GDI+图片类型转换（转自万一Blog）

unit Unit1;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls, ExtCtrls;

type
TForm1 = class(TForm)
OpenDialog1: TOpenDialog;
Button1: TButton;
Button2: TButton;
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
procedure FormPaint(Sender: TObject);
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

uses GDIPOBJ, GDIPAPI, GDIPUTIL;

const
OpenFileFilter =
'GDI+ 全部可以读取的图片格式|*.png;*.jpg;*.gif;*.bmp;*.tif;*.emf;*.wmf;*.ico' +
'|*.png|*.png' +
'|*.jpg|*.jpg' +
'|*.gif|*.gif' +
'|*.bmp|*.bmp' +
'|*.tif|*.tif' +
'|*.emf|*.emf' +
'|*.wmf|*.wmf' +
'|*.ico|*.ico';

ArrExt: array[0..4] of String = ('.png', '.jpg', '.gif', '.bmp', '.tif');
ArrEncodeName: array[0..4] of String =
('image/png', 'image/jpeg', 'image/gif', 'image/bmp', 'image/tiff');

var
FileName: string;
img: TGPImage;

procedure TForm1.FormCreate(Sender: TObject);
begin
img := TGPImage.Create;
Button1.Caption := '打开';
Button2.Caption := '保存';
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
img.Free;
end;

procedure TForm1.FormPaint(Sender: TObject);
var
g: TGPGraphics;
begin
if FileName <> '' then
begin
g := TGPGraphics.Create(Canvas.Handle);
g.DrawImage(img, 10, 10, img.GetWidth, img.GetHeight);
g.Free;
end;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
OpenDialog1.Filter := OpenFileFilter;
if OpenDialog1.Execute then
begin
FileName := OpenDialog1.FileName;
img.Free;
img := TGPImage.Create(FileName);
Repaint;
end;
end;

procedure TForm1.Button2Click(Sender: TObject);
var
ImgGUID: TGUID;
i: Integer;
begin
if FileName = '' then
begin
ShowMessage('先要打开文件');
Exit;
end;

{一次性保存为 5 种可能的格式}
for i := 0 to 4 do
begin
GetEncoderClsid(ArrEncodeName[i], ImgGUID); {先获取格式编码}
img.Save(ChangeFileExt(FileName, ArrExt[i]), ImgGUID);
end;

Beep;
end;

end.