Hi,

I'm trying to implement face detection in C#. I currently have a black + white outline of a photo with a face within it (Here). However i'm now trying to remove the noise and then dilate the image in order to improve reliability when i implement the detection.

The method I have so far is here:

    unsafe public Image Process(Image input)
        {
            Bitmap bmp = (Bitmap)input;
            Bitmap bmpSrc = (Bitmap)input;
            BitmapData bmData = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height),
                                ImageLockMode.ReadWrite,
                                PixelFormat.Format24bppRgb);
            int stride = bmData.Stride;
            int stride2 = bmData.Stride * 2;
            IntPtr Scan0 = bmData.Scan0;
            byte* p = (byte*)(void*)Scan0;

            int nOffset = stride - bmp.Width * 3;
            int nWidth = bmp.Width - 2;
            int nHeight = bmp.Height - 2;

            var w = bmp.Width;
            var h = bmp.Height;

            var rp = p;
            var empty = CompareEmptyColor;
            byte c, cm;
            int i = 0;

            // Erode every pixel
            for (int y = 0; y < h; y++)
            {
                for (int x = 0; x < w; x++, i++)
                {
                    // Middle pixel
                    cm = p[y * w + x];
                    if (cm == empty) { continue; }

                    // Row 0
                    // Left pixel
                    if (x - 2 > 0 && y - 2 > 0)
                    {
                        c = p[(y - 2) * w + (x - 2)];
                        if (c == empty) { continue; }
                    }
                    // Middle left pixel
                    if (x - 1 > 0 && y - 2 > 0)
                    {
                        c = p[(y - 2) * w + (x - 1)];
                        if (c == empty) { continue; }
                    }
                    if (y - 2 > 0)
                    {
                        c = p[(y - 2) * w + x];
                        if (c == empty) { continue; }
                    }
                    if (x + 1 < w && y - 2 > 0)
                    {
                        c = p[(y - 2) * w + (x + 1)];
                        if (c == empty) { continue; }
                    }
                    if (x + 2 < w && y - 2 > 0)
                    {
                        c = p[(y - 2) * w + (x + 2)];
                        if (c == empty) { continue; }
                    }

                    // Row 1
                    // Left pixel
                    if (x - 2 > 0 && y - 1 > 0)
                    {
                        c = p[(y - 1) * w + (x - 2)];
                        if (c == empty) { continue; }
                    }
                    if (x - 1 > 0 && y - 1 > 0)
                    {
                        c = p[(y - 1) * w + (x - 1)];
                        if (c == empty) { continue; }
                    }
                    if (y - 1 > 0)
                    {
                        c = p[(y - 1) * w + x];
                        if (c == empty) { continue; }
                    }
                    if (x + 1 < w && y - 1 > 0)
                    {
                        c = p[(y - 1) * w + (x + 1)];
                        if (c == empty) { continue; }
                    }
                    if (x + 2 < w && y - 1 > 0)
                    {
                        c = p[(y - 1) * w + (x + 2)];
                        if (c == empty) { continue; }
                    }

                    // Row 2
                    if (x - 2 > 0)
                    {
                        c = p[y * w + (x - 2)];
                        if (c == empty) { continue; }
                    }
                    if (x - 1 > 0)
                    {
                        c = p[y * w + (x - 1)];
                        if (c == empty) { continue; }
                    }
                    if (x + 1 < w)
                    {
                        c = p[y * w + (x + 1)];
                        if (c == empty) { continue; }
                    }
                    if (x + 2 < w)
                    {
                        c = p[y * w + (x + 2)];
                        if (c == empty) { continue; }
                    }

                    // Row 3
                    if (x - 2 > 0 && y + 1 < h)
                    {
                        c = p[(y + 1) * w + (x - 2)];
                        if (c == empty) { continue; }
                    }
                    if (x - 1 > 0 && y + 1 < h)
                    {
                        c = p[(y + 1) * w + (x - 1)];
                        if (c == empty) { continue; }
                    }
                    if (y + 1 < h)
                    {
                        c = p[(y + 1) * w + x];
                        if (c == empty) { continue; }
                    }
                    if (x + 1 < w && y + 1 < h)
                    {
                        c = p[(y + 1) * w + (x + 1)];
                        if (c == empty) { continue; }
                    }
                    if (x + 2 < w && y + 1 < h)
                    {
                        c = p[(y + 1) * w + (x + 2)];
                        if (c == empty) { continue; }
                    }

                    // Row 4
                    if (x - 2 > 0 && y + 2 < h)
                    {
                        c = p[(y + 2) * w + (x - 2)];
                        if (c == empty) { continue; }
                    }
                    if (x - 1 > 0 && y + 2 < h)
                    {
                        c = p[(y + 2) * w + (x - 1)];
                        if (c == empty) { continue; }
                    }
                    if (y + 2 < h)
                    {
                        c = p[(y + 2) * w + x];
                        if (c == empty) { continue; }
                    }
                    if (x + 1 < w && y + 2 < h)
                    {
                        c = p[(y + 2) * w + (x + 1)];
                        if (c == empty) { continue; }
                    }
                    if (x + 2 < w && y + 2 < h)
                    {
                        c = p[(y + 2) * w + (x + 2)];
                        if (c == empty) { continue; }
                    }

                    // If all neighboring pixels are processed 
                    // it's clear that the current pixel is not a boundary pixel.
                    rp[i] = cm;
                }
            }

            bmpSrc.UnlockBits(bmData);
            return bmpSrc;
        }

As I understand it, in order to erode the image (and remove the noise), we need to check each pixel to see if it's surrounding pixels are black, and if so, then it is a border pixel and we need not keep it, which i believe my code does, so it is beyond me why it doesn't work.

Any help or pointers would be greatly appreciated

Thanks, Chris