Abstract:
Character stroke is strengthened by processing video image data with a 16×16 kernal, and moving the kernal one pixel at a time through the image. For each pixel position, sections of the kernal, are selectively filled with black pixels in proportion to the number of black pixels in each section, in accordance with a set of predetermined rules.

Description:
BACKGROUND OF THE INVENTION 
     When digitizing a medium (paper or film) of low contrast containing alphanumeric characters, quite often the resulting output consists of weak or broken characters. For example, when a document written in light pencil is scanned and digitized, the resulting image may contain broken characters. If the digital signal from the scanner is sent to a processing device such as an optical character recognition (OCR) machine where connectivity of characters is essential to performance, the machine will not be able to perform adequately. The same problem arises when scanning a document printed by a dot matrix printer, where the dots are not connected. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to solve this problem by performing stroke strengthening to enhance contrast and to connect broken characters of a binary image. The character stroke is strengthened by processing the image with a 16×16 kernal, moving the kernal one pixel at a time. In each pixel position, the kernal, which is divided into sixteen square sections, is selectively filled with black pixels in proportion to the number of black pixels in each section, in accordance with a special set of rules. The rules are as follows: 
     1. If the number of black pixels in two neighboring sections are greater than the threshold and the number of black pixels in the section lying between them is greater than half the threshold value, all three sections are filled with all black pixels; 
     2. If the number of black pixels in each of two neighboring sections is greater than the threshold, then both sections are filled with all black pixels; 
     3. If the number of black pixels in each of three sections lying along a diagonal is greater than the threshold, then the diagonal regions adjacent the three sections, as well as the sections themselves, are filled with all black pixels; 
     4. If the number of black pixels in each of two sections arranged along a diagonal is greater than the threshold, then the diagonal regions adjacent the two sections, as well as the sections themselves, are filled with all black pixels; and 
     5. If the number of black pixels in each of two sections, displaced from one another by a knight&#39;s move as in the game of chess, is greater than the threshold and the number of black pixels in a connecting section lying between them is greater than half the threshold, then the connecting section is filled with all black pixels and the diagonal region between the connecting section and one of the other two sections is filled with all black pixels. 
     Preferably, the kernal comprises 16 columns and 16 rows of video pixels and each section of the kernal is a square of four columns of pixels by four rows of pixels, the kernal comprising 16 such sections arranged in a square array. Each time the data encompassed within a given kernal position is thus processed, the kernal is then moved by one video position (preferably to the next column position) and the entire process is repeated. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The invention may be understood by reference to the accompanying drawings, of which: 
     FIG. 1 is a block diagram of the system of the invention; 
     FIG. 2 is a diagram illustrating the 16×16 kernal used in processing the video data in accordance with the invention; and 
     FIGS. 3a-3e illustrate the basic rules for stroke strengthening using the kernal of FIG. 2. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, lines of incoming video data pass through a line counter 100, get copied by a copy circuit 101 and written to a pair of buffers 102 and 103. The buffers 102 and 103 each hold the same 16 lines of video data (one bit/pixel). The buffer 102 is simply used to hold the original data for counting purposes and is not modified in any way. Image processing is performed on the data stored in the buffer 103. After each new line of video data is shifted into the top row of buffers 102 and 103 (and the oldest line shifted out of the bottom row), a 16×16 kernal 120 (FIG. 2) is &#34;moved&#34; across the 16 lines of the buffer 102, one pixel at a time. For each pixel position, counters 104a-104p count the black pixels in each quadrant 122a-122p of the kernal 120. Each quadrant 122 in the kernal 120 is a 4×4 array of pixels. The 16×16 kernal 120 may be readily implemented (for example) by an address generator 102a which, for a given position of the 16×16 kernal 120 in the 16 video lines of data stored in the buffer 102, reads the 16 columns of pixels encompassed in the 16 video lines by the kernal 120 from the buffer 102 to the counters 106. The counts computed by the counters 106 are then input to a fill processor 105 which performs &#34;filling&#34; by transforming qualifying white pixels to black based upon the following criteria using a predetermined threshold: 
     (a) Three adjacent case (FIG. 3a): 
     If the number of black pixels in each of two end quadrants 122&#39;, 122&#34; is greater than the threshold and the number of black pixels in the middle quadrant 122&#39;&#34; is greater than half the threshold, fill all three quadrants 122&#39;, 122&#34;, 122&#39;&#34; with all black pixels; 
     (b) Two adjacent case (FIG. 3b): 
     If the number of black pixels in each of two neighboring quadrants 122&#39;, 122&#34; is greater than the threshold, fill both quadrants 122&#39;, 122&#34; with all black pixels; 
     (c) Three diagonal case (FIG. 3c): 
     If the number of black pixels in each of three diagonal quadrants 122&#39;, 122&#34;, 122&#39;&#34; is greater than the threshold, fill the diagonal regions 123 adjacent the three quadrants 122&#39;, 122&#34;, 122&#39;&#34;, as well as the three quadrants themselves, with all black pixels; 
     (d) Two diagonal case (FIG. 3d): 
     If the number of black pixels in each of two diagonal quadrants 122&#39;, 122&#34; is greater than the threshold, fill the diagonal regions 123 adjacent the two quadrants 122&#39;, 122&#34;, as well as the two quadrants themselves, with all black pixels; 
     (e) The &#34;knight&#34; case (FIG. 3e): 
     If the number of black pixels in an &#34;n&#34; quadrant 122&#39; is greater than the threshold and the number of black pixels in a &#34;kn&#34; quadrant 122&#39; (i.e., a quadrant located a knight&#39;s move away as in the game of chess--or, an &#34;L&#34; displacement) is greater than the threshold and the number of black pixels in the connecting quadrant 122&#39;&#34; between them is greater than half the threshold, treat the connecting quadrant 122&#39;&#34; as an (a) above and treat the diagonal regions 123 adjacent the connecting quadrant as in (d) above. 
     Once filling is performed while the kernal 120 resides at a given pixel location, the kernal 120 moves horizontally by one pixel, the quadrant counters 104a-104p are reinitialized to zero via a circuit 106, the quadrant counts are taken again and the data is modified as before. The process is repeated until the kernal 120 reaches the end of the line data. (At this point the first line of modified data in buffer 103 is written out.) In the buffers 102, 103, the video lines are shifted down one line and a new line of video data is brought into the buffer 102 and copied into the buffer 103. This entire process is repeated until there are no more available lines of video data, at which point the buffer 103 is empty (written out) and the process terminates. 
     The threshold value employed in the processing rules (a) through (e) above may be chosen, for example, to be one-half the number of pixels in a given quadrant (i.e., 8 in the present example). 
     Other embodiments of the invention may use, in general, an N by M kernal, where an N and M are other than 16 pixels, (e.g. 32×32 or 8×8, or etc . . . ). 
     Accordingly, while the invention has been described in detail with specific reference to a preferred embodiment thereof, variations and modifications thereof may be made without departing from the spirit and scope of the invention.