CODEWITHSUNDEEP
c++opencv
anarchy99
anarchy99

Reputation: 1023

How to clear the cv::Mat contents?

I have a cv::Mat but I have already inserted it with some values, how do I clear the contents in it?

Upvotes: 26

Views: 66264

Answers (5)

N. Ope
N. Ope

Reputation: 21

You could always redeclare it if you want to empty the mat but keep using the variable. Idk if that's what you want but since the other answer to "clearing" a mat is .release() I'd just go to mention this.

Edit: My bad. I didn't realise how unclear my answer was. I was just answering the question of "how to clear a Mat variable of it's contents". Another person had answered that one can just do .release() to the variable, like for example, the person has a variable like cv::Mat testMat; and later on it's declared (as the question implied). One person said that you could do a simple testMat.release(). And if that's what op wants then there you go. But in the off chance that op just wants to clear the declaration of the variable, i just thought to mention that he/she could just re-declare it, like do a simple testMat = *some new information* later on. Also, i mixed up define and declare. My bad

Upvotes: 0

CapelliC
CapelliC

Reputation: 60004

From the docs:

// sets all or some matrix elements to s
Mat& operator = (const Scalar& s);

then we could do

m = Scalar(0,0,0);

to fill with black pixels. Scalar has 4 components, the last - alpha - is optional.

Upvotes: 15

abggcv
abggcv

Reputation: 461

You can release the current contents or assign a new Mat. 

Mat m = Mat::ones(1, 5, CV_8U);

cout << "m: " << m << endl;
m.release();  //this will remove Mat m from memory

//Another way to clear the contents is by assigning an empty Mat:
m = Mat();

//After this the Mat can be re-assigned another value for example:
m = Mat::zeros(2,3, CV_8U);
cout << "m: " << m << endl;

Upvotes: 4

Alexey
Alexey

Reputation: 5978

If you want to release the memory of the Mat variable use release().

Mat m;
// initialize m or do some processing
m.release();

For a vector of cv::Mat objects you can release the memory of the whole vector with myvector.clear().

std::vector<cv::Mat> myvector;
// initialize myvector .. 

myvector.clear(); // to release the memory of the vector

Upvotes: 26

Poko
Poko

Reputation: 822

You should call release() function.

 Mat img = Mat(Size(width, height), CV_8UC3, Scalar(0, 0, 0));
 img.release();

Upvotes: 9

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