生成高品質小空間的縮略圖C#代碼

.net自帶的生成縮略圖的方法是Bitmap.GetThumbnailImage這個方法生成的縮略圖不夠清晰，一般我們會使用 Graphics高質量插值發生成清晰的縮略圖，這時候大小會不盡人意，怎么辦？我們可以使用jpeg壓縮的方法壓縮一下圖片，這樣圖片的大小會縮小到壓 縮前的十分之一。

下面是完成這項工作的代碼：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Drawing;
using System.IO;

namespace ConsoleApplication3_ThumbnailImg
{
    class Program
    {
        const int HEIGHT = 190;
        const int WIDTH = 190;
        static void Main(string[] args)
        {
            string srcImgPath = @"G:\photoes\20060725\Picture 057.jpg";
            string targetFolder = @"E:\Diary\Test\thumbnail";

        SetThumbnail_1(srcImgPath, targetFolder);
        SetThumbnail_2(srcImgPath, targetFolder);
        SetThumbnail_3(srcImgPath, targetFolder);

        Console.Read();
    }

    static void SetThumbnail_1(string srcImgPath, string targetFolder)
    {
        using (Bitmap source = new Bitmap(srcImgPath))
        {
            // return the source image if it's smaller than the designated thumbnail   
            int wi, hi;
            wi = WIDTH;
            hi = HEIGHT;

            // maintain the aspect ratio despite the thumbnail size parameters   
            if (source.Width > source.Height)
            {
                wi = WIDTH;
                hi = (int)(source.Height * ((decimal)WIDTH / source.Width));
            }
            else
            {
                hi = HEIGHT;
                wi = (int)(source.Width * ((decimal)HEIGHT / source.Height));
            }

            using (Image thumb = source.GetThumbnailImage(wi, hi, null, IntPtr.Zero))
            {
                string targetPath = Path.Combine(targetFolder, "th_1.jpg");
                thumb.Save(targetPath);
            }
        }
    }

    static void SetThumbnail_2(string srcImgPath, string targetFolder)
    {
        using (Bitmap source = new Bitmap(srcImgPath))
        {
            // return the source image if it's smaller than the designated thumbnail   
            int wi, hi;
            wi = WIDTH;
            hi = HEIGHT;

            // maintain the aspect ratio despite the thumbnail size parameters   
            if (source.Width > source.Height)
            {
                wi = WIDTH;
                hi = (int)(source.Height * ((decimal)WIDTH / source.Width));
            }
            else
            {
                hi = HEIGHT;
                wi = (int)(source.Width * ((decimal)HEIGHT / source.Height));
            }

            // original code that creates lousy thumbnails   
            // System.Drawing.Image ret = source.GetThumbnailImage(wi,hi,null,IntPtr.Zero);   
            using (System.Drawing.Bitmap thumb = new Bitmap(wi, hi))
            {
                using (Graphics g = Graphics.FromImage(thumb))
                {
                    g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                    g.FillRectangle(Brushes.White, 0, 0, wi, hi);
                    g.DrawImage(source, 0, 0, wi, hi);
                }
                string targetPath = Path.Combine(targetFolder, "th_2.jpg");
                thumb.Save(targetPath);
            }

        }
    }

    static void SetThumbnail_3(string srcImgPath, string targetFolder)
    {
        //Configure JPEG Compression Engine   
        System.Drawing.Imaging.EncoderParameters encoderParams = new System.Drawing.Imaging.EncoderParameters();
        long[] quality = new long[1];
        quality[0] = 75;
        System.Drawing.Imaging.EncoderParameter encoderParam = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
        encoderParams.Param[0] = encoderParam;

        System.Drawing.Imaging.ImageCodecInfo[] arrayICI = System.Drawing.Imaging.ImageCodecInfo.GetImageEncoders();
        System.Drawing.Imaging.ImageCodecInfo jpegICI = null;
        for (int x = 0; x < arrayICI.Length; x++)
        {
            if (arrayICI[x].FormatDescription.Equals("JPEG"))
            {
                jpegICI = arrayICI[x];
                break;
            }
        }

        using (Bitmap source = new Bitmap(srcImgPath))
        {
            int wi, hi;
            wi = WIDTH;
            hi = HEIGHT;

            // maintain the aspect ratio despite the thumbnail size parameters   
            if (source.Width > source.Height)
            {
                wi = WIDTH;
                hi = (int)(source.Height * ((decimal)WIDTH / source.Width));
            }
            else
            {
                hi = HEIGHT;
                wi = (int)(source.Width * ((decimal)HEIGHT / source.Height));
            }

            // original code that creates lousy thumbnails   
            // System.Drawing.Image ret = source.GetThumbnailImage(wi,hi,null,IntPtr.Zero);   
            using (System.Drawing.Bitmap thumb = new Bitmap(wi, hi))
            {
                using (Graphics g = Graphics.FromImage(thumb))
                {
                    g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                    g.FillRectangle(Brushes.White, 0, 0, wi, hi);
                    g.DrawImage(source, 0, 0, wi, hi);
                }
                string targetPath = Path.Combine(targetFolder, "th_3.jpg");
                thumb.Save(targetPath, jpegICI, encoderParams);
            }

        }

    }
}

}</pre>