OpenCV Mat数据成员访问 [英] OpenCV Mat data member access
问题描述
我已经看到很多OpenCV代码直接访问 cv :: Mat
的数据成员。 cv :: Mat
将指向数据的指针存储在 unsigned char * data
成员中。访问数据成员如下所示:
I've seen a lot of OpenCV code which accesses the data member of a cv::Mat
directly. cv::Mat
stores the pointer to the data in a unsigned char* data
member. Access to the data member looks like:
cv::Mat matUC(3,3,CV_8U)
int rowIdx = 1;
int colIdx = 1;
unsigned char val = matUC.data[ rowIdx * matUC.cols + colIdx]
我想知道这是否适用于 cv :: Mat
,其像素类型不是 unsigned char
。
I'm wondering if this works for a cv::Mat
with pixel type other than unsigned char
.
cv::Mat matF(3,3,CV_32F)
int rowIdx = 1;
int colIdx = 1;
float val = matF.data[ rowIdx * matF.cols + colIdx];
我的理解是需要使用类型转换来正确访问元素。类似于:
My understanding would be that a typecast is needed to access the elements correctly. Something like:
float val = ((float*)matF.data)[ rowIdx * matF.cols + colIdx];
我见过很多不使用类型转换的代码。所以我的问题是:类型转换是否必须访问正确的元素?
I've seen a lot of code which doesn't use a typecast. So my question is: Is the typecast mandatory to access the correct element?
推荐答案
Mat
数据是 uchar *
。如果你有一个浮动矩阵 CV_32FC1
,你需要以 float
的方式访问数据。
Mat
data is an uchar*
. If you have a, say, float matrix CV_32FC1
, you need to access data as float
.
你可以用不同的方式做,不一定使用演员:
You can do in different ways, not necessarily using casting:
#include <opencv2\opencv.hpp>
using namespace cv;
int main()
{
cv::Mat matF(3, 3, CV_32F);
randu(matF, Scalar(0), Scalar(10));
int rowIdx = 1;
int colIdx = 1;
// 1
float f1 = matF.at<float>(rowIdx, colIdx);
// 2
float* fData2 = (float*)matF.data;
float f2 = fData2[rowIdx*matF.step1() + colIdx];
// 3
float* fData3 = matF.ptr<float>(0);
float f3 = fData3[rowIdx*matF.step1() + colIdx];
// 4
float* fData4 = matF.ptr<float>(rowIdx);
float f4 = fData4[colIdx];
// 5
Mat1f mm(matF); // Or directly create like: Mat1f mm(3, 3);
float f5 = mm(rowIdx, colIdx);
// f1 == f2 == f3 == f4 == f5
return 0;
}
注释
- it's better to use
step1()
instead ofcols
when accessing directlydata
through pointers, since the image may not be continuous. Check here for more details. - The snippet is adapted from this my other answer
这篇关于OpenCV Mat数据成员访问的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!