OpenCV Study Notes: Mat - The Basic Image Container

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Mat

Mat is basically a class with two data parts: the matrix header and a pointer to the actual matrix

the copy operators will only copy the headers, which means that modifying on object would affect other objects with the same data.

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Mat A, C;  // creates just the header parts
A = imread(argv[1], IMREAD_COLOR); // here we'll know the method used (allocate matrix)
Mat B(A);  // Use the copy constructor
C = A;  // Assignment operator

All the above objects, in the end, point to the same single data matrix.

the headers are distinctive, so we can create objects with different regions of interest (ROI) while using the same data.

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Mat D (A, Rect(10, 10, 100, 100) ); // using a rectangle
Mat E = A(Range::all(), Range(1,3)); // using row and column boundaries

To truly copy images is still posible by using the cv::Mat::clone() and cv::Mat::copyTo() methods.

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Mat F = A.clone();
Mat G;
A.copyTo(G);

Now modifying F or G will not affect the matrix pointed by the Mat header.

Storing Methods

Several ways to store color:

  1. RGB
  2. HSV/HLS Hue, Saturation, and value/luminance
  3. YCrCb
  4. CIE L*a*b*