Load Jpg/Gif/Bitmap and convert to Bitmap - delphi

Question

I have to load an image from an XML file. There is no information in the XML file about whether the image is JPG/GIF/BMP. After loading the image, I need to convert it to Bitmap.
Does anyone have any clue how to convert images to Bitmap without knowing the actual file format? I'm using Delphi 2007/2009
Thank you.

Answer 1

Delphi 2009 comes with built in support for JPEG, BMP, GIF and PNG.
For earlier versions of Delphi you may need to find third party implementations for PNG and GIF, but in Delphi 2009 you simply add the Jpeg, pngimage and GIFImg units to your uses clause.
If the file has an extension you can use the following code, as noted by others the TPicture.LoadFromFile looks at the extensions registered by the inherited classes to determine which image to load.
uses
Graphics, Jpeg, pngimage, GIFImg;
procedure TForm1.Button1Click(Sender: TObject);
var
Picture: TPicture;
Bitmap: TBitmap;
begin
Picture := TPicture.Create;
try
Picture.LoadFromFile('C:\imagedata.dat');
Bitmap := TBitmap.Create;
try
Bitmap.Width := Picture.Width;
Bitmap.Height := Picture.Height;
Bitmap.Canvas.Draw(0, 0, Picture.Graphic);
Bitmap.SaveToFile('C:\test.bmp');
finally
Bitmap.Free;
end;
finally
Picture.Free;
end;
end;
If the file extension is not known one method is to look at the first few bytes to determine the image type.
procedure DetectImage(const InputFileName: string; BM: TBitmap);
var
FS: TFileStream;
FirstBytes: AnsiString;
Graphic: TGraphic;
begin
Graphic := nil;
FS := TFileStream.Create(InputFileName, fmOpenRead);
try
SetLength(FirstBytes, 8);
FS.Read(FirstBytes[1], 8);
if Copy(FirstBytes, 1, 2) = 'BM' then
begin
Graphic := TBitmap.Create;
end else
if FirstBytes = #137'PNG'#13#10#26#10 then
begin
Graphic := TPngImage.Create;
end else
if Copy(FirstBytes, 1, 3) = 'GIF' then
begin
Graphic := TGIFImage.Create;
end else
if Copy(FirstBytes, 1, 2) = #$FF#$D8 then
begin
Graphic := TJPEGImage.Create;
end;
if Assigned(Graphic) then
begin
try
FS.Seek(0, soFromBeginning);
Graphic.LoadFromStream(FS);
BM.Assign(Graphic);
except
end;
Graphic.Free;
end;
finally
FS.Free;
end;
end;

Answer 2

I've found a simpler way! It loads JPG/GIF/BMP etc. files automatically without even knowing/checking the file format, and convert that accordingly. It worked for me perfectly.
Sharing it here :)
Uses
Classes, ExtCtrls, Graphics, axCtrls;
Procedure TForm1.Button1Click(Sender: TObject);
Var
OleGraphic : TOleGraphic;
fs : TFileStream;
Source : TImage;
BMP : TBitmap;
Begin
Try
OleGraphic := TOleGraphic.Create; {The magic class!}
fs := TFileStream.Create('c:\testjpg.dat', fmOpenRead Or fmSharedenyNone);
OleGraphic.LoadFromStream(fs);
Source := Timage.Create(Nil);
Source.Picture.Assign(OleGraphic);
BMP := TBitmap.Create; {Converting to Bitmap}
bmp.Width := Source.Picture.Width;
bmp.Height := source.Picture.Height;
bmp.Canvas.Draw(0, 0, source.Picture.Graphic);
image1.Picture.Bitmap := bmp; {Show the bitmap on form}
Finally
fs.Free;
OleGraphic.Free;
Source.Free;
bmp.Free;
End;
End;

Answer 3

You can't use TPicture.LoadFromFile if you don't know what format the graphic has, as this method uses the file extension to determine which of the registered graphic formats needs to be loaded. There's a reason that there is no matching TPicture.LoadFromStream method.
An external library which can examine data and determine the graphic format at runtime would be the best solution. You could use the efg page as a starting point of your research.
A quick and dirty solution is to try the few formats you need to handle until one succeeds:
function TryLoadPicture(const AFileName: string; APicture: TPicture): boolean;
const
GraphicClasses: array[0..3] of TGraphicClass = (
TBitmap, TJPEGImage, TGIFImage, TPngImage);
var
FileStr, MemStr: TStream;
ClassIndex: integer;
Graphic: TGraphic;
begin
Assert(APicture <> nil);
FileStr := TFileStream.Create('D:\Temp\img.dat', fmOpenRead);
try
MemStr := TMemoryStream.Create;
try
MemStr.CopyFrom(FileStr, FileStr.Size);
// try various
for ClassIndex := Low(GraphicClasses) to High(GraphicClasses) do begin
Graphic := GraphicClasses[ClassIndex].Create;
try
try
MemStr.Seek(0, soFromBeginning);
Graphic.LoadFromStream(MemStr);
APicture.Assign(Graphic);
Result := TRUE;
exit;
except
end;
finally
Graphic.Free;
end;
end;
finally
MemStr.Free;
end;
finally
FileStr.Free;
end;
Result := FALSE;
end;
Edit:
The GraphicEx library has an example convert that uses
GraphicClass := FileFormatList.GraphicFromContent(...);
to determine the graphic format. This seems very similar to the VB6 way of doing this that you mention. Maybe you can use this library for your purpose.

Answer 4

I don't have Delphi 2007 or 2009 to see if this will work in either of those versions. However, in XE2, there is another class in Vcl.Graphics called TWICImage that handles images supported by the Microsoft Imaging Component, including BMP, GIF, ICO, JPEG, PNG, TIF and Windows Media Photo. It is capable of detecting the image type from a stream. Assuming you have a TImage on the form called Image1:
procedure LoadImageFromStream(Stream: TStream; Image: TImage);
var
wic: TWICImage;
begin
Stream.Position := 0;
wic := TWICImage.Create;
try
wic.LoadFromStream(Stream);
Image.Picture.Assign(wic);
finally
wic.Free;
end;
end;
procedure RenderImage(const Filename: string);
var
fs: TFileStream;
begin
fs := TFileStream.Create(Filename, fmOpenRead);
try
LoadImageFromStream(fs, Image1);
finally
fs.Free;
end;
end;
It works without adding PNGImage, GIFImg, or JPEG to your uses statement.
The other answers show how to convert the TImage to a BMP, so I'm not including that here. I'm just showing another way to load various graphic types into a TImage without knowing beforehand the image type, or the file extension...