How to achieve perfect printing of two-dimensional code
To achieve perfect printing of two-dimensional codes, it is necessary to have a clear understanding of two-dimensional codes. This is also what many print operators lack.
01, the structure of two-dimensional code
The two-dimensional codes currently used in the market are QR codes. Here, the structure of the two-dimensional codes is mainly focused on QR codes. There are 40 specifications for the QR code. The specification of the version X is (4X+17)×(4X+17). FIG. 1 shows the symbol structure of the QR code of the version 7. Each QR code symbol consists of a nominal square block, forming a square array, which consists of a coded area and functional patterns including position detection patterns, position detection pattern delimiters, positioning patterns, and correction patterns.
(1) Position detection pattern and position detection pattern delimiter: It is used for the positioning of two-dimensional code. For each QR code, the position is fixed, but the size and size will be different; these black and white rectangular blocks It is easy to detect image processing.
(2) Correction pattern: The number of correction patterns varies depending on the size. The correction pattern is mainly used for the correction of the shape of the QR code, especially when the QR code is printed on an uneven surface, or distortion occurs during photographing.
(3) Positioning pattern: These small black and white lattices are like axes, and a grid is defined on the QR code.
(4) Format information: It indicates the error correction level of this QR code and is divided into L, M, Q, and H.
(5) Data: Use black and white binary grid coding content. Eight cells can encode one byte.
(6) Version information: This is the specification of the QR code. Each version of the symbol adds 4 modules to each side of the previous version.
(7) Error correction code word: used to correct errors caused by QR code corruption.
02, two-dimensional code identification
Due to the different color objects, the wavelength of the visible light reflected by them is different, white objects can reflect visible light of various wavelengths, and black objects can absorb visible light of various wavelengths. Therefore, the two-dimensional code can be automatically identified by using the technical characteristics of the light reflection differences in the two-dimensional code symbols.
The recognition process is as follows: the light source emits light → shines on the surface of the QR code symbol → the light reflection → the photoelectric converter receives and performs the photoelectric conversion to produce the analog electrical signal → the analog electrical signal is amplified, filtered, and shaped to form the square wave signal → the decoder translates Code → digital signal.
Recognition generally requires a head reading rate of more than 85%, a bit error rate of less than 0.01%, and a rejection rate of less than 1%. Among them, the first reading rate = (first read out the number of two-dimensional code symbols / read the total number of two-dimensional code symbols) × 100%; bit error rate = (error recognition times / total number of error detection) × 100%; refused Recognition rate = (number of unrecognized two-dimensional code symbols / total number of two-dimensional code symbols) × 100%. For some important occasions, the required first-rate reading rate is 100%.