transparency

In more detail

Everything on a page is laid down in order, and what is laid down last normally hides what was under it. Transparency is how much of the older colour is still allowed through: none of it, all of it, or anything in between.

A second setting says how the two colours are to be mixed once they meet. One of those ways is how a highlighter pen behaves on paper: the ink darkens the words rather than covering them. Both settings are stated once and hold for everything drawn afterwards, until they are taken off again.

What it does on a real document

This is what lets a mark be laid across a whole page without touching a word of what is under it, and a highlight be a highlight rather than a blot. Nobody has to work out what the mixed colour would be and paint that instead.

A picture brings its own. A photograph cut out of its background arrives with a record of which of its parts are see-through, and that record travels into the document as it stands, so the corners of a logo do not come back as a white square.

Where it comes from, and why

The format had none of this for its first eight years: a page was opaque marks in order, and a designer who wanted a fade sent a photograph of one. It arrived in 2001, and printing works spent years flattening it back into ordinary marks before putting a file on a press, because their own equipment was older than the idea.

See it on a finished document

Transparency and blend modes One rectangle, four masks