Hello, I'm using this library to get EXIF data from images, and encountered a possible rounding error when getting the Shutter Speed tag value.
For example, when the actual shutter speed of the image is 1/30 sec, but somehow in the processed tag description, it says 1/29 sec.
What I'm thinking is that the rounding logic in the method below is a source of the problem.
protected string? GetShutterSpeedDescription(int tagId)
{
// I believe this method to now be stable, but am leaving some alternative snippets of
// code in here, to assist anyone who's looking into this (given that I don't have a public CVS).
// float apexValue = _directory.getFloat(ExifSubIFDDirectory.TAG_SHUTTER_SPEED);
// int apexPower = (int)Math.pow(2.0, apexValue);
// return "1/" + apexPower + " sec";
// TODO test this method
// thanks to Mark Edwards for spotting and patching a bug in the calculation of this
// description (spotted bug using a Canon EOS 300D)
// thanks also to Gli Blr for spotting this bug
if (!Directory.TryGetSingle(tagId, out float apexValue))
return null;
if (apexValue <= 1)
{
var apexPower = (float)(1 / Math.Exp(apexValue * Math.Log(2)));
var apexPower10 = (long)Math.Round(apexPower * 10.0);
var fApexPower = apexPower10 / 10.0f;
return fApexPower + " sec";
}
else
{
var apexPower = (int)Math.Exp(apexValue * Math.Log(2));
return "1/" + apexPower + " sec";
}
}
For the case when apexValue > 1, I think the code should be like this:
Hello, I'm using this library to get EXIF data from images, and encountered a possible rounding error when getting the
Shutter Speed
tag value.For example, when the actual shutter speed of the image is
1/30 sec
, but somehow in the processed tag description, it says1/29 sec
.What I'm thinking is that the rounding logic in the method below is a source of the problem.
For the case when
apexValue
> 1, I think the code should be like this:So compared to just naively converting it to
int
, the value falls to the nearest integer.I started using this library about 5 hours ago, and new to this area. Therefore I could be wrong about this.
Thank you for reading.