我们可以通过不同的方式做到这一点，
最好的方法之一是将所有图像转换为 jpeg，因为它会以更小的尺寸提供更好的清晰度，在这种情况下，我们不需要更改特定图像的任何高度或宽度
方法1：将所有图像转换为jpeg（无需额外压缩）
private static void VaryQualityLevel(Image imgToResize,string imageName)
{
// Get a bitmap.
Bitmap bmp1 = new Bitmap(imgToResize);
ImageCodecInfo jgpEncoder = GetEncoder(ImageFormat.Jpeg);
// Create an Encoder object based on the GUID
// for the Quality parameter category.
System.Drawing.Imaging.Encoder myEncoder =
System.Drawing.Imaging.Encoder.Quality;
// Create an EncoderParameters object.
// An EncoderParameters object has an array of EncoderParameter
// objects. In this case, there is only one
// EncoderParameter object in the array.
EncoderParameters myEncoderParameters = new EncoderParameters(1);
EncoderParameter myEncoderParameter = new EncoderParameter(myEncoder,
50L);
myEncoderParameters.Param[0] = myEncoderParameter;
var fileSavePath = Path.Combine(HttpContext.Current.Server.MapPath("~/Download/"), imageName+".jpeg");
bmp1.Save(fileSavePath, jgpEncoder,
myEncoderParameters);
//myEncoderParameter = new EncoderParameter(myEncoder, 100L);
//myEncoderParameters.Param[0] = myEncoderParameter;
//fileSavePath = Path.Combine(HttpContext.Current.Server.MapPath("~/Download/"), "TestPhotoQuality100.jpeg");
//bmp1.Save(fileSavePath, jgpEncoder,
// myEncoderParameters);
// Save the bitmap as a JPG file with 75 quality level compression.
myEncoderParameter = new EncoderParameter(myEncoder, 75L);
//myEncoderParameters.Param[0] = myEncoderParameter;
//fileSavePath = Path.Combine(HttpContext.Current.Server.MapPath("~/Download/"), "TestPhotoQuality75.jpeg");
//bmp1.Save(fileSavePath, jgpEncoder,
// myEncoderParameters);
}
private static ImageCodecInfo GetEncoder(ImageFormat format)
{
ImageCodecInfo[] codecs = ImageCodecInfo.GetImageDecoders();
foreach (ImageCodecInfo codec in codecs)
{
if (codec.FormatID == format.Guid)
{
return codec;
}
}
return null;
}
方法2：通过改变图像的高度和宽度（没有jpeg转换）
CommonConstant.CS
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
namespace EmptyDemo.compression
{
#region[Directive]
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
#endregion[Directive]
/// <summary>
/// This class is used to get the constants
/// </summary>
public class CommonConstant
{
public const string JPEG = ".jpeg";
public const string PNG = ".png";
public const string JPG = ".jpg";
public const string BTM = ".btm";
}
}
图像压缩.CS
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
namespace EmptyDemo.compression
{
#region[Directive]
using System;
using System.Collections.Generic;
using System.Linq;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
#endregion[Directive]
/// <summary>
/// This class is used to compress the image to
/// provided size
/// </summary>
public class ImageCompress
{
#region[PrivateData]
private static volatile ImageCompress imageCompress;
private Bitmap bitmap;
private int width;
private int height;
private Image img;
#endregion[Privatedata]
#region[Constructor]
/// <summary>
/// It is used to restrict to create the instance of the ImageCompress
/// </summary>
private ImageCompress()
{
}
#endregion[Constructor]
#region[Poperties]
/// <summary>
/// Gets ImageCompress object
/// </summary>
public static ImageCompress GetImageCompressObject
{
get
{
if (imageCompress == null)
{
imageCompress = new ImageCompress();
}
return imageCompress;
}
}
/// <summary>
/// Gets or sets Width
/// </summary>
public int Height
{
get { return height; }
set { height = value; }
}
/// <summary>
/// Gets or sets Width
/// </summary>
public int Width
{
get { return width; }
set { width = value; }
}
/// <summary>
/// Gets or sets Image
/// </summary>
public Bitmap GetImage
{
get { return bitmap; }
set { bitmap = value; }
}
#endregion[Poperties]
#region[PublicFunction]
/// <summary>
/// This function is used to save the image
/// </summary>
/// <param name="fileName"></param>
/// <param name="path"></param>
public void Save(string fileName, string path)
{
if (ISValidFileType(fileName))
{
string pathaname = path + @"\" + fileName;
save(pathaname, 60);
}
}
#endregion[PublicFunction]
#region[PrivateData]
/// <summary>
/// This function is use to compress the image to
/// predefine size
/// </summary>
/// <returns>return bitmap in compress size</returns>
private Image CompressImage()
{
if (GetImage != null)
{
Width = (Width == 0) ? GetImage.Width : Width;
Height = (Height == 0) ? GetImage.Height : Height;
Bitmap newBitmap = new Bitmap(Width, Height, PixelFormat.Format24bppRgb);
newBitmap = bitmap;
newBitmap.SetResolution(80, 80);
return newBitmap.GetThumbnailImage(Width, Height, null, IntPtr.Zero);
}
else
{
throw new Exception("Please provide bitmap");
}
}
/// <summary>
/// This function is used to check the file Type
/// </summary>
/// <param name="fileName">String data type:contain the file name</param>
/// <returns>true or false on the file extention</returns>
private bool ISValidFileType(string fileName)
{
bool isValidExt = false;
string fileExt = Path.GetExtension(fileName);
switch (fileExt.ToLower())
{
case CommonConstant.JPEG:
case CommonConstant.BTM:
case CommonConstant.JPG:
case CommonConstant.PNG:
isValidExt = true;
break;
}
return isValidExt;
}
/// <summary>
/// This function is used to get the imageCode info
/// on the basis of mimeType
/// </summary>
/// <param name="mimeType">string data type</param>
/// <returns>ImageCodecInfo data type</returns>
private ImageCodecInfo GetImageCoeInfo(string mimeType)
{
ImageCodecInfo[] codes = ImageCodecInfo.GetImageEncoders();
for (int i = 0; i < codes.Length; i++)
{
if (codes[i].MimeType == mimeType)
{
return codes[i];
}
}
return null;
}
/// <summary>
/// this function is used to save the image into a
/// given path
/// </summary>
/// <param name="path">string data type</param>
/// <param name="quality">int data type</param>
private void save(string path, int quality)
{
img = CompressImage();
////Setting the quality of the picture
EncoderParameter qualityParam =
new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
////Seting the format to save
ImageCodecInfo imageCodec = GetImageCoeInfo("image/jpeg");
////Used to contain the poarameters of the quality
EncoderParameters parameters = new EncoderParameters(1);
parameters.Param[0] = qualityParam;
////Used to save the image to a given path
img.Save(path, imageCodec, parameters);
}
#endregion[PrivateData]
}
}
在这里，我在 jquery 和 Web 服务的帮助下上传图像，并将文件作为 formdata 传递
[WebMethod]
public void UploadFile()
{
if (HttpContext.Current.Request.Files.AllKeys.Any())
{
// Get the uploaded image from the Files collection
var httpPostedFile = HttpContext.Current.Request.Files["UploadedImage"];
if (httpPostedFile != null)
{
ImageCompress imgCompress = ImageCompress.GetImageCompressObject;
imgCompress.GetImage = new System.Drawing.Bitmap(httpPostedFile.InputStream);
imgCompress.Height = 260;
imgCompress.Width = 358;
//imgCompress.Save(httpPostedFile.FileName, @"C:\Documents and Settings\Rasmi\My Documents\Visual Studio2008\WebSites\compressImageFile\Logo");
imgCompress.Save(httpPostedFile.FileName, HttpContext.Current.Server.MapPath("~/Download/"));
}
}
}