Question

I am making an XNA application where I capture the screenshot from a webcam 4 times a second and then I try to convert it into an Boolean array when the pixel color Red is below a certain threshold. When I convert it into a Texture2D it doesn’t lag but when I try to get the individual pixels it does lag, even when the webcam resolution is 176×144.

This is the code to grab the Bitmap:

public Bitmap getBitmap()
    {
        if (!panelVideoPreview.IsDisposed)
        {
            Bitmap b = new Bitmap(panelVideoPreview.Width, panelVideoPreview.Height, PixelFormat.Format32bppRgb);
            using (Graphics g = Graphics.FromImage(b))
            {
                Rectangle rectanglePanelVideoPreview = panelVideoPreview.Bounds;
                Point sourcePoints = panelVideoPreview.PointToScreen(new Point(panelVideoPreview.ClientRectangle.X, panelVideoPreview.ClientRectangle.Y));
                g.CopyFromScreen(sourcePoints, Point.Empty, rectanglePanelVideoPreview.Size);
            }

            return b;
        }
        else
        {
            Bitmap b = new Bitmap(panelVideoPreview.Width, panelVideoPreview.Height);
            return b;
        }
    }

This is the code to convert the Bitmap to a Boolean array:

public bool[,] getBoolBitmap(uint treshold)
    {
        Bitmap b = getBitmap();

        bool[,] ar = new bool[b.Width, b.Height];

        for (int y = 0; y < b.Height; y++)
        {
            for (int x = 0; x < b.Width; x++)
            {
                if (b.GetPixel(x, y).R < treshold)
                {
                    ar[x, y] = false;
                }
                else
                {
                    ar[x, y] = true;
                }
            }
        }

        return ar;
    }

Answer 1

The answer provided by Hans Passant is correct, it is better to use LockBits and process the data all at once.

You might also try writing a shader that thresholds the data and thereby utilize the power of the GPU to parallel-process the input image stream much, much faster.