Title: Determine image type
Question: How to determine image type (data level)
Answer:
Function GetGraphicClass(Source:TStream):TGraphicClass;
var
FStreamHeader : TStringStream;
StartPosition : Int64;
CONST
PNGFILE_HEADER = 'PNG';
BMPFILE_HEADER = 'BM';
JPGFILE_HEADER = '';
Begin
try
StartPosition := Source.Position;
IF Source.Size 0 Then
Source.Position := 0
else // Stream vaco
Raise Exception.Create('stream is empty');
FStreamHeader := TStringStream.Create('');
with FStreamHeader do
begin
CopyFrom(Source,512);
if pos(PNGFILE_HEADER,DataString) 0 Then
Result := TPNGObject
else if pos(BMPFILE_HEADER,DataString) 0 Then
Result := TBitmap
else if pos(JPGFILE_HEADER,DataString) 0 Then
Result := TJPEGImage
else
Result := TGraphic;
end;
finally
Source.Position := StartPosition;
end;
end;