unsafe static BitmapSource Brighten(BitmapSource image, double level)

{

    const int PIXEL_SIZE = 4;

    int height = image.PixelHeight;

    int width = image.PixelWidth;

    var bitmap = new WriteableBitmap(image);            

    bitmap.Lock();

    var backBuffer = (byte*)bitmap.BackBuffer.ToPointer();

    for (int y = 0; y < height; y++)

    {

        var row = backBuffer + (y * bitmap.BackBufferStride);

        for (int x = 0; x < width; x++)

            for (int i = 0; i < PIXEL_SIZE; i++)

                row[x * PIXEL_SIZE + i] = (byte)Math.Min(row[x * PIXEL_SIZE + i] + level, 255);

    }

    bitmap.AddDirtyRect(new Int32Rect(0, 0, width, height));

    bitmap.Unlock();

    return bitmap;

}