In recent work, a junior partner encountered a problem on two-dimensional code: Use zxing, given the size of the two-dimensional code specified size, when the size is smaller than a certain range, the resulting two-dimensional code size and size requirements are quite different. For example: For example, I have given the two-dimensional code generation size is 36 * ️36px, two-dimensional code is generated out of the actual size of 21 * 21 px.
principle
If the two-dimensional code mechanism for a better understanding of the students, should know, two-dimensional code with good error correction capability and a large amount of information carrying capacity. In order to achieve the different information processing scales better performance of the two-dimensional code provides 40 levels of specifications, to generate a size range of 21 to 177 * 21 * 177.
In our scenario above, we use ZXing to generate two-dimensional code is version 1, the two-dimensional code is returned back to a 21 * 21 matrix information, given the size of 36 * 36 is not an integer multiple of 21, receiving only a 21 * 21 size information, so we will be transformed into two-dimensional code information matrix picture when only 21 * 21 px generate two-dimensional code.
Specific generation principle and the details in this article has done a very detailed description, see the two-dimensional code (QR code) to generate the basic structure and principles . Here I list only the knowledge associated with this article:
1、Version
There are different versions of the two-dimensional code 1-40, and each version is inherently "symbol structure." (I.e., the square black and white two-dimensional code point) starts from version (21 symbols × 21 symbols), the longitudinal and transverse directions to each 4-symbol increments, up to the version 40 (177 symbols × 177 yards membered) .
2, error correction level
That fault rate, a total of four levels, the higher level error correction capability is also increased accordingly, but since the amount of data is increased, can also become large encoding sizes.
| Error correction level | Fault tolerance |
|---|---|
| L | About 7% |
| M | About 15% |
| THE | About 25% |
| Q | About 30% |
3, encoding
I.e., QR code encoding, two-dimensional code information can be encoded in numbers, alphanumeric, binary, Chinese, Japanese or the like.
How to solve
From the principle that the two-dimensional code, the two-dimensional code size is always 40 versions of a multiple of the size, and therefore smaller size for the generation of two-dimensional code, the two-dimensional code can be adjusted version of fault tolerance and encoding to demand as much as possible with a given size. In our production environment, we are using utf8 to encode information, so two-dimensional code size depends on the version and error correction level selected. Specific ideas are:
- 1, find the closest version of a given size
- 2, to determine whether the version can accommodate the given information to find the optimal level of fault tolerance
- 3, and returns the size of fault tolerance level code encoded as follows:
public class QrCodeTest {
//各尺寸最大容量，具体数据请参考 https://www.qrcode.com/zh/about/version.html
static final int[][] VERSION_ERROR_ARR = new int[][]{
{10,8,7,4},{20,16,12,8},{32,26,20,15},{48,38,28,21},
{65,52,37,27},{82,65,45,36},{95,75,53,39},{118,93,66,52},
{141,111,80,60},{167,131,93,74},{198,155,109,85},{226,177,125,96},
{262,204,149,109},{282,223,159,120},{320,254,180,136},{361,277,198,154},
{397,310,224,173},{442,345,243,191},{488,384,272,208},{528,410,297,235},
{572,438,314,248},{618,480,348,270},{672,528,376,284},{721,561,407,315},
{784,614,440,330},{842,652,462,365},{902,692,496,385},{940,732,534,405},
{1002,778,559,430},{1066,843,604,457},{1132,894,634,486},{1201,947,684,518},
{1273,1002,719,553},{1347,1060,756,590},{1417,1113,790,605},{1496,1176,832,647},
{1577,1224,876,673},{1661,1292,923,701},{1729,1362,972,750},{1817,1435,1024,784}
};
public static int[] getQrCodeVersionAndError(String str, int size) throws Exception{
if(21 > size){
throw new IllegalAccessException("二维码尺寸不能小于21*21px");
}
//查找最接近给定尺寸的version
int tVersion = (int)Math.floor((size - 21)/4.0);
int errorCode = -1;
int len = str.length();
int minLen = len;
int tLen1 = Math.abs(size - tVersion * 4 - 21);
int tLen2 = Math.abs(size - (tVersion + 1) * 4 - 21);
int version = tLen1 <= tLen2 ? tVersion : tVersion + 1;
if(VERSION_ERROR_ARR[version][0] > len){
return new int[]{version, 0};
}
//尺寸过小，不能容纳用户给定数据
for(int i = version+1; i < VERSION_ERROR_ARR.length; i++){
for(int j = 0; j < VERSION_ERROR_ARR[i].length; j++){
int min = Math.abs(len - VERSION_ERROR_ARR[i][j]);
if(min == 0){
minLen = min;
version = i;
errorCode = j;
break;
}else if(min <= minLen){
minLen = min;
version = i;
errorCode = j;
}
}
if(-1 != errorCode){
break;
}
}
if(-1 == errorCode){
throw new IllegalAccessException("该字符串内容过大");
}
return new int[]{version, errorCode};
}
public static void main(String[] args) throws Exception{
print("hello",21);
print("hello",22);
print("hellohellohellohellohello",42);
print("hello",43);
}
private static void print(String str, int size) throws Exception{
int[] result = getQrCodeVersionAndError(str,size);
System.out.println(str+","+size + ":["+result[0] + "," + result[1]+"]");
}
}
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