How to Darken an Image in WPF

I'm really getting carried away with playing with image manipulation in WPF. Here's a short post on how to darken an image using the WriteableBitmap class.

The process is fairly simple, I manipulate each pixel by decrementing each RGB value with the provided level

unsafe static BitmapSource Darken(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.Max(row[x * PIXEL_SIZE + i] - level, 0);

    }

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

    bitmap.Unlock();

    return bitmap;

}

Hope you found this useful.