for a corresponding unit of the image display signal.

2. A method as recited in claim 1, wherein:

each input image unit corresponds to a pixel of the input image as detected by a digital detector.

3. A method as recited in claim 1, wherein:

each input image unit corresponds to a scan line of an analog image detector.

4. A method as recited in claim 1, wherein:

the processing of each input image unit intensity, separately and directly, further comprises multiplying the output of the contrast modification function by the mean modification function result and producing the multiplication product as a first combined, corresponding mean modification and contrast modification processing result; and

the combining step further comprises combining the combined, corresponding mean modification function processing result and contrast modification function processing result with the mean modification processing result to produce, for each input image unit intensity, the respective output intensity, within the reduced intensity range, for the corresponding unit of the image display signal.

5. A method as recited in claim 1, wherein the processing of each input image unit intensity, separately and directly, further comprises:

multiplying the mean modification function result by a negative complement of the contrast modification function and producing the multiplication product as a first combined, and corresponding, mean modification function and contrast modification function processing result; and

multiplying the contrast modification function by the mean modification function by an inverse of the local mean estimate and by the input image unit intensity and producing the multiplication product as a second combined, and corresponding, mean modification function and contrast modification function processing result; and

the combining step further comprises combining the first and second combined, and corresponding, mean modification function and contrast modification function processing results to produce, for each input image unit intensity, a respective output intensity, within the reduced intensity range, for the corresponding unit of the image display signal.

6. A method as recited in claim 1, further comprising:

determining a contrast estimate as a function of a ratio, of a difference between the intensity of a unit of the input image and the local mean estimate thereof to the local mean estimate;

determining a sign of the contrast estimate; and

controlling the processing of each local mean estimate by the contrast modification function by employing the sign of the contrast estimate to manage positive and negative contrasts separately.

7. A method as recited in claim 1, further comprising:

processing the local mean estimate by temporally filtering same and producing a resultant, modified local mean estimate having enhanced dynamic range continuity, substantially independent of rapid changes in the dynamic intensity range of the input image; and

controlling the processing of each local mean estimate, including the processing thereof by the mean and contrast modification functions, in accordance with the modified local mean estimate.

8. A method as recited in claim 7, further comprising:

processing each local mean estimate and the mean and contrast modification function processing results and the output intensity corresponding to each unit of the input image, as respective, multiple bit values; and

limiting the number of bits of the output intensity of the corresponding unit of the image display signal to a predetermined number of bits, consistent with display range capabilities of an available display device.

9. A method as recited in claim 8, further comprising:

performing the processing of each local mean estimate in accordance with the mean and contrast modification functions and the multiplication of the modification results of same for producing multiplication products, in accordance with accessing respective look-up tables from which are produced the corresponding multiplication products and wherein each of the local mean estimate, the mean modification function and the contrast modification function processing results and the respective multiplication products thereof constitute respective, multiple bit values.

10. A method as recited in claim 9, further comprising:

determining a sign value of the contrast estimate, as a respective, single bit value for each local mean estimate; and

combining the sign of a contrast estimate with the local mean estimate for accessing each of the look-up tables.

11. A method as recited in claim 9, further comprising:

determining a sign of the contrast estimate, as a respective, single bit value for each local mean estimate;

forming the local mean estimate as an unsigned number of bits;

combining the sign of the contrast estimate with the unsigned number of bits representing the local mean estimate for accessing a first look-up table performing the contrast modification function; and

accessing a second look-up table performing the mean modification function using the unsigned number of bits representing the local mean estimate.

12. An apparatus compressing an intensity dynamic range of an input image to a reduced intensity dynamic range of an image display signal, each frame of the input image comprising plural units, the apparatus comprising:

a filter determining a local mean estimate of the intensity of each of the plural units of the input image;

a computer processing each local mean estimate, separately and directly, in accordance with;

a mean modification function to produce a corresponding mean modification processing result, and

a contrast function, comprising a contrast modification function, to produce a corresponding contrast modification processing result; and

the computer further comprising multiplying an output of the contrast modification function by a contrast estimate to produce the contrast modification processing result; and

the computer combining the corresponding mean modification function and contrast modification procession function results to produce, for each input image unit intensity, a respective output intensity, within the reduced intensity range, for a corresponding unit of the image display signal.

13. An apparatus as recited in claim 12, further comprising:

a digital image detector, each input image unit corresponding to a pixel of the input image as detected by the digital detector.

14. An apparatus as recited in claim 12, further comprising:

an analog image detector, each input image unit corresponding to a scan line of the input image as detected by the analog image detector.

15. An apparatus as recited in claim 12, wherein the processing of each, separately and directly, by the computer further comprises:

multiplying the output of the contrast modification function by the mean modification function result and producing the multiplication product as a first combined, corresponding mean modification and contrast modification processing result; and

combining the combined, corresponding mean modification function processing result and contrast modification function processing result with the mean modification processing result to produce, for each input image unit intensity, the respective output intensity, within the reduced intensity range, for the corresponding unit of the image display signal.

16. An apparatus as recited in claim 12, wherein the processing of each input image unit intensity, separately and directly, by the computer further comprises:

multiplying the mean modification function result by a negative complement of the contrast modification function and producing the multiplication product as a first combined, and corresponding, mean modification function and contrast modification function processing result;

multiplying the contrast modification function by the mean modification function and by an inverse of the local mean estimate and by the input image unit intensity and producing the multiplication product as a second combined, and corresponding, mean modification function and contrast modification function processing result; and

combining the first and second combined, and corresponding, mean modification function and contrast modification function processing results to produce, for each input image unit, a respective output intensity, within the reduced intensity range, for the corresponding unit of the image display signal.

17. An apparatus as recited in claim 12, wherein the processing by the computer further comprises:

determining a contrast estimate as a function of a ratio, of a difference between the intensity of a unit of the input image and the local mean estimate thereof to the local mean estimate;

determining a sign of the contrast estimate; and

controlling the processing of each local mean estimate by the contrast modification function by employing the sign of the contrast estimate to manage positive and negative contrasts separately.

18. An apparatus as recited in claim 12, wherein the processing by the computer further comprises:

processing the local mean estimate by temporally filtering same and producing a resultant, modified local mean estimate having enhanced dynamic range continuity, substantially independent of rapid changes in the dynamic intensity range of the input image; and

controlling the processing of each local mean estimate, including the processing thereof by the mean and contrast modification functions, in accordance with the modified local mean estimate.

19. An apparatus as recited in claim 18, wherein the processing by the computer further comprises:

processing each local mean estimate and the mean and contrast modification function processing results and the output intensity corresponding to each unit of the input image, as respective, multiple bit values; and

limiting the number of bits of the output intensity of the corresponding unit of the image display signal to a predetermined number of bits, consistent with display range capabilities of an available display device.

20. An apparatus as recited in claim 19, wherein the processing by the computer further comprises:

performing the processing of each local mean estimate in accordance with the mean and contrast modification functions and the multiplication of the modification results of same for producing multiplication products, in accordance with accessing respective look-up tables from which are produced the corresponding multiplication products and wherein each of the local mean estimate, the mean modification function and the contrast modification function processing results and the respective multiplication products thereof constitute respective, multiple bit values.

21. An apparatus as recited in claim 20, where the processing by the computer further comprises:

determining a sign value of the contrast estimate, as a respective, single bit value for each local mean estimate; and

combining the sign of a contrast estimate with the local mean estimate for accessing each of the look-up tables.

22. An apparatus as recited in claim 20, where the processing by the computer further comprises:

determining a sign of the contrast estimate, as a respective, single bit value for each local mean estimate;

forming the local mean estimate as an unsigned number of bits;

combining the sign of the contrast estimate with the unsigned number of bits representing the local mean estimate for accessing a first look-up table performing the contrast modification function; and

accessing a second look-up table performing the mean modification function using the unsigned number of bits representing the local mean estimate.

23. A method of compressing an intensity dynamic range of an input image to a reduced intensity dynamic range of an image display signal, comprising:

a) defining plural units of each frame of the input image, each input image unit having a corresponding intensity;

b) determining a local mean estimate of the intensity of each of the plural units of the input image;

c) processing each local mean estimate, separately and directly, in accordance with;

Y=M_Y(1+C_Y), where;

M_Y=F_M(M_X),

C_Y=F_C(M_X)*C_X, and

X_C=(X−

M_X)/M_X

X=input intensity

M_X=local mean estimate

C_X=contrast estimate

F_M( )=mean modification function

F_C( )=contrast modification function

Y=C-DRM output intensity

M_Y=modified local mean

C_Y=modified contrast; and

d) combining the corresponding mean modification function result and contrast modification function result to produce, for each input image unit intensity, a respective output intensity, within the reduced intensity range, for a corresponding unit of the image display signal.

24. A method as recited in claim 23, wherein:

the mean modification function achieves either a linear or a non-linear transformation of the mean component of the image; and

the contrast modification function applies a linear gain to the input contrast to the construct the output contrast.

25. A method as recited in claim 23, in which the input intensity value (X) of an input pixel is processed by a moving average function to produce the local mean estimate (M_X).

26. A method as recited in claim 23, wherein first and second look-up tables respectively perform the contrast modification function and the mean modification function respectively of the equations for determining C_Y and C_X.

27. A method as recited in claim 23, wherein the mean modification function transforms the mean from being linearly related to X-ray counts to being linearly related to an equivalent water thickness represented by the X-ray counts.

28. A method as recited in claim 23, wherein the contrast modification function C_Y is implemented in compliance with a requirement that F_C is monotonically increased in accordance with:

29. A method as recited in claim 23, further comprising:

processing of the equations for determining Y, M_Y, C_Y and C_X to produce the output intensity (Y) in accordance with;

$Y=\mathrm{CyMy}+\mathrm{My},\mathrm{where}<br><br>\text{;<br><br>}$$\mathrm{Cy}=\mathrm{fcCx}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{and}$$\mathrm{fc}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\mathrm{Mx}\right)=\mathrm{fc}$$Y=\mathrm{fcCxMy}+\mathrm{My},\mathrm{where}<br><br>\text{;<br><br>}$$\mathrm{cx}=\frac{x-\mathrm{Mx}}{\mathrm{Mx}}$$Y=\mathrm{fc}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(x-\mathrm{Mx}\right)<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\mathrm{My}/\mathrm{Mx}\right)+\mathrm{My}$$Y=X<br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{\mathrm{fcMy}}{\mathrm{Mx}}<br><br>\left[x-\mathrm{Mx}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(1-\frac{1}{\mathrm{fc}}\right)\right]$$Y=X<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\frac{\mathrm{fxMy}}{\mathrm{Mx}}\right)-\mathrm{Mx}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\frac{\mathrm{fcMy}}{\mathrm{Mx}}\right)<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(1-\frac{1}{\mathrm{fc}}\right)$$\mathrm{My}=\mathrm{fm}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\mathrm{Mx}\right)=\mathrm{fm}$$Y=X<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\frac{\mathrm{fcfm}}{\mathrm{Mx}}\right)-\mathrm{Mx}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\frac{\mathrm{fcfm}}{\mathrm{My}}\right)<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(1-\frac{1}{\mathrm{fc}}\right)$$Y=X<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\frac{\mathrm{fcfm}}{\mathrm{Mx}}\right)-\mathrm{Mx}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\frac{\mathrm{fcfm}}{\mathrm{My}}-\frac{\mathrm{fcfm}}{\mathrm{fcMx}}\right)$$Y=X<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\frac{\mathrm{fcfm}}{\mathrm{Mx}}\right)-\mathrm{Fm}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\mathrm{fc}-1\right)$$Y=X<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\frac{\mathrm{fcfm}}{\mathrm{Mx}}\right)+\mathrm{fm}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(1-\mathrm{fc}\right)$

the contrast modification function processing is performed in a first look-up table which computes;

30. A method as recited in claim 29, wherein the desired number of bits is eight bits.

31. A method as recited in claim 23 further comprising processing the equations for determining Y, M_Y, C_Y and C_X to produce the output intensity (Y) in accordance with:

32. A method as recited in claim 31, wherein the desired number of bits is eight bits.

33. An apparatus compressing an intensity dynamic range of an input image to a reduced intensity dynamic range of an image display signal, each frame of the input image comprising plural units, the apparatus comprising:

a filter determining a local mean estimate of the intensity of each of the plural units of the input image;

a computer processing each local mean estimate, separately and directly, in accordance with;

Y=M_Y(1+C_Y), where;

M_Y=F_M(M_X),

C_Y=F_C(M_X)*C_X, and

C_X=(X−

M_X)/M_X

X=input intensity

M_X=local mean estimate

C_X=contrast estimate

F_M( )=mean modification function

F_C( )=contrast modification function

Y=C-DRM output intensity

M_Y=modified local mean

C_Y=modified contrast; and

the computer combining the corresponding mean modification function result and contrast modification function result to produce, for each input image unit intensity, a respective output intensity, within the reduced intensity range, for a corresponding unit of the image display signal.

34. An apparatus as recited in claim 33, wherein:

the mean modification function achieves either a linear or a non-linear transformation of the mean component of the image; and

the contrast modification function applies a linear gain to the input contrast to the construct the output contrast.

35. An apparatus as recited in claim 33, in which the input intensity value (X) of an input pixel is processed by a moving average function to produce the local mean estimate (M_X).

36. An apparatus as recited in claim 33, wherein first and second look-up tables respectively perform the contrast modification function and the mean modification function respectively of the equations for determining C_Y and C_X.

37. An apparatus as recited in claim 33, wherein the mean modification function transforms the mean from being linearly related to X-ray counts to being linearly related to an equivalent water thickness represented by the X-ray counts.

38. An apparatus as recited in claim 33, wherein the contrast modification function C_Y is implemented in compliance with a requirement that F_C is monotonically increased in accordance with: