AutoIS and BaseISO tags

[mvadu]

Phil, I have an image which was shot by Canon t1i (500D) with ISO set to 100.

Canon Shot Info (from -U -v3) shows

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3)  CanonShotInfo (SubDirectory) -->
  | | |     - Tag 0x0004 (68 bytes, int16u[34]):
  | | |         0562: 44 00 00 00 a0 00 f8 00 80 00 20 01 f4 ff 00 00 [D......... .....]
  | | |         0572: 03 00 00 00 08 00 08 00 9b 00 00 00 00 00 00 00 [................]
  | | |         0582: 00 00 00 00 01 00 00 00 00 00 80 00 24 01 96 00 [............$...]
  | | |         0592: 00 00 00 00 f8 00 ff ff ff ff ff ff ff ff 00 00 [................]
  | | |         05a2: 00 00 00 00                                     [....]
  | | | + [BinaryData directory, 68 bytes]
  | | | | AutoISO = 0
  | | | | - Tag 0x0001 (2 bytes, int16s[1]):
  | | | |     0564: 00 00                                           [..]
  | | | | BaseISO = 160
  | | | | - Tag 0x0002 (2 bytes, int16s[1]):
  | | | |     0566: a0 00                                           [..]

So if we decode them using

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fValue=(lValue/32.0f*log(2.f))*100; (my code)
or ValueConv => 'exp($val/32*log(2))*100' (%Image::ExifTool::Canon::ShotInfo) we get
AutoISO=0 and BaseISO=347, But basic -all gives

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Auto ISO                        : 100
Base ISO                        : 100

I don't see any defaulting to 100 in %Image::ExifTool::Canon::ShotInfo.
Where is it getting converted to 100?

[Phil Harvey]

I think you forgot the last /32.

The conversion for BaseISO is exp($val/32*log(2))*100/32.

Which is different from the conversion for AutoISO.

Figuring out these conversions is why I get the big bucks.    Hey, wait!  I do this for free...

- Phil

[BogdanH]

See, see... did I just noticed great sense of humor?

[mvadu]

I am feeling ashamed, i misread "exp" function to be PERL equivalent of "eval" in javascript, so in my conversion I totally missed e^lValue/32.0f*log(2.f), and just considered lValue/32.0f*log(2.f). So stupid!! after adding "exp" to my code too I am matching the results.
Thank you for your guidance.. btw can you imagine if you have charged few bucks for each new tag for each user.. you could have retired by now

[Phil Harvey]

About retiring:  I have calculated that if I received 25 cents for every exiftool download I could live off that income.  (And that is just the exiftool home site -- I'm not even counting downloads from any of the dozens of other sites hosting versions of exiftool for download.)  The number of downloads is just crazy.  I can't believe that many people are actually using my tool.

- Phil