请问如何在把图片保存到数据库时，让图片变小

Question

请问如何在把图片保存到数据库时让图片变小就跟ps改变图像大小那样，尺寸而不改变图片本身现在一张图片一般都3mb左右

Answer 1

C#将图片像素变低，就可以变小了
http://topic.csdn.net/u/20100506/23/006f8270-4991-4279-ab20-0c274a76cb98.html?13579

Answer 2

像素变低就改变图片的质量了，可以先把图片读成byte[]，然后可以使用 GZip 等压缩方法进行压缩，可以有效压缩；const int UNZIP_BUFFER_LENGTH = 1024 * 1024;        /// <summary>压缩数据流</summary>
        /// <param name="fileByteArray">需要压缩的数据流</param>
        /// <returns>返回压缩后的数据流</returns>
        public static byte[] ZipFileStream(byte[] fileBytes)
        {
            if (fileBytes == null) return null;
            // 压缩数据流
            MemoryStream memStream = new MemoryStream();
            GZipStream zipStream = null;            try
            {
                // 创建压缩数据流
                zipStream = new GZipStream(memStream, CompressionMode.Compress);
                // 从指定的字节数组中将压缩的字节写入基础流
                zipStream.Write(fileBytes, 0, fileBytes.Length);
            }
            finally
            {
                if (zipStream != null) zipStream.Close();
                // 关闭压缩数据流
                memStream.Close();
            }
            return memStream.ToArray();
        }

Answer 3

等比例缩放图片
<script language="JavaScript">
var flag=false;
function DrawImage(ImgD,iwidth,iheight){
  var image=new Image();
  image.src=ImgD.src;
  if(image.width>0 && image.height>0){
  flag=true;
  if(image.width/image.height>= iwidth/iheight){
  if(image.width>iwidth){   
  ImgD.width=iwidth;
  ImgD.height=(image.height*iwidth)/image.width;
  }else{
  ImgD.width=image.width;   
  ImgD.height=image.height;
  }
  ImgD.alt=image.width+"×"+image.height;
  }
  else{
  if(image.height>iheight){   
  ImgD.height=iheight;
  ImgD.width=(image.width*iheight)/image.height;   
  }else{
  ImgD.width=image.width;   
  ImgD.height=image.height;
  }
  ImgD.alt=image.width+"×"+image.height;
  }  }
}onload="javascript:DrawImage1(this)">
上传图片生成缩略图
public static void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode)
{
System.Drawing.Image originalImage = System.Drawing.Image.FromFile(originalImagePath);
int towidth = width;
int toheight = height;
int x = 0;
int y = 0;
int ow = originalImage.Width;
int oh = originalImage.Height;
switch (mode)
{
case "HW":   
break;
case "W":
toheight = originalImage.Height * width / originalImage.Width;
break;
case "H":
towidth = originalImage.Width * height / originalImage.Height;
break;
case "Cut":
if ((double)originalImage.Width / (double)originalImage.Height > (double)towidth / (double)toheight)
{
oh = originalImage.Height;
ow = originalImage.Height * towidth / toheight;
y = 0;
x = (originalImage.Width - ow) / 2;
}
else
{
ow = originalImage.Width;
oh = originalImage.Width * height / towidth;
x = 0;
y = (originalImage.Height - oh) / 2;
}
break;
default:
break;
}
System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);
System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap);
g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
g.Clear(System.Drawing.Color.Transparent);
g.DrawImage(originalImage, new System.Drawing.Rectangle(0, 0, towidth, toheight),
new System.Drawing.Rectangle(x, y, ow, oh),
System.Drawing.GraphicsUnit.Pixel);try
{
bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
}
catch (System.Exception e)
{
throw e;
}
finally
{
originalImage.Dispose();
bitmap.Dispose();
g.Dispose();
}
} 
重画
Image oldImg = new Bitmap("d:/a.jpg");
Image newImg = new Bitmap(oldImg.Width, oldImg.Height - 100);Graphics g = Graphics.FromImage(newImg);
g.DrawImage(oldImg, new Point(0, 0));