What is the recognition principle of QR code? Can you fake it?

Two-dimensional bar code/two-dimensional code is distributed on the plane (two-dimensional direction) in a certain geometric figure according to a certain law to record data symbol information; The concepts of "0" and "1" bit streams, which constitute the internal logic foundation of computers, are skillfully used in coding.

A number of geometric figures corresponding to binary are used to represent alphanumeric information, which is automatically read by image input equipment or photoelectric scanning equipment to realize automatic information processing:

It has some characteristics of bar code technology: each coding system has its own specific character set; Each character occupies a certain width; It has certain verification function. At the same time, it also has the characteristics of automatically identifying different lines of information and dealing with the rotation and change of graphics. Two-dimensional code/two-dimensional code can express information in both horizontal and vertical directions at the same time, so it can express a lot of information in a small area.

The production of two-dimensional code generator needs a two-dimensional code generation algorithm or a two-dimensional code plug-in, and then a calling software is written in JAVA, C#, VB and other programming languages to make the two-dimensional code generator.

The QR code can be forged, and the general QR code has no anti-counterfeiting function; Individuals can download the automatic QR code generator from the Internet and make the QR code. Some criminals even designed a QR code with a virus to steal personal information from other people's mobile phones. Experts advise mobile phone users to pay attention to safety and not to easily scan suspicious QR codes of unknown origin.

Extended data:

Simply put, the QR code is to translate the information you want to express into two small black and white squares, and then fill in this big square. Similar to the answer sheet in our middle school, it is to translate our language into machine-readable language. To put it bluntly, it is to translate numbers, letters, Chinese characters and other information into binary 0 and 1 through specific codes. 0 is a small white square, and 1 is a small black square.

Of course, there are many error correcting codes. If there are 100 codewords to encode, and you want to correct half of them, that is, 50 codewords, the calculation method is as follows. Error correction requires twice as many symbols as codewords, so the number in this case is 50 × 2 = 100 codewords.

So the total number of codewords is 200, of which 50 are used for error correction, which means that 25% of the information in this two-dimensional code is used for error correction, indicating that the two-dimensional code can be recognized even if it is a little missing or wrinkled.

Some friends may ask, why are there three big black squares on each QR code? That involves the following: How does the mobile phone recognize the QR code?

Because different colors reflect different wavelengths of visible light, white objects can reflect various wavelengths of visible light, while black objects absorb various wavelengths of visible light.

Therefore, when the camera scans the black-and-white QR code, the mobile phone uses the threshold theory of point operation to change the collected image into a binary image, that is, binarizes the image to obtain a binary image, and then performs expansion operation on it, and carries out edge detection on the expanded image to obtain the outline of the barcode area.

References:

Baidu encyclopedia-QR code