Resource Management

Many OpenCvSharp types wrap native OpenCV objects. Dispose objects that implement IDisposable as soon as they are no longer needed so that long-running applications do not retain native memory.

Prefer using declarations

Use a using declaration for each Mat that owns a result:

using var source = Cv2.ImRead("input.jpg", ImreadModes.Color);
using var blurred = new Mat();

Cv2.GaussianBlur(source, blurred, new Size(5, 5), 0);
Cv2.ImWrite("blurred.png", blurred);

The variables are disposed automatically at the end of the current scope.

Dispose temporary results in loops

Objects created inside a loop should normally be disposed during each iteration:

foreach (var fileName in fileNames)
{
    using var source = Cv2.ImRead(fileName);
    using var resized = new Mat();

    Cv2.Resize(source, resized, new Size(640, 480));
    Cv2.ImWrite(Path.ChangeExtension(fileName, ".resized.jpg"), resized);
}

Waiting for garbage collection is not a substitute for deterministic disposal. The garbage collector tracks managed memory and does not have an accurate view of the native memory held by a Mat.

Mat expressions

OpenCvSharp arithmetic operators build a managed MatExpr expression. Intermediate expression nodes do not own native resources. Dispose the input matrices and the materialized result:

using var source = Cv2.ImRead("input.jpg", ImreadModes.Grayscale);
using Mat adjusted = 255 - source * 0.8;

Cv2.ImWrite("adjusted.png", adjusted);

The intermediate source * 0.8 expression does not need its own using declaration.

Returning a Mat

Do not dispose a Mat before returning it to the caller. Transfer ownership explicitly through the method contract:

static Mat LoadGrayscale(string fileName)
{
    using var source = Cv2.ImRead(fileName, ImreadModes.Color);
    var grayscale = new Mat();
    try
    {
        Cv2.CvtColor(source, grayscale, ColorConversionCodes.BGR2GRAY);
        return grayscale;
    }
    catch
    {
        grayscale.Dispose();
        throw;
    }
}

using var image = LoadGrayscale("input.jpg");

The caller owns and disposes the returned Mat. The method disposes the result itself if an exception occurs before ownership can be transferred to the caller.

Windows and UI objects

Window and other OpenCvSharp wrappers that implement IDisposable follow the same rule. Scope them with using rather than relying on finalization.

Official OpenCV references

Mat: the basic image container

The OpenCV reference explains native cv::Mat header and buffer ownership. OpenCvSharp adds managed IDisposable wrappers, so follow the .NET ownership rules in this guide even when translating a C++ example.

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