LightValue calculation & EC?

[Marsu42]

I've tried calculating the LV value with exiftool which seems to work just fine. What I don't understand is why it just takes Aperture/Shutter/ISO, but not exposure compensation (EC) of "-ExifIFD:ExposureCompensation" or "-Canon:ExposureCompensation" (maker tags are lost after exporting from Adobe).

Obviously you have to assume that the camera metering was correct for this, so it's only the LV of the metered spot or result of some magical camera matrix/evaluative calculation. But if I set EC to -3,  the values of LV calculated (example: 10) of just Aperture/Shutter/ISO are off by -3, too? Imho you need to subtract the EC, for example with the correct EC in this case would actually be 13 because with negative EC, you force the camera to think it's brighter than the metering says?

[Phil Harvey]

The term "light value" is not very well defined.  In many circles (I believe), it is just exposure value corrected by the ISO speed rating, which is what ExifTool is calculating.  If you want the metered intensity of the incoming light, then you do indeed need to correct for the exposure compensation setting.

- Phil

[Marsu42]

In many circles (I believe), it is just exposure value corrected by the ISO speed rating, which is what ExifTool is calculating.

I'd dare to say that these circles are used to old-school cameras w/o EC or external metering ... if you simply leave out EC from the calculation, I don't see the real world usage of this LV as it can be way off even considering that it's only based on camera metering.

Sure I'll adjust exiftool's current LV with EC or use the Canon MeasuredEV tag (which unfortunately isn't exported from Adobe w/o further hassle), but just saying that exiftool doing what it does might come as a surprise of people expect this LV to be about the LV of the scene...