保留Exif /图像属性

Question

在Web应用程序中，用户可以上传保存在服务器上的图像。它使用以下代码在后端创建图像的缩略图，但图像的所有exif数据都会丢失。

我想在整个过程中保留来自原始图像的exif数据，并将它包含在最终流中。我可以从图像中读取exif属性，但在保存时无法保存。为了说明一下，我没有试图读取，解析或者做任何特定于元数据本身的事情，我只是想保持它与图像处理过程中的原始图像完全一样。

Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) 

    'prepare image 
    Dim imgFullSize As System.Drawing.Image 

    'attempt to get the image  
    Dim sInputURL As String = HttpUtility.UrlDecode(Request.QueryString("IptFl")) 
    If InStr(sInputURL, "http://") > 0 Or InStr(sInputURL, "https://") Then 

     'from web url 
     Dim imgWebRequest As System.Net.WebRequest 
     Dim imgWebResponse As System.Net.WebResponse 
     imgWebRequest = System.Net.WebRequest.Create(sInputURL) 
     imgWebResponse = imgWebRequest.GetResponse() 
     imgFullSize = System.Drawing.Image.FromStream(imgWebResponse.GetResponseStream()) 

    Else 

     'from file 
     imgFullSize = System.Drawing.Image.FromFile(Server.MapPath(sInputURL)) 

    End If 



' Dim props As PropertyItem() = imgFullSize.PropertyItems 
' For Each prop As PropertyItem In props 
'  Response.Write(prop.Id.ToString() & "<br />") 
' Next 




    'determine type 
    Dim sFileExtension As String = "png" 
    If Left(Right(sInputURL, 4), 1) = "." Then sFileExtension = Right(sInputURL, 3) 'for jpg, gif, etc 
    If Left(Right(sInputURL, 5), 1) = "." Then sFileExtension = Right(sInputURL, 4) 'for tiff, jpeg, etc 


    Dim jpgEncoder As ImageCodecInfo = GetEncoder(ImageFormat.Jpeg) 
    Dim gifEncoder As ImageCodecInfo = GetEncoder(ImageFormat.Gif) 
    Dim pngEncoder As ImageCodecInfo = GetEncoder(ImageFormat.Png) 


    'set the quality 
    Dim myEncoder As System.Drawing.Imaging.Encoder = System.Drawing.Imaging.Encoder.Quality 
    Dim myEncoderParams As New EncoderParameters(1) 
    Dim myEncoderQuality As New EncoderParameter(myEncoder, CType(100L, Int32)) 
    myEncoderParams.Param(0) = myEncoderQuality 


    'save img to memory stream 
    Dim ms As New MemoryStream() 
    Select Case sFileExtension 
     Case "jpg" : imgFullSize.Save(ms, jpgEncoder, myEncoderParams) 
     Case "png", "gif" : imgFullSize.Save(ms, pngEncoder, myEncoderParams) 
     Case Else : imgFullSize.Save(ms, pngEncoder, myEncoderParams) 
    End Select 


    'output the memory stream 
    Response.ContentType = "image/" & sFileExtension 
    ms.WriteTo(Response.OutputStream) 

    '---> when I save the above image and look at the exif, it doesn't exist 

End Sub 


Private Function GetEncoder(ByVal format As ImageFormat) As ImageCodecInfo 
    Dim codecs As ImageCodecInfo() = ImageCodecInfo.GetImageDecoders() 
    Dim codec As ImageCodecInfo 
    For Each codec In codecs 
     If codec.FormatID = format.Guid Then Return codec 
    Next codec 
    Return Nothing 
End Function 

Answer 1

所以这就做到了。基本上我必须遍历源图像属性，并为每个属性设置新图像中的属性。

 'retrieve relative path to image 
     Dim sSrc As String = HttpUtility.UrlDecode(Request.QueryString("IptFl")) 


     'prepare image 
     Dim oImg As System.Drawing.Image 


     'attempt to get the image, either from web or local file 
     If InStr(sSrc, "http://") > 0 Or InStr(sSrc, "https://") Then 
      Dim oRequest As System.Net.WebRequest = System.Net.WebRequest.Create(sSrc) 
      Dim oResponse As System.Net.WebResponse = oRequest.GetResponse()   
      oImg = System.Drawing.Image.FromStream(oResponse.GetResponseStream()) 
      oResponse.Close() 
     Else 
      oImg = System.Drawing.Image.FromFile(Server.MapPath(sSrc)) 
     End If 

     'discard if image file not found 
     If oImg Is Nothing Then Response.End() 

     Dim sFileExt As String = Split(sSrc, ".")(UBound(Split(sSrc, "."))) 


     Dim oCanvas As System.Drawing.Bitmap = New System.Drawing.Bitmap(oImg.Width, oImg.Height, System.Drawing.Imaging.PixelFormat.Format16bppRgb555) 

     For Each pi As PropertyItem In oImg.PropertyItems 
      oCanvas.SetPropertyItem(pi) 
     Next 

     Dim oGraphic As System.Drawing.Graphics = System.Drawing.Graphics.FromImage(oCanvas) 
     oGraphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.Default 
     oGraphic.DrawImage(oImg, 0, 0, oImg.Width, oImg.Height) 
     Dim oStream As System.IO.MemoryStream = New System.IO.MemoryStream() 
     oCanvas.Save(oStream, System.Drawing.Imaging.ImageFormat.Jpeg) 

     Response.ContentType = "image/" & sFileExt 

     'output the memory stream 
     oStream.WriteTo(Response.OutputStream) 
     Response.End()