声明：
图片压缩算法，不建议对小图片进行压缩，一般文件小于1m的，真心没必要压缩，
图片很小的，例如：几百KB的图片，有可能不会减少图片体积，反而压缩后更大，也很正常，
请大家合理使用，并不是，所有图片，越压缩越好！！！！！
上面是我对2M多的图片进行了测试，压缩质量设置了50，压缩到了800KB，放大和缩小和原图，几乎没有什么区别。
代码如下：
private void button3_Click(object sender, EventArgs e)
{
using (OpenFileDialog ofd = new OpenFileDialog())
{
ofd.Filter = "图片|*.jpg;*.png;*.gif;*.jpeg;*.bmp";
if (ofd.ShowDialog() == DialogResult.OK)
{
using (FileStream file = new FileStream(ofd.FileName, FileMode.Open))
{
var img = CompressionImage(file, 50L);
MessageBox.Show(CreateImageFromBytes(AppDomain.CurrentDomain.BaseDirectory + @"\" + Guid.NewGuid().ToString(), img));
} }
}
} /// <summary>
/// Convert Byte[] to Image
/// </summary>
/// <param name="buffer"></param>
/// <returns></returns>
public static Image BytesToImage(byte[] buffer)
{
MemoryStream ms = new MemoryStream(buffer);
Image image = System.Drawing.Image.FromStream(ms);
return image;
} /// <summary>
/// Convert Byte[] to a picture and Store it in file
/// </summary>
/// <param name="fileName"></param>
/// <param name="buffer"></param>
/// <returns></returns>
public static string CreateImageFromBytes(string fileName, byte[] buffer)
{
string file = fileName;
Image image = BytesToImage(buffer);
ImageFormat format = image.RawFormat;
if (format.Equals(ImageFormat.Jpeg))
{
file += ".jpeg";
}
else if (format.Equals(ImageFormat.Png))
{
file += ".png";
}
else if (format.Equals(ImageFormat.Bmp))
{
file += ".bmp";
}
else if (format.Equals(ImageFormat.Gif))
{
file += ".gif";
}
else if (format.Equals(ImageFormat.Icon))
{
file += ".icon";
}
System.IO.FileInfo info = new System.IO.FileInfo(file);
System.IO.Directory.CreateDirectory(info.Directory.FullName);
File.WriteAllBytes(file, buffer);
return file;
}
/// <summary>
/// 壓縮圖片 /// </summary>
/// <param name="fileStream">圖片流</param>
/// <param name="quality">壓縮質量0-100之間 數值越大質量越高</param>
/// <returns></returns>
private byte[] CompressionImage(Stream fileStream, long quality)
{
using (System.Drawing.Image img = System.Drawing.Image.FromStream(fileStream))
{
using (Bitmap bitmap = new Bitmap(img))
{
ImageCodecInfo CodecInfo = GetEncoder(img.RawFormat);
System.Drawing.Imaging.Encoder myEncoder = System.Drawing.Imaging.Encoder.Quality;
EncoderParameters myEncoderParameters = new EncoderParameters();
EncoderParameter myEncoderParameter = new EncoderParameter(myEncoder, quality);
myEncoderParameters.Param[] = myEncoderParameter;
using (MemoryStream ms = new MemoryStream())
{
bitmap.Save(ms, CodecInfo, myEncoderParameters);
myEncoderParameters.Dispose();
myEncoderParameter.Dispose();
return ms.ToArray();
}
}
}
} private static ImageCodecInfo GetEncoder(ImageFormat format)
{
ImageCodecInfo[] codecs = ImageCodecInfo.GetImageDecoders();
foreach (ImageCodecInfo codec in codecs)
{
if (codec.FormatID == format.Guid)
{ return codec; }
}
return null;
}