アルファチャンネル
{ o u t A = s r c A s r c F + d s t A d s t F o u t R G B = ( s r c R G B s r c A s r c F + d s t R G B d s t A d s t F ) / o u t A {\displaystyle \left\{{\begin{array}{l}{\mathit {out}}_{\mathit {A}}={\mathit {src}}_{\mathit {A}}{\mathit {src}}_{\text{F}}+{\mathit {dst}}_{\mathit {A}}{\mathit {dst}}_{\text{F}}\\{\mathit {out}}_{\mathit {RGB}}=({\mathit {src}}_{\mathit {RGB}}{\mathit {src}}_{\mathit {A}}{\mathit {src}}_{\text{F}}+{\mathit {dst}}_{\mathit {RGB}}{\mathit {dst}}_{\mathit {A}}{\mathit {dst}}_{\text{F}})/{\mathit {out}}_{\mathit {A}}\end{array}}\right.}
この際、以下のように、A を RGB にあらかじめかけておくと、
{ o u t amp = o u t R G B × o u t A s r c amp = s r c R G B × s r c A d s t amp = d s t R G B × d s t A {\displaystyle \left\{{\begin{array}{l}{\mathit {out}}_{\text{amp}}={\mathit {out}}_{\mathit {RGB}}\times {\mathit {out}}_{\mathit {A}}\\{\mathit {src}}_{\text{amp}}={\mathit {src}}_{\mathit {RGB}}\times {\mathit {src}}_{\mathit {A}}\\{\mathit {dst}}_{\text{amp}}={\mathit {dst}}_{\mathit {RGB}}\times {\mathit {dst}}_{\mathit {A}}\end{array}}\right.