How to get the image zoom percentage with scipt？

I want to get the true value of width, height value,

When the zoom percentage of X and Y at the same, The width and the high value just I need.

But when the zoom percentage of X and Y is different, I need the big scaling value, to make my width...

The following example:

W=90.366           H=(98.465/0.64)*0.88

So,I need to know the scaling value,and  whicha scaling value is bigger.

Thank you~~