c++ - opencv 4.x API 与之前的版本有何不同？

Question

我注意到 opencv 4 已发布，其中一个区别是 API 更改为与 c++11 兼容。

这究竟意味着什么？

我应该如何更改我的代码以与此版本兼容？

Answer 1

我认为最不同的是，OpenCV 4.0 使用了更多的 C++11 特性。现在 cv::String == std::string 和 cv::Ptr 是 std::shared_ptr 之上的薄包装。

Opencv 4.0 删除文件夹include/opencv，只保留include/opencv2。 OpenCV 1.x 中的许多 C API 已被删除。受影响的模块是 objdetect、photo、video、videoio、imgcodecs、calib3d。不建议使用旧的宏定义或未命名的枚举，而是使用命名的枚举。

//! include/opencv2/imgcodes.hpp
namespace cv
{

//! @addtogroup imgcodecs
//! @{

//! Imread flags
enum ImreadModes {
       IMREAD_UNCHANGED            = -1, //!< If set, return the loaded image as is (with alpha channel, otherwise it gets cropped).
       IMREAD_GRAYSCALE            = 0,  //!< If set, always convert image to the single channel grayscale image (codec internal conversion).
       IMREAD_COLOR                = 1,  //!< If set, always convert image to the 3 channel BGR color image.
       IMREAD_ANYDEPTH             = 2,  //!< If set, return 16-bit/32-bit image when the input has the corresponding depth, otherwise convert it to 8-bit.
       IMREAD_ANYCOLOR             = 4,  //!< If set, the image is read in any possible color format.
       IMREAD_LOAD_GDAL            = 8,  //!< If set, use the gdal driver for loading the image.
       IMREAD_REDUCED_GRAYSCALE_2  = 16, //!< If set, always convert image to the single channel grayscale image and the image size reduced 1/2.
       IMREAD_REDUCED_COLOR_2      = 17, //!< If set, always convert image to the 3 channel BGR color image and the image size reduced 1/2.
       IMREAD_REDUCED_GRAYSCALE_4  = 32, //!< If set, always convert image to the single channel grayscale image and the image size reduced 1/4.
       IMREAD_REDUCED_COLOR_4      = 33, //!< If set, always convert image to the 3 channel BGR color image and the image size reduced 1/4.
       IMREAD_REDUCED_GRAYSCALE_8  = 64, //!< If set, always convert image to the single channel grayscale image and the image size reduced 1/8.
       IMREAD_REDUCED_COLOR_8      = 65, //!< If set, always convert image to the 3 channel BGR color image and the image size reduced 1/8.
       IMREAD_IGNORE_ORIENTATION   = 128 //!< If set, do not rotate the image according to EXIF's orientation flag.
     };

    // ...
}

比如读取图片时应该是这样的:

cv::Mat img = cv::imread("test.png", cv::IMREAD_COLOR);

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除了新功能外，大多数 C++ API 保持不变。虽然我发现最大的不同是 cv2.findContours(在 Python OpenCV 中):

在 OpenCV 3.4 中:

findContours(image, mode, method[, contours[, hierarchy[, offset]]]) -> image, contours, hierarchy

在 OpenCV 4.0 中:

findContours(image, mode, method[, contours[, hierarchy[, offset]]]) -> contours, hierarchy

使用 2.x 、3.x、4.x 的替代方法是:

cnts, hiers = cv2.findContours(...)[-2:]

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一些链接:

1. OpenCV Release
2. OpenCV ChangeLog
3. OpenCV Introduction
4. OpenCV Documentation
5. How to use `cv2.findContours` in different OpenCV versions?
6. OpenCV on Stackoverflow

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