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pixel to cm and cm to pixel how?

Posted on 2002-07-10
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Last Modified: 2007-12-19
Hi ,

  How can i convert pixel value to cm and cm to pixel ?

Thanks..
0
Comment
Question by:Mozzak
8 Comments
 
LVL 7

Expert Comment

by:Cynna
Comment Utility
Here's a simple example (copy/paste & place 2 buttons on the form...):

procedure CmPerPixel(canvas:TCanvas; var xcmpp,ycmpp: Real);
var h:HDC;
    hres,vres,hsiz,vsiz:integer;
begin
   h:=canvas.handle;
   hres := GetDeviceCaps(h,HORZRES);   {display width in pixels}
   vres := GetDeviceCaps(h,VERTRES);   {display height in pixels}
   hsiz := GetDeviceCaps(h,HORZSIZE);  {display width in mm}
   vsiz := GetDeviceCaps(h,VERTSIZE);  {display height in mm}
   xcmpp := hsiz/hres*0.1;
   ycmpp := vsiz/vres*0.1;
end;


procedure TForm1.Button1Click(Sender: TObject);
var xcmpp,ycmpp: Real; // pixel-> cm
begin
   CmPerPixel(Form1.Canvas, xcmpp,ycmpp);
   Caption:='100 pixels are '+FloatToStr(xcmpp*100)+' cm wide and '+FloatToStr(ycmpp*100)+' cm high';
end;

procedure TForm1.Button2Click(Sender: TObject);
var xcmpp,ycmpp: Real; // cm -> pixel
begin
   CmPerPixel(Form1.Canvas, xcmpp,ycmpp);
   Caption:='3 cm are '+FloatToStr(1/xcmpp*3)+' pixels wide and '+FloatToStr(1/ycmpp*3)+' pixels high';
end;

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LVL 2

Accepted Solution

by:
bugroger earned 50 total points
Comment Utility
hi,

try this function:

function GetPixelCM(pixelcount : integer) : extended;
begin
 // 1 inch = 2,54 cm
 Result := (2.54 / Screen.PixelsPerInch) * pixelCount;
end;

GL
 bug




0
 
LVL 2

Expert Comment

by:bugroger
Comment Utility
i was too slow :-(
0
 
LVL 3

Expert Comment

by:lopem
Comment Utility
listening...
0
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After years of analyzing threat actor behavior, it’s become clear that at any given time there are specific tactics, techniques, and procedures (TTPs) that are particularly prevalent. By analyzing and understanding these TTPs, you can dramatically enhance your security program.

 

Author Comment

by:Mozzak
Comment Utility
Bugroger i try to use your code because its easy..

Here is my code ;

MyPrinter = class
  function PixelToCM(pixelcount : integer):extended ;
  function CMToPixel(cm : extended):extended ;
end ;

function MyPrinter.CMToPixel(cm: extended):extended;
begin
  { i wrote }
  Result := (cm / 2.54) * Screen.PixelsPerInch ;
end;

function MyPrinter.PixelToCM(pixelcount: integer):extended;
begin
  { inch = 2,54 cm bugroger wrote }
  Result := (2.54 / Screen.PixelsPerInch) * pixelCount ;
end;
---------------------------------------------------------
when i try to use like these ;

procedure TForm1.Button1Click(Sender: TObject);
var
  vconv : TTinaPrinter ;
begin
  vconv := TTinaPrinter.Create ;
  Edit1.Text := Floattostr(vconv.PixelToCM(strtoint(Edit1.Text))) ;

end;

procedure TForm1.Button2Click(Sender: TObject);
var
  vconv : TTinaPrinter ;
begin
  vconv := TTinaPrinter.Create ;
  Edit1.Text := Floattostr(vconv.CMToPixel(strtofloat(Edit1.Text))) ;

end;
---------------------------------------------------------
problem occurs some times..for example try to calculate 5 first with button1 then use button2 for turn to 5 again but it will be 5,00000000000001.

  Can you give me the real value of inch/cm ? or different ssolution .
0
 

Author Comment

by:Mozzak
Comment Utility
I had solve the problem and the real rate must be 2.5400181214134702506795530051344 .

Best Regards..
0
 

Author Comment

by:Mozzak
Comment Utility
Still its not working after more than 2-3 try . For example 789 . What is the problem ? I'm taking 789,000000000002
0
 
LVL 2

Expert Comment

by:bugroger
Comment Utility
hi Mozzak

this occurs because of rounding in FloatToStr
if you convert the extended value
to string and back.

now it should work! I have used FloatToStrF instead
of FloatToStr

Have a look to Button3Click.
If you don't convert the extended value (test)
to string and back it works fine!


procedure TForm1.Button1Click(Sender: TObject);
var
 vconv : MyPrinter;
begin
 vconv := MyPrinter.Create ;
 Edit1.Text := FloatToStrF(vconv.PixelToCM(strtoInt(Edit1.Text)), ffGeneral, 20, 0) ;
 vconv.Free;
end;

procedure TForm1.Button2Click(Sender: TObject);
var
 vconv : MyPrinter;
begin
 vconv := MyPrinter.Create ;
 Edit1.Text := FloattostrF(vconv.CMToPixel(strtofloat(Edit1.Text)), ffGeneral, 5,0) ;
 vconv.Free;
end;

procedure TForm1.Button3Click(Sender: TObject);
var
 vconv : MyPrinter;
 test : extended;

begin
 vconv := MyPrinter.Create ;
 test := vconv.PixelToCM(strtoInt(Edit1.Text));
 Edit1.Text := Floattostr(vconv.CMToPixel(test));
 vconv.Free;
end;


Hope this solve your problems
GL
 bug
0

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