create Thumbnails?

Author: Roy Magne Klever  

{

 Here is the routine I use in my thumbnail component and I belive it is quite

 fast.

 A tip to gain faster loading of jpegs is to use the TJpegScale.Scale

 property. You can gain a lot by using this correct.

 This routine can only downscale images no upscaling is supported and you

 must correctly set the dest image size. The src.image will be scaled to fit

 in dest bitmap.

}

//Speed up by Renate Schaaf, Armido, Gary Williams...

procedure MakeThumbNail(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 <= FThumbSize) and (src.Height <= FThumbSize) 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;