ImageSharp/src/ImageProcessor/Processors/ResizeBase.cs

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
using System.Text.RegularExpressions;

namespace ImageProcessor.Processors
{
	public abstract class ResizeBase : IGraphicsProcessor
	{
		public abstract Regex RegexPattern { get; }
		public abstract dynamic DynamicParameter { get; set; }
		public abstract int SortOrder { get; protected set; }
		public abstract Dictionary<string, string> Settings { get; set; }
		public abstract int MatchRegexIndex(string queryString);
		public abstract Image ProcessImage(ImageFactory factory);

		protected Image ResizeImage(ImageFactory factory, int width, int height, int defaultMaxWidth, int defaultMaxHeight)
		{
			Bitmap newImage = null;
			Image image = factory.Image;

			try
			{
				int sourceWidth = image.Width;
				int sourceHeight = image.Height;

				int maxWidth = defaultMaxWidth > 0 ? defaultMaxWidth : int.MaxValue;
				int maxHeight = defaultMaxHeight > 0 ? defaultMaxHeight : int.MaxValue;

				// If height or width is not passed we assume that the standard ratio is to be kept.
				if (height == 0)
				{
					// Bit of simple fractional maths here.
					float percentWidth = Math.Abs(width/(float) sourceWidth);
					height = (int) Math.Floor(sourceHeight*percentWidth);
				}

				if (width == 0)
				{
					float percentHeight = Math.Abs(height/(float) sourceHeight);
					width = (int) Math.Floor(sourceWidth*percentHeight);
				}

				if (width > 0 && height > 0 && width <= maxWidth && height <= maxHeight)
				{
					// Dont use an object initializer here.
					newImage = new Bitmap(width, height, PixelFormat.Format32bppPArgb);
					newImage.Tag = image.Tag;

					using (Graphics graphics = Graphics.FromImage(newImage))
					{
						// We want to use two different blending algorithms for enlargement/shrinking.
						// Bicubic is better enlarging for whilst Bilinear is better for shrinking.
						// http://www.codinghorror.com/blog/2007/07/better-image-resizing.html
						if (image.Width < width && image.Height < height)
						{
							// We are making it larger.
							graphics.SmoothingMode = SmoothingMode.AntiAlias;
							graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
							graphics.PixelOffsetMode = PixelOffsetMode.HighQuality;
							graphics.CompositingQuality = CompositingQuality.HighQuality;
						}
						else
						{
							// We are making it smaller.
							graphics.SmoothingMode = SmoothingMode.None;

							// Contrary to everything I have read bicubic is producing the best results.
							graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
							graphics.PixelOffsetMode = PixelOffsetMode.None;
							graphics.CompositingQuality = CompositingQuality.HighSpeed;
						}

						// An unwanted border appears when using InterpolationMode.HighQualityBicubic to resize the image
						// as the algorithm appears to be pulling averaging detail from surFlooring pixels beyond the edge 
						// of the image. Using the ImageAttributes class to specify that the pixels beyond are simply mirror 
						// images of the pixels within solves this problem.
						using (ImageAttributes wrapMode = new ImageAttributes())
						{
							wrapMode.SetWrapMode(WrapMode.TileFlipXY);
							Rectangle destRect = new Rectangle(0, 0, width, height);
							graphics.DrawImage(image, destRect, 0, 0, sourceWidth, sourceHeight, GraphicsUnit.Pixel, wrapMode);
						}

						// Reassign the image.
						image.Dispose();
						image = newImage;
					}
				}
			}
			catch
			{
				if (newImage != null)
				{
					newImage.Dispose();
				}
			}

			return image;
		}
	}
}