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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.

marc_s
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ZSmain
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    Please stick to one question per post. The second question is not only confusing as it's currently written, but also appears to be unrelated to the first one. – E_net4 Oct 01 '18 at 11:48
  • @E_net4, thanks I'll change it according to your recommendation. – ZSmain Oct 01 '18 at 11:59

1 Answers1

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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).

Markus Sabin
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  • So, how can I make that transformation having that `EFV_Default` enum return from `getVoiLutFunction()`. – ZSmain Oct 01 '18 at 14:10
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    The same you would do it if you found the value LINEAR. – Markus Sabin Oct 01 '18 at 14:22
  • Thank you very much, now I understand that it's up to me to chose the transformation function whether it's linear or segmoid or else if there is an else? – ZSmain Oct 01 '18 at 14:41
  • Yes, up to you or to the user. Depending on the type of image you might find the attribute Pixel Intensity Relationship (0028,1040) telling you whether the raw pixel data is in linear (LIN), logarithmic (LOG) or anything else (OTHER). See https://dicom.innolitics.com/ciods/rt-image/rt-image/00281040 – Markus Sabin Oct 02 '18 at 06:09
  • that attribute (Pixel Intensity Relationship) is for RT images and I'm dealing with CT images, I thought that the only attribute that determines the way of transformation is just VOI LUT function! – ZSmain Oct 02 '18 at 12:49
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    Yes, might not be applicable. This is what I was trying to indicate with "depending on the type of image". CT comes in 2 flavors: "Traditional" CT and Enhanced CT. – Markus Sabin Oct 02 '18 at 13:33
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    Right, according to the documentation of EF_VoiLutFunction, EFV_Default means "default function (not explicitly set)". – J. Riesmeier Oct 02 '18 at 15:32