The VOI LUT operation applies only to grayscale values.
The value of interest (VOI) LUT transformation transforms the modality pixel values into pixel values that are meaningful for the user or the application.
Note: Photometric Interpretation (0028,0004) is ignored, since its effect is defined by the application of the grayscale transformations.
The Softcopy VOI LUT Module in the Presentation State is analogous to the VOI LUT Module in an Image.
In the case of a linear transformation, the VOI LUT is described by the Window Center (0028,1050) and Window Width (0028,1051). In the case of a non-linear transformation, the VOI LUT is described by the VOI LUT Sequence. A VOI LUT Function (0028,1056) may be present to define a potentially non-linear interpretation (e.g., SIGMOID) of the values of Window Center (0028,1050) and Window Width (0028,1051). The rules for application of the VOI LUT are defined in PS 3.3 Softcopy VOI LUT Module.
The VOI LUT may have sections with negative slope.
Note: In the Basic Print Service Class a VOI LUT may not have negative slope.
If a VOI LUT is part of both the Image and the Presentation State then the Presentation State VOI LUT shall be used instead of the Image VOI LUT. If a VOI LUT (that applies to the Image) is not present in the Presentation State , it shall be assumed to be an identity transformation. Any VOI LUT or equivalent values in the Image shall not be used.