OpenCV Mat::ones function

Question

According to the docs, this function should return a `Mat` with all elements as ones. ``` Mat m = Mat::ones(2, 2, CV_8UC3); ``` I was expecting to get a 2x2 matrix of `[1,1,1]`. Instead, I got this: ``` [1, 0, 0] [1, 0, 0] [1, 0, 0] [1, 0, 0] ``` Is this the expected behaviour?

Accepted Answer

It looks like `Mat::ones()` works as expected only for single channel arrays. For matrices with multiple channels `ones()` sets only the first channel to ones while the remaining channels are set to zeros.

Use the following constructor instead:

```
Mat m = Mat(2, 2, CV_8UC3, Scalar(1,1,1));
std::cout << m;
```

Edit. Calling

```
Mat m = Mat::ones(2, 2, CV_8UC3); 
```

is the same as calling

```
Mat m = Mat(2, 2, CV_8UC3, 1); // OpenCV replaces `1` with `Scalar(1,0,0)`
```

OpenCV Mat::ones function

Solution

Problem