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due to Printing equipment, paper, ink, human operation and other reasons, the QR code often has deviations in the printing process, causing many problems for the printing enterprise. Here, the author will share with you how to perfectly print the QR code, I hope to help everyone.
Unknown knowledge of QR code
In order to achieve the perfect printing of the QR code, it is necessary to have a clear understanding of the QR code. This is also lacking in many printing operators.
01 two-dimensional code structure
At present, the QR code used in the market is a QR code, and the structure of the two-dimensional code is introduced with the focus of the QR code. The QR code has 40 specifications. The specification of version X is (4X+17)×(4X+17), and FIG. 1 shows the symbol structure of the QR code of version 7. Each QR code symbol consists of a nominal square module that forms a square array consisting of a coded area and functional graphics including position detection patterns, position detection pattern separators, positioning patterns, and correction patterns.
Figure 1 Symbol structure of the QR code (Version 7)
(1) Position detection pattern, position detection pattern separator: used for positioning of two-dimensional code. For each QR code, the position is fixed, but the size specifications will be different; these black and white spaced rectangular blocks It is easy to detect image processing.
(2) Correction pattern: The number of correction patterns differs depending on the size. The correction pattern is mainly used for the correction of the QR code shape, especially when the QR code is printed on an uneven surface, or distortion occurs when photographing.
(3) Positioning graphics: These small black and white grids are like coordinate axes, and a grid is defined on the QR code.
(4) Format information: indicates the error correction level of the QR code, which is divided into L, M, Q, and H.
(5) Data: The content is encoded in a binary grid of black and white. 8 grids can encode one byte.
(6) Version information: that is, the specification of the QR code, each version of the symbol is increased by 4 modules per side than the previous version.
(7) Error correction code word: used to correct the error caused by QR code damage.
02 QR code recognition
Because of the different wavelengths of objects, the wavelength of visible light reflected is different, white objects can reflect visible light of various wavelengths, and black objects can absorb visible light of various wavelengths. Therefore, the automatic recognition of the two-dimensional code is realized by utilizing the technical characteristics of the light reflection difference of the color in the two-dimensional code symbol.
The recognition process is: light source illumination → illumination onto the surface of the two-dimensional code symbol → light reflection → photoelectric converter receiving and photoelectric conversion to generate analog electrical signal → analog electrical signal is amplified, filtered, shaped, and formed into a square wave signal → decoder translation Code → digital signal.
When identifying, the first reading rate is generally above 85%, the bit error rate is less than 0.01%, and the rejection rate is less than 1%. Among them, the first reading rate = (the first reading the number of two-dimensional code symbols / the total number of reading two-dimensional code symbols) × 100%; error rate = (number of false recognition / total number of error recognition) × 100%; rejected The recognition rate = (the number of two-dimensional code symbols that cannot be recognized / the total number of two-dimensional code symbols) × 100%. For some important occasions, the first reading rate is required to be 100%.
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