Алгоритм качественного Resize'a, если точнее, то уменьшения

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Code:

procedure MakeThumbNail(const Src, Dest: TBitmap);

type

PRGB24 = ^TRGB24;

TRGB24 = packed record

   B: Byte;

   G: Byte;

   R: Byte;

end;

var

x, y, ix, iy: integer;

x1, x2, x3: integer;

 

xscale, yscale: single;

iRed, iGrn, iBlu, iRatio: Longword;

p, c1, c2, c3, c4, c5: tRGB24;

pt, pt1: pRGB24;

iSrc, iDst, s1: integer;

i, j, r, g, b, tmpY: integer;

 

RowDest, RowSource, RowSourceStart: integer;

w, h: integer;

dxmin, dymin: integer;

ny1, ny2, ny3: integer;

dx, dy: integer;

lutX, lutY: array of integer;

begin

if src.PixelFormat <> pf24bit then src.PixelFormat := pf24bit;

if dest.PixelFormat <> pf24bit then dest.PixelFormat := pf24bit;

w := Dest.Width;

h := Dest.Height;

 

if (src.Width <= dest.Width) and (src.Height <= dest.Height) then

begin

   dest.Assign(src);

   exit;

end;

 

iDst := (w * 24 + 31) and not 31;

iDst := iDst div 8; //BytesPerScanline

iSrc := (Src.Width * 24 + 31) and not 31;

iSrc := iSrc div 8;

 

xscale := 1 / (w / src.Width);

yscale := 1 / (h / src.Height);

 

// X lookup table

SetLength(lutX, w);

x1 := 0;

x2 := trunc(xscale);

for x := 0 to w - 1 do

begin

   lutX[x] := x2 - x1;

   x1 := x2;

   x2 := trunc((x + 2) * xscale);

end;

 

// Y lookup table

SetLength(lutY, h);

x1 := 0;

x2 := trunc(yscale);

for x := 0 to h - 1 do

begin

   lutY[x] := x2 - x1;

   x1 := x2;

   x2 := trunc((x + 2) * yscale);

end;

 

dec(w);

dec(h);

RowDest := integer(Dest.Scanline[0]);

RowSourceStart := integer(Src.Scanline[0]);

RowSource := RowSourceStart;

for y := 0 to h do

begin

   dy := lutY[y];

   x1 := 0;

   x3 := 0;

   for x := 0 to w do

   begin

     dx:= lutX[x];

     iRed:= 0;

     iGrn:= 0;

     iBlu:= 0;

     RowSource := RowSourceStart;

     for iy := 1 to dy do

     begin

       pt := PRGB24(RowSource + x1);

       for ix := 1 to dx do

       begin

         iRed := iRed + pt.R;

         iGrn := iGrn + pt.G;

         iBlu := iBlu + pt.B;

         inc(pt);

       end;

       RowSource := RowSource - iSrc;

     end;

     iRatio := 65535 div (dx * dy);

     pt1 := PRGB24(RowDest + x3);

     pt1.R := (iRed * iRatio) shr 16;

     pt1.G := (iGrn * iRatio) shr 16;

     pt1.B := (iBlu * iRatio) shr 16;

     x1 := x1 + 3 * dx;

     inc(x3,3);

   end;

   RowDest := RowDest - iDst;

   RowSourceStart := RowSource;

end;

 

if dest.Height < 3 then exit;

 

// Sharpening...

s1 := integer(dest.ScanLine[0]);

iDst := integer(dest.ScanLine[1]) - s1;

ny1 := Integer(s1);

ny2 := ny1 + iDst;

ny3 := ny2 + iDst;

for y := 1 to dest.Height - 2 do

begin

   for x := 0 to dest.Width - 3 do

   begin

     x1 := x * 3;

     x2 := x1 + 3;

     x3 := x1 + 6;

 

     c1 := pRGB24(ny1 + x1)^;

     c2 := pRGB24(ny1 + x3)^;

     c3 := pRGB24(ny2 + x2)^;

     c4 := pRGB24(ny3 + x1)^;

     c5 := pRGB24(ny3 + x3)^;

 

     r := (c1.R + c2.R + (c3.R * -12) + c4.R + c5.R) div -8;

     g := (c1.G + c2.G + (c3.G * -12) + c4.G + c5.G) div -8;

     b := (c1.B + c2.B + (c3.B * -12) + c4.B + c5.B) div -8;

 

     if r < 0 then r := 0 else if r > 255 then r := 255;

     if g < 0 then g := 0 else if g > 255 then g := 255;

     if b < 0 then b := 0 else if b > 255 then b := 255;

 

     pt1 := pRGB24(ny2 + x2);

     pt1.R := r;

     pt1.G := g;

     pt1.B := b;

   end;

   inc(ny1, iDst);

   inc(ny2, iDst);

   inc(ny3, iDst);

end;

end;

 

 
Можно еще через StretchBlt, только перед ним надо задать
 

Code:

SetStretchBltMode(Canvas.Handle, HALFTONE);

 

 
 
Автор: s-mike
Взято из http://forum.sources.ru

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