Delphi TGPImage 把图像转存为其他格式

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代码文件:
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.

来源：https://www.cnblogs.com/del/archive/2008/07/07/1237697.html
 

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