The "membrane" or ridge separating one gravure cell from the next. Gravure, unlike most other printing processes, prints from ink-filled cells engraved into the surface of a copper-plated cylinder. A particular gravure image is composed of a series of cells, the thickness of the cell wall being one way of varying print density. Light areas or highlights of an image are either shallow or small cells separated from its neighbors by a thick cell wall. Shadows or other dark regions are composed of many deep, wide cells with very thin cell walls. The cell walls are needed in order to provide a surface for the doctor blade to scrape against (the doctor blade is the metal blade on a gravure press that scrapes off the excess ink from the non-printing surface of the cylinder); without cell walls, the doctor blade would remove ink from the cells, or wear away the image area of the cylinder. The cell walls, along with the other non-printing areas, are collectively known as the gravure cylinder's land area. See Gravure Engraving.