《learning opencv》第6章第2题解决方案
前言
opencv提供了方便的函数，用以处理在图像上输出字符的问题，而且支持多种字体的输出。但是opencv提供的功能只支持英文字符的输出，无法解决中文输出的问题。对于中文字符的输出，通过第三方提供的函数可以解决，本篇文章将会详细介绍了英文输出和中文输出。
有如下所示的图片：
实现以下功能：
- 将原始图像转换为三个通道的灰度图片（即是一个三通道图像，但视觉现象还是灰度图像）
- 在灰度图像中输出彩色的英文字符
在灰度图像中输出字符（串），主要通过cv::putText()函数，实现，该函数的详细介绍如下：
void putText( InputOutputArray img, const String& text, Point org,
int fontFace, double fontScale, Scalar color,
int thickness = 1, int lineType = LINE_8,
bool bottomLeftOrigin = false )
@param InputOutputArray img 字符输出的源图像
@param const String& text 输出字符串
@param Point org 输出字符串在图像中的位置
@param int fontFace 输出字符串的字体
@param double fontScale 输出字符串的大小
@param bool bottomLeftOrigin 如果为真，二维图像起点坐标以左下角，否则，为左上角
综上，在图像上实现字符串输出的代码如下：
Mat m = imread("timg.jpg");
Mat m2gray, gray2m;
cvtColor(m, m2gray, COLOR_BGR2GRAY);
cvtColor(m2gray, gray2m, COLOR_GRAY2BGR);
putText(gray2m,"Hello world",Point(500,200),FONT_HERSHEY_SCRIPT_COMPLEX,3.0,Scalar(14,173,,238),2,8);
其效果如下所示：
opencv对于中文字符的输出，需要引入以下两个文件
putText.h
#pragma once
#ifndef PUTTEXT_H_
#define PUTTEXT_H_
#include <windows.h>
#include <string>
#include <opencv2/opencv.hpp>
using namespace cv;
void GetStringSize(HDC hDC, const char* str, int* w, int* h);
void putTextZH(Mat& dst, const char* str, Point org, Scalar color, int fontSize,
const char* fn = "Arial", bool italic = false, bool underline = false);
#endif // PUTTEXT_H_
putText.cpp
#include "putText.h"
void GetStringSize(HDC hDC, const char* str, int* w, int* h)
{
SIZE size;
GetTextExtentPoint32A(hDC, str, strlen(str), &size);
if (w != 0) *w = size.cx;
if (h != 0) *h = size.cy;
}
void putTextZH(Mat& dst, const char* str, Point org, Scalar color, int fontSize, const char* fn, bool italic, bool underline)
{
CV_Assert(dst.data != 0 && (dst.channels() == 1 || dst.channels() == 3));
int x, y, r, b;
if (org.x > dst.cols || org.y > dst.rows) return;
x = org.x < 0 ? -org.x : 0;
y = org.y < 0 ? -org.y : 0;
LOGFONTA lf;
lf.lfHeight = -fontSize;
lf.lfWidth = 0;
lf.lfEscapement = 0;
lf.lfOrientation = 0;
lf.lfWeight = 5;
lf.lfItalic = italic; //斜体
lf.lfUnderline = underline; //下划线
lf.lfStrikeOut = 0;
lf.lfCharSet = DEFAULT_CHARSET;
lf.lfOutPrecision = 0;
lf.lfClipPrecision = 0;
lf.lfQuality = PROOF_QUALITY;
lf.lfPitchAndFamily = 0;
strcpy_s(lf.lfFaceName, fn);
HFONT hf = CreateFontIndirectA(&lf);
HDC hDC = CreateCompatibleDC(0);
HFONT hOldFont = (HFONT)SelectObject(hDC, hf);
int strBaseW = 0, strBaseH = 0;
int singleRow = 0;
char buf[1 << 12];
strcpy_s(buf, str);
char* bufT[1 << 12]; // 这个用于分隔字符串后剩余的字符，可能会超出。
//处理多行
{
int nnh = 0;
int cw, ch;
const char* ln = strtok_s(buf, "\n", bufT);
while (ln != 0)
{
GetStringSize(hDC, ln, &cw, &ch);
strBaseW = max(strBaseW, cw);
strBaseH = max(strBaseH, ch);
ln = strtok_s(0, "\n", bufT);
nnh++;
}
singleRow = strBaseH;
strBaseH *= nnh;
}
if (org.x + strBaseW < 0 || org.y + strBaseH < 0)
{
SelectObject(hDC, hOldFont);
DeleteObject(hf);
DeleteObject(hDC);
return;
}
r = org.x + strBaseW > dst.cols ? dst.cols - org.x - 1 : strBaseW - 1;
b = org.y + strBaseH > dst.rows ? dst.rows - org.y - 1 : strBaseH - 1;
org.x = org.x < 0 ? 0 : org.x;
org.y = org.y < 0 ? 0 : org.y;
BITMAPINFO bmp = { 0 };
BITMAPINFOHEADER& bih = bmp.bmiHeader;
int strDrawLineStep = strBaseW * 3 % 4 == 0 ? strBaseW * 3 : (strBaseW * 3 + 4 - ((strBaseW * 3) % 4));
bih.biSize = sizeof(BITMAPINFOHEADER);
bih.biWidth = strBaseW;
bih.biHeight = strBaseH;
bih.biPlanes = 1;
bih.biBitCount = 24;
bih.biCompression = BI_RGB;
bih.biSizeImage = strBaseH * strDrawLineStep;
bih.biClrUsed = 0;
bih.biClrImportant = 0;
void* pDibData = 0;
HBITMAP hBmp = CreateDIBSection(hDC, &bmp, DIB_RGB_COLORS, &pDibData, 0, 0);
CV_Assert(pDibData != 0);
HBITMAP hOldBmp = (HBITMAP)SelectObject(hDC, hBmp);
//color.val[2], color.val[1], color.val[0]
SetTextColor(hDC, RGB(255, 255, 255));
SetBkColor(hDC, 0);
//SetStretchBltMode(hDC, COLORONCOLOR);
strcpy_s(buf, str);
const char* ln = strtok_s(buf, "\n", bufT);
int outTextY = 0;
while (ln != 0)
{
TextOutA(hDC, 0, outTextY, ln, strlen(ln));
outTextY += singleRow;
ln = strtok_s(0, "\n", bufT);
}
uchar* dstData = (uchar*)dst.data;
int dstStep = dst.step / sizeof(dstData[0]);
unsigned char* pImg = (unsigned char*)dst.data + org.x * dst.channels() + org.y * dstStep;
unsigned char* pStr = (unsigned char*)pDibData + x * 3;
for (int tty = y; tty <= b; ++tty)
{
unsigned char* subImg = pImg + (tty - y) * dstStep;
unsigned char* subStr = pStr + (strBaseH - tty - 1) * strDrawLineStep;
for (int ttx = x; ttx <= r; ++ttx)
{
for (int n = 0; n < dst.channels(); ++n) {
double vtxt = subStr[n] / 255.0;
int cvv = vtxt * color.val[n] + (1 - vtxt) * subImg[n];
subImg[n] = cvv > 255 ? 255 : (cvv < 0 ? 0 : cvv);
}
subStr += 3;
subImg += dst.channels();
}
}
SelectObject(hDC, hOldBmp);
SelectObject(hDC, hOldFont);
DeleteObject(hf);
DeleteObject(hBmp);
DeleteDC(hDC);
}
引入以上两个文件后，可以很方便的实现，在图像上输出中文字符的功能，代码如下：
#include<iostream>
#include<opencv2/opencv.hpp>
#include"putText.h"
using namespace cv;
/*
load and display grayscale image
draw color text onto image
*/
int main()
{
Mat m = imread("timg.jpg");
Mat m2gray, gray2m;
cvtColor(m, m2gray, COLOR_BGR2GRAY);
cvtColor(m2gray, gray2m, COLOR_GRAY2BGR);
putTextZH(m, "长\n云\n", Point(1150, 120), Scalar(230, 230, 230), 55, "迷你简启体");
putTextZH(m, "暗\n雪\n山\n", Point(1220, 185), Scalar(230, 230, 230), 55, "迷你简启体");
imshow("image_text", m);
imwrite("image_textZH.jpg", m);
waitKey(0);
return 0;
}
其效果如下：
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