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details: some things about qr code

Posted by millikan at 2020-03-01
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introduce

With the increasing use of smart phones, more and more applications based on QR code. Today, let's talk about QR code with you.

The two-dimensional code is an extension of one-dimensional code, which has readability. It uses black-and-white rectangular pattern to represent binary data. After being scanned by the device, the information contained in it can be obtained.

One dimensional code records data only horizontally, and ISBN on books is a typical one dimensional code.

ISBN

The QR code records data in both horizontal and vertical directions. We often say that QR code is actually QR code, which is one of many kinds of QR code.

QR code

As shown in the figure, quick response code is usually a square composed of black and white squares. In the upper left, upper right and lower left corner, there is a "back" word like location mark to ensure that the program can correctly identify when reading content.

At the same time, QR code also has a fault-tolerant mechanism, even if the pattern has some damage, it can still ensure that the content can be read correctly. The fault tolerance rate of generated QR code pattern is generally 7%, and the maximum is 30%. The following figure is an example of 30% fault tolerance for the same content.

30% fault tolerance

Common uses

QR code has a wide range of applications, and now it's very common. Here are a few examples:

WeChat

Wechat QR code

The QR code of wechat adds some beautification elements on the basis of the original two-dimensional code pattern.

Sina micro-blog

Sina micro-blog

Sina Weibo makes good use of the QR code fault tolerance mechanism, adding user's head image to the QR code pattern to enhance recognition.

QQ browser

Website QR code

QQ browser integrates the function of generating QR code from web address. It can generate a QR code picture from the currently visited web address, which can be accessed quickly when scanning with mobile app.

Application method

We must be very familiar with the basic usage of QR Code:

Pick up the mobile phone, open the QR code scanning application, and then point the camera at the QR code pattern on the poster or propaganda page, and you can see the displayed content in a few seconds.

Next, let's talk about some other applications of QR code.

Redesign of pattern

Because QR code has a good fault-tolerant and positioning mechanism, we can completely redesign on the basis of the original black-and-white pattern.

Change colors and lines

Change shape

As long as enough contrast is ensured, the content of the QR code image can be easily read out.

Log in after scanning

Because the content of QR code can be a piece of customized text, we can do many "magic" operations through it. The login of wechat web page is one example.

When we visit wechat webpage, we will have a prompt like this:

WeChat webpage

This QR code actually contains a customized URL https://login.weixin.qq.com/l/ key. When the QR code is scanned by wechat on the mobile terminal, it will automatically access the URL and send the login information to the server. After receiving the login information, the server completes the login operation on the web page.

https://login.weixin.qq.com/l/密匙

Open home page after scanning

Wechat's public platform QR code is similar to personal QR code.

Wechat public platform

They all contain http://weixin.qq.com/r/key of the same format. When wechat is scanned, it will automatically read the information of the user or the public platform and prompt the user to pay attention.

http://weixin.qq.com/r/密匙

Another way

In addition to wechat like processing methods, there is another application mode:

The generated QR code image no longer contains the URL, but a string of formatted text, such as

操作代码+间隔符号+密匙

for example

A:5C73EB9ED98D4ED542F2406C09279FDDBC1CE4BE [email protected]= ……

When the program reads the content, it performs the corresponding operations according to the built-in judgment conditions, such as a is "visit the specified URL", B is "display the specified text", etc.

summary

In summary, the basic application process of QR code is shown in the figure below:

Simple process

Simply put the content into the QR code - > read the content and display it. The common application process is shown as follows:

将内容放入二维码 -> 读取内容之后显示

Technological process

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