C++&Python&C# 三语言OpenCV从零开发(7):图像的阈值

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OpenCV一个窗口同时显示多张图片 (C++)

前言

我感觉我之前的比较实在是太过于偏代码了，缺少了图形学的知识的记录。之后的笔记我会把图形学的知识也记录上去。

阈值

阈值简单来说就是增强图片的对比。用过Ps的人就知道阈值是什么意思，在电脑绘画中用的还是比较多的

阈值使用

代码

Python

# %%
# 导入包
import cv2
import matplotlib.pyplot as plt
import numpy as np

image = {
    "image":'',
    "gray":'',
    
}

image["image"] = cv2.imread("D:/workSpace/OpenCV/HellOpenCV/Resources/image/cat.png")

# 获取颜色通道，因为cv2是BGR的顺序，所以这里是B 灰度
image["gray"]= cv2.split(image['image'])[0]

thresh = {
    '1' : '','2': '','3': '','4': '','5': ''
}

# 调用不同的阈值处理算子
ret , thresh['1'] = cv2.threshold(image['gray'],127,255,cv2.THRESH_BINARY)
ret , thresh['2'] = cv2.threshold(image['gray'],127,255,cv2.THRESH_BINARY_INV)
ret , thresh['3'] = cv2.threshold(image['gray'],127,255,cv2.THRESH_TRUNC)
ret , thresh['4'] = cv2.threshold(image['gray'],127,255,cv2.THRESH_TOZERO)
ret , thresh['5'] = cv2.threshold(image['gray'],127,255,cv2.THRESH_TOZERO_INV)

# 将数据总和成数组
titles = ['iamge','binary','binary inv','trunc','tozero','tozero inv']
images = [image['gray'],thresh['1'],thresh['2'],thresh['3'],thresh['4'],thresh['5']]

# 循环赋值到plt中
for i in range(6):
    plt.subplot(2,3,i+1),plt.imshow(images[i],'gray')
    plt.title(titles[i])
    plt.xticks([]),plt.yticks([])

plt.show()

C++

这里为了一次性展示多个窗口，我就CSDN上面找了个方法

OpenCV一个窗口同时显示多张图片 (C++)

#include   
#include   
#include   
#include   
#include  
#include 
using namespace std;
using namespace cv;


vector<Mat> imageVector;

void multipleImage(vector<Mat> imgVector, Mat& dst, int imgCols)
{
	const int MAX_PIXEL = 300;
	int imgNum = imgVector.size();
	//选择图片最大的一边 将最大的边按比例变为300像素
	Size imgOriSize = imgVector[0].size();
	int imgMaxPixel = max(imgOriSize.height, imgOriSize.width);
	//获取最大像素变为MAX_PIXEL的比例因子
	double prop = imgMaxPixel < MAX_PIXEL ? (double)imgMaxPixel / MAX_PIXEL : MAX_PIXEL / (double)imgMaxPixel;
	Size imgStdSize(imgOriSize.width * prop, imgOriSize.height * prop); //窗口显示的标准图像的Size

	Mat imgStd; //标准图片
	Point2i location(0, 0); //坐标点(从0,0开始)
	//构建窗口大小 通道与imageVector[0]的通道一样
	Mat imgWindow(imgStdSize.height * ((imgNum - 1) / imgCols + 1), imgStdSize.width * imgCols, imgVector[0].type());
	for (int i = 0; i < imgNum; i++)
	{
		location.x = (i % imgCols) * imgStdSize.width;
		location.y = (i / imgCols) * imgStdSize.height;
		resize(imgVector[i], imgStd, imgStdSize, prop, prop, INTER_LINEAR); //设置为标准大小
		imgStd.copyTo(imgWindow(Rect(location, imgStdSize)));
	}
	dst = imgWindow;
}

int main()
{
	auto image = imread("D:/workSpace/OpenCV/HellOpenCV/Resources/image/cat.png");
	Mat showImage;

	Mat bgr[3];
	split(image, bgr);
	Mat gray = bgr[0];

	Mat thresh[5];

	threshold(gray, thresh[0], 127, 255, THRESH_BINARY);
	threshold(gray, thresh[1], 127, 255, THRESH_BINARY_INV);
	threshold(gray, thresh[2], 127, 255, THRESH_TRUNC);
	threshold(gray, thresh[3], 127, 255, THRESH_TOZERO);
	threshold(gray, thresh[4], 127, 255, THRESH_TOZERO_INV);


	vector<Mat> images{gray,thresh[0],thresh[1], thresh[2], thresh[3], thresh[4], };

	multipleImage(images, showImage, 3);

	imshow("C++", showImage);

	waitKey(0);
	destroyAllWindows();
	return 0;
}

Csharp

还是那句话，C++跑通了，Csharp抄抄就可以了。

using OpenCvSharp;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Numerics;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;

namespace HelloOpenCV.Utils
{
    public static class MyOpenCV_Extensions
    {

        /// 

        /// 3通道遍历
        /// 
        /// 
        /// 
        public static int[,,] MatToArray(Mat mat)
        {

            var res = new int[mat.Rows, mat.Cols, mat.Channels()];
            for (var i = 0; i < mat.Rows; i++)
            {

                for (var j = 0; j < mat.Cols; j++)
                {
                    var temp = mat.At<Vec3b>(i, j);
                    res[i, j, 0] = temp[0];
                    res[i, j, 1] = temp[1];
                    res[i, j, 2] = temp[2];
                }
            }
            return res;
        }

        public static Mat MultipleImage(List<Mat> lists, int imgCols)
        {
            const int MAX_PIXEL = 300;
            int imgNum = lists.Count;
            //选择图片最大的一边 将最大的边按比例变为300像素
            Size imgOriSize = lists[0].Size();
            int imgMaxPixel = Math.Max(imgOriSize.Height, imgOriSize.Width);
            //获取最大像素变为MAX_PIXEL的比例因子
            double prop = imgMaxPixel < MAX_PIXEL ? (double)imgMaxPixel / MAX_PIXEL : MAX_PIXEL / (double)imgMaxPixel;
            Size imgStdSize= new Size(imgOriSize.Width* prop, imgOriSize.Height* prop); //窗口显示的标准图像的Size

            Mat imgStd = new Mat(); //标准图片
            
            Point location = new Point(0, 0); //坐标点(从0,0开始)
                                    //构建窗口大小 通道与imageVector[0]的通道一样
            Mat imgWindow = new Mat(imgStdSize.Height* ((imgNum -1) / imgCols + 1), imgStdSize.Width* imgCols, lists[0].Type());
            for (int i = 0; i < imgNum; i++)
            {
                location.X = (i % imgCols) * imgStdSize.Width;
                location.Y = (i / imgCols) * imgStdSize.Height;
                Cv2.Resize(lists[i], imgStd, imgStdSize, prop, prop, InterpolationFlags.Linear); //设置为标准大小
                imgStd.CopyTo(new Mat(imgWindow, new Rect(location, imgStdSize)) ); 
            }
            return imgWindow;
        }
    }
}

运行代码

 static void Main(string[] args)
 {
     Mat image = Cv2.ImRead("D:/workSpace/OpenCV/HellOpenCV/Resources/image/cat.png");

     Mat[] bgr = new Mat[3];
     Cv2.Split(image, out bgr);
     Mat gray = bgr[0];

     Mat[] threshs = new Mat[5];
     for(var i = 0; i < threshs.Length; i++)
     {
         threshs[i] = new Mat();
     }
     Cv2.Threshold(gray, threshs[0], 127, 255, ThresholdTypes.Binary);
     Cv2.Threshold(gray, threshs[1], 127, 255, ThresholdTypes.BinaryInv);
     Cv2.Threshold(gray, threshs[2], 127, 255, ThresholdTypes.Trunc);
     Cv2.Threshold(gray, threshs[3], 127, 255, ThresholdTypes.Tozero);
     Cv2.Threshold(gray, threshs[4], 127, 255, ThresholdTypes.TozeroInv);

     var res = MyOpenCV_Extensions.MultipleImage(new List<Mat>() {
         gray, threshs[0], threshs[1], threshs[2], threshs[3], threshs[4] 
     }, 3);


     Cv2.ImShow("Csharp", res);

     Cv2.WaitKey(0);
     Cv2.DestroyAllWindows();


 }

csharp代码问题

遇到了几个坑

C++是能直接把变量当做构造函数的，C# 对应的代码是构造函数里面带Mat参数的

而且C++的构造函数还不好定位，我进去找不到源码。我不知道C++ 的代码是怎么调试的，毕竟没怎么接触过

总结

跟之前的套路差不多，Python跑通，C++ 翻译Python+上网查资料，Csharp翻译C++。我还是觉得Csharp优雅多了，写起来舒服，C++ 这个语法用起来有点痛苦。而且C++ 报错天天给我报内存变量报错，我哪里能看得懂啊，顶多定位到哪行代码。