Lung contrast normalization on direct digital and digitized chest images for computer-aided detection (CAD) of early-stage lung cancer

1 . A method of processing x-ray images in digital form, the method comprising:

inputting an x-ray image in digital form;

determining a first normalization factor, N, based on a pixel size of the input x-ray image;

determining a second normalization factor, K, based on one or more pixel values of the input x-ray image;

performing normalization on the input x-ray image by applying the normalization factors, K and N, to the pixels of the input x-ray image; and

outputting a normalized digital x-ray image.

2 . The method according to claim 1 , wherein said determining a normalization factor, N, comprises:

determining an input pixel size of the pixels of the input x-ray image; and

dividing a target pixel size by the input pixel size to determine the normalization factor, N;

and wherein said performing normalization comprises adjusting a resolution of the input x-ray image according to the normalization factor, N, to obtain an adjusted-resolution x-ray image.

3 . The method according to claim 2 , wherein said adjusting the resolution comprises:

considering N×N blocks of pixels in the input x-ray image;

for each N×N block of pixels, computing an average value of the pixel values in the block; and

defining an adjusted-resolution pixel value for the block to have the average value.

4 . The method according to claim 2 , wherein said determining a second normalization factor, K, comprises:

finding a maximum pixel value over the adjusted-resolution x-ray image;

finding a minimum pixel value over the adjusted-resolution x-ray image; and

computing said second normalization factor, K, based on the maximum and minimum pixel values.

5 . The method according to claim 4 , wherein said computing the second normalization factor, K, comprises:

computing a difference between the maximum and minimum pixel values and adding one to the difference to determine a numerator; and

dividing the numerator by a desired total number of possible pixel values.

6 . The method according to claim 4 , wherein each pixel value comprises a gray-scale value.

7 . The method according to claim 4 , further comprising:

subtracting from each pixel value of the adjusted-resolution x-ray image the minimum pixel value to determine a difference; and

dividing the difference by the second normalization factor, K, to obtain a normalized pixel value.

8 . The method according to claim 1 , wherein said determining a second normalization factor, K, comprises:

finding a maximum pixel value over the input x-ray image;

finding a minimum pixel value over the input x-ray image; and

computing the second normalization factor, K, based on the maximum and minimum pixel values.

9 . The method according to claim 8 , wherein said computing the second normalization factor, K, comprises:

computing a difference between the maximum and minimum pixel values and adding one to the difference to determine a numerator; and

dividing the numerator by a desired total number of possible pixel values.

10 . The method according to claim 8 , wherein each pixel value comprises a gray-scale value.

11 . The method according to claim 8 , wherein said performing normalization comprises:

subtracting from each pixel value of the input x-ray image the minimum pixel value to determine a difference; and

dividing the difference by the second normalization factor, K, to obtain a normalized pixel value.

12 . A computer-readable medium containing software implementing the method according to claim 1 .

13 . A computer system comprising:

a processor; and

the computer-readable medium according to claim 12 .

14 . The computer system according to claim 13 , further comprising means for receiving x-ray images in digital form.

15 . The computer system according to claim 13 , further comprising means for displaying the normalized digital x-ray image.