From: Jacques Oberto <oberto@NOSPAM.ibpc.fr>
Subject: Re: detecting borders
Date: 07 Mar 2000 00:00:00 GMT
Message-ID: <38C5309D.66C0@NOSPAM.ibpc.fr>
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Newsgroups: borland.public.delphi.graphics

Hi Kolbeinn:

You will find below an example unit to "autocrop" a bitmap in
response to your first question. The Scanline stuff is inspired
from E.F.Glynn's code. If you solve the multiple crop problem,
please let me know.
I hope it helps,

Jacques


Kolbeinn Sigurjonsson wrote:
> I have a bitmap that contains a graphic, but the images is larger so that
> the graphic is surrounded with white (or any color) borders. (typically when
> scanned).
>
> Is there a good algorythm that will help me to detect the "upperleft" end
> "lowerright" corners of the graphic, therefore enabling me to exclude the
> surrounding area with a rubberband?
>
> Far better:
> I have one bitmap which contains two or more small images in it (I scan
> multiple photos in a row from my scanner) and I want to be able to detect
> the border of every single photo....

_________________________________________

unit Unit1;
  
 interface
  
 uses
   Windows, Messages, SysUtils, Classes, Graphics,
   Controls, Forms, Dialogs, StdCtrls, ExtCtrls;
  
 const
   PixelCountMax = 32768;
  
 type
   pRGBArray = ^TRGBArray;
   TRGBArray = array[0..PixelCountMax-1] of TRGBTriple;
  
 type
   TForm1 = class(TForm)
     Button1: TButton;
     procedure FormCreate(Sender: TObject);
     procedure FormDestroy(Sender: TObject);
     procedure Button1Click(Sender: TObject);
   private
     { Private declarations }
   public
     { Public declarations }
   end;
  
 var
   Form1: TForm1;
   OBitmap, DBitmap : TBitmap;
  
 implementation
  
 {$R *.DFM}
  
 procedure TForm1.FormCreate(Sender: TObject);
 begin
   Form1.color := clLtGray;
   OBitmap := TBitmap.Create;
   OBitmap.PixelFormat := pf24bit;
   DBitmap := TBitmap.Create;
   DBitmap.PixelFormat := pf24bit;
 end;
  
 procedure TForm1.FormDestroy(Sender: TObject);
 begin
   Obitmap.Free;
   DBitmap.Free;
 end;
  
 procedure TForm1.Button1Click(Sender: TObject);
 var
   BackColor : TColor ;
   i : INTEGER;
   j : INTEGER;
   Row: pRGBArray;
   IsBlack : Integer;
   MyTop, MyBottom, MyLeft, MyRight : Integer;
   TempTop, TempBottom : Integer;
  
 begin
   OBitmap.Width := 100;
   Obitmap.Height := 100;
   OBitmap.Canvas.TextOut(20,20,'Hello World !!!');
   Form1.Canvas.Draw(0,0,OBitmap);
   //Retrieve Background Color
   BackColor := OBitmap.Canvas.Pixels[0,0];
   MyTop := 0;
   TempTop := 0;
   MyBottom := 0;
   TempBottom := OBitmap.Height;
   MyLeft := OBitmap.Width;
   MyRight := 0;
  
   //Find Top
   for j := 0 to OBitmap.Height-1 do
   begin
     Row := pRGBArray(OBitmap.Scanline[j]);
     isBlack := 0;
     for i := 0 to OBitmap.Width-1 do
     begin
     if (Row[i].rgbtRed  <> GetRvalue(BackColor)) and
       (Row[i].rgbtGreen <> GetGvalue(BackColor)) and
       (Row[i].rgbtBlue  <> GetBvalue(BackColor)) then
     inc(isBlack);
     end;
     if isBlack = 0 then Inc(TempTop);
     if isBlack <> 0 Then MyTop := TempTop;
   end;
  
   //Find Bottom
   for j := OBitmap.Height-1 Downto 0 do
   begin
     Row := pRGBArray(OBitmap.Scanline[j]);
     isBlack := 0;
     for i := 0 to OBitmap.Width-1 do
     begin
     if (Row[i].rgbtRed  <> GetRvalue(BackColor)) and
       (Row[i].rgbtGreen <> GetGvalue(BackColor)) and
       (Row[i].rgbtBlue  <> GetBvalue(BackColor)) then
     inc(isBlack);
     end;
     if isBlack = 0 then Dec(TempBottom);
     if isBlack <> 0 Then MyBottom := TempBottom;
   end;
  
   //Find Left
   for j := 0 to OBitmap.Height-1 do
   begin
     Row := pRGBArray(OBitmap.Scanline[j]);
     for i := 0 to OBitmap.Width-1 do
     begin
       if (Row[i].rgbtRed  <> GetRvalue(BackColor)) and
         (Row[i].rgbtGreen <> GetGvalue(BackColor)) and
         (Row[i].rgbtBlue  <> GetBvalue(BackColor)) then
       if i < MyLeft then MyLeft := i;
     end;
   end;
  
   //Find Right
   for j := 0 to OBitmap.Height-1 do
   begin
     Row := pRGBArray(OBitmap.Scanline[j]);
     for i := OBitmap.Width-1  downto 0 do
     begin
       if (Row[i].rgbtRed  <> GetRvalue(BackColor)) and
         (Row[i].rgbtGreen <> GetGvalue(BackColor)) and
         (Row[i].rgbtBlue  <> GetBvalue(BackColor)) then
       if i > MyRight then MyRight := i;
     end;
   end;
  
   DBitmap.Width := MyRight - MyLeft + 4;
   Dbitmap.Height := MyBottom - MyTop + 4;
  
   BitBlt(DBitmap.canvas.Handle,-MyLeft+2,-MyTop+3,MyLeft+
         MyRight,MyTop+MyBottom, OBitmap.Canvas.Handle,0,0,
         SRCCOPY);
  
   Form1.Canvas.Draw(0,120,DBitmap);
 end;
  
 end.