c# 生成自定义图片

using system.drawing;
using system.io;
using system.drawing.imaging;
using system;

namespace treads
{
    /// <summary>
    /// 生成略缩图
    /// </summary>
    public class class2
    {
        private image srcimage;
        private string srcfilename= @"x";//获取图片的路径
        private string srcfilename1 = @"x";//要保持图片的新路径

        /// <summary>
        /// 回调
        /// </summary>
        /// <returns></returns>
        public bool thumbnailcallback()
        {
            return false;
        }
        /// <summary>
        /// 保存缩略图
        /// </summary>
        /// <param name="width"></param>
        /// <param name="height"></param>
        public void savethumbnailimage(int width, int height)
        {
            switch (path.getextension(srcfilename).tolower())
            {
                case ".png":
                    saveimage(width, height, imageformat.png);
                    break;
                case ".gif":
                    saveimage(width, height, imageformat.gif);
                    break;
                default:
                    saveimage(width, height, imageformat.jpeg);
                    break;
            }
        }

        /// <summary>
        /// 生成缩略图并保存
        /// </summary>
        /// <param name="width">缩略图的宽度</param>
        /// <param name="height">缩略图的高度</param>
        /// <param name="imgformat">保存的图像格式</param>
        /// <returns>缩略图的image对象</returns>
        public void saveimage(int width, int height, imageformat imgformat)
        {
            srcimage = image.fromfile(srcfilename);
            if (imgformat != imageformat.gif && (srcimage.width > width) || (srcimage.height > height))
            {
                image img;
                image.getthumbnailimageabort callb = new image.getthumbnailimageabort(thumbnailcallback);
                img = srcimage.getthumbnailimage(width, height, callb, intptr.zero);
                srcimage.dispose();
                img.save(srcfilename1, imgformat);
                img.dispose();
            }
        }

    }
}

 制作网络下载的略缩图

  /// <summary>
        /// 制作远程缩略图
        /// </summary>
        /// <param name="url">图片url</param>
        /// <param name="newfilename">新图路径</param>
        /// <param name="maxwidth">最大宽度</param>
        /// <param name="maxheight">最大高度</param>
        public static void makeremotethumbnailimage(string url, string newfilename, int maxwidth, int maxheight)
        {
            stream stream = getremoteimage(url);
            if (stream == null)
                return;
            image original = image.fromstream(stream);
            stream.close();
            makethumbnailimage(original, newfilename, maxwidth, maxheight);
        }

   /// <summary>
        /// 获取图片流
        /// </summary>
        /// <param name="url">图片url</param>
        /// <returns></returns>
        private static stream getremoteimage(string url)
        {
            httpwebrequest request = (httpwebrequest)httpwebrequest.create(url);
            request.method = "get";
            request.contentlength = 0;
            request.timeout = 20000;
            httpwebresponse response = null;

            try
            {
                response = (httpwebresponse)request.getresponse();
                return response.getresponsestream();
            }
            catch
            {
                return null;
            }
        }

 /// <summary>
        /// 裁剪图片并保存
        /// </summary>
        /// <param name="filename">源图路径（绝对路径）</param>
        /// <param name="newfilename">缩略图路径（绝对路径）</param>
        /// <param name="maxwidth">缩略图宽度</param>
        /// <param name="maxheight">缩略图高度</param>
        /// <param name="cropwidth">裁剪宽度</param>
        /// <param name="cropheight">裁剪高度</param>
        /// <param name="x">x轴</param>
        /// <param name="y">y轴</param>
        public static bool makethumbnailimage(string filename, string newfilename, int maxwidth, int maxheight, int cropwidth, int cropheight, int x, int y)
        {
            byte[] imagebytes = file.readallbytes(filename);
            image originalimage = image.fromstream(new system.io.memorystream(imagebytes));
            bitmap b = new bitmap(cropwidth, cropheight);
            try
            {
                using (graphics g = graphics.fromimage(b))
                {
                    //设置高质量插值法
                    g.interpolationmode = interpolationmode.highqualitybicubic;
                    //设置高质量,低速度呈现平滑程度
                    g.smoothingmode = smoothingmode.antialias;
                    g.pixeloffsetmode = pixeloffsetmode.highquality;
                    //清空画布并以透明背景色填充
                    g.clear(color.transparent);
                    //在指定位置并且按指定大小绘制原图片的指定部分
                    g.drawimage(originalimage, new rectangle(0, 0, cropwidth, cropheight), x, y, cropwidth, cropheight, graphicsunit.pixel);
                    image displayimage = new bitmap(b, maxwidth, maxheight);
                    saveimage(displayimage, newfilename, getcodecinfo("image/" + getformat(newfilename).tostring().tolower()));
                    return true;
                }
            }
            catch (system.exception e)
            {
                throw e;
            }
            finally
            {
                originalimage.dispose();
                b.dispose();
            }
        }