tcc/Controllers/Blur.cs

using ImageMagick;
using Microsoft.AspNetCore.Mvc;

namespace tcc_app.Controllers
{
    [ApiController]
    [Route("")]
    public class ImageController : ControllerBase
    {
        [HttpPost("blur")]
        public async Task<IActionResult> BlurImage()
        {
            MemoryStream mstream = new MemoryStream();
            await HttpContext.Request.Body.CopyToAsync(mstream);

            var image = new MagickImage(new MemoryStream(mstream.ToArray()));
            var blurredImage = new MagickImage(image);
            var pixels = image.GetPixels();
            var blurredPixels = blurredImage.GetPixelsUnsafe();

            foreach (var pixel in pixels)
            {
                int x = pixel.X,
                    y = pixel.Y;

                long rTotal = 0, gTotal = 0, bTotal = 0;
                int pixelCount = 0;
                for (short offsetY = -5; offsetY <= 5; offsetY++)
                {
                    for (short offsetX = -5; offsetX <= 5; offsetX++)
                    {
                        int newX = x + offsetX;
                        int newY = y + offsetY;

                        if (newX >= 0 && newX < image.Width && newY >= 0 && newY < image.Height)
                        {
                            var pixelColor = pixels[newX, newY];
                            rTotal += pixelColor.GetChannel(0);
                            gTotal += pixelColor.GetChannel(1);
                            bTotal += pixelColor.GetChannel(2);
                            pixelCount++;
                        }
                    }
                }

                blurredPixels[x, y].SetChannel(0, Convert.ToUInt16(rTotal / pixelCount));
                blurredPixels[x, y].SetChannel(1, Convert.ToUInt16(gTotal / pixelCount));
                blurredPixels[x, y].SetChannel(2, Convert.ToUInt16(bTotal / pixelCount));
            }

            var blurredImageStream = new MemoryStream();
            blurredImage.Write(blurredImageStream);
            blurredImageStream.Position = 0;

            return File(blurredImageStream, "image/png");
        }

    }
}