Resizing a bitmap...

[Gadget]

Resizing a bitmap...

Anyone know of a good way to resize a bitmap? I mean an algorithm that produces a smooth looking resized image, unlike stretch draw!

Maybe if I get the 'average' pixel colour per block of pixels that I want to resize?? It doesn't have to look great, just better than stretchdraw!

[Alimonster]

Either GraphicsEx.pas by Mike Lischke or Graphics32 contains good resampling filters (like Lanczos3, Mitchell, etc). I can't remember what's in them, though, so have a look through the source code yourself.

[Gadget]

Thankyou

Yet again I am in debt to you!

[Gadget]

Yeah, I know I am replying to myself... But this may help someone else with the same question:-

http://www.torry.net/vcl/graphics/bitmap/resample.zip

[peterbone]

here's some code I wrote to shrink an image using pixel-averaging (smooth resultant image).

// shrink image by a given ratio
function Shrink(ARatio : Real ; ABitmap : TBitmap) : TBitmap;
Var
  Lx, Ly : integer;
  LyBox, LxBox : integer;
  TR, TG, TB : integer;
  avR, avG, avB : integer;
  LRowIn, LRowOut : pRGBTripleArray;
  LBoxCount : integer;
  LRatio : Real;
begin
  LRatio := 1 / ARatio;

  Result := TBitmap.Create;
  Result.PixelFormat := pf24bit;
  Result.Width := trunc(ABitmap.Width / LRatio);
  Result.Height := trunc(ABitmap.Height / LRatio);

  for Ly := 0 to Result.Height-1 do begin
    LRowOut := Result.ScanLine[Ly];
    for Lx := 0 to Result.Width-1 do begin

      TR := 0; TG := 0; TB := 0;
      LBoxCount := 0;
      for LyBox := trunc(Ly*LRatio) to trunc((Ly+1)*LRatio) - 1 do begin
        LRowIn := ABitmap.ScanLine[LyBox];
        for LxBox := trunc(Lx*LRatio) to trunc((Lx+1)*LRatio) - 1 do begin
          TR := TR + LRowIn[LxBox].rgbtRed;
          TG := TG + LRowIn[LxBox].rgbtGreen;
          TB := TB + LRowIn[LxBox].rgbtBlue;
          Inc(LBoxCount);
        end;
      end;

      avR := TR div LBoxCount;
      avG := TG div LBoxCount;
      avB := TB div LBoxCount;
      LRowOut[Lx].rgbtBlue := avB;
      LRowOut[Lx].rgbtGreen := avG;
      LRowOut[Lx].rgbtRed := avR;
    end;
  end;

  ABitmap.Free;
end;

Hope it helps

Peter