1、C#生成图片缩略图
/// <summary> /// 生成缩略图:背景颜色可以设置 /// </summary> /// <param name="originalImagePath">源图路径（物理路径）</param> /// <param name="thumbnailPath">缩略图路径（物理路径）</param> /// <param name="width">缩略图宽度</param> /// <param name="height">缩略图高度</param> /// <param name="byColor">空白背景填充颜色</param> public static void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string byColor) { //获取原始图片 System.Drawing.Image originalImage = System.Drawing.Image.FromFile(originalImagePath); //缩略图画布宽高 int towidth = width; int toheight = height; //原始图片写入画布坐标和宽高(用来设置裁减溢出部分) int x = 0; int y = 0; int ow = originalImage.Width; int oh = originalImage.Height; //原始图片画布,设置写入缩略图画布坐标和宽高(用来原始图片整体宽高缩放) int bg_x = 0; int bg_y = 0; int bg_w = towidth; int bg_h = toheight; //倍数变量 double multiple = 0; //获取宽长的或是高长与缩略图的倍数 if (originalImage.Width >= originalImage.Height) { multiple = (double)originalImage.Width / (double)width; } else { multiple = (double)originalImage.Height / (double)height; } //上传的图片的宽和高小等于缩略图 if (ow <= width && oh <= height) { //缩略图按原始宽高 bg_w = originalImage.Width; bg_h = originalImage.Height; //空白部分用背景色填充 bg_x = Convert.ToInt32(((double)towidth - (double)ow) / 2); bg_y = Convert.ToInt32(((double)toheight - (double)oh) / 2); } //上传的图片的宽和高大于缩略图 else { //宽高按比例缩放 bg_w = Convert.ToInt32((double)originalImage.Width / multiple); bg_h = Convert.ToInt32((double)originalImage.Height / multiple); //空白部分用背景色填充 bg_y = Convert.ToInt32(((double)height - (double)bg_h) / 2); bg_x = Convert.ToInt32(((double)width - (double)bg_w) / 2); } //新建一个bmp图片,并设置缩略图大小. System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight); //新建一个画板 System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap); //设置高质量插值法 g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBilinear; //设置高质量,低速度呈现平滑程度 g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality; //清空画布并设置背景色 g.Clear(System.Drawing.ColorTranslator.FromHtml(byColor)); //在指定位置并且按指定大小绘制原图片的指定部分 //第一个System.Drawing.Rectangle是原图片的画布坐标和宽高,第二个是原图片写在画布上的坐标和宽高,最后一个参数是指定数值单位为像素 g.DrawImage(originalImage, new System.Drawing.Rectangle(bg_x, bg_y, bg_w, bg_h), new System.Drawing.Rectangle(x, y, ow, oh), System.Drawing.GraphicsUnit.Pixel); try { //获取图片类型 string fileExtension = System.IO.Path.GetExtension(originalImagePath).ToLower(); //按原图片类型保存缩略图片,不按原格式图片会出现模糊,锯齿等问题. switch (fileExtension) { case ".gif": bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Gif); break; case ".jpg": bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg); break; case ".bmp": bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Bmp); break; case ".png": bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Png); break; } } catch (System.Exception e) { throw e; } finally { originalImage.Dispose(); bitmap.Dispose(); g.Dispose(); } } /// <summary> /// 生成缩略图：无填充背景 /// </summary> /// <param name="originalImagePath">源图路径（物理路径）</param> /// <param name="thumbnailPath">缩略图路径（物理路径）</param> /// <param name="width">缩略图宽度</param> /// <param name="height">缩略图高度</param> public static void MakeThumbnail2(string originalImagePath, string thumbnailPath, int width, int height) { //获取原始图片 System.Drawing.Image originalImage = System.Drawing.Image.FromFile(originalImagePath); //缩略图画布宽高 int towidth = width;//缩略图宽度 int toheight = height;//缩略图高度 //原始图片写入画布坐标和宽高(用来设置裁减溢出部分) int x = 0; int y = 0; int ow = originalImage.Width;//原图宽度 int oh = originalImage.Height;//原图高度 //先判断宽，宽大于指定宽度的话将宽设置为指定宽度，高度等比例缩放。 if (originalImage.Width > width) { towidth = width; toheight = originalImage.Height * towidth / originalImage.Width; } else { towidth = originalImage.Width; toheight = originalImage.Height; } //再判断高，高大于指定高度的话将高设置为指定高度，宽度等比例缩放。 if (toheight > height) { toheight = height; towidth = originalImage.Width * toheight / originalImage.Height; } //新建一个bmp图片 System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight); //新建一个画板 Graphics g = System.Drawing.Graphics.FromImage(bitmap); //设置高质量插值法 g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High; //设置高质量,低速度呈现平滑程度 g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.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, towidth, toheight), new Rectangle(x, y, ow, oh), GraphicsUnit.Pixel); try { //获取图片类型 string fileExtension = System.IO.Path.GetExtension(originalImagePath).ToLower(); //按原图片类型保存缩略图片,不按原格式图片会出现模糊,锯齿等问题. switch (fileExtension) { case ".gif": bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Gif); break; case ".jpg": bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg); break; case ".bmp": bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Bmp); break; case ".png": bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Png); break; } } catch (System.Exception e) { throw e; } finally { originalImage.Dispose(); bitmap.Dispose(); g.Dispose(); } }
2、C#等比缩放图片
protected void Page_Load(object sender, EventArgs e) { //测试 string picUrl = "/upload/1.png"; string picPath = Server.MapPath(picUrl); ChangePicSize(picPath, 800); Response.Write("<img src='" + picUrl + "'>"); } /// <summary> /// 等比缩放图片 /// </summary> /// <param name="pathImageFrom">图片地址（服务器绝对路径）</param> /// <param name="maxSize">宽和高最大值</param> public void ChangePicSize(string pathImageFrom, int maxSize) { System.Drawing.Image imageFrom = null; if (File.Exists(pathImageFrom)) { imageFrom = System.Drawing.Image.FromFile(pathImageFrom); // 源图宽度及高度 int imageFromWidth = imageFrom.Width; int imageFromHeight = imageFrom.Height; // 生成的缩略图实际宽度及高度 int bitmapWidth = imageFromWidth; int bitmapHeight = imageFromHeight; if (imageFromWidth > maxSize || imageFromHeight > maxSize) { if (imageFromWidth > imageFromHeight) { bitmapWidth = maxSize; bitmapHeight = imageFromHeight * maxSize / imageFromWidth; } else { bitmapWidth = imageFromWidth * maxSize / imageFromHeight; bitmapHeight = maxSize; } } // 创建画布 System.Drawing.Bitmap bmp = new System.Drawing.Bitmap(bitmapWidth, bitmapHeight); System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bmp); // 用白色清空 g.Clear(System.Drawing.Color.White); // 指定高质量的双三次插值法。执行预筛选以确保高质量的收缩。此模式可产生质量最高的转换图像。 g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic; // 指定高质量、低速度呈现。 g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality; // 在指定位置并且按指定大小绘制指定的 Image 的指定部分。 g.DrawImage(imageFrom, new System.Drawing.Rectangle(0, 0, bitmapWidth, bitmapHeight), new System.Drawing.Rectangle(0, 0, imageFromWidth, imageFromHeight), System.Drawing.GraphicsUnit.Pixel); imageFrom.Dispose(); bmp.Save(pathImageFrom, System.Drawing.Imaging.ImageFormat.Jpeg); //释放资源 bmp.Dispose(); g.Dispose(); } }