5.图像操作

1.主要内容

• 读写图像
• 读写像素
• 修改像素值

2.读写图像

imread 可以指定加载为灰度或者RGB图像 
imwrite 保存图像文件，类型由扩展名决定

3.读写像素

 读一个GRAY像素点的像素值（CV_8UC1）

Scalar intensity = img.at<uchar>(y, x);

或者

 Scalar intensity = img.at<uchar>(Point(x, y)); 

 读一个RGB像素点的像素值

Vec3f intensity = img.at<Vec3f>(y, x); 
float blue = intensity.val[0];  
float green = intensity.val[1];  
float red = intensity.val[2];

4.修改像素值

灰度图像

img.at<uchar>(y, x) = 128;

RGB三通道图像

img.at<Vec3b>(y,x)[0]=128; // blue 
img.at<Vec3b>(y,x)[1]=128; // green 
img.at<Vec3b>(y,x)[2]=128; // red

空白图像赋值

img = Scalar(0);

ROI选择

Rect r(10, 10, 100, 100);  
Mat smallImg = img(r);

5.Vec3b与Vec3F

 Vec3b对应三通道的顺序是blue、green、red的uchar类型数据。
 Vec3f对应三通道的float类型数据
 把CV_8UC1转换到CV32F1实现如下：

src.convertTo(dst, CV_32F);

6.课外扩展：

 OpenCv中向量模板类Vec的表示
https://blog.csdn.net/mangobar/article/details/82863558
 ROI（region of interest）百度百科
https://baike.baidu.com/item/ROI/1125333?fr=aladdin
 图像的ROI区域选择与复制
https://www.cnblogs.com/nicewe/p/8461994.html
 range()函数用法
https://blog.csdn.net/u011973222/article/details/79929366
 sobel函数
https://blog.csdn.net/qq_18343569/article/details/47835679
 opencv入门笔记at的用法
https://blog.csdn.net/visionfuture/article/details/77092695
 像素值的读写opencv的at函数
https://blog.csdn.net/qq_36503007/article/details/79895610
 opencv笔记——OpenCV轮廓vector
https://blog.csdn.net/qq_37764129/article/details/82142400
 C++/opencv学习笔记（Vector用法）
https://blog.csdn.net/Zouziceng/article/details/78052203
 opencv3::Mat元素的获取、at，ptr
https://blog.csdn.net/BoaHock/article/details/80790323
 opencv MAT中维度(dims)和通道(channels)的理解和区别
https://blog.csdn.net/chengde6896383/article/details/83444874
 opencv学习（十六）之颜色空间转换cvtColor()
https://blog.csdn.net/keith_bb/article/details/53470170
 OpenCV之bitwise_and、bitwise_not等图像基本运算及掩膜
https://blog.csdn.net/u011028345/article/details/77278467