Spiral search of an image
lazarus / 39-Graphics

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user5 · 2025-04-28 14:05

I'm back after a long absence and I thought that I would share some
code in case anyone is interested. The code below searches
through a picture or video frame image in a clockwise spiral from any
given point. It searches for a target solid colored area and then
flood fills that area with the chosen fill color. The example here
stops processing after the flood fill is done but it could be easily
modified
to continue through all the pixels of the image to flood fill all
instances of the target search color.
    For purposes of illustration a TImage is used here but in actual
practice a TBGRABitmap would be used to get the fastest possible
speed.
    The attached picture shows the search pattern with red being the
first search, blue being the second search and so on. The starting
point is the black pixel and the red pixel diagonally to the right of
the black pixel is where the next search begins.
    The beauty about searching in a spiral from a given point instead
of starting at any corner of the image is that this type of flood fill
process can work with target areas that change shape and even move
around. The user would make one click on a target color and then the
program would do the rest.
    For example, the user clicks a target red area on the first frame
of a video to get X and Y. In the second frame that area has changed
its
shape and has also moved to a different location some distance from
where it used to be. In the second frame the program searches from
the previous click location for that red area and then flood fills it.
Ta Ta.

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.Button1Click(Sender: TObject);var
count,X,Y,factor,newx,newy:integer;    go,gothit,gonow:boolean;   
searchcolor:TColor;    size:integer;begin//Set size to the largest
dimension.size := image1.width div 2;if image1.height > image1.width
then size := image1.height div 2; searchcolor := clRed; //target color
to fillimage1.Canvas.Brush.Color := clLime;//In this case start the
search at the center of the image.X := 150;Y := 150; factor := 0;go :=
true;gothit := false;//If the starting pixel is the target color then
skip the searchif image1.canvas.pixels[X,Y] = searchcolor then go :=
false; while go do begin  //Search from top to bottom  factor :=
factor + 1;  newx := X + factor;  newy := Y - factor;   if
(image1.canvas.pixels[newx,newy] = searchcolor) and ((newx >= 0) and
(newx <= (image1.width - 1)) and (newy >= 0) and (newy <=
(image1.height - 1))) then   begin    go := false;    gothit := true; 
  X := newx;    Y := newy;   end  else   begin    //do nothing 
 end;   if go then   begin    gonow := true;    count := 0;    while
(gonow) and (count < (factor * 2)) do     begin      count := count +
1;      newy := newy + 1;       if (image1.canvas.pixels[newx,newy] =
searchcolor) and ((newx >= 0) and (newx <= (image1.width - 1)) and
(newy >= 0) and (newy <= (image1.height - 1))) then       begin      
X := newx;        Y := newy;        gonow := false;        gothit :=
true;        go := false;       end;     end;   end;   //Search from
right to left.  if go then   begin    newx := X + factor;    newy := Y
+ factor;     if go then     begin      gonow := true;      count :=
0;      while (gonow) and (count < (factor * 2)) do       begin      
count := count + 1;        newx := newx - 1;         if
(image1.canvas.pixels[newx,newy] = searchcolor) and ((newx >= 0) and
(newx <= (image1.width - 1)) and (newy >= 0) and (newy <=
(image1.height - 1))) then         begin          X := newx;         
Y := newy;          gothit := true;          gonow := false;         
go := false;         end;       end;     end;   end;   //Search from
bottom to top.  if go then   begin    newx := X - factor;    newy := Y
+ factor;     if go then     begin      gonow := true;      count :=
0;      while (gonow) and (count < (factor * 2)) do       begin      
count := count + 1;        newy := newy - 1;         if
(image1.canvas.pixels[newx,newy] = searchcolor) and ((newx >= 0) and
(newx <= (image1.width - 1)) and (newy >= 0) and (newy <=
(image1.height - 1))) then         begin          X := newx;         
Y := newy;          gothit := true;          gonow := false;         
go := false;         end;       end;     end;   end;   //Search from
left to right.  if go then   begin    newx := X - factor;    newy := Y
- factor;     if go then     begin      gonow := true;      count :=
0;      while (gonow) and (count < (factor * 2)) do       begin      
count := count + 1;        newx := newx + 1;         if
(image1.canvas.pixels[newx,newy] = searchcolor) and ((newx >= 0) and
(newx <= (image1.width - 1)) and (newy >= 0) and (newy <=
(image1.height - 1))) then         begin          gothit := true;    
    X := newx;          Y := newy;          gonow := false;         
go := false;         end;       end;     end;   end;  //Stop the loop
is the entire image has been searched.  if (gothit = false) and
(factor >= size) then   go := false; end; if gothit then begin  image1
.Canvas.FloodFill(X,Y,searchcolor,fssurface); end; showmessage('Proces
s done.'); end;