Resampling an image problem

[AP81]

This is a really a logic or maths problem, but I can't get my head around it. Maybe someone can help me.

I have written a small app which resamples an image if the width is greater than 640 pixels or the height is greater than 480 pixels.

My problem is I want to maintain the aspect ratio (the ratio between the width and the height), and find the maximum it can fit within 640 x 480 (for display on TV),

e.g. width = 200, height = 900
-> Given that the max width is 640 and the max height = 480, what is the maximum width/height that can fit in the boundaries of 640x480?

Can you see my problem here? If I get a standard size image (e.g. 800x600) and resize it, it will be fine. If I get an image which is 200 x 900 and resample it to 640x480, the images is stretched.

Any ideas appreciated. This is really simple, I have just hit a mental block!





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There's no place like 127.0.0.1
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[towerbase]

Here's some code that takes an oldHeight and oldWidth value from TEdits and puts the updated values in newHeight and newWidth TEdits.

procedure TForm1.Button1Click(Sender: TObject);
const
  MaxHeight = 480;
  MaxWidth = 640;
  Aspect = MaxWidth / MaxHeight;
var
  w: Single;
  h: Single;
  ratio: Single;
begin
  w := StrToIntDef ( oldwidth.text, 0 ) + 0.0;
  h := StrToIntDef ( oldheight.Text, 0 ) + 0.0;
  Assert ( w * h > 0 );
  ratio := w / h;
  if ratio > Aspect then begin
    newWidth.text := IntToStr(MaxWidth);
    newHeight.text := IntToStr ( Round ( h * MaxWidth / w ) ) ;
  end
  else begin
    newHeight.text := IntToStr(MaxHeight);
    newWidth.text := IntToStr ( Round ( w * MaxHeight / h ) );
  end;

Hopefully it's self explanatory and you can adapt it for your requirements.


Andrew
Hampshire, UK

 

[AP81]

Thanks, that works very well.

I worked it out yesterday, but your code is very neat. Thanks again.




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There's no place like 127.0.0.1
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