show an image stored in a database

Hi friends

I have an interbase 6  database. One table has a blob field holding a picture and I need to show it.
The problem is that I don't know in wish format is stored this picture. I ran a routine to show a jpg picture and it failed, I got an JPEG ERROR #52.
How can I know the format of this picture and show it?

thanks in advance
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ahllAsked:
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Mohammed NasmanSoftware DeveloperCommented:
Hello

 Take a look to this article
http://delphi.about.com/library/weekly/aa030601c.htm

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jcondeCommented:
You must parse the first couple of bytes stored in the blob-field to know which type of picture-format is stored in the field.

If you *know* the picture is a JPEG, try the following code:

procedure TForm1.Button4Click(Sender: TObject);
var
  t : TBlobField;
  jpg: TJpegImage;
   x: TMemoryStream;
begin
  t := MyDataSet1.FieldByName('myblob') as TBlobField;
  X := TMemoryStream.Create;
  try
  t.SaveToStream(x);
  if (x.Size > 0) then
  begin
    jpg := TJpegImage.Create;
    x.Position := 0;
    try
    jpg.LoadFromStream(x);
    Image1.Picture.Assign(jpg);
    finally
    jpg.free;
    end;
  end;
  finally
  x.free;
  end;
end;

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mocartsCommented:
hi, ahll
try this out:

uses jpeg;

function GetGraphicFromBlob(aField: TBlobField): TGraphic;
var
 s: TStream;
 buf: word;
begin
 assert(aField <> nil);
 Result := nil;
 s := aField.DataSet.CreateBlobStream(aField, bmRead);
 try
   if s.read(buf, sizeof(buf)) <> sizeOf(buf) then exit;
   s.Position := 0;
   if buf = $D8FF then
     Result := TJPEGImage.Create
   else if buf = $4D42 then
     Result := TBitmap.Create
   else if buf = $CDD7 then
     Result := TMetafile.Create
   else if buf = 0 then
     Result := TIcon.Create;
   if assigned(Result) then begin
     try
       Result.LoadFromStream(s);
     except
       Result.Free;
       Result := nil;
     end;
   end;
 finally
   s.Free;  // must free stream
 end;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  i: integer;
begin
  i := 1;
  with Table1 do begin
    Open;
    try
      // if image will not load from blob then result of getGraphicFromBlob
      // will be nil and Image1 will be empty
     // you can of course check result to give an error to user by using intermediate var
      Image1.Picture.Assign(GetGraphicFromBlob(TBlobField(FieldByName('img'))));
    finally
      close;
    end;
  end;
end;

wbr, mo.
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ahllAuthor Commented:
OK, I tried all this things and no results.
I saved the file to the HD and it doesn' t look like a jpg. I read the link posted by mnasman and it's very interesting but it didn't help me.
How I need this very much I'll increase my points on this question.

Thanks all
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mocartsCommented:
what is first two bytes of saved file (hex representation)?
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ahllAuthor Commented:
all the files begin with diferents bytes, I saved some blob fields to the HD and they are all differents
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ahllAuthor Commented:
please adm, can you delete this quiestion? I think nobody has an answer for my problem

thanks all anyway
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ChrisLMCommented:
Hi,
    I don't have any experenice with interbase databases but you can try this. Instead of storing the file in the database, keep the file on the hard-drive and put the path to the image in the database. eg (C:\Images\xxx.bmp). You will need to change the blob
field to a string field. If you use the TDataSource component then put this code under the 'DataSourceDataChange' event:

   if not FileExists(Table.FieldByName('Image').AsString) then              
      Image.Picture := nil            
    else                                                                
      Image.Picture.LoadFromFile(Table.FieldByName('Image').AsString);

Table = 'Your Table Component'.
('Image') = 'The field that has the image path'.
Image = 'Picture Component'.

Chris.
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ahllAuthor Commented:
Thanks Chris, but I have tha database full of data and I need to retrieve it.
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ahllAuthor Commented:
I need to delete this quiestion, please

thanks
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