C# 图片按比例进行压缩

1、对图片进行压缩，保存在本地

对于一个200k的png文件按0.6的缩放比例进行压缩，压缩后的大小为20k左右

对于一个80k的jpg文件按0.6的缩放比例压缩，压缩后为13k左右

public void imageZoom(string name, Double zoomScale){Bitmap btImage = new Bitmap(name);Image serverImage = btImage;int width = (int)(serverImage.Width * zoomScale);int height = (int)(serverImage.Height * zoomScale);//画板大小int finalWidth = width, finalHeight = height;int srcImageWidth = serverImage.Width;int srcImageHeight = serverImage.Height;if (srcImageWidth > srcImageHeight){finalHeight = srcImageHeight * width / srcImageWidth;}else{finalWidth = srcImageWidth * height / srcImageHeight;}//新建一个bmp图片Image newImage = new Bitmap(width, height);//新建一个画板Graphics g = Graphics.FromImage(newImage);//设置高质量插值法g.InterpolationMode = InterpolationMode.High;//设置高质量,低速度呈现平滑程度g.SmoothingMode = SmoothingMode.HighQuality;//清空画布并以透明背景色填充g.Clear(Color.White);//在指定位置并且按指定大小绘制原图片的指定部分g.DrawImage(serverImage, new Rectangle((width - finalWidth) / 2, (height - finalHeight) / 2, finalWidth, finalHeight), 0, 0, srcImageWidth, srcImageHeight, GraphicsUnit.Pixel);//以jpg格式保存缩略图MemoryStream msSaveImage = new MemoryStream();newImage.Save(@"D:\1.png",ImageFormat.Jpeg);serverImage.Dispose();newImage.Dispose();g.Dispose();}

 private void button1_Click(object sender, EventArgs e){OpenFileDialog ofd = new OpenFileDialog();ofd.ShowDialog();imageZoom(ofd.FileName,0.6);}

2、对图片进行压缩，转换成Base64后进行传输，可测量字符串长度来对比

对一张图片转换成base64后，测量base64字符串的长度，对于一个80k的图片，压缩前长度为110800多，压缩后长度不到20000，减小了很多，便于传输。

网上有关于对字符串进行压缩的，那是针对纯字符串，对于已经转换成base64的字符串，使用GZipStream类来压缩数据基本上没有效果。

public  string ImageToBase64(string name,Double zoomScale){Bitmap btImage = new Bitmap(name);Image serverImage = btImage;int width = (int)(serverImage.Width * zoomScale);int height = (int)(serverImage.Height * zoomScale);//画板大小int finalWidth = width, finalHeight = height;int srcImageWidth = serverImage.Width;int srcImageHeight = serverImage.Height;if (srcImageWidth > srcImageHeight){finalHeight = srcImageHeight * width / srcImageWidth;}else{finalWidth = srcImageWidth * height / srcImageHeight;}//新建一个bmp图片Image newImage = new Bitmap(width, height);//新建一个画板Graphics g = Graphics.FromImage(newImage);//设置高质量插值法g.InterpolationMode = InterpolationMode.High;//设置高质量,低速度呈现平滑程度g.SmoothingMode = SmoothingMode.HighQuality;//清空画布并以透明背景色填充g.Clear(Color.White);//在指定位置并且按指定大小绘制原图片的指定部分g.DrawImage(serverImage, new Rectangle((width - finalWidth) / 2, (height - finalHeight) / 2, finalWidth, finalHeight), 0, 0, srcImageWidth, srcImageHeight, GraphicsUnit.Pixel);//以jpg格式保存缩略图MemoryStream msSaveImage = new MemoryStream();newImage.Save(msSaveImage, ImageFormat.Jpeg);serverImage.Dispose();newImage.Dispose();g.Dispose();byte[] imageBytes = msSaveImage.ToArray();msSaveImage.Close();return Convert.ToBase64String(imageBytes);}