再学 GDI+[89]: TGPImage(9) 图像缩放时的质量(算法)

本例效果图:

---

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:

---

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. }