Question

I am modifying jpeg EXIF data. Some data requires to be defined as a fractions.
Here, I have two problems:
1.) Which is the correct fraction “format”? For instance when I have an exposure time (“ExposureTime”) of 30000µs and store it as 30000/1000000 the EXIF viewer shows the wrong exposure. Storing as “1/30” returns the correct result. Do all fractions have to be “1/x”?

2.) How can I calculate the fraction fast? The method I am using now (similar to “Dec2Frac” in [1]) is very slow.

Regards,

[1] Calculating EXIF exposure time as a fraction (Delphi)

Answer 1

This is the code I have used in C# for calculating a fraction for EXIF GPS data. The method returns an array of two integers – one being the numerator and one the denominator.

public static int[] GetFraction(Decimal value)
        {
            int denominator = 1;
            int numeratorMultiplier = 1;
            Decimal numerator = value * numeratorMultiplier;
            int failSafe = 0;

            while (Decimal.Remainder(numerator, 1m) != 0m && failSafe < 20 && ((long)numerator * 10) < Int32.MaxValue)
            {
                denominator *= 10;
                numeratorMultiplier *= 10;

                numerator = value * numeratorMultiplier;
                failSafe++;
            }

            return new int[] {Decimal.ToInt32(numerator), denominator};
        }