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JPEG

Posted on 1998-12-07
6
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Last Modified: 2013-11-19
How can I verify a JPEG file is valid or not ? Because it will halt if I pass a file name of invalid JPEG file to LoadFromFile, so, how can I prevent it halt again !

Andrew
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Question by:andrewyu
6 Comments
 

Expert Comment

by:v_pasupuleti
ID: 1349715
Hi Andrew
Use a try exception in ur code.Put ur Loadfromfile in the try block and a default jpg image in the exception block

Vijay
0
 
LVL 1

Accepted Solution

by:
EmmDieh earned 20 total points
ID: 1349716
A JPEG file contains block markers followed by a block of a certain type. For example a jpeg file will start with the two byte FF D8 and end with the two byte FF D9. Sometimes one ore more extra byte are added to the end of the file due to bugs in transfer software. These files still display but you can delete the extra byte form the end. One time I had a file with more than 1000 extra byte.
I use the following function:
function IsJPEGFileOK(aFileName: string): Boolean;
var
  fs: tFileStream;
  JPEGSign: array[1..2] of Byte;
begin
  Result := false;
  fs := tFileStream.Create(aFileName, fmOpenRead);
  try
    try
        { Check for JPEG-File Beginnmarker }
      fs.Seek(0, soFromBeginning);
      fs.ReadBuffer(JPEGSign, 2);
      Result := (JPEGSign[1] = $FF) and (JPEGSign[2] = $D8);  { $FFD8 }
      if not Result then Exit;
        { Check for JPEG-File Endmarker }
      fs.Seek(-2, soFromEnd);
      fs.ReadBuffer(JPEGSign, 2);
      Result := (JPEGSign[1] = $FF) and (JPEGSign[2] = $D9);  { $FFD9 }
    except
      on E: Exception do
        ErrorMessage('IsJPEGFileOK', E.Message);
    end;
  finally
    fs.Free;
  end;
end;   { IsJPEGFileOK }

0
 

Author Comment

by:andrewyu
ID: 1349717
I understand, but, actually I want to know whether Delphi will raise a exception for a "BUG" JPEG file ?

Andrew
0
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Expert Comment

by:bryan7
ID: 1349718
use      with jpgimage     try jpgxx.loadfromfil...

bryan
0
 
LVL 3

Expert Comment

by:bryan7
ID: 1349719
what kind of bugs ?

bryan
0
 

Author Comment

by:andrewyu
ID: 1349720
I meant a worong content of JPEG file !

Andrew
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