Tips on reverse-engineering new tags?

[horshack]

I've noticed exiftool periodically adds new tags that presumably were discovered via reverse engineering. I was wondering if you have any tips on the most effective way to find new tags for particular camera settings or status conditions. Is it just a matter of varying the camera's settings/config via multiple shots and comparing the resulting tag data, using the html dump option for example to see what's changed? So much exif varies between frames that it's hard to isolate what field actually correlates to the settings/config element I'm trying to isolate. Any tips would be greatly appreciated.

[Phil Harvey]

Yes.  Setting the camera to manual exposure helps keep other things from changing, then changing only one setting and comparing the -U output is how I do it.  Depending on how the setting is stored, sometimes it takes a number of redundant shots to identify the location unambiguously.  For a difficult on/off setting I often use a 7-shot series: on,off,off,on,on,on,off then look for the 1001110 (or 0110001) pattern in some bit of the output files.  I have some utilities I wrote (one attached below) to help with the multi-file comparison.

- Phil

[horshack]

Thanks Phil, I was unaware of -U, and shooting multiple shots looking for a binary pattern across instances to match the settings flipping is a great idea.