The Presentation LUT operation applies only to grayscale values.
The Presentation LUT transformation transforms the pixel values into P-Values, a device independent perceptually linear space as defined in PS 3.14 Grayscale Display Function Standard. It may be an identity function if the output of the VOI LUT transformation is in P-Values.
Note: If the Presentation LUT and VOI LUT step are identity transformations, and the Mask Module is absent, then the output of the Modality LUT must be, by definition, P-Values.
No output space other than P-Values is defined for the Grayscale Softcopy Presentation State Storage SOP Classes.
In the case of a linear transformation, the Presentation LUT is described by the Presentation LUT Shape (2050,0020). In the case of a non-linear transformation, the Presentation LUT is described by the Presentation LUT Sequence. The rules for application of the Presentation LUT are defined in PS 3.3 Softcopy Presentation LUT Module.
Notes: 1. Since the grayscale transformation pipeline fully defines all transformations applied to the stored pixel values in the referenced image object, the value of Photometric Interpretation (0028,0004) in the referenced image object is ignored and overridden. This implies that either the creator of the presentation state chose a pipeline that reflects the Photometric Interpretation (0028,0004) , or chose to ignore or override the Photometric Interpretation, and invert the image relative to what is specified by Photometric Interpretation. If the Modality LUT and VOI LUT do not have a negative slope, one can achieve the effect of inversion of the polarity of an image by choosing Presentation LUT Shape of IDENTITY or INVERSE that displays the minimum pixel value as white rather than black in the case of a Photometric Interpretation of MONOCHROME2, or black rather than white in the case of a Photometric Interpretation of MONOCHROME1. If Presentation LUT Data is sent, then one can invert the value of the entries in the LUT table to achieve inversion of polarity.
2. The minimum P-Value (zero) always commands that the lowest intensity be displayed.
3. No separate Polarity transformation is defined.
A Softcopy Presentation LUT Module is always present in a Presentation State. If a Presentation LUT is present in the Image then the Presentation State Presentation LUT shall be used instead of the Image Presentation LUT.