Opencv uses freetype to display Chinese

because Opencv Chinese is not displayed by default , So we need some libraries to set OpenCV Support Chinese display

Code instructions

Project needs ft2build.h, It is freetype A header file in the Library . So in shell Execute the following statement to install freetype：

sudo apt-get install libfreetype6-dev 

Then use the following statement to find ft2build.h And in cmake Just link in

sudo find / -name ft2build.h

  test freetype Can you use

#include <stdio.h>
#include <string.h>
#include <math.h>
 
#include <ft2build.h>
#include FT_FREETYPE_H
 
 
#define WIDTH   80
#define HEIGHT  80
 
 
/* origin is the upper left corner */
unsigned char image[HEIGHT][WIDTH];
 
 
/* Replace this function with something useful. */
 
void
draw_bitmap( FT_Bitmap*  bitmap,
             FT_Int      x,
             FT_Int      y)
{
  FT_Int  i, j, p, q;
  FT_Int  x_max = x + bitmap->width;
  FT_Int  y_max = y + bitmap->rows;
 
 
  for ( i = x, p = 0; i < x_max; i++, p++ )
  {
    for ( j = y, q = 0; j < y_max; j++, q++ )
    {
      if ( i < 0      || j < 0       ||
           i >= WIDTH || j >= HEIGHT )
        continue;
 
      image[j][i] |= bitmap->buffer[q * bitmap->width + p];
    }
  }
}
 
 
void
show_image( void )
{
  int  i, j;
 
 
  for ( i = 0; i < HEIGHT; i++ )
  {
    for ( j = 0; j < WIDTH; j++ )
      putchar( image[i][j] == 0 ? ' '
                                : image[i][j] < 128 ? '+'
                                                    : '*' );
    putchar( '\n' );
  }
}
 
 
int
main( int     argc,
      char**  argv )
{
  FT_Library    library;
  FT_Face       face;
 
  FT_GlyphSlot  slot;
  FT_Matrix     matrix;                 /* transformation matrix */
  FT_Vector     pen;                    /* untransformed origin  */
  FT_Error      error;
 
  char*         filename;
  char*         text;
 
  double        angle;
  int           target_height;
  int           n, num_chars;
 
 
  if ( argc != 3 )
  {
    fprintf ( stderr, "usage: %s font sample-text\n", argv[0] );
    exit( 1 );
  }
 
  filename      = argv[1];                           /* first argument     */
  text          = argv[2];                           /* second argument    */
  num_chars     = strlen( text );
  angle         = ( 0.0 / 360 ) * 3.14159 * 2;      /* use 25 degrees     */
  target_height = HEIGHT;
 
  error = FT_Init_FreeType( &library );              /* initialize library */
  /* error handling omitted */
 
  error = FT_New_Face( library, argv[1], 0, &face ); /* create face object */
  /* error handling omitted */
 
#if 0
  /* use 50pt at 100dpi */
  error = FT_Set_Char_Size( face, 50 * 64, 0,
                            100, 0 );                /* set character size */
 
	/* pixels = 50 /72 * 100 = 69  */
#else
	FT_Set_Pixel_Sizes(face, 24, 0);
#endif
  /* error handling omitted */
 
  slot = face->glyph;
 
  /* set up matrix */
  matrix.xx = (FT_Fixed)( cos( angle ) * 0x10000L );
  matrix.xy = (FT_Fixed)(-sin( angle ) * 0x10000L );
  matrix.yx = (FT_Fixed)( sin( angle ) * 0x10000L );
  matrix.yy = (FT_Fixed)( cos( angle ) * 0x10000L );
 
  /* the pen position in 26.6 cartesian space coordinates; */
  /* start at (0,40) relative to the upper left corner  */
  pen.x = 0 * 64;
  pen.y = ( target_height - 40 ) * 64;
 
  for ( n = 0; n < num_chars; n++ )
  {
    /* set transformation */
    FT_Set_Transform( face, &matrix, &pen );
 
    /* load glyph image into the slot (erase previous one) */
    error = FT_Load_Char( face, text[n], FT_LOAD_RENDER );
    if ( error )
      continue;                 /* ignore errors */
 
    /* now, draw to our target surface (convert position) */
    draw_bitmap( &slot->bitmap,
                 slot->bitmap_left,
                 target_height - slot->bitmap_top );
 
    /* increment pen position */
    pen.x += slot->advance.x;
    pen.y += slot->advance.y;
  }
 
  show_image();
 
  FT_Done_Face    ( face );
  FT_Done_FreeType( library );
 
  return 0;
}

gcc -o test test.cpp -I/usr/include/freetype2/ -lfreetype -lm

./test ./simhei.ttf hello

 

 

 

• simhei.ttf Is a font file , Can be in windows The system indexes directly , Just change your favorite default font .

cmake file

cmake_minimum_required(VERSION 3.12)
project(chinese)

set(CMAKE_CXX_STANDARD 14)

find_package(OpenCV REQUIRED)

message(STATUS ${OpenCV_LIBRARY_DIRS})

include_directories(
        /usr/include/freetype2/
        ${OpenCV_INCLUDE_DIRS}
        )

#link_directories(${OpenCV_LIBRARY_DIRS} )

add_executable(chinese main.cpp CvxText.cpp CvxText.h)

target_link_libraries(chinese ${OpenCV_LIBS} freetype)

CvxText.h

#ifndef OPENCV_CVX_TEXT_HPP_
#define OPENCV_CVX_TEXT_HPP_

// source from: http://www.opencv.org.cn/forum.php?mod=viewthread&tid=2083&extra=&page=1
//  Support OpenCV Chinese character input 

#include <ft2build.h>
#include FT_FREETYPE_H

#include <opencv2/opencv.hpp>

class CvxText {
public:
    /**
    *  Load font file 
    */
    CvxText(const char* freeType);
    virtual ~CvxText();

    /**
    *  Get the font . At present, some parameters do not support .
    *
    * \param font         Font type ,  Currently not supported 
    * \param size         font size / Blank scale / Interval ratio / Rotation Angle 
    * \param underline    Draw the line down 
    * \param diaphaneity  transparency 
    *
    * \sa setFont, restoreFont
    */
    void getFont(int* type, cv::Scalar* size=nullptr, bool* underline=nullptr, float* diaphaneity=nullptr);

    /**
    *  Set the font . At present, some parameters do not support .
    *
    * \param font         Font type ,  Currently not supported 
    * \param size         font size / Blank scale / Interval ratio / Rotation Angle 
    * \param underline    Draw the line down 
    * \param diaphaneity  transparency 
    *
    * \sa getFont, restoreFont
    */
    void setFont(int* type, cv::Scalar* size=nullptr, bool* underline=nullptr, float* diaphaneity=nullptr);

    /**
    *  Restore the original font settings .
    *
    * \sa getFont, setFont
    */
    void restoreFont();

    /**
    *  Output Chinese characters ( The default color is black ). If you encounter characters that cannot be output, you will stop .
    *
    * \param img   Output image 
    * \param text  Text content 
    * \param pos   Text location 
    *
    * \return  Returns the length of characters successfully output , Failure to return -1.
    */
    int putText(cv::Mat& img, char* text, cv::Point pos);

    /**
    *  Output Chinese characters ( The default color is black ). If you encounter characters that cannot be output, you will stop .
    *
    * \param img   Output image 
    * \param text  Text content 
    * \param pos   Text location 
    *
    * \return  Returns the length of characters successfully output , Failure to return -1.
    */
    int putText(cv::Mat& img, const wchar_t* text, cv::Point pos);

    /**
    *  Output Chinese characters . If you encounter characters that cannot be output, you will stop .
    *
    * \param img    Output image 
    * \param text   Text content 
    * \param pos    Text location 
    * \param color  text color 
    *
    * \return  Returns the length of characters successfully output , Failure to return -1.
    */
    int putText(cv::Mat& img, const char* text, cv::Point pos, cv::Scalar color);

    /**
    *  Output Chinese characters . If you encounter characters that cannot be output, you will stop .
    *
    * \param img    Output image 
    * \param text   Text content 
    * \param pos    Text location 
    * \param color  text color 
    *
    * \return  Returns the length of characters successfully output , Failure to return -1.
    */
    int putText(cv::Mat& img, const wchar_t* text, cv::Point pos, cv::Scalar color);

private:
    //  prohibit copy
    CvxText& operator=(const CvxText&);
    //  Output the current character ,  to update m_pos Location 
    void putWChar(cv::Mat& img, wchar_t wc, cv::Point& pos, cv::Scalar color);

    FT_Library   m_library;   //  Word stock 
    FT_Face      m_face;      //  typeface 

    //  Default font output parameters 
    int         m_fontType;
    cv::Scalar   m_fontSize;
    bool      m_fontUnderline;
    float      m_fontDiaphaneity;
};

#endif // OPENCV_CVX_TEXT_HPP_

CvxText.cpp

#include <wchar.h>
#include <assert.h>
#include <locale.h>
#include <ctype.h>
#include <cmath>

#include "CvxText.h"

//  Open the font 
CvxText::CvxText(const char* freeType)
{
    assert(freeType != NULL);

    //  Open the font file ,  Create a font 
    if(FT_Init_FreeType(&m_library)) throw;
    if(FT_New_Face(m_library, freeType, 0, &m_face)) throw;

    //  Set font output parameters 
    restoreFont();

    //  Set up C Language character set environment 
    setlocale(LC_ALL, "");
}

//  Release FreeType resources 
CvxText::~CvxText()
{
    FT_Done_Face(m_face);
    FT_Done_FreeType(m_library);
}

//  Set font parameters :
//
// font         -  Font type ,  Currently not supported 
// size         -  font size / Blank scale / Interval ratio / Rotation Angle 
// underline   -  Draw the line down 
// diaphaneity   -  transparency 
void CvxText::getFont(int* type, cv::Scalar* size, bool* underline, float* diaphaneity)
{
    if (type) *type = m_fontType;
    if (size) *size = m_fontSize;
    if (underline) *underline = m_fontUnderline;
    if (diaphaneity) *diaphaneity = m_fontDiaphaneity;
}

void CvxText::setFont(int* type, cv::Scalar* size, bool* underline, float* diaphaneity)
{
    //  Parameter validity check 
    if (type) {
        if(type >= 0) m_fontType = *type;
    }
    if (size) {
        m_fontSize.val[0] = std::fabs(size->val[0]);
        m_fontSize.val[1] = std::fabs(size->val[1]);
        m_fontSize.val[2] = std::fabs(size->val[2]);
        m_fontSize.val[3] = std::fabs(size->val[3]);
    }
    if (underline) {
        m_fontUnderline   = *underline;
    }
    if (diaphaneity) {
        m_fontDiaphaneity = *diaphaneity;
    }

    FT_Set_Pixel_Sizes(m_face, (int)m_fontSize.val[0], 0);
}

//  Restore the original font settings 
void CvxText::restoreFont()
{
    m_fontType = 0;            //  Font type ( I won't support it )

    m_fontSize.val[0] = 20;      //  font size 
    m_fontSize.val[1] = 0.5;   //  White space character size ratio 
    m_fontSize.val[2] = 0.1;   //  Interval size ratio 
    m_fontSize.val[3] = 0;      //  Rotation Angle ( I won't support it )

    m_fontUnderline   = false;   //  Draw the line down ( I won't support it )

    m_fontDiaphaneity = 1.0;   //  Color ratio ( Can produce a transparent effect )

    //  Set character size 
    FT_Set_Pixel_Sizes(m_face, (int)m_fontSize.val[0], 0);
}

//  Output function ( The default color is white )
int CvxText::putText(cv::Mat& img, char* text, cv::Point pos)
{
    return putText(img, text, pos, CV_RGB(255, 255, 255));
}

int CvxText::putText(cv::Mat& img, const wchar_t* text, cv::Point pos)
{
    return putText(img, text, pos, CV_RGB(255,255,255));
}

int CvxText::putText(cv::Mat& img, const char* text, cv::Point pos, cv::Scalar color)
{
    if (img.data == nullptr) return -1;
    if (text == nullptr) return -1;

    int i;
    for (i = 0; text[i] != '\0'; ++i) {
        wchar_t wc = text[i];

        //  Parsing double byte symbols 
        if(!isascii(wc)) mbtowc(&wc, &text[i++], 2);

        //  Output the current character 
        putWChar(img, wc, pos, color);
    }

    return i;
}

int CvxText::putText(cv::Mat& img, const wchar_t* text, cv::Point pos, cv::Scalar color)
{
    if (img.data == nullptr) return -1;
    if (text == nullptr) return -1;

    int i;
    for(i = 0; text[i] != '\0'; ++i) {
        //  Output the current character 
        putWChar(img, text[i], pos, color);
    }

    return i;
}

//  Output the current character ,  to update m_pos Location 
void CvxText::putWChar(cv::Mat& img, wchar_t wc, cv::Point& pos, cv::Scalar color)
{
    //  according to unicode Generate binary bitmap of font 
    FT_UInt glyph_index = FT_Get_Char_Index(m_face, wc);
    FT_Load_Glyph(m_face, glyph_index, FT_LOAD_DEFAULT);
    FT_Render_Glyph(m_face->glyph, FT_RENDER_MODE_MONO);

    FT_GlyphSlot slot = m_face->glyph;

    //  Number of rows and columns 
    int rows = slot->bitmap.rows;
    int cols = slot->bitmap.width;

    for (int i = 0; i < rows; ++i) {
        for(int j = 0; j < cols; ++j) {
            int off  = i * slot->bitmap.pitch + j/8;

            if (slot->bitmap.buffer[off] & (0xC0 >> (j%8))) {
                int r = pos.y - (rows-1-i);
                int c = pos.x + j;

                if(r >= 0 && r < img.rows && c >= 0 && c < img.cols) {
                    cv::Vec3b pixel = img.at<cv::Vec3b>(cv::Point(c, r));
                    cv::Scalar scalar = cv::Scalar(pixel.val[0], pixel.val[1], pixel.val[2]);

                    //  Color fusion 
                    float p = m_fontDiaphaneity;
                    for (int k = 0; k < 4; ++k) {
                        scalar.val[k] = scalar.val[k]*(1-p) + color.val[k]*p;
                    }

                    img.at<cv::Vec3b>(cv::Point(c, r))[0] = (unsigned char)(scalar.val[0]);
                    img.at<cv::Vec3b>(cv::Point(c, r))[1] = (unsigned char)(scalar.val[1]);
                    img.at<cv::Vec3b>(cv::Point(c, r))[2] = (unsigned char)(scalar.val[2]);
                }
            }
        }
    }

    //  Modify the output position of the next word 
    double space = m_fontSize.val[0]*m_fontSize.val[1];
    double sep   = m_fontSize.val[0]*m_fontSize.val[2];

    pos.x += (int)((cols? cols: space) + sep);
}

main.cpp 

#include <iostream>
#include <fstream>
#include <stdlib.h>
//#include <io.h>
#include <string>
#include <vector>
#include "opencv2/opencv.hpp"
#include "time.h"
#include "CvxText.h"

static int ToWchar(char* &src, wchar_t* &dest, const char *locale = "zh_CN.utf8")
{
    if (src == NULL) {
        dest = NULL;
        return 0;
    }

    //  Set according to the environment variable locale
    setlocale(LC_CTYPE, locale);

    //  Get the required wide character size 
    int w_size = mbstowcs(NULL, src, 0) + 1;

    // w_size = 0  explain mbstowcs The return value is -1. That is, illegal characters are encountered during operation ( It is likely to make locale
    //  Not set correctly )
    if (w_size == 0) {
        dest = NULL;
        return -1;
    }

    //wcout << "w_size" << w_size << endl;
    dest = new wchar_t[w_size];
    if (!dest) {
        return -1;
    }

    int ret = mbstowcs(dest, src, strlen(src)+1);
    if (ret <= 0) {
        return -1;
    }
    return 0;
}

int main()
{
    cv::Mat img = cv::imread("./demo.jpg");
    if (!img.data || img.channels() != 3) {
        fprintf(stderr, "read image fail\n");
        return -1;
    }

    CvxText text("./simhei.ttf"); // Specified font 
    cv::Scalar size1{ 80, 0.5, 0.1, 0 }; // ( font size ,  invalid ,  Between characters ,  invalid  }

    text.setFont(nullptr, &size1, nullptr, 0);
    char* str = (char *)" Hello , Li Jiawang ";
    wchar_t *w_str;
    ToWchar(str,w_str);
    text.putText(img, w_str, cv::Point(50,100), cv::Scalar(0, 0, 255));
    cv::resize(img, img, cv::Size(300,300));
    cv::imshow("demo", img);
    cv::waitKey(0);
    cv::imwrite("./res.jpg", img);
    return 0;
}