Your First Application

This example reads an image, converts it to grayscale, and saves the result. It does not open a native window, so it also works with the Linux headless runtime package.

Prepare an input image

Place a JPEG or PNG image named input.jpg in the project directory. Configure it to be copied to the output directory by adding the following item to the project file:

<ItemGroup>
  <None Update="input.jpg" CopyToOutputDirectory="PreserveNewest" />
</ItemGroup>

Add the code

Replace Program.cs with:

using OpenCvSharp;

using var source = Cv2.ImRead("input.jpg", ImreadModes.Color);
if (source.Empty())
{
    throw new IOException("Could not read input.jpg.");
}

using var grayscale = new Mat();
Cv2.CvtColor(source, grayscale, ColorConversionCodes.BGR2GRAY);

if (!Cv2.ImWrite("output.png", grayscale))
{
    throw new IOException("Could not write output.png.");
}

Console.WriteLine($"Created output.png ({grayscale.Width} x {grayscale.Height}).");

Run the application

dotnet run

The application creates output.png in its working directory.

What the code does

Cv2.ImRead decodes the input file into a Mat.
source.Empty() detects a missing or unsupported input image.
Cv2.CvtColor converts the image from OpenCV's default BGR channel order to grayscale.
Cv2.ImWrite selects an encoder from the output file extension and writes the image.
The using declarations release the native memory owned by both Mat instances.

OpenCvSharp objects that own native resources must be disposed. Read Resource Management before building a long-running application.

Next steps