System and method for bidirectional adaptive thresholding

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.

A method for processing an image comprising the steps of:

• sensing a plurality of pixels of a grayscale image and generating corresponding grayscale image data;
• storing said grayscale image data in a storage means;
• forward tracking said grayscale image data by reading sets of said image data from said storage means in a forward sequence along a scan line, and providing forward tracked background and peak functions having values for each of a plurality of pixels along the scan line;
• reverse tracking said grayscale image data by reading said sets from said storage means in a reverse sequence, and providing background and peak tracked functions having values for each of a plurality of pixels along the scan line;
• generating threshold levels for pixels along the scan line derived from either said forward or said reverse tracked functions;
• and
• thresholding said grayscale image data using said threshold levels to provide binary image data.

A method for processing an image comprising the steps of:

• sensing a plurality of pixels of a grayscale image and generating corresponding grayscale image data;
• storing said grayscale image data in a storage means;
• forward tracking said grayscale image data by reading sets of said image data from said storage means in a forward sequence, and providing forward tracked background and peak functions as first and third functions of said set;
• reverse tracking said grayscale image data by reading said sets from said storage means in a reverse sequence, and providing reverse background and peak tracked functions as second and fourth functions of said set;
• generating a threshold level that is a proportional function of either said forward or said reverse tracked functions;
• and
• thresholding said grayscale image data using said threshold levels 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 said second rate is greater than said first rate.