The median filter is a non-linear digital filtering technique, often used to remove noise from an image or signal. Such noise reduction is a typical pre-processing step to improve the results of later processing (for example, edge detection on an image). Median filtering is very widely used in digital image processing because, under certain conditions, it preserves edges while removing noise (but see the discussion below), also having applications in signal processing. (1)

• C#
• .NET
• BenchmarkDotNet
• managedCUDA (library for CUDA usage from C#)
• CUDA

Optimalization of median filtering is using Divide-And-Conquer technique.

We are calculating median for each of ARGB value per pixel and deciding which one should be at output image.

Input	Result

Computer data: CPU: AMD Ryzen 5 4800H ( 8 cores, 16 threads) 2.9Ghz to 4.2Ghz RAM: 16GB 2300Mhz GPU: NVidia RTX2060 6GB

As we can see switching calculations to GPU gives us a lot of improvement.

using(var image = Image(path)
{
    using(var filter = BasicMedianFilter(image))
    {
        //CPU
	    filter.CalculateOnCPU(numberOfThreads);
	    //GPU
		filter.PrepareForGPU(); // this would allocate memory on our GPU and transfer the data
		var timeOfExcecution = filter.CalculateOnGpu();
		calculator.FinalizeGpu(); //transfer the data from device to host
    }
}

1. Median filter - Wikipedia

2. Free High-Resolution Satellite Images Samples | EffigisI've decided not to test on 1 thread because it's taking too much time to complete the task.