need more speed calculating average colour of a bitmap

I have a BMP (or JPG) image in a TImage component. Im calculating the average colour of the bitmap using the next code fragment:
Count := 0;
for y := 0 to Image1.Picture.Height-1 do
  begin
    for x := 0 to Image1.Picture.Width -1 do
    begin
      inc(Count);
      L := Form1.Image1.Picture.Bitmap.Canvas.Pixels[x,y];
      R := R + ((L shr 16) and $FF);
      G := G + ((L shr 8) and $FF);
      B := B + (L and $FF);
    end;
  end;
  R1 := R div Count;
  G1 := G div Count;
  B1 := B div Count;
  showmessage(inttostr(R1)+','+inttostr(G1)+','+inttostr(B1));

This code fragment does the work, but it is very slow (around 30 secs. for a 960x1200 pixels image...).

Do any expert have a code to speed up this routine?

Thanks in advance,
Manuel López (lopem)
LVL 3
lopemAsked:
Who is Participating?
 
ptmcompCommented:
procedure TForm1.Button1Click(Sender: TObject);
var
  x, y: Integer;
  L: Integer;
  R, G, B: Int64;
  Count: Int64;
  res: Integer;
  OldTick: Cardinal;
begin
  R:=0; G:=0; B:=0;
  OldTick:= GetTickCount;
  with Form1.Image1.Picture.Bitmap do
  begin
    Count := Int64(Height * Width);
    if Count=0 then
      raise Exception.Create('Error Count=0');
    for y := 0 to Height-1 do
      for x := 0 to Width -1 do
      begin
        L := Canvas.Pixels[x,y];
        inc(R, ((L shr 16) and $FF));
        inc(G, ((L shr 8) and $FF));
        inc(B, (L and $FF));
      end;
    res:= (R+G+B) div Count;
  end;
  Label1.Caption:= IntToStr(GetTickCount-OldTick);
  Label2.Caption:= IntToStr(res);
end;

This is *MUCH* faster!:

procedure TForm1.Button2Click(Sender: TObject);
var
  x, x1, y: Integer;
  L: Integer;
  R, G, B: Int64;
  Count: Int64;
  res: Integer;
  OldTick: Cardinal;
  P : PByteArray;
begin
  R:=0; G:=0; B:=0;
  OldTick:= GetTickCount;
  with Form1.Image1.Picture.Bitmap do
  begin
    Count := Int64(Height * Width);
    if Count=0 then
      raise Exception.Create('Error Count=0');
    case PixelFormat of
      pf8bit:
        begin
          for y := 0 to Height-1 do
          begin
            P := ScanLine[y];
            for x := 0 to Width -1 do
            begin
              L := P[x];
              inc(R, ((L shr 16) and $FF));
              inc(G, ((L shr 8) and $FF));
              inc(B, (L and $FF));
            end;
          end;
        end;
      pf24bit:
        begin
          for y := 0 to Height-1 do
          begin
            P := ScanLine[y];
            x1:=0;
            for x := 0 to Width -1 do
            begin
              inc(R, P[x1]);
              inc(x1);
              inc(G, P[x1]);
              inc(x1);
              inc(B, P[x1]);
              inc(x1);
            end;
          end;
        end;
      else
        ShowMessage('Format not supported');
    end;
    res:= (R+G+B) div Count;
  end;
  Label1.Caption:= IntToStr(GetTickCount-OldTick);
  Label2.Caption:= IntToStr(res);
end;

Regards, ptm.
0
 
simonetCommented:
For one, you can remove the
  inc(Count)
line, because it will always evaluate to (Image1.Picture.Height * Image1.Picture.WIdth). Therefore, you can save remove it from the loop and add this to next line AFTER the loop:

  Count := Image1.Picture.Height * Image1.Picture.Width;

Besides, using WITH can speed up something:

  with Form1.Image1.Picture do
  begin
    for y := 0 to Height-1 do
      for x := 0 to Width -1 do
      begin
        L := Bitmap.Canvas.Pixels[x,y];
        R := R + ((L shr 16) and $FF);
        G := G + ((L shr 8) and $FF);
        B := B + (L and $FF);
      end;
    Count := Height * Width;
  end;
  R1 := ...

Try making the modifications above to the code and see how much improvement there is.

Yours,

Alex
 

0
 
simonetCommented:
By the way: for saving a few CPU cycles, you should rewrite the routine I just sent you like this:

  with Form1.Image1.Picture do
  begin
    for y := 0 to Height-1 do
      for x := 0 to Width -1 do
      begin
        L := Bitmap.Canvas.Pixels[x,y];
        inc(R, ((L shr 16) and $FF));
        inc(G, ((L shr 8) and $FF));
        inc(B, (L and $FF));
      end;
    Count := Height * Width;
  end;
 
Make sure R, G and B are of an ordinal type (integer, longint, cardinal, word, etc);

Yours,

Alex
0
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ptmcompCommented:
The access over the pixels property is slow. Perhaps you should use scanlines or something else.
0
 
lopemAuthor Commented:
Thank you... You re very kind!

Best regards,
Manuel López (lopem)
0
 
simonetCommented:
His answer was pretty good. Why did you give him a B? Besides, it's only a 30 points question.
0
 
ptmcompCommented:
Well, I gave you only the implementation for 8 and 24 bits per pixel, but the other formats are seldoma and it's quite easy to implement the others.
0
 
ptmcompCommented:
EE needs a spell checking option... ("seldoma"->"seldom")
0
 
lopemAuthor Commented:
Hi Simonet,

Maybe I guess was not a very difficult question... I'm not quite sure how to qualify an answer properly. Do you think he deserves more points? If this is the case, I apologize and I promise to give to him some more points...

Any suggestion is welcome, as usual!

Best regards,
Manuel López (lopem)
0
 
ptmcompCommented:
How does the point system work?

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0
 
lopemAuthor Commented:
Hi ptmcomp,

Just one little fix to your code:

                             :
                             :
                             :
       ShowMessage('Format not supported');
     end;
     res:= (R+G+B) div Count;
     end;
     Label1.Caption:= IntToStr(GetTickCount-OldTick);
                             :
                             :

res should be

                      res := ((R*65536)+(G*255)+(B));

Thank you again.

Best regards,
Manuel López

0
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