Question

I am doing an image processing assignment where I want to implement erosion and dilation algorithm. It needs to look for each pixel in all directions (in this case up, down, left and right), so i’m using a plus structuring element. Here is my problem: I’ve got 4 for loops nested, which makes this operation very slow.
Can anyone tell me how to make the erosion process quicker without using unsafe method?
Here is what I have:

        colorlistErosion = new List<Color>();
        int colorValueR, colorValueG, colorValueB;
        int tel = 0;

        for (int y = 0; y < bitmap.Height; y++)
        {
            for (int x = 0; x < bitmap.Width; x++)
            {
                Color col = bitmap.GetPixel(x, y);
                colorValueR = col.R; colorValueG = col.G; colorValueB = col.B;
                //Erosion
                for (int a = -1; a < 2; a++)
                {
                    for (int b = -1; b < 2; b++)
                    {
                        try
                        {
                            Color col2 = bitmap.GetPixel(x + a, y + b);
                            colorValueR = Math.Min(colorValueR, col2.R);
                            colorValueG = Math.Min(colorValueG, col2.G);
                            colorValueB = Math.Min(colorValueB, col2.B);
                        }
                        catch
                        {
                        }
                    }
                }
                colorlistErosion.Add(Color.FromArgb(0 + colorValueR, 0+colorValueG, 0+colorValueB));
            }
        }
        for (int een = 0; een < bitmap.Height; een++)
            for (int twee = 0; twee < bitmap.Width; twee++)
            {
                bitmap.SetPixel(twee, een, colorlistErosion[tel]);
                tel++;
            }

Answer 1

how to make the erosion process quicker without using unsafe method?

You can turn the inner loops into Parallel.For().

But I’m not 100% sure if GetPixel() and especially SetPixel() are thread-safe. That is a deal-breaker.