The Print Management Service Class supports two grayscale transformations and spatial transformations that converts an original image into a printed image.
The sequence of spatial transformations (e.g., magnification and merging of annotation with images) and their relationships with the grayscale transformations are implementation specific and fall beyond the scope of the DICOM Standard.
The sequence of grayscale transformations is important for achieving consistent image quality because of the non-orthogonal nature of the different transformations. Figure H.2-2 describes the sequence of grayscale transformations.
Note: This section previously described Modality LUT and VOI LUT transformations in more detail. Since Referenced Print SOP Classes have been retired, these descriptions no longer apply to the Print Management Service Class. See PS 3.4-1998.
[pic] Figure H.2-2 PRINT MANAGEMENT DATA FLOW MODEL
Examples of these transformations are Modality LUT, Mask Subtraction, and VOI LUT.
The Modality LUT transforms manufacturer dependent pixel values into pixel values which are meaningful for the modality and which are manufacturer independent.
The VOI LUT transforms the modality pixel values into pixel values which are meaningful for the user or the application. For example it selects of a range of pixel values to be optimized for display, such as soft tissue or bone windows in a CT image.
Polarity specifies whether minimum input pixel values shall be displayed as black or white. If Polarity (2020,0020) is NORMAL then the pixels will be displayed as specified by Photometric Interpretation; if Polarity is REVERSE then the pixels will be displayed with the opposite polarity as specified by Photometric Interpretation.
Polarity (2020,0020) is an Attribute of the Image Box IOD.
The Presentation LUT transforms the polarity pixel values into Presentation Values (P-Values), which are meaningful for display of the images. P-Values are approximately related to human perceptual response. They are intended to facilitate consistent display with common input for both hardcopy and softcopy display devices and be independent of the specific class or characteristics of the display device. It is used to realize image display tailored for specific modalities, applications, and user preferences
In the Print Management Service Class, the Presentation LUT is part of the Presentation LUT IOD.
Hardcopy devices convert P-Values into optical density for printing. This conversion depends on desired image D-max and D-min. It also depends on expected viewing conditions such as lightbox intensity for transparency films. The conversion to printed density is specified in the Presentation LUT SOP Class.
If the modality desires to natively specify P-Values as its output, it can negotiate for support of the Presentation LUT, but specify a LUT that is an identity function. The identity function informs the display device that no further translation is necessary.
Note: Performing this translation in the printer prevents potential loss of precision (detail) that would occur if this translation were to be performed on many of the existing 8-bit modalities.