each of the Picture Modes in the jpeg rendering options of Olympus cameras allows you set a parameter called “gradation”
setting a gradation value other than Normal may result in your RAW file exposure being inaccurate!
Auto setting and Low-Key setting will generally result in under-exposure of the RAW file
gradation = Auto
the Olympus image processing engine attempts to get as much dynamic range (range of brightness from very dark to very bright) as possible squeezed into the jpeg file
best used for high contrast scenes where you want both highlight and shadow detail
the modern Olympus cameras can achieve a remarkable dynamic range:
Comparison jpeg results of dynamic range from dpreview.com
gradation = normal
no gradation algorithms are applied
gradation = LOW KEY
Gradation is applied that best suits a dark subject that NORMAL gradation would process to be lighter.
It can be used to make images that have a somewhat somber mood and are darker but retain shadow detail
gradation = HIGH KEY
Gradation is applied that best suits a bright subject, such as silhouettes on a foggy day.
It processes images so they are bright with slightly higher contrast in the brightest areas.