How to resize a picture?

Question

I have image (500x500) but I need to resize it to 200x200 and paint it on TImage. How to achieve such result?

Note
I know about Stretch

Answer 1

Please see this simple example on how to resize an image using two TBitmap32 objects. The TBitmap32 is the best in terms of speed/image quality ratio.

It requires the https://github.com/graphics32 library.

uses 
  GR32, GR32_Resamplers;

procedure Resize(InputPicture: TBitmap; OutputImage: TImage; const DstWidth, DstHeigth: Integer);
var
  Src, Dst: TBitmap32;
begin
  Dst := nil;
  try
    Src := TBitmap32.Create;
    try
      Src.Assign(InputPicture);
      SetHighQualityStretchFilter(Src);
      Dst := TBitmap32.Create;
      Dst.SetSize(DstWidth, DstHeigth);
      Src.DrawTo(Dst, Rect(0, 0, DstWidth, DstHeigth), Rect(0, 0, Src.Width, Src.Height));
    finally
      FreeAndNil(Src);
    end;
    OutputImage.Assign(Dst);
  finally
    FreeAndNil(Dst);
  end;
end;

// If you need to set a highest quality resampler, use this helper routine to configure it
procedure SetHighQualityStretchFilter(B: TBitmap32);
var
  KR: TKernelResampler;
begin
  if not (B.Resampler is TKernelResampler) then
  begin
    KR := TKernelResampler.Create(B);
    KR.Kernel := TLanczosKernel.Create;
  end
  else
  begin
    KR := B.Resampler as TKernelResampler;
    if not (KR.Kernel is TLanczosKernel) then
    begin
      KR.Kernel.Free;
      KR.Kernel := TLanczosKernel.Create;
    end;
  end;
end;