一文学会opencv(一)——加载，修改，保存图像

加载，修改，保存图像

主要内容

imread()函数

2. cvtColor()函数

3. imwrite()函数

imread()函数

imread函数的功能是加载一张图像，并将其存储至一个Mat类型的对象中。第一个参数为图像文件名称，可以是相对路径，也可以是绝对路径。
第二个参数就是加载图像时，读入的类型。这里我们几个参数选择。如下图所示：

示例代码：

int main(){
    Mat src; // 定义一个Mat类型对象
    src = imread("./1.jpg", IMREAD_COLOR); // 读入一个图像
    if (src.empty()){ // 当图像为空时，执行if语句判断
        cout << "img empty" << endl; // 输出 img empty
    }

    imshow("src", src); // 显示图像
    waitKey(0); // 设定等待时间为无限等待
    return 0; // 返回值
}
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cvtColor()函数

cvtColor()函数的功能是将一个图像从一个色彩空间转换到另一个色彩空间。需要三个参数，第一个参数为输入图像，第二个参数为输出图像。第三个参数为转换的色彩空间类型。
第三个参数种类如下所示：

cv::ColorConversionCodes { 
  cv::COLOR_BGR2BGRA = 0, 
  cv::COLOR_RGB2RGBA = COLOR_BGR2BGRA, 
  cv::COLOR_BGRA2BGR = 1, 
  cv::COLOR_RGBA2RGB = COLOR_BGRA2BGR, 
  cv::COLOR_BGR2RGBA = 2, 
  cv::COLOR_RGB2BGRA = COLOR_BGR2RGBA, 
  cv::COLOR_RGBA2BGR = 3, 
  cv::COLOR_BGRA2RGB = COLOR_RGBA2BGR, 
  cv::COLOR_BGR2RGB = 4, 
  cv::COLOR_RGB2BGR = COLOR_BGR2RGB, 
  cv::COLOR_BGRA2RGBA = 5, 
  cv::COLOR_RGBA2BGRA = COLOR_BGRA2RGBA, 
  cv::COLOR_BGR2GRAY = 6, 
  cv::COLOR_RGB2GRAY = 7, 
  cv::COLOR_GRAY2BGR = 8, 
  cv::COLOR_GRAY2RGB = COLOR_GRAY2BGR, 
  cv::COLOR_GRAY2BGRA = 9, 
  cv::COLOR_GRAY2RGBA = COLOR_GRAY2BGRA, 
  cv::COLOR_BGRA2GRAY = 10, 
  cv::COLOR_RGBA2GRAY = 11, 
  cv::COLOR_BGR2BGR565 = 12, 
  cv::COLOR_RGB2BGR565 = 13, 
  cv::COLOR_BGR5652BGR = 14, 
  cv::COLOR_BGR5652RGB = 15, 
  cv::COLOR_BGRA2BGR565 = 16, 
  cv::COLOR_RGBA2BGR565 = 17, 
  cv::COLOR_BGR5652BGRA = 18, 
  cv::COLOR_BGR5652RGBA = 19, 
  cv::COLOR_GRAY2BGR565 = 20, 
  cv::COLOR_BGR5652GRAY = 21, 
  cv::COLOR_BGR2BGR555 = 22, 
  cv::COLOR_RGB2BGR555 = 23, 
  cv::COLOR_BGR5552BGR = 24, 
  cv::COLOR_BGR5552RGB = 25, 
  cv::COLOR_BGRA2BGR555 = 26, 
  cv::COLOR_RGBA2BGR555 = 27, 
  cv::COLOR_BGR5552BGRA = 28, 
  cv::COLOR_BGR5552RGBA = 29, 
  cv::COLOR_GRAY2BGR555 = 30, 
  cv::COLOR_BGR5552GRAY = 31, 
  cv::COLOR_BGR2XYZ = 32, 
  cv::COLOR_RGB2XYZ = 33, 
  cv::COLOR_XYZ2BGR = 34, 
  cv::COLOR_XYZ2RGB = 35, 
  cv::COLOR_BGR2YCrCb = 36, 
  cv::COLOR_RGB2YCrCb = 37, 
  cv::COLOR_YCrCb2BGR = 38, 
  cv::COLOR_YCrCb2RGB = 39, 
  cv::COLOR_BGR2HSV = 40, 
  cv::COLOR_RGB2HSV = 41, 
  cv::COLOR_BGR2Lab = 44, 
  cv::COLOR_RGB2Lab = 45, 
  cv::COLOR_BGR2Luv = 50, 
  cv::COLOR_RGB2Luv = 51, 
  cv::COLOR_BGR2HLS = 52, 
  cv::COLOR_RGB2HLS = 53, 
  cv::COLOR_HSV2BGR = 54, 
  cv::COLOR_HSV2RGB = 55, 
  cv::COLOR_Lab2BGR = 56, 
  cv::COLOR_Lab2RGB = 57, 
  cv::COLOR_Luv2BGR = 58, 
  cv::COLOR_Luv2RGB = 59, 
  cv::COLOR_HLS2BGR = 60, 
  cv::COLOR_HLS2RGB = 61, 
  cv::COLOR_BGR2HSV_FULL = 66, 
  cv::COLOR_RGB2HSV_FULL = 67, 
  cv::COLOR_BGR2HLS_FULL = 68, 
  cv::COLOR_RGB2HLS_FULL = 69, 
  cv::COLOR_HSV2BGR_FULL = 70, 
  cv::COLOR_HSV2RGB_FULL = 71, 
  cv::COLOR_HLS2BGR_FULL = 72, 
  cv::COLOR_HLS2RGB_FULL = 73, 
  cv::COLOR_LBGR2Lab = 74, 
  cv::COLOR_LRGB2Lab = 75, 
  cv::COLOR_LBGR2Luv = 76, 
  cv::COLOR_LRGB2Luv = 77, 
  cv::COLOR_Lab2LBGR = 78, 
  cv::COLOR_Lab2LRGB = 79, 
  cv::COLOR_Luv2LBGR = 80, 
  cv::COLOR_Luv2LRGB = 81, 
  cv::COLOR_BGR2YUV = 82, 
  cv::COLOR_RGB2YUV = 83, 
  cv::COLOR_YUV2BGR = 84, 
  cv::COLOR_YUV2RGB = 85, 
  cv::COLOR_YUV2RGB_NV12 = 90, 
  cv::COLOR_YUV2BGR_NV12 = 91, 
  cv::COLOR_YUV2RGB_NV21 = 92, 
  cv::COLOR_YUV2BGR_NV21 = 93, 
  cv::COLOR_YUV420sp2RGB = COLOR_YUV2RGB_NV21, 
  cv::COLOR_YUV420sp2BGR = COLOR_YUV2BGR_NV21, 
  cv::COLOR_YUV2RGBA_NV12 = 94, 
  cv::COLOR_YUV2BGRA_NV12 = 95, 
  cv::COLOR_YUV2RGBA_NV21 = 96, 
  cv::COLOR_YUV2BGRA_NV21 = 97, 
  cv::COLOR_YUV420sp2RGBA = COLOR_YUV2RGBA_NV21, 
  cv::COLOR_YUV420sp2BGRA = COLOR_YUV2BGRA_NV21, 
  cv::COLOR_YUV2RGB_YV12 = 98, 
  cv::COLOR_YUV2BGR_YV12 = 99, 
  cv::COLOR_YUV2RGB_IYUV = 100, 
  cv::COLOR_YUV2BGR_IYUV = 101, 
  cv::COLOR_YUV2RGB_I420 = COLOR_YUV2RGB_IYUV, 
  cv::COLOR_YUV2BGR_I420 = COLOR_YUV2BGR_IYUV, 
  cv::COLOR_YUV420p2RGB = COLOR_YUV2RGB_YV12, 
  cv::COLOR_YUV420p2BGR = COLOR_YUV2BGR_YV12, 
  cv::COLOR_YUV2RGBA_YV12 = 102, 
  cv::COLOR_YUV2BGRA_YV12 = 103, 
  cv::COLOR_YUV2RGBA_IYUV = 104, 
  cv::COLOR_YUV2BGRA_IYUV = 105, 
  cv::COLOR_YUV2RGBA_I420 = COLOR_YUV2RGBA_IYUV, 
  cv::COLOR_YUV2BGRA_I420 = COLOR_YUV2BGRA_IYUV, 
  cv::COLOR_YUV420p2RGBA = COLOR_YUV2RGBA_YV12, 
  cv::COLOR_YUV420p2BGRA = COLOR_YUV2BGRA_YV12, 
  cv::COLOR_YUV2GRAY_420 = 106, 
  cv::COLOR_YUV2GRAY_NV21 = COLOR_YUV2GRAY_420, 
  cv::COLOR_YUV2GRAY_NV12 = COLOR_YUV2GRAY_420, 
  cv::COLOR_YUV2GRAY_YV12 = COLOR_YUV2GRAY_420, 
  cv::COLOR_YUV2GRAY_IYUV = COLOR_YUV2GRAY_420, 
  cv::COLOR_YUV2GRAY_I420 = COLOR_YUV2GRAY_420, 
  cv::COLOR_YUV420sp2GRAY = COLOR_YUV2GRAY_420, 
  cv::COLOR_YUV420p2GRAY = COLOR_YUV2GRAY_420, 
  cv::COLOR_YUV2RGB_UYVY = 107, 
  cv::COLOR_YUV2BGR_UYVY = 108, 
  cv::COLOR_YUV2RGB_Y422 = COLOR_YUV2RGB_UYVY, 
  cv::COLOR_YUV2BGR_Y422 = COLOR_YUV2BGR_UYVY, 
  cv::COLOR_YUV2RGB_UYNV = COLOR_YUV2RGB_UYVY, 
  cv::COLOR_YUV2BGR_UYNV = COLOR_YUV2BGR_UYVY, 
  cv::COLOR_YUV2RGBA_UYVY = 111, 
  cv::COLOR_YUV2BGRA_UYVY = 112, 
  cv::COLOR_YUV2RGBA_Y422 = COLOR_YUV2RGBA_UYVY, 
  cv::COLOR_YUV2BGRA_Y422 = COLOR_YUV2BGRA_UYVY, 
  cv::COLOR_YUV2RGBA_UYNV = COLOR_YUV2RGBA_UYVY, 
  cv::COLOR_YUV2BGRA_UYNV = COLOR_YUV2BGRA_UYVY, 
  cv::COLOR_YUV2RGB_YUY2 = 115, 
  cv::COLOR_YUV2BGR_YUY2 = 116, 
  cv::COLOR_YUV2RGB_YVYU = 117, 
  cv::COLOR_YUV2BGR_YVYU = 118, 
  cv::COLOR_YUV2RGB_YUYV = COLOR_YUV2RGB_YUY2, 
  cv::COLOR_YUV2BGR_YUYV = COLOR_YUV2BGR_YUY2, 
  cv::COLOR_YUV2RGB_YUNV = COLOR_YUV2RGB_YUY2, 
  cv::COLOR_YUV2BGR_YUNV = COLOR_YUV2BGR_YUY2, 
  cv::COLOR_YUV2RGBA_YUY2 = 119, 
  cv::COLOR_YUV2BGRA_YUY2 = 120, 
  cv::COLOR_YUV2RGBA_YVYU = 121, 
  cv::COLOR_YUV2BGRA_YVYU = 122, 
  cv::COLOR_YUV2RGBA_YUYV = COLOR_YUV2RGBA_YUY2, 
  cv::COLOR_YUV2BGRA_YUYV = COLOR_YUV2BGRA_YUY2, 
  cv::COLOR_YUV2RGBA_YUNV = COLOR_YUV2RGBA_YUY2, 
  cv::COLOR_YUV2BGRA_YUNV = COLOR_YUV2BGRA_YUY2, 
  cv::COLOR_YUV2GRAY_UYVY = 123, 
  cv::COLOR_YUV2GRAY_YUY2 = 124, 
  cv::COLOR_YUV2GRAY_Y422 = COLOR_YUV2GRAY_UYVY, 
  cv::COLOR_YUV2GRAY_UYNV = COLOR_YUV2GRAY_UYVY, 
  cv::COLOR_YUV2GRAY_YVYU = COLOR_YUV2GRAY_YUY2, 
  cv::COLOR_YUV2GRAY_YUYV = COLOR_YUV2GRAY_YUY2, 
  cv::COLOR_YUV2GRAY_YUNV = COLOR_YUV2GRAY_YUY2, 
  cv::COLOR_RGBA2mRGBA = 125, 
  cv::COLOR_mRGBA2RGBA = 126, 
  cv::COLOR_RGB2YUV_I420 = 127, 
  cv::COLOR_BGR2YUV_I420 = 128, 
  cv::COLOR_RGB2YUV_IYUV = COLOR_RGB2YUV_I420, 
  cv::COLOR_BGR2YUV_IYUV = COLOR_BGR2YUV_I420, 
  cv::COLOR_RGBA2YUV_I420 = 129, 
  cv::COLOR_BGRA2YUV_I420 = 130, 
  cv::COLOR_RGBA2YUV_IYUV = COLOR_RGBA2YUV_I420, 
  cv::COLOR_BGRA2YUV_IYUV = COLOR_BGRA2YUV_I420, 
  cv::COLOR_RGB2YUV_YV12 = 131, 
  cv::COLOR_BGR2YUV_YV12 = 132, 
  cv::COLOR_RGBA2YUV_YV12 = 133, 
  cv::COLOR_BGRA2YUV_YV12 = 134, 
  cv::COLOR_BayerBG2BGR = 46, 
  cv::COLOR_BayerGB2BGR = 47, 
  cv::COLOR_BayerRG2BGR = 48, 
  cv::COLOR_BayerGR2BGR = 49, 
  cv::COLOR_BayerBG2RGB = COLOR_BayerRG2BGR, 
  cv::COLOR_BayerGB2RGB = COLOR_BayerGR2BGR, 
  cv::COLOR_BayerRG2RGB = COLOR_BayerBG2BGR, 
  cv::COLOR_BayerGR2RGB = COLOR_BayerGB2BGR, 
  cv::COLOR_BayerBG2GRAY = 86, 
  cv::COLOR_BayerGB2GRAY = 87, 
  cv::COLOR_BayerRG2GRAY = 88, 
  cv::COLOR_BayerGR2GRAY = 89, 
  cv::COLOR_BayerBG2BGR_VNG = 62, 
  cv::COLOR_BayerGB2BGR_VNG = 63, 
  cv::COLOR_BayerRG2BGR_VNG = 64, 
  cv::COLOR_BayerGR2BGR_VNG = 65, 
  cv::COLOR_BayerBG2RGB_VNG = COLOR_BayerRG2BGR_VNG, 
  cv::COLOR_BayerGB2RGB_VNG = COLOR_BayerGR2BGR_VNG, 
  cv::COLOR_BayerRG2RGB_VNG = COLOR_BayerBG2BGR_VNG, 
  cv::COLOR_BayerGR2RGB_VNG = COLOR_BayerGB2BGR_VNG, 
  cv::COLOR_BayerBG2BGR_EA = 135, 
  cv::COLOR_BayerGB2BGR_EA = 136, 
  cv::COLOR_BayerRG2BGR_EA = 137, 
  cv::COLOR_BayerGR2BGR_EA = 138, 
  cv::COLOR_BayerBG2RGB_EA = COLOR_BayerRG2BGR_EA, 
  cv::COLOR_BayerGB2RGB_EA = COLOR_BayerGR2BGR_EA, 
  cv::COLOR_BayerRG2RGB_EA = COLOR_BayerBG2BGR_EA, 
  cv::COLOR_BayerGR2RGB_EA = COLOR_BayerGB2BGR_EA, 
  cv::COLOR_BayerBG2BGRA = 139, 
  cv::COLOR_BayerGB2BGRA = 140, 
  cv::COLOR_BayerRG2BGRA = 141, 
  cv::COLOR_BayerGR2BGRA = 142, 
  cv::COLOR_BayerBG2RGBA = COLOR_BayerRG2BGRA, 
  cv::COLOR_BayerGB2RGBA = COLOR_BayerGR2BGRA, 
  cv::COLOR_BayerRG2RGBA = COLOR_BayerBG2BGRA, 
  cv::COLOR_BayerGR2RGBA = COLOR_BayerGB2BGRA, 
  cv::COLOR_COLORCVT_MAX = 143 
}
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示例代码：

int main(){
    Mat src; // 定义一个Mat类型对象
    Mat src_gray; // 定义一个Mat类型对象
    src = imread("./1.jpg", IMREAD_COLOR); // 读入一个图像
    if (src.empty()){ // 当图像为空时，执行if语句判断
        cout << "img empty" << endl; // 输出 img empty
    }

    imshow("src", src); // 显示图像
    cvtColor(src, src_gray, COLOR_RGB2GRAY); // 将src转换为灰度图像存储至src_gray
    waitKey(0); // 设定等待时间为无限等待
    return 0; // 返回值
}
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imwrite()函数

imwrite()函数的功能是将图像保存到指定的路径下。参数有两个。第一个是存储路径，第二个是待存储的Mat对象。这个函数比较简单没什么好解释的。
示例代码：

int main(){
    Mat src; // 定义一个Mat类型对象
    Mat src_gray; // 定义一个Mat类型对象
    src = imread("./1.jpg", IMREAD_COLOR); // 读入一个图像
    if (src.empty()){ // 当图像为空时，执行if语句判断
        cout << "img empty" << endl; // 输出 img empty
    }

    imshow("src", src); // 显示图像
    cvtColor(src, src_gray, COLOR_RGB2GRAY); // 将src转换为灰度图像存储至src_gray
    imwrite("./save.jpg", src_gray); // 将src_gray这个图像存储到相对路径下，并且命名为save.jpg
    waitKey(0); // 设定等待时间为无限等待
    return 0; // 返回值
}
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