How to print matrix values in OpenCvSharp library

user_4990642 0
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I'm trying to find homography matrix of two sources using Cv2.FindHomography method. Everything works fine up to here. The problem is that I cannot get/print matrix values. I'm really beginner-level for C#. I've found a sort of documentation belonging to it. However, I don't understand how to iterate over the values.

this[int startCol, int endCol]
override MatExpr OpenCvSharp.Mat.ColExprIndexer.this[int startCol, int endCol]
getset
Creates a matrix header for the specified column span.

Parameters
startCol    An inclusive 0-based start index of the column span.
endCol  An exclusive 0-based ending index of the column span.
Returns

My code,

Point2d[] points1 = new Point2d[]
{
  new Point2d(141, 131), new Point2d(480, 159)
};
Point2d[] points2 = new Point2d[]
{
  new Point2d(318, 256),
  new Point2d(5, 1)
};

Mat hCv = Cv2.FindHomography(points1, points2);
// I want to print the the resultant matrix
opencv iterator matrix c#
2 Answers

First method is using Data method.

byte[] data = new byte[hCv.Width * hCv.Height];
Marshal.Copy(hCv.DataPointer, data, 0, hCv.Width * hCv.Height);

for(int i = 0; i < data.Length; i++)
{
    // Print data[i]
}

Type depends on type of matrix, if its CV_8, then use byte, in case of CV_32, use float etc.

According to this - another method is to create image or matrix (additional copy) and then access each elements

Image<Bgr, Byte> img = hCv.ToImage<Bgr, Byte>();

The pixel data can then be accessed using the Image<,>.Data property.

You can also convert the Mat to an Matrix<> object. Assuming the Mat contains 8-bit data

Matrix<Byte> matrix = new Matrix<Byte>(hCv.Rows, hCv.Cols, mat.NumberOfChannels);
hCv.CopyTo(matrix);

The pixel data can then be accessed using the Matrix<>.Data property.

user_82546990

Here's an approach that doesn't involve making a copy of the Mat:

for (var rowIndex = 0; rowIndex < hCv.Rows; rowIndex++)
{
    for (var colIndex = 0; colIndex < hCv.Cols; colIndex++)
    {
        Debug.Write($"{hCv.At<double>(rowIndex, colIndex)} ");
    }
    Debug.WriteLine("");
}

Just make sure the type inside the angle brackets (double in this case) is correct. Otherwise you'll get nonsense values.

user_768100
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