再学 GDI+[89]: TGPImage(9) - 图像缩放时的质量(算法)

本例效果图:

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代码文件:

---

unit Unit1;



interface



uses

  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

  Dialogs, StdCtrls;



type

  TForm1 = class(TForm)

    ListBox1: TListBox;

    procedure FormPaint(Sender: TObject);

    procedure FormCreate(Sender: TObject);

    procedure ListBox1Click(Sender: TObject);

  end;



var

  Form1: TForm1;



implementation



{$R *.dfm}



uses GDIPOBJ, GDIPAPI;



var

  n: Single = 0.75; {缩放倍数}



procedure TForm1.FormCreate(Sender: TObject);

begin

  ListBox1.Align := alRight;

  with ListBox1.Items do

  begin

    add('InterpolationModeInvalid            ');

    add('InterpolationModeDefault            ');

    add('InterpolationModeLowQuality         ');

    add('InterpolationModeHighQuality        ');

    add('InterpolationModeBilinear           ');

    add('InterpolationModeBicubic            ');

    add('InterpolationModeNearestNeighbor    ');

    add('InterpolationModeHighQualityBilinear');

    add('InterpolationModeHighQualityBicubic ');

  end;

  ListBox1.ItemIndex := 1;

end;



procedure TForm1.FormPaint(Sender: TObject);

var

  g: TGPGraphics;

  img: TGPImage;

  rt: TGPRectF;

begin

  g := TGPGraphics.Create(Self.Canvas.Handle);

  img := TGPImage.Create('C:\temp\test.png');



  g.DrawImage(img, 4, 4, img.GetWidth, img.GetHeight);



  rt := MakeRect(4+img.GetWidth+4, 4, img.GetWidth * n, img.GetHeight * n);



  g.SetInterpolationMode(ListBox1.ItemIndex - 1);

  g.DrawImage(img, rt, 0, 0, img.GetWidth, img.GetHeight, UnitPixel);



  img.Free;

  g.Free;

end;



procedure TForm1.ListBox1Click(Sender: TObject);

begin

  Repaint;

end;



end.


 
   

窗体文件:

---

object Form1: TForm1

  Left = 0

  Top = 0

  Caption = 'Form1'

  ClientHeight = 213

  ClientWidth = 550

  Color = clBtnFace

  Font.Charset = DEFAULT_CHARSET

  Font.Color = clWindowText

  Font.Height = -11

  Font.Name = 'Tahoma'

  Font.Style = []

  OldCreateOrder = False

  Position = poDesktopCenter

  OnCreate = FormCreate

  OnPaint = FormPaint

  PixelsPerInch = 96

  TextHeight = 13

  object ListBox1: TListBox

    Left = 357

    Top = 32

    Width = 185

    Height = 97

    ItemHeight = 13

    TabOrder = 0

    OnClick = ListBox1Click

  end

end


 
   

缩放时的算法模式(TInterpolationMode 枚举)列表:

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InterpolationModeInvalid             = -1; {等效于 QualityMode 枚举的 Invalid 元素. }

InterpolationModeDefault             = 0;  {指定默认模式. }

InterpolationModeLowQuality          = 1;  {指定低质量插值法. }

InterpolationModeHighQuality         = 2;  {指定高质量插值法. }

InterpolationModeBilinear            = 3;  {指定双线性插值法. 不进行预筛选. 将图像收缩为原始

                                                  大小的 50% 以下时，此模式不适用. }

InterpolationModeBicubic             = 4;  {指定双三次插值法. 不进行预筛选. 将图像收缩为原始

                                                  大小的 25% 以下时，此模式不适用. }

InterpolationModeNearestNeighbor     = 5;  {指定最临近插值法. }

InterpolationModeHighQualityBilinear = 6;  {指定高质量的双线性插值法. 执行预筛选以确保高质量

                                                  的收缩.  }

InterpolationModeHighQualityBicubic  = 7;  {指定高质量的双三次插值法. 执行预筛选以确保高质量

                                                  的收缩. 此模式可产生质量最高的转换图像. }