如何在将图像存储到asp.net之前对图像进行压缩？

Question

这是我添加的图片代码。

protected void SubmitButton_Click(object sender, EventArgs e) 
     { 
      ProductImages productImage = new ProductImages(); 
      productImage.ProductID = Convert.ToInt32(ProductDropDownList.SelectedValue.ToString()); 

      if (!FileUpload1.HasFile) 
      { 
       MessageLabel1.Text = "Please Select Image File"; //checking if file uploader has no file selected 
      } 
      else 
      { 
       int length = FileUpload1.PostedFile.ContentLength; 
       productImage.ProductImage = new byte[length]; 

       FileUpload1.PostedFile.InputStream.Read(productImage.ProductImage, 0, length); 

       try 
       { 
        ProductImageBL.AddProductImages(productImage); 
        MessageLabel1.Text = "Product Image has been successfully added!"; 
       } 
       catch (Exception ex) 
       { 
        MessageLabel1.Text = "Some error occured while processing the request. Error Description <br/>" + ex.Message; 
       } 
      } 
     } 

Answer 1

图像压缩取决于图像类型和图像上的内容。真实生活对象的照片通常以.jpg为单位，如果没有明显的质量损失，您无法将它们压缩太多。

可能你真正想要做的是将图像尺寸调整为500 * 500这样的较小尺寸，如果你知道这将足够满足你的所有需求。请注意在调整大小时保存图像宽高比。

相关SO问题： Resize an Image C#

Answer 2

的SO link发表dlxeon非常出色。我自己使用那些例子。 但是，所有这些示例都会调整图像的大小，但您也可以增加jpeg文件中的压缩和\或降低DPI。

下面是如何调整和压缩jpeg的完整示例。例如，它还检查图像是否需要旋转以防手机垂直放置。如果你想让图像呈方形，你可以添加填充。

请注意，如果您按原样使用此示例，那么.png和.gif文件的透明度将因为转换为jpg而丢失。

protected void SubmitButton_Click(object sender, EventArgs e) 
    { 
     if (FileUpload1.HasFile == true) 
     { 
      using (Bitmap postedImage = new Bitmap(FileUpload1.PostedFile.InputStream)) 
      { 
       byte [] bin = Common.scaleImage(postedImage, 400, 400, false); 
       Image1.ImageUrl = "data:image/jpeg;base64," + Convert.ToBase64String(bin); 
      } 
     } 
    } 


    public static byte[] scaleImage(Image image, int maxWidth, int maxHeight, bool padImage) 
    { 
     try 
     { 
      int newWidth; 
      int newHeight; 
      byte[] returnArray; 

      //check if the image needs rotating (eg phone held vertical when taking a picture for example) 
      foreach (var prop in image.PropertyItems) 
      { 
       if (prop.Id == 0x0112) 
       { 
        int rotateValue = image.GetPropertyItem(prop.Id).Value[0]; 
        RotateFlipType flipType = getRotateFlipType(rotateValue); 
        image.RotateFlip(flipType); 
        break; 
       } 
      } 

      //apply padding if needed 
      if (padImage == true) 
      { 
       image = applyPaddingToImage(image); 
      } 

      //check if the with or height of the image exceeds the maximum specified, if so calculate the new dimensions 
      if (image.Width > maxWidth || image.Height > maxHeight) 
      { 
       var ratioX = (double)maxWidth/image.Width; 
       var ratioY = (double)maxHeight/image.Height; 
       var ratio = Math.Min(ratioX, ratioY); 

       newWidth = (int)(image.Width * ratio); 
       newHeight = (int)(image.Height * ratio); 
      } 
      else 
      { 
       newWidth = image.Width; 
       newHeight = image.Height; 
      } 

      //start with a new image 
      var newImage = new Bitmap(newWidth, newHeight); 

      //set the new resolution, 72 is usually good enough for displaying images on monitors 
      newImage.SetResolution(72, 72); 
      //or use the original resolution 
      //newImage.SetResolution(image.HorizontalResolution, image.VerticalResolution); 

      //resize the image 
      using (var graphics = Graphics.FromImage(newImage)) 
      { 
       graphics.CompositingMode = CompositingMode.SourceCopy; 
       graphics.CompositingQuality = CompositingQuality.HighQuality; 
       graphics.SmoothingMode = SmoothingMode.HighQuality; 
       graphics.InterpolationMode = InterpolationMode.HighQualityBicubic; 
       graphics.PixelOffsetMode = PixelOffsetMode.HighQuality; 

       graphics.DrawImage(image, 0, 0, newWidth, newHeight); 
      } 
      image = newImage; 

      //save the image to a memorystream to apply the compression level, higher compression = better quality = bigger images 
      using (MemoryStream ms = new MemoryStream()) 
      { 
       EncoderParameters encoderParameters = new EncoderParameters(1); 
       encoderParameters.Param[0] = new EncoderParameter(Encoder.Quality, 80L); 
       image.Save(ms, getEncoderInfo("image/jpeg"), encoderParameters); 

       //save the stream as byte array 
       returnArray = ms.ToArray(); 
      } 

      //cleanup 
      image.Dispose(); 
      newImage.Dispose(); 

      return returnArray; 
     } 
     catch (Exception ex) 
     { 
      //there was an error: ex.Message 
      return null; 
     } 
    } 


    private static ImageCodecInfo getEncoderInfo(string mimeType) 
    { 
     ImageCodecInfo[] encoders = ImageCodecInfo.GetImageEncoders(); 
     for (int j = 0; j < encoders.Length; ++j) 
     { 
      if (encoders[j].MimeType.ToLower() == mimeType.ToLower()) 
       return encoders[j]; 
     } 
     return null; 
    } 


    private static Image applyPaddingToImage(Image image) 
    { 
     //get the maximum size of the image dimensions 
     int maxSize = Math.Max(image.Height, image.Width); 
     Size squareSize = new Size(maxSize, maxSize); 

     //create a new square image 
     Bitmap squareImage = new Bitmap(squareSize.Width, squareSize.Height); 

     using (Graphics graphics = Graphics.FromImage(squareImage)) 
     { 
      //fill the new square with a color 
      graphics.FillRectangle(Brushes.Red, 0, 0, squareSize.Width, squareSize.Height); 

      graphics.CompositingMode = CompositingMode.SourceCopy; 
      graphics.CompositingQuality = CompositingQuality.HighQuality; 
      graphics.SmoothingMode = SmoothingMode.HighQuality; 
      graphics.InterpolationMode = InterpolationMode.HighQualityBicubic; 
      graphics.PixelOffsetMode = PixelOffsetMode.HighQuality; 

      //put the original image on top of the new square 
      graphics.DrawImage(image, (squareSize.Width/2) - (image.Width/2), (squareSize.Height/2) - (image.Height/2), image.Width, image.Height); 
     } 

     return squareImage; 
    } 


    private static RotateFlipType getRotateFlipType(int rotateValue) 
    { 
     RotateFlipType flipType = RotateFlipType.RotateNoneFlipNone; 

     switch (rotateValue) 
     { 
      case 1: 
       flipType = RotateFlipType.RotateNoneFlipNone; 
       break; 
      case 2: 
       flipType = RotateFlipType.RotateNoneFlipX; 
       break; 
      case 3: 
       flipType = RotateFlipType.Rotate180FlipNone; 
       break; 
      case 4: 
       flipType = RotateFlipType.Rotate180FlipX; 
       break; 
      case 5: 
       flipType = RotateFlipType.Rotate90FlipX; 
       break; 
      case 6: 
       flipType = RotateFlipType.Rotate90FlipNone; 
       break; 
      case 7: 
       flipType = RotateFlipType.Rotate270FlipX; 
       break; 
      case 8: 
       flipType = RotateFlipType.Rotate270FlipNone; 
       break; 
      default: 
       flipType = RotateFlipType.RotateNoneFlipNone; 
       break; 
     } 

     return flipType; 
    }