C# JPG图片压缩（指定大小压缩和指定尺寸压缩）

最近在我的项目中需要对图片进行压缩， 解决问题之后，把调通的两种方式分享一下。

方法一原理：设置图片质量通过降低质量从而压缩大小，质量越低压缩比越高。

方法二原理：设置图片尺寸从而压缩大小。

PS:如碰到图片资源占用提示参考评论解决方式。

一、按大小压缩测试代码：

一测试效果：

一主要代码：

/// <summary>/// 压缩图片至200 Kb以下/// </summary>/// <param name="img">图片</param>/// <param name="format">图片格式</param>/// <param name="targetLen">压缩后大小</param>/// <param name="srcLen">原始大小</param>/// <returns>压缩后的图片</returns>public Image ZipImage(Image img, ImageFormat format, long targetLen, long srcLen = 0){//设置大小偏差幅度 10kbconst long nearlyLen = 10240;//内存流 如果参数中原图大小没有传递 则使用内存流读取var ms = new MemoryStream();if (0 == srcLen){img.Save(ms, format);srcLen = ms.Length;}//单位 由Kb转为byte 若目标大小高于原图大小，则满足条件退出targetLen *= 1024;if (targetLen > srcLen){ms.SetLength(0);ms.Position = 0;img.Save(ms, format);img = Image.FromStream(ms);return img;}//获取目标大小最低值var exitLen = targetLen - nearlyLen;//初始化质量压缩参数 图像 内存流等var quality = (long)Math.Floor(100.00 * targetLen / srcLen);var parms = new EncoderParameters(1);//获取编码器信息//ImageCodecInfo formatInfo = null;//var encoders = ImageCodecInfo.GetImageEncoders();//foreach (ImageCodecInfo icf in encoders)//{// if (icf.FormatID == ImageFormat.Jpeg.Guid)// {// formatInfo = icf;// break;// }//}// 创建目标图像的编码参数，通过JPEG质量参数指定压缩质量ImageCodecInfo formatInfo = GetEncoder(ImageFormat.Jpeg);//使用二分法进行查找 最接近的质量参数long startQuality = quality;long endQuality = 100;quality = (startQuality + endQuality) / 2;while (true){//设置质量parms.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);//清空内存流 然后保存图片ms.SetLength(0);ms.Position = 0;img.Save(ms, formatInfo, parms);//若压缩后大小低于目标大小，则满足条件退出if (ms.Length >= exitLen && ms.Length <= targetLen){break;}else if (startQuality >= endQuality) //区间相等无需再次计算{break;}else if (ms.Length < exitLen) //压缩过小,起始质量右移{startQuality = quality;}else //压缩过大 终止质量左移{endQuality = quality;}//重新设置质量参数 如果计算出来的质量没有发生变化，则终止查找。这样是为了避免重复计算情况{start:16,end:18} 和 {start:16,endQuality:17}var newQuality = (startQuality + endQuality) / 2;if (newQuality == quality){break;}quality = newQuality;//Console.WriteLine("start:{0} end:{1} current:{2}", startQuality, endQuality, quality);}img = Image.FromStream(ms);return img;}/// <summary>///获取图片格式/// </summary>/// <param name="img">图片</param>/// <returns>默认返回JPEG</returns>public ImageFormat GetImageFormat(Image img){if (img.RawFormat.Equals(ImageFormat.Jpeg)){return ImageFormat.Jpeg;}if (img.RawFormat.Equals(ImageFormat.Gif)){return ImageFormat.Gif;}if (img.RawFormat.Equals(ImageFormat.Png)){return ImageFormat.Png;}if (img.RawFormat.Equals(ImageFormat.Bmp)){return ImageFormat.Bmp;}return ImageFormat.Jpeg;//根据实际情况选择返回指定格式还是null}/// <summary>/// 按指定压缩质量进行压缩/// 调用示例CompressImage("test.png", "tests.png", 50L);/// </summary>/// <param name="sourcePath">原图路径</param>/// <param name="destinationPath">保存路径</param>/// <param name="quality">压缩质量</param>public static void CompressImage(string sourcePath, string destinationPath, long quality){// 加载原始图片Image sourceImage = Image.FromFile(sourcePath);// 创建目标图像的编码参数，通过JPEG质量参数指定压缩质量ImageCodecInfo jpegCodec = GetEncoder(ImageFormat.Jpeg);EncoderParameters encoderParameters = new EncoderParameters(1);encoderParameters.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);// 保存压缩后的图片sourceImage.Save(destinationPath, jpegCodec, encoderParameters);// 释放资源sourceImage.Dispose();}private static ImageCodecInfo GetEncoder(ImageFormat format){// 获取所有支持的图像编码器ImageCodecInfo[] codecs = ImageCodecInfo.GetImageDecoders();// 找到第一个支持指定格式的编码器foreach (ImageCodecInfo codec in codecs){if (codec.FormatID == format.Guid){return codec;}}// 如果没有找到匹配的编码器则抛出异常throw new ArgumentException("No appropriate encoder found.", nameof(format));}

二、按尺寸压缩测试代码：

二测试效果：

二主要代码：

/// <summary>/// 不管多大的图片都能在指定大小picturebox控件中显示/// </summary>/// <param name="bitmap">图片</param>/// <param name="destHeight">picturebox控件高</param>/// <param name="destWidth">picturebox控件宽</param>/// <returns></returns>private Image ZoomImage(Image bitmap, int destHeight, int destWidth){try{System.Drawing.Image sourImage = bitmap;int width = 0, height = 0;//按比例缩放 int sourWidth = sourImage.Width;int sourHeight = sourImage.Height;if (sourHeight > destHeight || sourWidth > destWidth){if ((sourWidth * destHeight) > (sourHeight * destWidth)){width = destWidth;height = (destWidth * sourHeight) / sourWidth;}else{height = destHeight;width = (sourWidth * destHeight) / sourHeight;}}else{width = sourWidth;height = sourHeight;}Bitmap destBitmap = new Bitmap(destWidth, destHeight);Graphics g = Graphics.FromImage(destBitmap);g.Clear(Color.Transparent);//设置画布的描绘质量 positingQuality = System.positingQuality.HighQuality;g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;g.DrawImage(sourImage, new Rectangle((destWidth - width) / 2, (destHeight - height) / 2, width, height), 0, 0, sourImage.Width, sourImage.Height, GraphicsUnit.Pixel);//g.DrawImage(sourImage, new Rectangle(0, 0, destWidth, destHeight), new Rectangle(0, 0, sourImage.Width, sourImage.Height), GraphicsUnit.Pixel);g.Dispose();//设置压缩质量 System.Drawing.Imaging.EncoderParameters encoderParams = new System.Drawing.Imaging.EncoderParameters();long[] quality = new long[1];quality[0] = 100;System.Drawing.Imaging.EncoderParameter encoderParam = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);encoderParams.Param[0] = encoderParam;sourImage.Dispose();return destBitmap;}catch (Exception ex){return bitmap;}}

注意：

方法一按指定的大小进行压缩，得到的图片尺寸和原图一样

方法二按指定的尺寸进行压缩，得到的图片尺寸是指定的尺寸和原图不一样

附赠一个简易的bitmap防内存溢出方法

#region Bitmap 避免内存溢出/// <summary>/// 修改Bitmap 尺寸 避免内存溢出/// </summary>/// <param name="bmp">Bitmap原图</param>/// <param name="newW">修改指定宽</param>/// <param name="newH">修改指定高</param>/// <returns></returns>public static Bitmap KiResizeImage(Bitmap bmp, int newW, int newH){//Stopwatch stopwatch = new Stopwatch();//stopwatch.Start();try{Bitmap b = new Bitmap(newW, newH);Graphics g = Graphics.FromImage(b);g.InterpolationMode = InterpolationMode.HighQualityBicubic;g.DrawImage(bmp, new System.Drawing.Rectangle(0, 0, newW, newH), new System.Drawing.Rectangle(0, 0, bmp.Width, bmp.Height), GraphicsUnit.Pixel);g.Dispose();//stopwatch.Stop();//TimeSpan timespan = stopwatch.Elapsed;//Console.WriteLine("KiResizeImage函数运行时长：" + timespan.TotalMilliseconds);return b;}catch{//stopwatch.Stop();//TimeSpan timespan = stopwatch.Elapsed;//Console.WriteLine("KiResizeImage函数运行时长(异常)：" + timespan.TotalMilliseconds);return null;}}#endregion