System and method for bidirectional adaptive thresholding

Claim 2

An image processing system comprising: a pixel sensor means for sensing a plurality of pixels of a grayscale image and for generating grayscale image data; storage means connected to said sensor means for storing said grayscale image data: forward tracking means for reading sets of said image data from said storage means and wherein each said set is read in a forward sequence along a scan line and for providing forward tracked background and peak functions having values for each of a plurality of pixels along the scan line; reverse tracking means for reading said sets from said storage means in a reverse sequence and for providing reverse tracked background and peak functions having values for each of a plurality of pixels along the scan line; threshold level means connected to said forward and reverse tracking means for generating threshold levels for pixels along the scan line derived from either said forward or said reverse tracked functions; and a thresholding means for thresholding said grayscale image data, using said threshold levels, to provide binary image data.

Claim 3

The system of claim 1 wherein said forward tracking means provides said forward tracked background and peak functions as first and third functions of said image data, and said reverse tracking means provides said reverse tracked background and peak functions as second and fourth functions of said image data.

Claim 4

An image processing system comprising: a pixel sensor means for sensing a plurality of pixels of a grayscale image and for generating grayscale image data; storage means connected to said sensor means for storing said grayscale image data: forward tracking means for reading sets of said image data from said storage means and wherein each said set is read in a forward sequence and for providing forward tracked background and peak functions as first and third functions of said set; reverse tracking means for reading said sets from said storage means in a reverse sequence and for providing reverse tracked background and peak functions as second and fourth functions of said set; threshold level means connected to said forward and reverse tracking means for generating a threshold level that is a proportional function of either said forward or said reverse tracked functions; and a thresholding means for thresholding said grayscale image data, using said threshold level, to provide binary image data; wherein said first function is such that said forward tracked background function will increase at a first rate if said grayscale image data is greater than said forward tracked background function and will decrease at a second rate if said grayscale image data is less than said forward tracked background function, and said forward tracked peak function will increase at said second rate if said grayscale image data is greater than said forward tracked peak function and will decrease at said first rate if said grayscale image data is less than said forward tracked peak function, and wherein the second rate is greater than the first rate.

Claim 5

An image processing system comprising: a pixel sensor means for sensing a plurality of pixels of a grayscale image and for generating grayscale image data; storage means connected to said sensor means for storing said grayscale image data: forward tracking means for reading sets of said image data from said storage means and wherein each said set is read in a forward sequence and for providing forward tracked background and peak functions as first and third functions of said set; reverse tracking means for reading said sets from said storage means in a reverse sequence and for providing reverse tracked background and peak functions as second and fourth functions of said set; threshold level means connected to said forward and reverse tracking means for generating a threshold level that is a proportional function of either said forward or said reverse tracked functions; and a thresholding means for thresholding said grayscale image data, using said threshold level, to provide binary image data; wherein said first function is such that said forward tracked background function will increase at a first rate if said grayscale image data is greater than said forward tracked background function and will decrease at a second rate if said grayscale image data is less than said forward tracked background function, and said forward tracked peak function will increase at said second rate if said grayscale image data is greater than said forward tracked peak function and will decrease at said first rate if said grayscale image data is less than said forward tracked peak function, and wherein the second rate is greater than the first rate.

Claim 6

The system of claim 3 wherein said second function is such that said reverse tracked background function will increase at the first rate if said grayscale image data is greater than said reverse tracked background function and will decrease at the second rate if said grayscale image data is less than said reverse tracked background function, and said reverse tracked peak function will increase at the second rate if said grayscale image data is greater than said reverse tracked peak function and will decrease at the first rate if said grayscale image data is less than said reverse tracked peak function.

Claim 7

The system of claim 4 wherein said first rate is linear and said second rate is exponential.

Claim 8

The system of claim 4 wherein said grayscale image includes digital data stored on film.

Claim 9

The system of claim 6 wherein said sets of grayscale image data correspond to data line pixels extending between different edges of said image.

Claim 10

The system of claim 7 wherein said digital data is stored in data cells arranged on said film in a two-dimensional array of rows and columns and wherein said data line pixels extend over the center portion of said data cells.

Claim 11

The system of claim 4 wherein said sets of grayscale image data correspond to lines of pixels extending between different edges of said image, and wherein said forward sequence starts at one of said edges and extends to the other of said edges and said reverse sequence starts at said other of said edges and extends to said one of said edges.

Claim 12

The system of claim 4 wherein said threshold level means includes comparator means for comparing said forward tracked function and said reverse tracked function against predetermined criteria and, depending on the results of the comparison, generating said threshold level as a function of either said forward or said reverse tracked functions.

Claim 13

The system of claim 10 wherein said proportional function is the average of said peak and background functions.

Claim 14

The system of claim 10 wherein said comparator means includes contrast means for determining validity of said forward and reverse tracked functions based on contrast criteria by comparing a difference between said forward tracked peak and background functions against a predetermined contrast standard, and by comparing a difference between said reverse tracked peak and background functions against said predetermined contrast standard.

Claim 15

The system of claim 12 wherein said comparator means includes crossing means for determining the validity based on whether said forward and reverse tracked peak functions have crossed and whether said forward and reverse tracked background functions have crossed.

Claim 16

The system of claim 13 wherein said threshold level means includes select means for selecting either said forward or said reverse tracked function for generating said threshold level based on the following rules: if both of the forward and the reverse tracked background functions are valid, select the maximum of the forward and reverse tracked background functions, or if either of the forward or reverse tracked background functions is valid, select the valid forward or reverse tracked background function, or if neither is valid, select the minimum of the forward and reverse tracked background functions; if both of the forward and reverse tracked peak functions are valid, select the minimum of the forward and reverse tracked peak functions, or if either one of the forward or reverse tracked peak functions is valid, select the valid forward or reverse tracked peak function, or if neither of the forward or reverse tracked peak functions is usable, select a value equaling a function of a selected background function and said contrast standard.

Claim 19

The method of claim 15 wherein said forward tracking provides said forward tracked background and peak functions as first and third functions of said image data, and said reverse tracking provides said reverse tracked background and peak functions as second and fourth functions of said image data.

Claim 22

The method of claim 17 wherein said second function is such that said reverse tracked background function will increase at said first rate if said grayscale image data is greater than said reverse tracked background function, and will decrease at said second rate if said grayscale image data is less than said reverse tracked background function, and said reverse tracked peak function will increase at said second rate if said grayscale image data is greater than said reverse tracked peak function, and will decrease at said first rate if said grayscale image data is less than said reverse tracked peak function.

Claim 23

The method of claim 18 wherein said first rate is linear and said second rate is exponential.

Claim 24

The method of claim 18 wherein said grayscale image includes digital data stored on film.

Claim 25

The method of claim 20 wherein said sets of grayscale image data correspond to data line pixels extending between different edges of said image.

Claim 26

The method of claim 21 wherein said digital data is stored in data cells arranged on said film in a two-dimensional array of rows and columns and wherein said data line pixels extend over the center portion of said data cells.

Claim 27

The method of claim 18 wherein said sets of grayscale image data correspond to lines of pixels extending between different edges of said image, and wherein said forward sequence involves reading said data sequentially by starting at one of said edges and ending at the other of said edges and said reverse sequence involves reading said data sequentially by starting at said other of said edges and ending at said one of said edges.

Claim 28

The method of claim 18 wherein said generating threshold level step includes comparing said forward tracked function and said reverse tracked function against predetermined criteria and, depending on the results of the comparison, generating said threshold level as a function of either said forward or said reverse tracked functions.

Claim 29

The method of claim 24 wherein said proportional function is the average of said peak and background functions.

Claim 30

The method of claim 24 wherein said comparing step includes determining validity of said forward and reverse tracked functions based on contrast criteria by comparing a difference between said forward tracked peak and background functions against a predetermined contrast standard, and by comparing the difference between said reverse tracked peak and background functions against said predetermined contrast standard.

Claim 31

The method of claim 26 wherein said comparing step includes determining the validity of said forward and reverse tracked functions based on whether said forward and reverse tracked peak functions have crossed and whether said tracked background functions have crossed.

Claim 32

The method of claim 27 wherein said threshold level generating step comprises the step of selecting either said forward or said reverse tracked function for generating said threshold level based on the following rules: if both of said forward and said reverse tracked background functions are valid, select the maximum of the forward and reverse tracked background functions, or if either of the forward or reverse tracked background functions is valid, select the valid forward or reverse tracked background function, or if neither is valid, select the minimum of the forward and reverse tracked background functions; if both of the forward and said reverse tracked peak functions are valid, select the minimum of the forward and reverse tracked peak functions, or if either of the forward and reverse tracked peak functions is valid, select the valid forward or reverse tracked peak function, or if neither of the forward or reverse tracked peak functions is usable, select a value equaling a function of a selected background function and said contrast standard.