# 1, Principle of digital dot matrix library

## 1. Chinese character coding

### Location code

It is stipulated in the national standard GD2312-80 that all national standard Chinese characters and symbols are allocated in a square matrix with 94 rows and 94 columns. Each row of the square matrix is called an "area", numbered from 01 to 94, and each column is called a "bit", numbered from 01 to 94, The area code and tag number of each Chinese character and symbol in the square array are combined to form four Arabic numerals, which are their "location code". The first two digits of the location code are its area code and the last two digits are its bit code. A Chinese character or symbol can be uniquely determined by location code. Conversely, any Chinese character or symbol also corresponds to a unique location code. The location code of the Chinese character "mother" is 3624, indicating that it is 24 digits in area 36 of the square matrix. If the location code of the question mark "?" is 0331, it is 31 digits in area 03.

### Parking code

The internal code of Chinese characters refers to the code that represents a Chinese character in the computer. The internal code is slightly different from the location code. As mentioned above, the area code and bit code of Chinese location code are between 1-94. If the location code is directly used as the internal code, it will be confused with the basic ASCII code. In order to avoid the conflict between the internal code and the basic ASCII code, it is necessary to avoid the control code (00H~1FH) in the basic ASCII code and distinguish it from the characters in the basic ASCII code. In order to achieve these two points, 20H can be added to the area code and bit code respectively, and 80h can be added on this basis (here "H" means that the first two digits are hexadecimal numbers). After these processes, it takes two bytes to represent a Chinese character with internal code, which are called high byte and low byte respectively. The internal code of these two bytes is represented according to the following rules:
High byte = area code + 2 0h + 8 0h (or area code + A 0H)
Low byte = bit code + 2 0h + 8 0h (or bit code + A 0H)

Since the hexadecimal numbers in the value range of area code and bit code of Chinese characters are 01h ~ 5eh (i.e. 01 ~ 94 in decimal system), the value range of high-order byte and low-order byte of Chinese characters is A1H ~ FEH (i.e. 61 ~ 254 in decimal system). For example, the location code of the Chinese character "ah" is 1601, and the area code and bit code are expressed in hexadecimal respectively, that is, 1001H. The high byte of its internal code is B0H, the low byte is A1H, and the internal code is B0A1H.

## 2. Lattice font structure

### Lattice font storage

In the dot matrix font of Chinese characters, each bit of each byte represents a point of a Chinese character. Each Chinese character is composed of a rectangular dot matrix. 0 represents no and 1 represents a point. Draw 0 and 1 in different colors to form a Chinese character. There are three commonly used dot matrix font types: 1212, 1414 and 16 * 16.
The font can be divided into horizontal matrix and vertical matrix according to the different points represented by bytes. At present, most font libraries are stored in horizontal matrix (the most used should be the early UCDOS font library). The vertical matrix is generally because some LCD adopts the vertical scanning display method. In order to improve the display speed, the font matrix is made into vertical matrix, Save matrix conversion when displaying. What we describe next refers to the horizontal matrix font.

## 2, In ubantu, call OpenCV with c + + to overlay Chinese characters on the picture

Open the file for this job
Write text.cpp

## The code is as follows

```#include<iostream>
#include<opencv/cv.h>
#include"opencv2/opencv.hpp"
#include<opencv/cxcore.h>
#include<opencv/highgui.h>
#include<math.h>

using namespace cv;
using namespace std;

void paint_chinese(Mat& image,int x_offset,int y_offset,unsigned long offset);
void paint_ascii(Mat& image,int x_offset,int y_offset,unsigned long offset);
void put_text_to_image(int x_offset,int y_offset,String image_path,char* logo_path);

int main(){
String image_path="leimu.jpg";//Name of picture
char* logo_path="logo.txt";//Name of Chinese character file
put_text_to_image(150,110,image_path,logo_path);//change txt place
return 0;
}

void paint_ascii(Mat& image,int x_offset,int y_offset,unsigned long offset){
//Coordinates of the starting point of the drawing
Point p;
p.x = x_offset;
p.y = y_offset;
//Storing ascii word film
char buff[16];
//Open ascii font file
FILE *ASCII;

if ((ASCII = fopen("Asci0816.zf", "rb")) == NULL){
printf("Can't open ascii.zf,Please check the path!");
//getch();
exit(0);
}

fseek(ASCII, offset, SEEK_SET);

int i, j;
Point p1 = p;
for (i = 0; i<16; i++)                  //Sixteen char s
{
p.x = x_offset;
for (j = 0; j < 8; j++)              //One char and eight bit s
{
p1 = p;
if (buff[i] & (0x80 >> j))    /*Test whether the current bit is 1*/
{
/*
Because the original ascii word film was 8 * 16, it was not large enough,
So the original pixel is replaced by four pixels,
After replacement, there are 16 * 32 pixels
ps: I think it's unnecessary to write code like this, but I only think of this method for the time being
*/
circle(image, p1, 0, Scalar(0, 0, 255), -1);
p1.x++;
circle(image, p1, 0, Scalar(0, 0, 255), -1);
p1.y++;
circle(image, p1, 0, Scalar(0, 0, 255), -1);
p1.x--;
circle(image, p1, 0, Scalar(0, 0, 255), -1);
}
p.x+=2;            //One pixel becomes four, so x and y should both be + 2
}
p.y+=2;
}
}
void paint_chinese(Mat& image,int x_offset,int y_offset,unsigned long offset){//Draw Chinese characters on the picture
Point p;
p.x=x_offset;
p.y=y_offset;
FILE *HZK;
char buff[72];//72 bytes for storing Chinese characters

if((HZK=fopen("HZKf2424.hz","rb"))==NULL){
printf("Can't open HZKf2424.hz,Please check the path!");
exit(0);//sign out
}
fseek(HZK, offset, SEEK_SET);/*Move the file pointer to the offset position*/
fread(buff, 72, 1, HZK);/*Read 72 bytes from the offset position, and each Chinese character occupies 72 bytes*/
bool mat[24][24];//Define a new matrix to store the transposed text film
int i,j,k;
for (i = 0; i<24; i++)                 /*24x24 Dot matrix Chinese characters, a total of 24 lines*/
{
for (j = 0; j<3; j++)                /*There are 3 bytes in the horizontal direction, and the value of each byte is determined by cycle*/
for (k = 0; k<8; k++)              /*Each byte has 8 bits, and the loop judges whether each byte is 1*/
if (buff[i * 3 + j] & (0x80 >> k))    /*Test whether the current bit is 1*/
{
mat[j * 8 + k][i] = true;          /*1 is stored in a new word film*/
}
else {
mat[j * 8 + k][i] = false;
}
}

for (i = 0; i < 24; i++)
{
p.x = x_offset;
for (j = 0; j < 24; j++)
{
if (mat[i][j])
circle(image, p, 1, Scalar(255, 0, 0), -1);		  //Write (replace) pixels
p.x++;                                                //Shift right one pixel
}
p.y++;                                                    //Move down one pixel
}
}

void put_text_to_image(int x_offset,int y_offset,String image_path,char* logo_path){//Put Chinese characters on the picture
//x and y are the starting coordinates of the first word on the picture
//Get pictures through picture path
int length=17;//The length of characters to be printed (the length can be as many bytes as you print, which can be adjusted according to your own situation)
unsigned char qh,wh;//Define area code and tag number
unsigned long offset;//Offset
FILE* file_logo;

if ((file_logo = fopen(logo_path, "rb")) == NULL){
printf("Can't open txtfile,Please check the path!");
//getch();
exit(0);
}

fseek(file_logo, 0, SEEK_SET);
int x =x_offset,y = y_offset;//x. Y: the starting coordinate of the text drawn on the picture

for(int m=0;m<length;){
if(hexcode[m]==0x23){
break;//It ends when the # number is read
}
else if(hexcode[m]>0xaf){
qh=hexcode[m]-0xaf;//The font used starts with Chinese characters, not Chinese symbols
wh=hexcode[m+1] - 0xa0;//Calculation bit code
offset=(94*(qh-1)+(wh-1))*72L;
paint_chinese(image,x,y,offset);
/*
Calculate the offset in the Chinese character library
Each Chinese character is represented by a 24 * 24 dot matrix
A line has three bytes, a total of 24 lines, so 72 bytes are required
*/

m=m+2;//The internal code of a Chinese character occupies two bytes,
x+=24;//A Chinese character has 24 * 24 pixels. Because it is placed horizontally, it moves 24 pixels to the right
}

else{
//When the read character is ASCII
wh=hexcode[m];
offset=wh*16l;//Calculate the offset of English characters
paint_ascii(image,x,y,offset);
m++;//English characters only occupy one byte in the file, so just move back one bit
x+=16;
}

}

cv::imshow("image", image);
cv::waitKey();
}

```

Enter the following command to run:

```g++ text.cpp -o text `pkg-config --cflags --libs opencv`

```

Then enter. / text

# 3, Summary

1. Learn and understand the internal code, location code coding rules and font data storage format of Chinese characters.
2. At the same time, through this experiment, I am familiar with calling opencv library with C/C + + (or python) under Ubuntu again
3. Learn to display a picture through programming, open a text file and overlay Chinese characters on the picture.

Posted on Wed, 17 Nov 2021 05:21:49 -0500 by Tobeon