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Answer 1

+2 A:

It's simple mathematics: simply divide the top and bottom of the fraction by the top value.

  15625 / 10000000
= (15625/15625) / (10000000/15625)
= 1 / 640

In PHP, you can do it like this:

$exposure = "15625/10000000";
$parts = explode("/", $exposure);
$exposure = implode("/", array(1, $parts[1]/$parts[0]));

echo $exposure;

Dean Harding 2010-06-16 00:33:35

So long as the top is never 0, nor an imperfect fraction nor a fraction that has a non-1 numerator when reduced. Other wise agree

ircmaxell 2010-06-16 00:38:55

@ircmaxell: Right, it's also assuming that it's numerical and all that, but I assume you'd have error checking in place. The problem is, you can't always trust that whatever wrote the files is putting the correct thing in there :)

Dean Harding 2010-06-16 00:44:03

Thanks, exactly what I was looking for.

MarkL 2010-06-16 01:28:13

Answer 2

A:

This is the code I use to normalize the exposure,

                    if (($bottom % $top) == 0) {
                            $data = '1/'.round($bottom/$top, 0).' sec';
                    }       else {
                            if ($bottom == 1) {
                                    $data = $top.' sec';
                            } else {
                                    $data = $top.'/'.$bottom.' sec';
                            }
                    }

It handles most exposures correctly but I see some weird ones once a while.

ZZ Coder 2010-06-16 00:39:10

Thanks, I'll use it.

MarkL 2010-06-16 13:06:33

Answer 3

A:

You can use Euclid's algorithm to find the greatest common divisor, which will help you reduce the fraction.

AbeVoelker 2010-06-16 00:41:13

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Parsing EXIF's "ExposureTime" using PHP

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