How to translate shutter speed values into usable data?

I'm gathering light statistics of EXIF data for a large collection of photos and I'm trying to find the simplest way (i.e. performance doesn't matter) of translating Exposure Time values to/from usable data. There is (as far as I can find) no standard for what values camera manufacturers might use i.e. I can't just scan the web for random images and hard-code a map.

Here are is a sample set of values I've encountered (" indicates seconds):

279", 30", 5", 3.2", 1.6", 1.3", 1", 1/1.3, 1/1.6, 1/2, 1/2.5, 1/3, 1/4, 1/5, 1/8, 1/13, 1/8000, 1/16000

Also take into consideration that I'd also like to find the average (mean) ... but it should be one of the actual shutter speeds collected and not just some arbitrary number.

EDIT: By usable data I mean some sort of creative? numbering system that I can convert to/from for performing calculations. I thought about just multiplying everything by 1,000,000 except some fractions when divided are quite exotic.

EDIT #2: To clarify, I'm using ExposureTime instead of ShutterSpeed because it contains photographer friendly values e.g. 1/50. ShutterSpeed is more of an approximat开发者_如何学Goion (which varies between camera manufacturers) and leads to values such as 1/49.

You want to parse them into some kind of time-duration object.

A simple way, looking at that data, would be to check wheter " or / occurs, if " parse as seconds, / parse as fraction of seconds. I don't really understand what else you could mean. For an example you'd need to specify a language--also, there might be a parser out there already.

Shutter speed is encoded in the EXIF metadata as an SRATIONAL, 32-bits for the numerator and 32-bits for the denominator. Sample code that retrieves it, using System.Drawing:

        var bmp = new Bitmap(@"c:\temp\canon-ixus.jpg");
        if (bmp.PropertyIdList.Contains(37377)) {
            byte[] spencoded = bmp.GetPropertyItem(37377).Value;
            int numerator = BitConverter.ToInt32(spencoded, 0);
            int denominator = BitConverter.ToInt32(spencoded, 4);
            Console.WriteLine("Shutter speed = {0}/{1}", numerator, denominator);
        }

Output: Shutter speed = 553859/65536, sample image retrieved here.

It seems there are three types of string you will encounter:

1. String with double quotes " for seconds
2. String with leading 1/
3. String with no special characters

I propose you simply test for these conditions and parse the value accordingly using floats:

    string[] InputSpeeds = new[] { "279\"", "30\"", "5\"", "3.2\"", "1.6\"", "1.3\"", "1\"", "1/1.3", "1/1.6", "1/2", "1/2.5", "1/3", "1/4", "1/5", "1/8", "1/13", "1/8000", "1/16000" };
    List<float> OutputSpeeds = new List<float>();

    foreach (string s in InputSpeeds)
    {
        float ConvertedSpeed;
        if (s.Contains("\""))
        {
            float.TryParse(s.Replace("\"", String.Empty), out ConvertedSpeed);
            OutputSpeeds.Add(ConvertedSpeed);
        }
        else if (s.Contains("1/"))
        {
            float.TryParse(s.Remove(0, 2), out ConvertedSpeed);
            if (ConvertedSpeed == 0)
            {
                OutputSpeeds.Add(0F);
            }
            else
            {
                OutputSpeeds.Add(1 / ConvertedSpeed);
            }
        }
        else
        {
            float.TryParse(s, out ConvertedSpeed);
            OutputSpeeds.Add(ConvertedSpeed);
        }
    }

If you want TimeSpans simply change the List<float> to List<TimeSpan> and instead of adding the float to the list, use TimeSpan.FromSeconds(ConvertedSpeed);