All printing process are concerned with two kinds of areas on the final output:
-Image of printing areas,
-Non-image or non-printing areas
After the information has been prepared for production (the prepress step), each printing process has definitive means of separating the image from the non-image areas.
Conventional printing has four types of process:
-Planographics, in which the printing and non-printing areas are on the same plane surface and the difference between them is maintained chemically or by physical properties, the examples are: offset lithography, collotype, and screenless printing.
-Relief, in which the printing areas are on a plane surface and the non printing areas are below the surface, examples: flexography and letterpress.
-Intaglio, in which the non-printing areas are on a plane surface and the printing area are etched or engraved below the surface, examples: steel die engraving, rotogravure
-Porous, in which the printing areas are on fine mesh screens through which ink can penetrate, and the non-printing areas are a stencil over the screen to block the flow of ink in those areas, examples: screen printing, stencil duplicator.
Offset printing is a widely used printing technique. Offset printing is where the inked image is transferred (or "offset") from a plate to a rubber blanket. An offset transfer moves the image to the printing surface. When used in combination with the lithographic process, a process based on the repulsion of oil and water; the offset technique employs a flat (planographic) image carrier. So, the image to be printed obtains ink from ink rollers, while the non-printing area attracts a film of water, keeping the non-printing areas ink-free.
Currently, most books and newspapers are printed using the technique of offset lithography.