|Exif TIFF Tag BrightnessValue|
TIFF Tag Reference
TIFF Tag BrightnessValue
The value of brightness.
The unit is the APEX (Additive System of Photographic Exposure) setting.
Ordinarily it is given in the range of -99.99 to 99.99. Note that if the numerator of the recorded value is hex FFFFFFFF, Unknown shall be indicated.