aspect ratio a calculation

Question

afternoon all. Iv'e come across some mathematical problems that im not too good at. does anyone know how to calculate the ratio for Height against width?

Regards Phil

Answer 1

Pseudo code:

newWidth = newHeight / oldHeight * oldWidth

OR

newHeight = newWidth / oldwidth * oldHeight

Answer 2

If you mean the aspect ratio of a height and width, it's just height / width reduced to its greatest common factor.

For instance, if your monitor is 1600 x 1200, it's 1600/1200 reduced to 4/3. To do this:

In math terms, you have to find the "Greatest Common Factor" and divide both values (1600 and 1200) by that. In this case, it's 400.

A very simple (and relatively) algorithm for this is:

for i <= min( 1600, 1200 ); i > 0; --i );
  if( 1600 % i == 0 && 1200 % i == 0 ) {
    minTop = 1600 / i;
    minBottom = 1200 / i;
    break;
  }
}

Your answer is minTop / minBottom. Replace 1600 and 1200 with the width and height you want, respectively.

Basically, the algorithm goes like this: count down from the lesser of the two numbers and find the first number into which both 1600 and 1200 divide into evenly (using the mod operator, so remainder == 0). That will end up being 400. That leads you with (1600 / 400) / (1200 / 400), or 4/3.

Hope this helps; leave a comment with any questions and I'll try to help further.

Answer 3

Here is a simple function that should give you the aspect ratio (simplified and in javascript)

function getAspectRatio(w, h)
    {
        var rem;
        var newW = w;
        var newH = h;

        while (h != 0)
        {
            rem = w % h;
            w = h;
            h = rem;
        }

        newH = newH / w;
        newW = newW / w;

        alert("Aspect Ratio: " + newW + ":" + newH);
    }

getAspectRatio(800,600); results in 4:3.

Hope this helps

G

EDIT: I forgot to mention, it calculates the gcd of the two numbers and does not check for division by zero, so you might want to add that. :)