public void InvertColorsEffect1 ()
		{
			var src = GetSourceImage ("input.png");

			var effect = new InvertColorsEffect ();
			effect.Render (src);

			Compare (src, "invertcolors.png");
		}
		/// <summary>
		/// Creates a new effect that will make the image look like a pencil sketch.
		/// </summary>
		/// <param name="pencilSize">Size of the pencil to use. Valid range is 1 - 20.</param>
		/// <param name="colorRange">Range of color to use. Valid range is -20 - 20.</param>
		public PencilSketchEffect (int pencilSize = 2, int colorRange = 0)
		{
			if (pencilSize < 1 || pencilSize > 20)
				throw new ArgumentOutOfRangeException ("pencilSize");
			if (colorRange < -20 || colorRange > 20)
				throw new ArgumentOutOfRangeException ("colorRange");

			this.pencil_size = pencilSize;
			this.color_range = colorRange;

			blur_effect = new GaussianBlurEffect (pencil_size);
			desaturate_op = new DesaturateOp ();
			invert_effect = new InvertColorsEffect ();
			bac_adjustment = new BrightnessContrastEffect (-color_range, -color_range);
			color_dodge_op = new ColorDodgeBlendOp ();
		}
        /// <summary>
        /// Creates a new effect that will make the image look like a pencil sketch.
        /// </summary>
        /// <param name="pencilSize">Size of the pencil to use. Valid range is 1 - 20.</param>
        /// <param name="colorRange">Range of color to use. Valid range is -20 - 20.</param>
        public PencilSketchEffect(int pencilSize = 2, int colorRange = 0)
        {
            if (pencilSize < 1 || pencilSize > 20)
            {
                throw new ArgumentOutOfRangeException("pencilSize");
            }
            if (colorRange < -20 || colorRange > 20)
            {
                throw new ArgumentOutOfRangeException("colorRange");
            }

            this.pencil_size = pencilSize;
            this.color_range = colorRange;

            blur_effect    = new GaussianBlurEffect(pencil_size);
            desaturate_op  = new DesaturateOp();
            invert_effect  = new InvertColorsEffect();
            bac_adjustment = new BrightnessContrastEffect(-color_range, -color_range);
            color_dodge_op = new ColorDodgeBlendOp();
        }