WO1997046965A2 - High speed image acquisition system and method - Google Patents
High speed image acquisition system and method Download PDFInfo
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- WO1997046965A2 WO1997046965A2 PCT/US1997/009447 US9709447W WO9746965A2 WO 1997046965 A2 WO1997046965 A2 WO 1997046965A2 US 9709447 W US9709447 W US 9709447W WO 9746965 A2 WO9746965 A2 WO 9746965A2
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- WIPO (PCT)
- Prior art keywords
- barcode
- symbology
- barcode symbol
- pixels
- wide
- Prior art date
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Classifications
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
- G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
- G06K7/14—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation using light without selection of wavelength, e.g. sensing reflected white light
- G06K7/1404—Methods for optical code recognition
- G06K7/1439—Methods for optical code recognition including a method step for retrieval of the optical code
- G06K7/1443—Methods for optical code recognition including a method step for retrieval of the optical code locating of the code in an image
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
- G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
- G06K7/14—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation using light without selection of wavelength, e.g. sensing reflected white light
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
- G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
- G06K7/14—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation using light without selection of wavelength, e.g. sensing reflected white light
- G06K7/1404—Methods for optical code recognition
- G06K7/1439—Methods for optical code recognition including a method step for retrieval of the optical code
- G06K7/1456—Methods for optical code recognition including a method step for retrieval of the optical code determining the orientation of the optical code with respect to the reader and correcting therefore
Definitions
- the present invention generally relates to a system and method for acquiring an image in the form of coded information symbols. More particularly, the present invention relates to a system and method for locating and decoding barcode symbols which may be partially obscured, poorly printed or contaminated.
- Barcode symbols are formed from bars or elements that are typically rectangular in shape with a variety of possible widths.
- the specific arrangement of elements defines a character according to a set of rules specified by the code or "symbology" used.
- a collection of element arrangements are concatenated to form a complete barcode symbol, with each character of the message being represented by a unique group of elements.
- a unique "start” and “stop” character is also used to indicate where the barcode symbol begins and ends respectively.
- Scanning systems typically include a laser light source to illuminate the barcode symbol and a photodetector to detect light reflected from the symbol.
- Another common type of optical scanner incorporates a non-laser light source and a charge coupled device (CCD) detector. A portion of the light which is reflected off the symbol is detected by the CCD detector and converted into an electrical signal which provides a digital image of the barcode symbol that has been scanned. The digital image is then processed and decoded according to the specific barcode symbology used.
- CCD charge coupled device
- barcode symbols can be easily read in ideal conditions, such as when the barcode symbol is stationary, clearly visible and without flaws.
- a barcode symbol is located on an object moving at a high speed, narrow bars and spaces cannot be easily located. Smearing of bars may result from low resolution imaging or high-speed motion of the barcode symbol in relation to the scanner. Extraneous markings or other contaminants may also partially obscure the barcode symbol.
- the present invention is an apparatus and method for high speed acquisition, location and decoding of a barcode symbol.
- the system locates a series of potential barcode candidates within a scanned image and filters the candidates to eliminate invalid data. This approach allows computational resources to be focused on decoding the information most likely to be an actual barcode symbol.
- a potential barcode candidate Once a potential barcode candidate has been located, the barcode symbol is processed to determine the barcode symbol orientation and symbology. The elements within the barcode symbol are then detected and the barcode symbol is decoded in accordance with the specific symbology.
- Figure 1 is a barcode scanner made in accordance with the present invention
- Figures 2A and 2B are flow diagrams of the barcode symbol locating procedure in accordance with the present invention
- Figure 2C-2F illustrates the tracing method in accordance with the present invention
- Figure 2G shows the procedure for skipping to the end of a bar code to avoid speaker reflection
- Figure 2H is a flow diagram of the procedure for determining the difference between two-and multi-width barcode symbols
- Figure 3 shows the equally sized image blocks created by the horizontal and vertical grid lines
- Figure 4 is an enlarged view of a trigger line
- Figure 5 is a diagram of the data from the trigger line
- Figure 6 illustrates selection of a neighboring scan line and comparison to the trigger line
- Figures 7A and 7B are flow diagrams of the preferred method of decoding a barcode symbol in accordance with the present invention
- Figure 8 is a flow diagram of procedure for finding the peaks and valleys of the scan line data
- Figure 9 illustrates peaks and valleys
- Figure 10 is a diagram of the dynamic range of the data in a trigger line
- Figures 11A-11C are examples of the start of a barcode symbol
- Figure 12 is a flow diagram of the determination of the number of wide bars and wide spaces
- Figures 13A and 13B are flow diagrams of the method of determining the orientation of a barcode symbol
- Figure 14 is a flow diagram of the method for determining the number of wide bars and wide spaces in accordance with the present invention
- Figures 15A and 15B are flow diagrams of a method for processing barcode symbol information in accordance with the present invention
- Figure 16A is a gray scale image of barcode symbol having a plurality of unreadable regions
- Figure 16B is a plot of the gray scale amplitude from a selected scan line before sorting
- Figure 16C is the gray scale image of Figure 16A after sorting
- Figure 16D is a plot of the gray scale amplitude from the scan line of Figure 16B after sorting
- Figure 16E shows aliasing which occurs due to pixel misalignment
- Figure 16F is a table of non-sorted gray scale values associated with the image
- Figure 16G is a table of sorted gray scale values associated with the image
- Figures 17A and 17B are flow diagrams of an alternative method for locating barcode symbols in accordance with the present invention.
- Figure 18A is an imposter after color blob analysis
- Figure 18B is a valid barcode symbol after color analysis
- Figure 19 is a method of decoding a Code 128 barcode symbology
- Figure 20 is a plot of the gray scale amplitude from a multi-width barcode symbol; and Figure 21 shows gray scale composition in accordance with the present invention.
- the scanning system 10 comprises a light source 12 which illuminates a subject barcode symbol 18.
- Light reflected from the barcode symbol 18 is detected by a photo-sensitive detector 20.
- the detector 20 produces an electrical signal representative of the light reflected from the barcode symbol 18 which is output to the processor 22.
- the processor 22 decodes the signal and forwards the resulting information, which corresponds to the information encoded in the barcode symbol 18 to an output means 24.
- the output means 24 may be a printer, a CRT or an information system as is well known by those skilled in the art.
- the scanning system 10 shown in Figure 1 may be embodied in a mobile hand-held unit, or may be a stationary unit wherein an object carrying the barcode symbol 18 is passed under the light source 12 either manually or via a conveyor.
- the detector 20 is a charge coupled device (CCD) one dimensional array (line) detector which detects and stores an electronic image of the barcode symbol 18. Additional detail regarding the scanning system 10 may be obtained with reference to currently pending U.S. Patent Application Serial No. (Not Yet Known) filed on February 23, 1996 entitled "HIGH SPEED IMAGING APPARATUS FOR CCD BASED SCANNERS", assigned to the present assignee.
- the scanning system 10 utilizes a two step approach to decoding barcode symbols: 1) locating valid barcode candidates on an object; and 2) determining the type of barcode symbology which has been detected and decoding the barcode symbol in accordance with that symbology.
- the system 10 performs a barcode symbol locating procedure 40 as shown.
- Light reflected from the barcode symbol 18 is detected by an array of light sensitive pixels within the CCD detector 20, thus creating an electronic image of the barcode symbol 18.
- Each pixel has a specific gray scale value which represents the amount of light detected by the pixel.
- the image is divided (step 42) into a grid having equally sized image blocks 74.
- the size of the blocks 74 depend on the height of the barcode symbol 18 and on the resolution of the image. As shown in Figure 3, the equally sized image blocks 74 are created by horizontal grid lines 70 and vertical grid lines 72.
- the pixel array is 4096 by 1024 pixels and the horizontal and vertical grid lines 70, 72 are thirty- two pixels apart in the vertical and horizontal direction respectively.
- the system 10 begins searching for the barcode symbol by performing a series of grid line analyses.
- the horizontal grid lines (in a "picket fence” orientation) and vertical grid lines (in a "ladder” orientation) are analyzed to determine if a potential barcode candidate exists (step 43) .
- the trigger line 78 is in the middle of the grid.
- the trigger line 78 is analyzed for potential barcode candidates (step 46) by seeking for a transition pattern along the trigger line 78 (skipping every other pixel to increase the speed) .
- a transition pattern is defined as two successively chosen pixels having a gray scale magnitude difference of at least 20 (out of 255 gray scale levels) .
- the transition pattern must have a quiet zone of a minimum number of pixels followed by a "threshold" number of transitions within the selected length of pixels, such as at the beginning of a barcode symbol, or a threshold number of transitions within selected length of pixels followed by quiet zone, such as at the end of a barcode symbol.
- the selected length of pixels is 140 in the vertical direction and 90 in the horizontal direction
- the threshold number of transitions is 16
- the threshold quiet zone is a minimum of 20 pixels.
- Successful barcode candidate locations comprising grid line and pixel coordinates are queued in a barcode candidate list.
- the sign (positive or negative) of the candidate position indicates whether the quiet zone of the candidate appeared prior to the transitions, indicating the beginning of a barcode symbol, or after the transitions, indicating the end of the barcode symbol.
- the candidates are filtered (step 48) to eliminate illegal candidates. In filtering the candidates
- step 48 the system 10 analyzes a predetermined number of pixels along the trigger line 78, as shown in Figure 5, and determines whether a threshold number of bars and spaces are present within that region.
- the threshold is two bars and two spaces in a region 65 pixels long. However, the threshold is dependent upon the specific application.
- the system 10 determines the number of bars and spaces by analyzing the region and determining black and white thresholds utilizing the following equations:
- a bar is defined when successive pixels have a gray scale value less than the black level threshold and the number of pixels is greater than a predetermined minimum width.
- a space is defined when successive pixels have a gray scale value greater than the white level and the width is greater than a predetermined minimum width.
- the number of bars and spaces in the region is then determined. If any bar is wider than the maximum width, the region fails because a wide bar in a barcode symbol cannot be greater than the maximum width. Although similar reasoning can be applied to a space, specular light reflection may "wash out" the CCD detector 20 in certain regions, thereby causing the detector 20 to interpret these washed out regions as spaces that are too wide. Accordingly, in the preferred embodiment, the width of spaces is not used to filter out potential candidates. Once the number of bars and spaces has been determined, it is compared to a threshold number. Any barcode candidate having less than the threshold number bars and spaces is discarded.
- a verification is performed by matching pixels in adjacent scan lines to pixels in the trigger line 78 (step 50) .
- the system 10 selects a neighboring scan line, for example line 98 in Figure 6, that is a predetermined number of scans away from the trigger line 78; preferably eight pixels from the trigger line 78.
- the system 10 begins the matching process by collecting pixels starting at point Z x , which is an offset of approximately 12 pixels to left of X j .
- the first transition, a gray scale difference of 20, is identified at Y x .
- Gray scale values of 40 pixels to the right of Y 1 are then collected (Y t ...Y 4t) ) and compared with gray values of 40 pixels to right of X x (X 1 ...X 40 ) .
- the mean of the absolute value of the difference is calculated using:
- ABS (Y 1 - X + ABS (Y 2 - X 2 ) + . . . ABS (Y N - X N )
- the candidate has passed the matching test. If the adjacent scan line 98 fails to match the trigger line 78, a second scan line 100 on the other side of the trigger line 78 is selected. If this second scan line 100 fails the matching test (step 50) , the candidate is rejected. At this point, barcode candidates have been selected and confirmed as the beginning of a detected barcode symbol 18.
- the system 10 must then analyze the first wide bar to ensure that the bar is not too tall, too short and also that the bar does not curve (step 52) . The leading edge of the bar is traced to the top of the bar and to the bottom of the bar to define the first two corners of the barcode symbol. The tracing procedure will be described with reference to Figures 2C-2F.
- the height is compared to a predetermined threshold to determine whether the bar is too tall or too short.
- the system 10 begins tracing the detected bar at point 1.
- the initial direction of travel depends upon whether the barcode candidate was located from the horizontal search or the vertical search and on sign of the barcode candidate. For example, consider a horizontal candidate with a negative sign.
- the system 10 starts at point 1, which is in a quiet zone, and traverses from the quiet zone to the detected bar in direction DRO, as shown in the mapping table in Figure 2D.
- DRO clockwise
- DRO counter-clockwise
- the system 10 initially moves in direction DRO and detects a black pixel at point 2, a pixel having a gray scale value less than the black level threshold of Equation 3. Initially, the system 10 travels in the counter-clockwise direction. If the current pixel is a black pixel, the system 10 continues searching for a white pixel by incrementing the direction number to DR1. Accordingly, the system 10 will be at point 3, which is a white pixel. The gray scale value and coordinates of each pixel are stored in a buffer. The direction number is then remapped based on the table shown in Figure 2E. The new direction number is DR6 since the last direction was DR1. The system 10 then traverses from point 3 to point 4.
- the system 10 calculates a vector direction. If the vector direction diverts from the reference vector by an error threshold, the third to the last point stored in the buffer is selected and marked as one of the corners. The opposite end of the barcode element is found by tracing the element using the same procedure as described above, however, the system 10 moves in a clockwise direction using the mapping table shown in Figure 2F. After the edge has been traced, the system 10 stores the coordinates of the first two corners of the barcode symbol for later use.
- the system 10 initiates a search for the opposite end of the barcode symbol (step 54) .
- the coordinates of a line perpendicular to the first edge are calculated and the system 10 moves along that perpendicular line while searching for another quiet zone. If a quiet zone has not been found within a reasonable distance, the barcode candidate is eliminated.
- the distance may be predetermined or may be based upon the height of the first bar, thereby maintaining a preset height- to-width aspect ratio.
- the second edge is traced to detect height and curvature (step 52) .
- the length of the barcode symbol is then checked (step
- Step 50 may be performed on the last bar to confirm whether it is a valid barcode. If the barcode candidate passes the check length procedure of step 56, a "bounding box" is determined, whereby the coordinates of the four corners of a barcode symbol are stored for later use. At this point, the system 10 must determine whether a two-width or a multi-width barcode has been located since the subsequent decoding steps will be dependent upon the type (two-or multi-width) of barcode that has been detected.
- a multi-width barcode symbology is defined as any symbology having greater than two different width elements .
- the procedure for determining whether the code is a two-width or a multi-width code is shown.
- the system 10 extracts data corresponding to the start/stop characters of the barcode symbol (step 61) . This encompasses approximately forty pixels at the beginning and forty pixels at the end of the barcode symbol .
- the width of each bar and space is calculated (step 62) and the system 10 determines whether the symbology is Code 128 (step 63) , PDF 417 (step 65) or some other type of multi-width symbology (step 67) .
- the barcode candidate is a multi- width symbology, it is processed in accordance with its respective symbology (steps 64, 66, 68) . If the candidate fails all of the multi-width symbology tests, it is assumed that the detected barcode symbol is a two-width code.
- each candidate is decoded as will be explained in greater detail hereinafter. It will be appreciated by skilled artisans that several barcode labels are often located on a single object. To locate vertical barcodes in a ladder orientation the system 10 proceeds to perform a vertical grid line analysis (step 59) in the same manner as the horizontal grid line analysis was performed (step 43) . The present invention will be able to simultaneously locate the coordinates of a plurality of barcode labels on an object.
- the system 10 extracts the coordinates of the barcode symbol and associated data from the image buffer (step 200) .
- the image buffer includes location coordinates and gray scale data for the area of interest which approximates an electronic image of the barcode symbol in pixel format .
- the system 10 copies gray scale values for pixels of each scan line into a separate portion of memory for processing as needed (step 202) .
- the peaks and valleys of the line data are found (step 204) and the exact start and stop location of the barcode symbol is determined (step 206) .
- the number of wide bars and wide spaces are detected (step 208) in order to specify the type of barcode symbology which is being used in the detected barcode symbol.
- the barcode symbol information is then processed (step 210) in accordance with the type of symbology which has been determined in step 208.
- the system 10 After processing of the barcode symbol has been confirmed (step 212) , the system 10 outputs a signal that the barcode symbol was successfully read (step 214) and the system 10 returns to the barcode symbol location procedure.
- step 216 If processing of the barcode symbol has not been confirmed (step 212) , an analysis of up to ten scan lines (step 216) is repeated. If no confirmation of the barcode symbol is made after ten attempts (step 216) , the data is reorganized (step 220) and five more attempts to decode the barcode symbol are made (step 222) . Once a total of fifteen attempts have been made to decode and confirm the barcode symbol without success (step 222) , a "no read" signal is returned to the operator (step 224) and the barcode candidate is discarded. It should be recognized by those skilled in the art that the number of attempts could be a parameter set by the operator depending upon the application.
- Peaks and valleys are defined as portions of the barcode symbol data which have a first derivative of zero and thus no slope. Portions of the barcode symbol that have been determined to be peaks are given a positive (+) identifier and values that have been determined to be valleys are given a negative (-) identifier as shown in Figure 9.
- the system 10 determines whether a point is a peak or a valley by calculating first and second derivatives. If a point has a first derivative equal to zero and a second derivative less than zero, the point is classified as a peak.
- a point has a first derivative equal to zero and a second derivative greater than zero, the point is classified as a valley. Essentially, if neighboring pixels of pixel x have values less than pixel x, pixel x is a peak. If the neighboring pixels of pixel x have values greater than pixel x, pixel x is a valley.
- the system 10 then calculates threshold levels (step 204B) for comparison to the transition from one peak/valley to the next peak/valley.
- the thresholds are dependent upon the location of the transition within the dynamic range of the barcode symbol data.
- the dynamic range for an illustrative barcode symbol is shown in Figure 10. The dynamic range is calculated at the beginning of each scan line and then segmented into five distinct regions. Near the middle of the dynamic range 300, the threshold is fixed at a "low" value. Located above and below the middle of the dynamic range are two regions of the dynamic range wherein a variable threshold 302, 304 is calculated. At the upper and lower limits of the dynamic range 306, 308, the threshold is fixed at a "high" value.
- the system 10 has an 8 bit gray scale resolution resulting in 256 available gray scale levels (0-255) .
- the threshold in the middle of the dynamic range 300 is fixed.
- a variable threshold 302, 304 is calculated, a linear approximation is performed.
- the threshold is fixed at a minimum threshold of 5.
- the threshold at the upper and lower limits of the dynamic range 306, 308 is fixed at 20 gray scale levels.
- Noise is greater at higher and lower gray scale levels due to variations in printing and reflection characteristics of a label. Noise in the middle of the gray scale, typically caused by thermal (CCD noise) , is significantly lower. Specular reflection and other variations greatly effect the barcode symbol data at the upper and lower limits of the dynamic range. These variable thresholds are effective in distinguishing a valid barcode symbol transition from noise and specular reflections.
- step 204C if the transition value is greater than the calculated threshold (step 204C) , the data is stored (step 204D) and the next pixel is analyzed (step 204E) . If the transition value is smaller than the calculated threshold (step 204C) , then the system 10 proceeds directly to the next pixel (step 204E) . Once the end of the scan line data has been reached (step 204F) the routine is exited (step 204G) .
- the location of the beginning and end of a barcode symbol is often difficult to ascertain since narrow bars and spaces may be marred or blurred.
- the location of the beginning and end edges of the barcode symbol must be determined with accuracy.
- the method of locating the edges of the barcode symbol (step 206 shown in Figure 7A) will now be described in detail with reference to Figures 11A-C.
- the system 10 searches for the first wide bar and the quiet zone. This provides a region of interest in which computational resources are focused on a detailed analysis. Typically, narrow bars and spaces will be present between the quiet zone and the first wide bar.
- the system 10 calculates the slope, or first derivative, for every two pixels between the quiet zone and the first wide bar.
- first derivative approaches zero, or a plateau is present, a narrow bar has been detected. This is shown in Figures 11A-C.
- a narrow bar 153 is clearly present between the quiet zone and the first wide bar 152.
- Figures 11B and 11C although a clear plateau is not detected, the slight slope indicates that a narrow bar 156, 161 is present.
- step 208 of Figure 7A The determination of the number of wide bars and wide spaces (step 208 of Figure 7A) , will be explained in greater detail with reference to Figure 12.
- the system 10 first finds a reference wide bar/space and narrow bar/space (step 300A) . A region of the scan line data which encompasses the first sixteen peaks and valleys is analyzed to determine the dynamic range and the highest and lowest values of the data.
- the highest value and lowest value are discarded and the second to the highest peak is marked as a reference wide space and the second to the lowest valley is marked as a reference wide bar.
- the reference narrow bar and space are initially set to be equal to the average value of peaks and valleys.
- the system 10 subsequently analyzes each peak and valley (step 300B) . If the transition is a peak (or a space) the system 10 proceeds to step 300C to determine whether the peak is closer to a reference wide space or narrow space. If the peak is closer to a reference wide space, it is designated to be a wide space (step 300D) and the reference wide space is updated (step 300E) by averaging the reference wide space with the current wide space. This provides a weighted average of the wide spaces. The counter is then incremented at step 300H. If the peak is closer to a narrow space (step 300C) the counter is incremented (step 300H) . If a valley has been detected (step 300B) then the system
- step 300M determines whether the valley (or bar) is closer to a reference wide bar or narrow bar. If the valley is closer to the reference wide bar, the distance DI from the wide bar to the end of the barcode symbol (step 300G) is measured. This procedure is repeated (step 3001) for the opposite end of the barcode symbol to obtain the distance from the first wide bar D2 to the end of the barcode symbol .
- step 300N the system 10 determines whether the orientation is forward or backward (300J) . In all widely used 2-width barcode symbologies, the first wide bar is further from the beginning of the barcode symbol than the last wide bar is to the end of the barcode symbol. Accordingly, if DI is greater than D2, the orientation of the barcode symbol is forward (step 30OK) , whereas if D2 is greater than DI than the orientation of the barcode symbol is reverse (step 300L) . After the barcode symbol orientation has been determined
- step 300 the system 10 determines the number of wide bars and wide spaces (step 302) using the process shown in Figure 14. This procedure is similar to the procedure shown in Figure 13, however, the system 10 analyzes every bar and space to determine whether the bar and space is narrow or wide.
- the system 10 determines the type of barcode symbology being used. If the number of wide spaces is approximately equal to the number of wide bars (step 304) the barcode symbology is Interleaved 2 of 5 (step 306) . If the number of wide spaces is approximately equal to one-half ( ) the number of wide bars
- step 308 the barcode symbology is Code 39 (step 310) . If the number of wide spaces is approximately two times the number of wide bars (step 312) , the barcode symbology is Codabar (step 314) . If the barcode symbology has been determined to the I 2 of 5, Code 39 or Codabar, the barcode symbol is then processed (step 318) in accordance with the symbology. If the barcode symbol which has been detected fails all of the tests (steps 304, 308 and 312) , then the symbology is unknown (step 316) . It will be appreciated by those skilled in the art that additional tests may be included to detect (step 315) and decode (step 317) other types of barcode symbologies.
- the barcode symbol information is processed in accordance with the rules of construction for the type of symbology 210. This is shown in greater detail in Figures 15A and 15B.
- a simple decode procedure is initiated (step 600) .
- the system 10 determines whether the number of peaks and valleys in the line scan data is equal to the expected number of peaks and valleys for the particular symbology.
- the number of characters in the barcode symbol is determined by counting the number of wide bars and spaces as follows: If the code is code 12 of 5 then the number of characters is equal to the number of wide spaces or one less than the number of wide bars.
- the number of characters is equal to the number of wide spaces, or half the number of wide bars minus one (WB/2 -1) .
- For Codabar the number of characters is equal to the number of wide bars. It should be appreciated that the number of Code 39 characters includes start and stop characters.
- the scan line data is divided into segments (step 604) .
- the highest peaks are designated as wide spaces and the lowest valleys are designated as wide bars with the remainder of the elements designated as narrow elements (step 606) .
- Each character, or character pair, is then decoded (step 608) which completes processing of the barcode symbol (step 405) .
- step 602 If it has been determined (step 602) that the number of peaks and valleys is not equal to the expected number of peaks and valleys for that particular symbology, (step 602) then a more detailed decoding procedure as shown in Figure 15B is required.
- the entire scan line is divided into character segments and the highest peaks are designated as reference wide spaces and the lowest valleys are designated as reference wide bars (step 401) .
- the system 10 measures the distance between the wide elements and calculates the number of narrow elements that should be located between the wide elements (step 402) .
- the measurement of the distance may be adjusted based on symbology characteristics. For example, at the boundary between two characters, it may initially be unclear whether a wide bar or space pertains to the first character or the second character.
- the present procedure permits a decoding attempt of the first character by using one or more of the wide elements located within the border region. If the attempt is unsuccessful, the wide elements may be associated with the second character in -25- attempting a decoding of the second character.
- the system 10 then decodes the character, or character pair if the particular symbology requires decoding of pairs (step 403) . Once all of the characters have been processed (step 404) the barcode symbol has been decoded.
- the processing of the barcode symbol must then be confirmed (step 212) as shown in Figure 7A.
- the confirmation of the processing of the barcode symbol comprises comparing the decoding of a subsequent scan line with an earlier scan line to determine if they are the same.
- the confirmation threshold may be set as desired by the operator for "two out of three" or "three out of four" scan lines that match. If the barcode symbol has not been confirmed after ten passes
- step 216 the data is reorganized for specular preprocessing
- Step 220 This process (step 220) will be described hereinafter with reference to Figures 16A-16C.
- Step 220 may be either a primary or a secondary operation. For example, if specular reflection is anticipated on packages to be scanned, the system 10 may proceed directly to step 220 after enough scans have been acquired.
- a gray scale image of a barcode symbol 700 having a plurality of unreadable regions 702, 704, 706, 708 is shown.
- the system 10 will be unable to obtain a completely readable confirm scan line due to the unreadable regions 702, 704, 706, 708.
- the regions 702, 704, 706, 708 may be caused by specular reflections 704, 706, 708 that wash out the CCD detector 20 or may be contaminants or markings 702 located on the barcode symbol 700.
- a region of interest 703, showing a plurality of scan lines 705 will be discussed hereinafter.
- FIG. 16B a plot of the gray scale amplitude for scan line number 5 in the area of interest 703 is shown.
- the specular reflection and dark markings upon the barcode symbol 700 create large differences in the gray scale values of the pixels along the scan line.
- specular reflection causes the gray scale values of selective pixels to be extremely high.
- black marks upon the barcode symbol 700 cause the gray scale values to be extremely low. This may lead to errors in decoding the barcode symbol 700.
- the data is reorganized so that the decoding of the barcode symbol 700 may be performed.
- the pixels in each column are sorted such that the largest value in each column appears in the top row and the smallest value appears in the bottom row.
- the portions of the image due to specular reflection float to the top and the portions of the image due to dark markings sink to the bottom.
- the center rows contain data which is most likely to be correctly representative of a complete barcode symbol. Sorting of the data acts as a low-pass filter on the image due to the low resolution of the CCD pixel grid utilized to acquire the image and slight alignment irregularities .
- a gray scale image which has been sorted in accordance with the present invention is shown in Figure 16C. It can clearly be seen that the higher (and thus brighter) gray scale values are located at the top of the gray scale image and the lower (and thus darker) values are located at the bottom of the image 709. The middle portion of the image 709 contains accurate information which is representative of the barcode symbol.
- the gray scale values associated with the sorted image 709 are shown in Figure 16G.
- FIG 16D a plot along scan line 5 after sorting of the data associated with each pixel is shown. The sorting process normalizes the data by eliminating the excessive peaks and valleys which are most likely not representative of the actual barcode symbol .
- Sorting of the pixels also removes the effects of pixel aliasing.
- the gray scale value is a function of the pixel alignment on the barcode image. Aliasing occurs when the CCD pixels are misaligned with respect to the bars and spaces. For example, as shown in Figure 16E, if the pixels are misaligned with the space, a lower amplitude pulse will be obtained. However, if the pixels are correctly aligned a higher, squarer pulse output will be obtained. Sorting the pixel values normalizes the inconsistencies such that similar width elements in a scan line have similar gray values. Once the effects of aliasing are removed, subsequent gray scale composition analysis can - 28 - be performed on any multi-width element codes to determine the encoded information. Gray scale composition analysis will be described in detail hereinafter with reference to Figure 19
- step 914 Referring to Figures 17A and 17B, an alternate method
- step 800 for locating barcode symbols in accordance with the present invention is shown.
- the image buffer is copied into memory for analysis (step 802) .
- the image is binarized
- step 804 whereby pixels having a gray scale value greater than the threshold limit are designated as white and those having a gray scale value less than the threshold are designated as black.
- the image is divided into a grid (step 806) wherein horizontal and vertical lines are placed throughout the image.
- the grid lines are evenly spaced in both directions (e.g., every 32 pixels in the horizontal and vertical directions) , but it is not essential that blocks are square.
- the system 10 searches for a transition near the center of each grid element (step 808) .
- the objective is to locate the longest spanning line in the block to eliminate noise caused by contaminants and other extraneous marks on the barcode symbol.
- the block is divided by placing "cross hairs" on the center of the block. Starting from the center of the cross hairs and moving outward, the system 10 searches for the first transition (black-to-white or white-to-black) within the block. If no transitions are found (step 810) in either of the horizontal or vertical direction, the block is -29- considered to contain no spanning line. For faster processing, the system 10 may only consider transitions near the center of the cross hairs. If no transition is found, a new grid block is selected (step 812) and the search for a transition (step 808) begins again.
- step 810) the edge of the transition must be traced.
- edge will eventually reach the edge of the grid block; or 2) the edge will wrap around on itself to the same point as the starting point. If the edge does wrap around (step 816) that the grid block is considered to have no spanning lines and a new grid block is examined (step 812) .
- the system 10 must then determine if the edge exceeds the maximum number of pixels along a straight line between the initial transition and the furthest grid element edge. If the maximum number of pixels has been exceeded before reaching the edge of a block (step 818) , the search can be terminated since the transition edge can not lead to a spanning line. Using the maximum pixel count will eliminate wandering transition edges that eventually reach the edge of a block, for example, a spiral.
- the system 10 returns to the initial transition and traces the edge in the opposite direction (step 822) . If a trace of the opposite direction fails to reach the block edge within the maximum number of pixels, the block is considered to contain no spanning line.
- a series of tests is performed to confirm that the line is a true spanning line. First, the system 10 determines whether both ends of the spanning line reach the same side of the block (step 824) . If so, the spanning line is invalid. Next, the system 10 determines whether the entire spanning line exceeds the maximum number of pixels (step 826) .
- the spanning line has been confirmed as a valid spanning line (step 830) .
- a valid spanning line has been determined for a particular block, the same procedure is performed for all blocks.
- the orientation of each spanning line may be determined by using the slope formed by the end points of each traced edge. The orientation of a line is the angle of that particular line.
- the oriented blocks must then be clustered into barcode candidates. In a typical situation, most of the blocks will have no spanning lines. The blocks with no spanning lines will have no orientation. The blocks from a valid barcode candidate should have the same spanning line orientation within a certain tolerance level. In simple cases, a standard color blob analysis algorithm is performed. In a color blob analysis, each orientation of a line is assigned a particular color. All squares with similar colors are grouped together form one blob.
- the system 10 analyzes the start and stop pattern of the multi-width barcode symbol to determine what type of symbology is present .
- Code 128, UPC and EAN comprise bars and spaces having 4 different widths, (1, 2, 3 and 4 elements wide) . Some codes have even more, such as PDF417 with 6 widths.
- Gray scale amplitude levels are selected for each the different widths of the bar and space elements after the effects of pixel aliasing have been removed.
- the gray scale level may be calculated by analyzing the start and stop patterns, or may be determined by ranking the gray scale amplitudes located within the area of interest, in terms of width; wherein the highest plateau having the longest duration corresponds to the widest spaces and the lowest plateau having the longest duration corresponds to the widest bars.
- the gray scale levels reach a plateau, for example the 4X elements in Figure 20, that element width is considered to be resolved.
- Gray scale composition analysis examines the remainder of the unresolved element widths. These element widths will proportionally fall between the widest elements (4X) as shown in Figure 20.
- the system 10 subsequently extracts data along a trigger line within the barcode symbol (step 904) and numerically sorts the data corresponding to each pixel (step 906) to filter out specular reflections and damaged or otherwise unreadable portions of the barcode symbol. Even in the absence of specular or damaged barcode symbols, sorting of data corresponding to each pixel is required to normalize the amplitudes of the peaks and valleys. The sorting procedure was previously described with reference to Figures 16A - 16C. After a data set has been determined, the system 10 calculates the run length (step 908) which is basically the width of a bar or space. Referring to Figure 21, the width is determined by calculating the area under a selected portion of the gray scale waveform corresponding to the bar or space using the following equation: b
- Min-area is the area of the narrowest element in the start/stop pattern.
- a Code 128 barcode is used in the present example, it should be understood that this procedure is equally applicable to any multi-width symbology.
- each character has three bars and three spaces and the width of each character is the same for all characters. Accordingly, the width of the character is evaluated (step 910) to determine whether the sum of the widths of six elements does not exceed the predetermined value for the width of a Code 128 character.
- the system 10 determines whether the character is decodable based solely upon analysis of the run length data (step 912) . If the character is decodable, the character is decoded (step 916) . If the character is not decodable, the widths of the unresolved elements are resolved using gray scale composition analysis (step 914) . For example, consider the situation where a 2 width bar is preceded by a one width space and a one width bar which have merged together. This provides an element of width . When the gray scale value of that 4 width element is analyzed, it becomes apparent that the gray scale value is closer to a 2 width bar than to a 4 width bar. In this manner, the system 10 determines the presence of a 2 width bar. The remaining elements are subsequently analyzed in the same manner. Accordingly, using Equation (7) , the bars and spaces present within the portion of the character being decoded may be resolved:
- step 914) the character is decoded (step 916) .
- the system 10 may determine that there are too many elements present. In this case, once a character having six elements is resolved (step 914) and decoded (step 916) the extra elements are carried over for further analysis (step 920) . If there is more data present (step 918) the system 10 analyzes the next character
- step 920 and the evaluation of that character is performed as described above. If no more data is present (step 918) the barcode symbol has been successfully decoded (step 922) .
Abstract
Description
Claims
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Also Published As
Publication number | Publication date |
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WO1997046965A3 (en) | 1998-02-26 |
US6015089A (en) | 2000-01-18 |
CA2255576A1 (en) | 1997-12-11 |
JP2000507727A (en) | 2000-06-20 |
CA2255576C (en) | 2002-01-22 |
ATE225539T1 (en) | 2002-10-15 |
EP1278151A3 (en) | 2003-02-12 |
US6193158B1 (en) | 2001-02-27 |
DE69716087D1 (en) | 2002-11-07 |
EP0917685B1 (en) | 2002-10-02 |
EP1278151A2 (en) | 2003-01-22 |
US20010006191A1 (en) | 2001-07-05 |
EP0917685A2 (en) | 1999-05-26 |
DE69716087T2 (en) | 2003-07-03 |
US6386454B2 (en) | 2002-05-14 |
AU3152897A (en) | 1998-01-05 |
US5969325A (en) | 1999-10-19 |
JP3115610B2 (en) | 2000-12-11 |
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