Apparatus and method for smoothing regions and enhancing edges in gray scale images

• US 5,271,064 A
• Filed: 06/14/1991
• Issued: 12/14/1993
• Est. Priority Date: 06/14/1991
• Status: Expired due to Fees

• Current Assignee: University of Cincinnati
• Original Assignee: University of Cincinnati
• Inventors: Dhawan, Atam P., Dufresne, Thomas E.
• Primary Examiner(s): Moore, David K.
• Application Number:
  US07/715,455
• Time in Patent Office: 914 Days
• Field of Search: 382/6, 382/22, 382/27, 382/49, 382/54
• US Class Current: 382/266
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06V 10/20 Image preprocessing
• CPC Class Codes: G06V 30/10 Character recognition

Abstract

An apparatus and method for enhancing image data elements used to form a gray scale image are disclosed. The apparatus includes an adaptive neighborhood mask that is applied to a group of data image elements centered about a selected pixel to segregate the elements into center and surround regions about the selected element or pixel. The mask further modifies the elements with weighting factors to derive a contrast vector for the selected data elements in the adaptive neighborhood. This vector is compared to a smoothing window and a pair of edge enhancement windows to determine whether the selected element requires smoothing or enhancement to more clearly define a surface or an edge, respectively. If the element requires smoothing or enhancing, its gray scale value is modified, otherwise it is not modified. The device performs this task for each data element. The enhanced data is analyzed to determine if further enhancement is possible and, if so, the process continues upon the adjusted data until the enhancement of the image data is maximized. An edge area selector may further enhance the image data elements by selecting a small group of elements at the unterminated end of a detected edge in the enhance image. The selected group is enhanced by adjusting the edge enhancement window or by changing the weighting factors and restoring the gray scale values of the selected group to their unenhanced values.

Claims

1. A device for enhancing a plurality of image data elements stored in an image array, each of said data elements having a gray scale value, said device comprising:

means for selecting one of the plurality of image data elements stored in the image array;

means for retrieving a group of image data elements from an area about and including said selected data element, said area being defined by an adaptive neighborhood mask, said adaptive neighborhood mask having a plurality of weighting factors, each one of said weighting factors corresponding to one of said data elements in said area;

means for summing the product of said selected data element and said one weighting factor corresponding with said selected data element and the product of one of said retrieved data elements and said one weighting factor corresponding with said selected retrieved data element to form a contrast link;

means for summing all said contrast link to form a contrast vector;

means for adjusting the gray scale value of said selected data element by

     1) adding a predetermined quantum to the gray scale value of said selected data element when a) said contrast vector is greater than zero and within said edge enhancement window and b) said contrast vector is less than zero and within said smoothing window and

     2) by subtracting said predetermined quantum from said selected data element when c) said contrast vector is less than zero and within said enhancement window and d) said contrast vector is greater than zero and within said smoothing window;

means for measuring the enhancement of the gray scale values of said adjusted data elements in said array after each of said data elements in the image array have been selected by said selecting means, said measuring means generating a signal indicative that the enhancement of said adjusted data elements is maximized; and

means for transferring said adjusted data elements to a display generator in response to said signal from said measuring means whereby the image produced by the display generator is enhanced.

2. The device of claim 1 wherein said quantum is one gray scale level.

3. A device for enhancing a plurality of image data elements stored in an image array, each of said data elements having a gray scale value, said device comprising:

means for selecting one of the plurality of image data elements stored in the image array;

means for retrieving a group of image data elements from an area about and including said selected data element, said area being defined by an adaptive neighborhood mask, said adaptive neighborhood mask having a plurality of weighting factors, each one of said weighting factors corresponding to one of said data elements in said area;

means for summing the product of said selected data element and said one weighting factor corresponding with said selected data element and the product of one of said retrieved data elements and said one weighting factor corresponding with said selected retrieved data element to form a contrast link;

means for summing all said contrast link to form a contrast vector;

means for adjusting the gray scale value of said selected data element when said contrast vector is within one of an edge enhancement window and a smoothing window;

means for detecting edges and a propagation direction associated with said detected edge from contrast vectors formed for each of the data elements in the image array;

means for selecting a group of data elements proximate an unterminated end of said detected edge;

means for modifying said edge enhancement window with respect to said smoothing window;

means for enabling said contrast link forming means, said contrast vector forming means and said gray scale value adjusting means for said selected group of data elements;

means for measuring the enhancement of the gray scale values of said adjusted data elements in said array after each of said data elements in the image array have been selected by said selecting means, said measuring means generating a signal indicative that the enhancement of said adjusted data elements is maximized; and

means for transferring said adjusted data elements to a display generator in response to said signal from said measuring means whereby the image produced by the display generator is enhanced.

4. A device for enhancing a plurality of image data elements stored in an image array, each of said data elements having a gray scale value, said device comprising:

means for selecting one of the plurality of image data elements stored in the image array;

means for retrieving a group of image data elements from an area about and including said selected data element, said area being defined by an adaptive neighborhood mask, said adaptive neighborhood mask having a plurality of weighting factors, each one of said weighting factors corresponding to one of said data elements in said area;

means for summing the product of said selected data element and said one weighting factor corresponding with said selected data element and the product of one of said retrieved data elements and said one weighting factor corresponding with said selected retrieved data element to form a contrast link;

means for summing all said contrast link to form a contrast vector;

means for adjusting the gray scale value of said selected data element when said contrast vector is within one of an edge enhancement window and a smoothing window;

means for detecting edges and a propagation direction associated with said detected edge from contrast vectors formed for each of the data elements in the image array;

means for selecting a group of data elements proximate an unterminated end of said detected edge;

means for replacing said adjusted data elements with said unadjusted data elements corresponding to said adjusted elements;

means for changing said weighting factors to a second set of weighting factors corresponding to a second neighborhood adaptive mask;

means for enabling said contrast link forming means, said contrast vector forming means ad said gray scale value adjusting means for said selected group of data elements;

means for measuring the enhancement of the gray scale values of said adjusted data elements in said array after each of said data elements in the image array have been selected by said selecting means, said measuring means generating a signal indicative that the enhancement of said adjusted data elements is maximized; and

means for transferring said adjusted data elements to a display generator in response to said signal from said measuring means whereby the image produced by the display generator is enhanced.

5. A method for enhancing a plurality of image data elements stored in an image array, each of said data elements having a gray scale value, said method comprising:

selecting one of the plurality of image data elements stored in the image array;

retrieving a group of image data elements from an area about and including said selected data element, said area being defined by an adaptive neighborhood mask, said adaptive neighborhood mask having a plurality of weighting factors, each one of said weighting factors corresponding to one of said data elements in said area;

summing the product of said selected data element and said one weighting factor corresponding with said selected data element and the product of one of said retrieved data elements and said one weighting factor corresponding with said selected retrieved data element to form a contrast link;

summing all said contrast link to form a contrast vector;

adding a predetermined quantum to the gray scale value of said selected data element when a) said contrast vector is greater than zero and within said edge enhancement window and b) said contrast vector is less than zero and within said smoothing window;

subtracting said predetermined quantum from said selected data element when c) said contrast vector is less than zero and within said edge enhancement window and d) said contrast vector is greater than zero and within said smoothing window;

measuring the enhancement of the gray scale values of said adjusted data elements in said array after each of said data elements in the image array have been selected by said selecting means, said measuring means generating a signal indicative that the enhancement of said adjusted data elements is maximized; and

means for transferring said adjusted data elements to a display generator in response to said signal from said measuring means whereby the image produced by the display generator is enhanced.

6. A method for enhancing a plurality of image data elements stored in an image array, each of said data elements having a gray scale value, said method comprising:

selecting one of the plurality of image data elements stored in the image array;

retrieving a group of image data elements from an area about and including said selected data element, said area being defined by an adaptive neighborhood mask, said adaptive neighborhood mask having a plurality of weighting factors, each one of said weighting factors corresponding to one of said data elements in said area;

summing the product of said selected data element and said one weighting factor corresponding with said selected data element and the product of one of said retrieved data elements and said one weighting factor corresponding with said selected retrieved data element to form a contrast link;

summing all said contrast link to form a contrast vector;

detecting edges and a propagation direction associated with said detected edge from said contrast vectors formed for each of the data elements in the image array;

selecting a group of data elements proximate an unterminated end of said detected edge;

modifying said edge enhancement window with respect to said smoothing window;

performing said contrast link forming step, said contrast vector forming vector step and said gray scale value adjusting step for said selected group of data elements only;

measuring the enhancement of the gray scale values of said adjusted data elements in said array after each of said data elements in the image array have been selected by said selecting means, said measuring means generating a signal indicative that the enhancement of said adjusted data elements is maximized; and

means for transferring said adjusted data elements to a display generator in response to said signal from said measuring means whereby the image produced by the display generator is enhanced.

7. A device for enhancing a plurality of image data elements stored in an image array, each of said data elements having a gray scale value, said device comprising:

means for selecting one of the plurality of image data elements stored in the image array;

means for retrieving a group of image data elements from an area about and including said selected data element, said area being defined by an adaptive neighborhood mask, said adaptive neighborhood mask having a plurality of weighting factors, each one of said weighting factors corresponding to one of said data elements in said area;

means for summing the product of said selected data element and said one weighting factor corresponding with said selected data element and the product of one of said retrieved data elements and said one weighting factor corresponding with said selected retrieved data element to form a contrast link;

means for summing all said contrast link to form a contrast vector;

means for adjusting the gray scale value of said selected data element when said contrast vector is within one of an edge enhancement window and a smoothing window;

detecting edges and a propagation direction associated with said detected edge from contrast vectors formed for each of the data elements in the image array;

selecting a group of data elements proximate an unterminated end of said detected edge;

for replacing said adjusted data elements with said unadjusted data elements corresponding to said adjusted elements;

changing said weighting factors to a second set of weighting factors corresponding to a second neighborhood adaptive mask;

enabling said contrast link forming step, said contrast vector forming step and said gray scale value adjusting step for said selected group of data elements only;

means for measuring the enhancement of the gray scale values of said adjusted data elements in said array after each of said data elements in the image array have been selected by said selecting means, said measuring means generating a signal indicative that the enhancement of said adjusted data elements is maximized; and

means for transferring said adjusted data elements to a display generator in response to said signal from said measuring means whereby the image produced by the display generator is enhanced.