TJPEGImage.SaveToStream problem

[peterbone]

if I set DIBNeeded won't that make the jpeg the same size as a bitmap when I save it to stream? The reason I'm using jpeg is to make the stream as small as possible.

my method still isn't working, If I put some data in the stream before the jpeg I get a jpeg error #53 when I try to read the jpeg even though it's now in the right position. Anyone know what #53 is?

Peter

[Paulius]

When saving,
AStream.Seek(8, LStart);
should be
AStream.Seek(8, soFromCurrent);
Edit: Error 53 is "File Not Found", check msdn for error codes

[cairnswm]

What I have done is the following:

[pascal]procedure TForm1.Button1Click(Sender: TObject);
Var
F : TFileStream;
M,M2 : TMemoryStream;
J,J1 : TJPEGImage;
X,Y,Z : Integer;
begin
J := TJPEGImage.Create;
J.LoadFromFile('C:\cairnsgames\letter.jpg'); // Load an Image
X := 100;
M := TMemoryStream.Create;
M2 := TMemoryStream.Create;
M.Write(X,SizeOf(Integer)); // Write Tag Information
J.SaveToStream(M2);
X := M2.Size; // Calculate the size of the JPEG
M2.Free;
M.Write(X,SizeOf(Integer)); // Write Size
J.SaveToStream(M); // Write Image
J1 := TJPEGImage.Create; // Create a New Image
M.Seek(0,soBeginning); // Move to start of stream
M.Read(Y,SizeOf(Integer)); // Load Tag Information
M.Read(Z,SizeOf(Integer)); // Load Size Information
J1.LoadFromStream(M); // Load JPEG
J1.SaveToFile('C:\cairnsgames\letter1.jpg'); // Write Out (to compare vs Original)
ShowMessage(IntToStr(Z)); // Display Size info
J1.Free;
J.Free;
end;[/pascal]

And it works fine

I think I understand what it is doing. As JPEGs allow additional information such as who took the photo, commetns and even a thumbnail of the image the load from stream seems to read from the current position in the stream until the end, but only uses the JPEG information it needs to recreate the image in memory. Therefore when you add information at the end of the stream the LoadFromStream reads right past the JPEG size and over tha additional information.

Hope this helps.

[peterbone]

When saving,
AStream.Seek(8, LStart);
should be
AStream.Seek(8, soFromCurrent);
Edit: Error 53 is "File Not Found", check msdn for error codes

Thanks, but wouldn't soFromCurrent be the same as LStart as LStart is the current position - since the line before it is LStart := AStream.Position; ?

Peter

[Paulius]

Thanks, but wouldn't soFromCurrent be the same as LStart as LStart is the current position - since the line before it is LStart := AStream.Position; ?

No, you misunderstood the origin parameter, itis only supposed to be constants soFromBeginning, soFromCurrentg or soFromEnd. It probably defaults to one of these if the value is incorrect.

[peterbone]

oh, I see - thanks. The word origin makes it sound like the position you're offsetting from. It works fine now!

Thanks for everyone's help

Peter