OpenCV Mat 元素类型及其大小

Question

我对 OpenCV Mat 元素类型感到困惑。这是来自文档:

There is a limited fixed set of primitive data types the library can operate on.
That is, array elements should have one of the following types:

8-bit unsigned integer (uchar) 
8-bit signed integer (schar)
16-bit unsigned integer (ushort)
16-bit signed integer (short)
32-bit signed integer (int)
32-bit floating-point number (float)
64-bit floating-point number (double)
...

For these basic types, the following enumeration is applied:
enum { CV_8U=0, CV_8S=1, CV_16U=2, CV_16S=3, CV_32S=4, CV_32F=5, CV_64F=6 };

众所周知，C++ 标准没有以字节为单位定义基本类型的大小，那么他们如何使用这样的假设呢？我应该期待什么类型，比方说，CV_32S，是 int32_t 还是 int？

Answer 1

从 Miki's answer 开发,
在 OpenCV 3 中，定义已移至 modules/core/include/opencv2/core/traits.hpp，您可以在其中找到:

/** @brief A helper class for cv::DataType

The class is specialized for each fundamental numerical data type supported by OpenCV. It provides
DataDepth<T>::value constant.
*/
template<typename _Tp> class DataDepth
{
public:
    enum
    {
        value = DataType<_Tp>::depth,
        fmt   = DataType<_Tp>::fmt
    };
};



template<int _depth> class TypeDepth
{
    enum { depth = CV_USRTYPE1 };
    typedef void value_type;
};

template<> class TypeDepth<CV_8U>
{
    enum { depth = CV_8U };
    typedef uchar value_type;
};

template<> class TypeDepth<CV_8S>
{
    enum { depth = CV_8S };
    typedef schar value_type;
};

template<> class TypeDepth<CV_16U>
{
    enum { depth = CV_16U };
    typedef ushort value_type;
};

template<> class TypeDepth<CV_16S>
{
    enum { depth = CV_16S };
    typedef short value_type;
};

template<> class TypeDepth<CV_32S>
{
    enum { depth = CV_32S };
    typedef int value_type;
};

template<> class TypeDepth<CV_32F>
{
    enum { depth = CV_32F };
    typedef float value_type;
};

template<> class TypeDepth<CV_64F>
{
    enum { depth = CV_64F };
    typedef double value_type;
};

在大多数情况/编译器中，您应该可以使用 C++ 精确数据类型。单字节数据类型( CV_8U -> uint8_t 和 CV_8U -> int8_t )不会有问题 unambiguously defined in C++ . float (32bit) and double (64bit) 相同.但是，对于其他数据类型，确实可以完全确保您使用了正确的数据类型(例如，当使用 at<> 方法时)，您应该使用例如:

typedef TypeDepth<CV_WHATEVER_YOU_USED_TO_CREATE_YOUR_MAT>::value_type access_type;
myMat.at<access_type>(y,x) = 0;

附带说明一下，我很惊讶他们决定采用这种模棱两可的方法，而不是简单地使用确切的数据类型。

因此，关于您的最后一个问题:

What type should I expect from, let's say, CV_32S?

我相信在 OpenCV 3 中最准确的答案是:

TypeDepth<CV_32S>::value_type