Weighting Transfer Function Sequence Attribute
| Tag | (0070,1806) |
|---|---|
| Type | Required (1) |
| Keyword | WeightingTransferFunctionSequence |
| Value Multiplicity | 1 |
| Value Representation | Sequence (SQ) |
Transfer functions used to derive the weighting factors for each of the two RGB inputs from both input Alphas. Each function is represented by the formula
f(Alpha1,Alpha2) = WeightingFactor
The function is specified in the form of a table.
Two Items shall be included in this Sequence.
The order is significant. The first Item specifies the weighting factor for RGB1 and the second Item specifies the weighting factor for RGB2.
See Section C.11.27.4.
Section C.11.27.4
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.