C#学习笔记之以指定的大小缩放图片

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Drawing;
using System.Drawing.Drawing2D;
 
namespace QingdaoZenius
{
    class ScalPhoto
    {
        /// <summary> 
        /// 按照指定大小缩放图片，但是为了保证图片宽高比自动截取 
        /// </summary> 
        /// <param name="srcPath">原图片路径</param> 
        /// <param name="destWidth">目标图片宽</param> 
        /// <param name="destHeight">目标图片高</param> 
        /// <returns></returns> 
        public static Bitmap SizeImageWithOldPercent(string srcPath, int destWidth, int destHeight)
        {
            Image srcImage = Image.FromFile(srcPath);
            try
            {
                // 要截取图片的宽度（原始宽度） 
                int srcWidth = srcImage.Width;
                // 要截取图片的高度（原始高度） 
                int srcHeight = srcImage.Height;
                // 截取开始横坐标
                int newX = 0;
                // 截取开始纵坐标 
                int newY = 0;
 
                // 截取比例 
                double whPercent = ((double)destWidth / (double)destHeight) * ((double)srcImage.Height / (double)srcImage.Width);
                if (whPercent > 1)
                {
                    // 当前图片宽度对于要截取比例过大时 
                    srcWidth = int.Parse(Math.Round(srcImage.Width / whPercent).ToString());
                }
                else if (whPercent < 1)
                {
                    // 当前图片高度对于要截取比例过大时 
                    srcHeight = int.Parse(Math.Round(srcImage.Height * whPercent).ToString());
                }
 
                if (srcWidth != srcImage.Width)
                {
                    // 宽度有变化时，调整开始截取的横坐标 
                    newX = Math.Abs(int.Parse(Math.Round(((double)srcImage.Width - srcWidth) / 2).ToString()));
                }
                else if (srcHeight == srcImage.Height)
                {
                    // 高度有变化时，调整开始截取的纵坐标 
                    newY = Math.Abs(int.Parse(Math.Round(((double)srcImage.Height - (double)srcHeight) / 2).ToString()));
                }
 
                // 将原始图片画到目标画布上，返回目标图片
                Bitmap cutedImage = CutImage(srcImage, newX, newY, srcWidth, srcHeight);
 
                // 在创建一个新的画布
                Bitmap bmp = new Bitmap(destWidth, destHeight);
                Graphics g = Graphics.FromImage(bmp);
                // 插值算法的质量 
                g.InterpolationMode = InterpolationMode.Default;
                g.DrawImage(cutedImage, new Rectangle(0, 0, destWidth, destHeight), new Rectangle(0, 0, cutedImage.Width, cutedImage.Height), GraphicsUnit.Pixel);
                g.Dispose();
 
                return bmp;
            }
            catch (Exception)
            {
                return null;
            }
        }
 
        /// <summary> 
        /// 剪裁 -- 用GDI+ 
        /// </summary> 
        /// <param name="image">原始图片</param> 
        /// <param name="StartX">开始坐标X</param> 
        /// <param name="StartY">开始坐标Y</param> 
        /// <param name="destWidth">目标图片宽度</param> 
        /// <param name="destHeight">目标图片高度高度</param> 
        /// <returns>剪裁后的Bitmap</returns> 
        private static Bitmap CutImage(Image image, int StartX, int StartY, int destWidth, int destHeight)
        {
            int srcWidth = image.Width;
            int srcHeight = image.Height;
            if (StartX >= srcWidth || StartY >= srcHeight)
            {
                // 开始截取坐标过大时，结束处理 
                return null;
            }
 
            if (StartX + destWidth > srcWidth)
            {
                // 宽度过大时只截取到最大大小 
                destWidth = srcWidth - StartX;
            }
 
            if (StartY + destHeight > srcHeight)
            {
                // 高度过大时只截取到最大大小 
                destHeight = srcHeight - StartY;
            }
 
            try
            {
                // 根据目标图片的大小，实例化一个画布
                Bitmap bmpOut = new Bitmap(destWidth, destHeight);
                // 实例化一个画笔
                Graphics g = Graphics.FromImage(bmpOut);
                // 将原始图片画到目标画布上
                g.DrawImage(image, new Rectangle(0, 0, destWidth, destHeight), new Rectangle(StartX, StartY, destWidth, destHeight), GraphicsUnit.Pixel);
                g.Dispose();
 
                return bmpOut;
            }
            catch
            {
                return null;
            }
        }
    }
}