Patent application title: Apparatus for Reading a Color Symbol
Kazukuni Hosoi (Saitama Pref., JP)
Haruo Matsuoka (Saitama Pref., JP)
OPTOELECTRONICS CO., LTD.
IPC8 Class: AG01N2125FI
Class name: Optics: measuring and testing by shade or color trichromatic examination
Publication date: 2008-10-09
Patent application number: 20080246967
The present invention provides an apparatus for reading a color symbol,
which comprises a matrix of color filters arranged in front of a
detector. Light received from the filters of some colors is used to
locate the color symbol, while light received from all the filters is
used to read and decode the located symbol. Preferably, the filters used
for locating the symbol are of the colors to which the detector is most
sensitive. Preferably, the filters for locating the symbol are dominant
1. Apparatus for reading a colored symbol comprising a matrix of filters
of at least two different wavelengths of light placed in front of a
detector, wherein a majority of the filters filter a dominant color
substantially equal to a wavelength of said detector.
2. Apparatus of claim 1 wherein a wavelength reflected by the colored symbol is substantially equal to the wavelength of said detector.
3. Apparatus of claim 1 wherein the matrix of filters comprises a majority of filters substantially equal to the wavelength of said detector.
4. Apparatus of claim 1 comprising at least three filters of different wavelengths.
5. Apparatus of claim 2 wherein said wavelengths are of the color Cyan, Magenta, and Yellow.
6. Apparatus of claim 2 wherein said wavelengths are of the color Red, Green, and Blue.
7. A method of locating and reading a symbol comprising locating the symbol by detecting light through filters arranged in a first pattern, and reading the symbol by detecting light through filters arranged in a second pattern.
8. A method of locating and reading a color symbol from a pattern, said method comprising using a matrix of filters of at least three different colors, wherein light passing through filters of a first color is used to locate the color symbol, and light passing through of a second and third color is used to read the symbol.
9. The method of claim 8 wherein at least one of said colors is yellow.
10. The method of claim 8 wherein filters of the first color are approximately equal in number to filters of the second and third colors combined.
11. The method of claim 8 wherein filters of the first color are arranged in a zig-zag pattern.
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation application to U.S. patent application Ser. No. 10/996,802, filed Nov. 24, 2004, now issued as U.S. Pat. No. 7,124,957, granted Oct. 24, 2006, and U.S. patent application Ser. No. 11/551,918, filed Oct. 23, 2006, now allowed, the disclosures of which are hereby incorporated by reference in their entireties.
TECHNICAL FIELD OF THE INVENTION
The present invention relates to symbol reading and decoding techniques, and more particularly, to apparatus for reading color symbols, such as color one and two dimensional barcodes, with higher sensitivity and resolution.
BACKGROUND OF THE INVENTION
Barcodes, with various desired information encoded therein, are universally used in many circumstances. There are many types of barcodes, such as 1-D barcodes stacked barcodes, 2-D barcodes, etc. These barcodes are usually monochrome symbols that are encoded with information in specified patterns of barcode elements (or cells) of two sharply contrasted colors such as black and white. To increase the "information density" (i.e., the information included in the limited symbol area), various colors are also used as the barcode elements as in color barcodes. The color barcodes are usually also read by monochrome readers which identify different colors by different levels of electrical signals generated from light reflected from the symbol elements of different colors. However, the sensitivity and resolution of reading color symbols by monochrome readers is not satisfactory, especially when the color symbols are buried in a colorful background such as a color picture.
One technique of reading such color symbols employs plural primary color filters, such as Red-Green-Blue filters. A drawback of such an arrangement is that significant loss of sensitivity results from the filtering of the light reflected from the symbol.
Therefore, there exists a need for a reading system that can read a color symbol with high sensitivity and resolution, even if the color symbol is buried in a colorful background.
SUMMARY OF THE INVENTION
The present invention provides an apparatus for reading a color symbol, which comprises a matrix of color filters provided in front of a detector. According to the teachings of the present invention, light received from the filters of some colors is used to locate the color symbol, while light received from other filters or all the filters is used to read and decode the located symbol.
Preferably, the colors of the filters used for locating the symbol are in the range of wavelengths at which the detector is most sensitive. Preferably, the filters for locating the symbol are of the same color, which is preferably of a wavelength of the detector.
Preferably, the pattern of the filters for locating the symbol is of a zigzag pattern, which is a part of the whole filter matrix.
Preferably, one color of filters is used to locate the symbol, and all the filters are used to decode it.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically illustrates an exemplary color symbol reading system according the concept of the present invention;
FIG. 2 illustrates a matrix of filters of an embodiment according to the present invention; and
FIG. 3 illustrates a zigzag line resulted from the zigzag pattern of the dominant color filters in the matrix of FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the color symbol reading apparatus according to the present invention is schematically illustrated in FIG. 1, which generally comprises a light source 14 (such as LED) for projecting light 1 to a color symbol (such as a color barcode) 20, a detector 11 for receiving light 2 reflected from the symbol 20 and for generating electrical signals from the received reflectance light 2, an amplifier circuitry 12 for amplifying the signals generated by the detector 12, and a decoding circuit 13 for decoding the amplified electrical signals received from the amplifier circuitry 12 to obtain a reading result.
According to the present invention, a color filter array (CFA) or filter matrix 10 which comprises filters of various colors is provided in front of the detector 11 for filtering the reflectance light 2 before it is received by the detector 11. Only the light passing the filters of some (but not all) colors are utilized to locate the color symbol 20, while the light passing all the filters are utilized to read and decode the symbol 20.
An exemplary embodiment of the filter matrix 10 is illustrated in FIG. 2, which comprises filters of three different colors, i.e., the three component colors Cyan, Yellow, Magenta of CYM color system, which is expected to pass through more light than RGB filter system. In FIG. 2, yellow filters are represented by "white" squares 15, cyan filters by "gray" squares 16, and magenta filters by "dark" squares 17. For clarity, only some of the filters are designated by reference numbers 15, 16 and 17.
Noticeably in FIG. 2, yellow filters 15 are dominant in number throughout the area of the filter matrix 10. In the example here, there are twice as many filters of yellow color as of each of the other two colors. The yellow filters 15 subtract blue color in principle and pass other spectrum of light onto the detector 11. In this preferred embodiment, the reflectance light 2 that passes the yellow filters 15 to be received by the detector 11 is utilized to locate the colored symbol 20. The symbol 20 is located as a whole symbol block but not by symbol elements. In this embodiment, detector 11 has a dominant sensitivity for the colors passing through the yellow filter. Thus, a high sensitivity of the detector in locating the color symbol 20 is achieved.
After the color symbol 20 is located by the light 2 passing the yellow filters 15, the light 2 that passes all the color filters 15, 16 and 17 in the filter matrix 10 is utilized to read and decode the colored symbol 20, which achieves a higher resolution as compared to prior color symbol readers.
In order to calculate run-length with minimum noise, pixels of the same color should be used. To this end, as illustrated in FIG. 2, the dominant yellow filters 15 are preferably arranged in the filter matrix in a zigzag pattern both horizontally and vertically. This generates a zigzag line 15a (see FIG. 3) for calculating run-length with minimum noise. Once a finder of the barcode or color symbol 20 is found, the colors of the symbol 20 can be then evaluated, which is useful for remaining processing of the symbol 20.
Though the yellow filters 15 are utilized as the dominant color filters in the preferred embodiment illustrated in FIG. 2, any other color (such as cyan or magenta) may also be used as a dominant color to locate the colored symbol 20. Preferably, the detector 11 has the most sensitivity for the wavelength of the same color of the dominant color filter, or is the most sensitive to the color of the dominant color filters.
Other color systems can also be utilized. For example, filters can have red, green and blue colors as in an RGB color system, with one (e.g., red) of the colors as the color of the dominant filters for locating the symbol 20. Filter matrices containing more than three types of filters could also be employed. It is desirable, although not critical to the present invention, that the wavelength at which the detector 11 is most sensitive and the filter used to locate the symbol have similar wavelengths, in order to maximize the sensitivity.
Alternatively, the matrix filters 10 may comprise more than three colors and the filters for locating the symbol 20 may comprise more than one color (such as yellow in FIG. 2). For example, the filters for locating the symbol 20 may comprise filters of several different colors. If so, the colors are preferably close to each other and the detector 11 is more sensitive to them than other colors.
Though the above describes the preferred embodiments of the present invention, it will be appreciated that, without departing the spirit of the present invention, numerous adaptations, variations and modifications are readily available to a person with ordinary skill in the art. For example, the color filters 15, 16, 17 can be of other types of patterns other than that shown in FIG. 2, such as honeycomb pattern. The color symbol 20 can be a linear barcode of any dimension, a stacked barcode, a matrix barcode, etc., buried in a colorful background or not. The filters used for locating the color symbol 20 may or may not be dominant in number as compared to other filters. Therefore, the scope of the present invention is intended to be solely defined in the accompanying claims.
Patent applications by Haruo Matsuoka, Saitama Pref. JP
Patent applications by Kazukuni Hosoi, Saitama Pref. JP
Patent applications by OPTOELECTRONICS CO., LTD.
Patent applications in class Trichromatic examination
Patent applications in all subclasses Trichromatic examination