gistfile1.cs

namespace MonoColorMatrix
{
    using System.Drawing;
    using System.Drawing.Imaging;

    public class Program
    {
        public static void Main()
        {
            var brightnessFactor = -0.05f;

            var image = Image.FromFile("input.jpg");
            
            var colorMatrix = new ColorMatrix(
                                            new float[][]
                                                        {
                                                            new float[] { 1, 0, 0, 0, 0 }, 
                                                            new float[] { 0, 1, 0, 0, 0 },
                                                            new float[] { 0, 0, 1, 0, 0 },
                                                            new float[] { 0, 0, 0, 1, 0 },
                                                            new float[] { brightnessFactor, brightnessFactor, brightnessFactor, 0, 1 }
                                                      });


            using (var graphics = Graphics.FromImage(image))
            {
                using (var imageAttributes = new ImageAttributes())
                {
                    imageAttributes.SetColorMatrix(colorMatrix);

                    graphics.DrawImage(image, new Rectangle(0, 0, image.Width, image.Height), 0, 0, image.Width, image.Height, GraphicsUnit.Pixel, imageAttributes);

                }
            }

            // Saving the images results in incorrect images being output on Mono, for any chosen image format
            image.Save("output.jpg", ImageFormat.Jpeg);
            image.Save("output.png", ImageFormat.Png);
            image.Save("output.bmp", ImageFormat.Bmp);
        }
    }
}