Reading Pixels and finding specific RGB - delphi

Question

I would like to load an image, and read pixels to find a certain RGB, but then check the next pixels across to make sure they match, and i am at the right position of the bitmap.
I know the below code is wrong, but i am not sure how to go about correcting it. I also know Pixels is not the fastest way to read pixels.
Thanks guys!
procedure RGB(Col: TColor; var R, G, B: Byte);
var
Color: $0..$FFFFFFFF;
begin
Color := ColorToRGB(Col);
R := ($000000FF and Color);
G := ($0000FF00 and Color) Shr 8;
B := ($00FF0000 and Color) Shr 16;
end;
procedure TForm1.Button1Click(Sender: TObject);
var
x,y : Integer;
ColorN: TColor;
R, G, B: Byte;
begin
for Y := 0 to Image1.Picture.Bitmap.Height -1 do
begin
for X := 0 to Image1.Picture.Bitmap.Width -1 do
begin
inc(i);
ColorN := Image1.Canvas.Pixels[x, y];
RGB(ColorN, R, G, B);
//Memo1.Lines.Append('Line: '+IntToStr(i)+' Y: '+IntToStr(Y)+' X: '+IntToStr(X)+' R: '+IntToStr(R)+' G: '+IntToStr(G)+' B: '+IntToStr(B));
if (IntToStr(R) = '235') and (IntToStr(G) = '235') and (IntToStr(B) = '235') then //Y: 500 X: 587
begin
//Image1.Canvas.MoveTo(X,Y);
//Image1.Canvas.LineTo(X,Y);
ColorN := Image1.Canvas.Pixels[x +1, y];
RGB(ColorN, R, G, B);
end;
if (IntToStr(R) = '232') and (IntToStr(G) = '232') and (IntToStr(B) = '232') then //RGB:232,232,232 Y: 500 X: 588
begin
ColorN := Image1.Canvas.Pixels[x +1, y];
RGB(ColorN, R, G, B);
ShowMessage('Test1');
end;
if (IntToStr(R) = '231') and (IntToStr(G) = '231') and (IntToStr(B) = '231') then //RGB: 231,231,231 Y: 500 X: 589
begin
ColorN := Image1.Canvas.Pixels[x +1, y];
RGB(ColorN, R, G, B);
ShowMessage('Test2');
end;
if (IntToStr(R) = '230') and (IntToStr(G) = '230') and (IntToStr(B) = '230') then //RGB: 230,230,230 Y: 500 X: 590
begin
ShowMessage('Test3');
end;
end;
end;
end;
procedure TForm1.FormCreate(Sender: TObject);
var
b: TBitmap;
begin
Image1.Picture.LoadFromFile('E:\Delphi Projects\Detect(XE6)\screen\1.png');
b := TBitmap.Create;
b.Assign(Image1.Picture.Graphic);
Image1.Picture.bitmap := b;
FreeAndNil(b);
end;

Answer 1

There are several big issues in this code:
Instead of IntToStr(R) = '235' it would be much faster to just check R=235
Instead of checking R, G and B individually, it would be easier to just check if ColorN=C_Gray235 where C_Gray235 = #00EBEBEB;
For the application as a whole I'd use a single if:
if (GetPixel(x, y) = C_Gray235) and
(GetPixel(x+1, y) = C_Gray232) and
(GetPixel(x+2, y) = C_Gray231) and
(GetPixel(x+3, y) = C_Gray230) then
begin
//do stuff here
end;
please note that the for-loop should be for x := 0 to myBitmap.Width - 4 (there's no way for the if to succeed once you have less than 4 pixels left on the line. Actually you may even get an AV if you try to access them, depending on the way you get the pixels).
Now if the bitmap already is a 24-bit or 32-bit bitmap, you can improve the performance quite a bit by using Bitmap.ScanLine[iLine]...