C#对照片流进行压缩

有时候在开发项目时会遇到限制图片大小的应用场景，这时候就需要对上传或下载的图片流进行压缩，以达到限制图片大小的目的，具体实现代码如下：

/// <summary>
/// 降低图片质量
/// </summary>
/// <param name="sFile">文件流</param>
/// <param name="flag">压缩倍率（1-100）</param>
/// <param name="size">输出最大流尺寸（单位：MB）</param>
/// <param name="sfsc">是否第一次执行方法</param>
/// <returns></returns>
private static Stream ReducePictureQuality(Stream sFile, int flag = 90, double size = 0.18, bool sfsc = true)
{
        MemoryStream outStream = new MemoryStream();

        //如果是第一次调用，原始图像的大小小于要压缩的大小，则直接复制文件，并且返回true
        if (sfsc == true && sFile.Length < size * 1024 * 1024)
        {
            return sFile;
        }

        Image iSource = Image.FromStream(sFile);
        ImageFormat tFormat = iSource.RawFormat;
        int dHeight = iSource.Height / 2;
        int dWidth = iSource.Width / 2;

        int sW = 0, sH = 0;
        //按比例缩放
        Size tem_size = new Size(iSource.Width, iSource.Height);
        if (tem_size.Width > dHeight || tem_size.Width > dWidth)
        {
            if ((tem_size.Width * dHeight) > (tem_size.Width * dWidth))
            {
                sW = dWidth;
                sH = (dWidth * tem_size.Height) / tem_size.Width;
            }
            else
            {
                sH = dHeight;
                sW = (tem_size.Width * dHeight) / tem_size.Height;
            }
        }
        else
        {
            sW = tem_size.Width;
            sH = tem_size.Height;
        }
        Bitmap ob = new Bitmap(dWidth, dHeight);
        Graphics g = Graphics.FromImage(ob);
        g.Clear(Color.WhiteSmoke);

        g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;

        g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

        g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;

        g.DrawImage(iSource, new Rectangle((dWidth - sW) / 2, (dHeight - sH) / 2, sW, sH), 0, 0, iSource.Width, iSource.Height, GraphicsUnit.Pixel);

        g.Dispose();

        //以下代码为保存图片时，设置压缩质量

        EncoderParameters ep = new EncoderParameters();

        long[] qy = new long[1];

        qy[0] = flag;//设置压缩的比例1-100

        EncoderParameter eParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, qy);

        ep.Param[0] = eParam;

        try
        {
            ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();

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

            if (jpegICIinfo != null)
            {
                ob.Save(outStream, jpegICIinfo, ep);//dFile是压缩后的新路径////
                //FileInfo fi = new FileInfo();
                if (outStream.Length > 1024 * 1024 * size)
                {
                    flag = flag - 10;

                    ReducePictureQuality(outStream, flag, size, false);

                }

            }

            else
            {

                ob.Save(outStream, tFormat);

            }
            return outStream;

        }

        catch (Exception ex)
        {
            return null;
        }

        finally
        {
            iSource.Dispose();
            ob.Dispose();

        }
    }

注：如果有对上述实例代码不明白的，可以直接在文章下方留言，作者看到了会进行回复和探讨。