Full Idea
In the case of millions of pixels making up a picture on a computer screen, the supervenience is reduction.
Clarification
'Supervenience' is the total mapping of one thing onto another
Gist of Idea
Where pixels make up a picture, supervenience is reduction
Source
David Lewis (Lewis: reduction of mind (on himself) [1994], p.414)
Book Reference
'A Companion to the Philosophy of Mind', ed/tr. Guttenplan,Samuel [Blackwell 1995], p.414
A Reaction
Since 'supervenience' seems a suspect relationship about which no one is clear, this is a point very much worth making.