image resizing, optimize

[tux]

hi, i found this code liying around:

[pascal]procedure ResizeBitmap(imgo, imgd: TBitmap; nw, nh: Integer);
var
xini, xfi, yini, yfi, saltx, salty: single;
x, y, px, py, tpix: integer;
PixelColor: TColor;
r, g, b: longint;

function MyRound(const X: Double): Integer;
begin
Result := Trunc(x);
if Frac(x) >= 0.5 then
if x >= 0 then Result := Result + 1
else
Result := Result - 1;
//Result := Trunc(X + (-2 * Ord(X < 0) + 1) * 0.5);
end;

begin
// Set target size

imgd.Width := nw;
imgd.Height := nh;

// Calcs width & height of every area of pixels of the source bitmap

saltx := imgo.Width / nw;
salty := imgo.Height / nh;


yfi := 0;
for y := 0 to nh - 1 do
begin
// Set the initial and final Y coordinate of a pixel area

yini := yfi;
yfi := yini + salty;
if yfi >= imgo.Height then yfi := imgo.Height - 1;

xfi := 0;
for x := 0 to nw - 1 do
begin
// Set the inital and final X coordinate of a pixel area

xini := xfi;
xfi := xini + saltx;
if xfi >= imgo.Width then xfi := imgo.Width - 1;


// This loop calcs del average result color of a pixel area
// of the imaginary grid

r := 0;
g := 0;
b := 0;
tpix := 0;

for py := MyRound(yini) to MyRound(yfi) do
begin
for px := MyRound(xini) to MyRound(xfi) do
begin
Inc(tpix);
PixelColor := ColorToRGB(imgo.Canvas.Pixels[px, py]);
r := r + GetRValue(PixelColor);
g := g + GetGValue(PixelColor);
b := b + GetBValue(PixelColor);
end;
end;

// Draws the result pixel

imgd.Canvas.Pixels[x, y] :=
rgb(MyRound(r / tpix),
MyRound(g / tpix),
MyRound(b / tpix)
);
end;
end;
end;[/pascal]

and its kinda reall slow, so does anyone know how to do scanline instead of direct pixle?

[Harry Hunt]

Scanline is no big deal really. All you need to remember is that when using scanlines, the pixel format is important.

Here's an example:

const
  MaxPixelCount = 65536;  // Change this if necessary

type
  TRGBArray = array[0..MaxPixelCount - 1] of TRGBTriple;
  pRGBArray = ^TRGBArray;

var
  I, J: Integer;
  Row: pRGBArray;
begin
Bitmap := TBitmap.Create;
Bitmap.Width := 400;
Bitmap.Height := 300;
Bitmap.PixelFormat := pf24Bit; // 1 Byte per color
for J := 0 to Bitmap.Height - 1 do
begin
  Row := Bitmap.ScanLine[J];
  for I := 0 to Bitmap.Width - 1 do
  begin
    Row[I].rgbtRed := Random(256);
    Row[I].rgbtGreen := Random(256);
    Row[I].rgbtBlue := Random(256);
  end;  
end;
end;

This example should generate some random color noise but I think it illustrates quite well how to access individual pixels using scanlines. Make sure that the color values you assign to rgbtRed, Green and Blue are between 0 and 255. You will get some really funky results if your values are either too large or too small.

[Alimonster]

I could rewrite it to use Scanline tomorrow if you want (not tonight unfortunately - been a hectic week).

EDIT: as a thought, Anders Melander (cool Delphi dude who wrote a gif component, maybe called TGifImage) has a zip somewhere out there that deals with this - it's called resample.zip or something like that. Sorry about being hazy on the details but his site has been down for a while, unfortunately (his life got too busy to maintain it IIRC from news://borland.public.graphics). It's meant to be quite good if you {$DEFINE USE_SCANLINE} or something like that. Umm, maybe this vague info will be helpful, though it may involve more than a little hunting around :?

[Alimonster]

Aaah! Here's another example of me forgetting about things! Sigh. By "tomorrow", of course, I meant "quite a few days from the time of that post".

Whoops. It'll get rewritten soon-ish if you still want that, dUmAsS. In my defence, it's been a busy few days (and I have a promotion interview on Wednesday, so hopefully once that's done things will get quiet again).

[tux]

hi, thanks man

no problems, ive been busy myself. and it involves a suprise car on my bday yay :shock:

[tux]

um, i tryed myself but failed missrebly (scanline index out of range)


heres the code

procedure ResizeBitmapNew(imgo, imgd: TBitmap; nw, nh: Integer);
const
  MaxPixelCount = 65536;  // Change this if necessary

type
  TRGBArray = array[0..MaxPixelCount - 1] of TRGBTriple;
  pRGBArray = ^TRGBArray;

var
  Row: pRGBArray;

var
  xini, xfi, yini, yfi, saltx, salty: single;
  x, y, px, py, tpix: integer;
  PixelColor: TColor;
  r, g, b: longint;

  function MyRound(const X: Double): Integer;
  begin
    Result := Trunc(x);
    if Frac(x) >= 0.5 then
      if x >= 0 then Result := Result + 1
      else
        Result := Result - 1;
     //Result &#58;= Trunc&#40;X + &#40;-2 * Ord&#40;X < 0&#41; + 1&#41; * 0.5&#41;;
  end;

begin
  // Set target size

  imgd.Width  &#58;= nw;
  imgd.Height &#58;= nh;

  // Calcs width & height of every area of pixels of the source bitmap

  saltx &#58;= imgo.Width / nw;
  salty &#58;= imgo.Height / nh;


  yfi &#58;= 0;
  for y &#58;= 0 to nh - 1 do
  begin
    Row &#58;= imgd.ScanLine&#91;y&#93;;

    // Set the initial and final Y coordinate of a pixel area

    yini &#58;= yfi;
    yfi  &#58;= yini + salty;
    if yfi >= imgo.Height then yfi &#58;= imgo.Height - 1;

    xfi &#58;= 0;
    for x &#58;= 0 to nw - 1 do
    begin
      // Set the inital and final X coordinate of a pixel area

      xini &#58;= xfi;
      xfi  &#58;= xini + saltx;
      if xfi >= imgo.Width then xfi &#58;= imgo.Width - 1;


      // This loop calcs del average result color of a pixel area
      // of the imaginary grid

      r &#58;= 0;
      g &#58;= 0;
      b &#58;= 0;
      tpix &#58;= 0;

      for py &#58;= MyRound&#40;yini&#41; to MyRound&#40;yfi&#41; do
      begin
        for px &#58;= MyRound&#40;xini&#41; to MyRound&#40;xfi&#41; do
        begin
          Inc&#40;tpix&#41;;
          PixelColor &#58;= ColorToRGB&#40;imgo.Canvas.Pixels&#91;px, py&#93;&#41;;
          r &#58;= r + GetRValue&#40;PixelColor&#41;;
          g &#58;= g + GetGValue&#40;PixelColor&#41;;
          b &#58;= b + GetBValue&#40;PixelColor&#41;;
        end;
      end;


      // Draws the result pixel

      Row&#91;x&#93;.rgbtRed &#58;= MyRound&#40;r / tpix&#41;;
      Row&#91;x&#93;.rgbtGreen &#58;= MyRound&#40;g / tpix&#41;;
      Row&#91;x&#93;.rgbtBlue &#58;= MyRound&#40;b / tpix&#41;;

&#123;      imgd.Canvas.Pixels&#91;x, y&#93; &#58;=
        rgb&#40;MyRound&#40;r / tpix&#41;,
        MyRound&#40;g / tpix&#41;,
        MyRound&#40;b / tpix&#41;
        &#41;;   &#125;
    end;
  end;
end;

as you can see im crap at image work

[Harry Hunt]

You need to do Bitmap.PixelFormat := pf24Bit; with all your bitmaps...
Also, make sure that the values you assign to rgtbRed,... never get larger than 255 or smaller than 0 or you'll get really weird results.