Previous Next

                                                                                  544
     CHAPTER 7                                                                          Transparency



7.3.7 Summary of Group Compositing Computations

     The following restatement of the group compositing formulas also takes isolated
     groups and knockout groups into account. See Tables 7.7 and 7.8 on pages 534
     and 536 for the meanings of the variables.
        〈 C, f, α 〉 = Composite (C 0, α 0, G )

     • Initialization:
        fg = αg = 0
          0    0

       α0 = 0                               if the group is isolated

     • For each group element Ei ∈ G (i = 1, … , n):
            ⎧ 0                             if the group is knockout
        b = ⎨
            ⎩i–1                            otherwise
                             ⎧ Composite ( C b , α b , E i )                                  if E i is a group
        〈 Cs , f j , α j 〉 = ⎨
            i     i     i    ⎩ intrinsic color, shape, and ( shape × opacity ) of E i         otherwise
         fs = fj × fm × fk
           i    i    i     i
        αs = αj × ( fm × qm ) × ( fk × qk )
           i      i    i     i      i    i
        f g = Union ( f g , f s )
           i             i–1    i
       αg = ( 1 – fs ) × αg       + ( fs – αs ) × αg + αs
           i        i        i–1        i    i      b     i
        α i = Union ( α 0 , α g )
                                                    i
        Ct = ( fs – αs ) × αb × Cb + αs × ( ( 1 – αb ) × Cs + αb × Bi ( Cb , Cs ) )
                 i    i                i                   i                   i
              ( 1 – fs ) × αi – 1 × Ci – 1 + Ct
                             i
                                                                                    -
        C i = -----------------------------------------------------------------------
                                                  αi

Previous Next