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DICOM PS3.3 2020a - Information Object Definitions |
•Component Type (0070,1802) value of ONE_TO_RGBA specifies that of one processed input value is transformed into the RGBA output value
•Component Type (0070,1802) value of TWO_TO_RGBA specifies that of two processed input values are transformed into the RGBA output value.
The internal structure of each classification component is described in Section FF.2.3.3 “Internal Structure of Components” in PS3.4.
C.11.27.3 Compositor Component Usage
If Pixel Presentation (0008,9205) is TRUE_COLOR and there are more than one Item in the Presentation State Classification Com- ponent Sequence (0070,1801), the Presentation State Compositor Component Sequence (0070,1805) defines the transformations of the multiple RGB data streams produced by the Classification components into one RGB output stream, a process known as "compositing".
Note
IfthereisonlyoneIteminPresentationStateClassificationSequence(0070,1801),PresentationStateCompositorSequence (0070,1801) is empty since there is only one RGB data stream so there is no need to composite.
Each Item in Presentation State Compositor Component Sequence (0070,1805) describes one two-input "compositing component" inwhichtwoRGBAinputsarecompositedintooneRGBoutput.ThefirstcompositorcomponentintheSequencecombinestheoutputs of the first two classification components to produce one RGB output. Subsequent compositor components combine the output of the previous compositor component with the output of the next classification component to produce one RGB output. This process con- tinues until the RGB outputs of all classification components are composited into a single RGB output.
Each classification component produces a RGBA output, while each compositor component has two RGBA inputs to produce a RGB output.ThismeansthatallcompositorcomponentsafterthefirstintheSequencehaveonlyoneAlphainputavailable,thatistheAlpha value from the next classification component output to be composited. In this case, (1-Alpha) is used in place of the Alpha input missing from the previous compositing component.
Note
Through the use of (1-Alpha 2) as Alpha 1for the input from the previous Compositor, the Compositor performs standard Porter-Duff "A over B" compositing in all but the first compositor [Porter and Duff 1984].
The internal structure and usage of the Compositor component is described in Section FF.2.3.3.2 “Internal Structure of RGB and RGBA Compositor Components” in PS3.4.
C.11.27.4 Weighting Transfer Function
In some situations, it is desirable to consider both Alpha inputs to the compositor in determining the weight to be given to each of the two RGB inputs to the compositing operation. This is accomplished by providing two weighting transfer functions
f(Alpha1,Alpha2) = WeightingFactorn
one for each of the two RGB inputs to the compositor.
In the degenerate (and common) case where simple additive compositing (RGB1*Alpha1)+(RGB2* (1-Alpha1)) is desired, identity weighting transfer functions can be specified to just pass through the Alpha 1and (1-Alpha 1) values (or Alpha 1and Alpha 2values) to be the weighing factors for the RGB inputs.
For ease of specification of these transfer functions and for maximum flexibility, each of these weighting transfer functions is defined as a look-up table with inputs Alpha1 and Alpha2. Each LUT contains 8-bit integer values which are then normalized to the range 0.0 to 1.0 by dividing by 255 (28-1).
See Section FF.2.3.3.2 “Internal Structure of RGB and RGBA Compositor Components” in PS3.4 for details on the use of these weighting transfer functions, and see Section XXX.5 “Compositing and the Use of Weighting Transfer Functions” in PS3.17 for clinical applications.
