如何将纵横比降低到最低值？

Giving an aspect ratio X:Y, is it possible to get its lowest terms?

For example, if an aspect ratio is 6:4, I want to get 3:2

And if an aspect ratio is 16:10, I want to get 8:5

X and Y are both positive integers

You need to use the function gmp_gcd

GMP gmp_gcd ( GMP $a , GMP $b )
Calculate greatest common divisor of a and b. The result is always positive even if either of, or both, input operands are negative.

http://php.net/manual/en/function.gmp-gcd.php

You would divide each side of the ratio by the given result to find the lowest ratio.

You can use phospr/fraction for simplification and convert from float number to fraction, which cover all possible aspect.

In your case you can use like below

<?php
function fraction($n,$d){
    $a = abs($n);
    $b = abs($d);
    if ($a < $b) {
        $c = $a;
        $a = $b;
        $b = $c;
    }
    $r = $a % $b;
    while ($r > 0) {
        $a = $b;
        $b = $r;
        $r = $a % $b;
    }
    $gcd = $b;
    $n /= $gcd;
    $d /= $gcd;
    return "$n:$d";
}
$ar_str = '6:4';
$ar_arr = explode(":",$ar_str);
$simplified = fraction($ar_arr[0],$ar_arr[1]);
echo "Simplified of $ar_str is : ".$simplified;
?>

Demo of above example