What is the matching VOI LUT function value for EFV_Default in DCMTK library?

I'm using Dcmtk library and I used the getVoiLutFunction() and this function return three different enum outputs (EFV_Linear, EFV_Sigmoid, EFV_Default), and for my current CT image I get the the EFV_Default value.

I looked into the standard documentation, and I found that a VOI LUT function can have one of three values (LINEAR, LINEAR_EXACT, SIGMOID), and they mention that LINEAR in the default one when (VOI LUT Function) attribute is absent, I'm confused, what is the matching one for DCMTK's EFV_Default enum

PS: I'm dealing with CT images.

Solution

AFAIK, EFV_Default is the enumeration literal expressing "not set to a well-known value yet", e.g.:

in (default) constructor
when reading a monchrome image for which the VOI LUT attributes are not present

It might e.g. be used to trigger calculation of a window from the image's histogram.

So you should not set this value explicitly but read it as an indication whether the pixel data is non-linear (explicitly set), linear (explicitly set) or linear (by default).