Colour systems for the print process

Print vs screen

Assigning colour to adjustable document.

Subtractive

Screen

Additive

Print

CMYK vs RGB

RGB-Image on screen

Image view gamut

A typical CRT gamut.
The grayed-out horseshoe shape is the entire range of possible chromaticities. The colored triangle is the gamut available to a typical computer monitor; it does not cover the entire space. The corners of the triangle are theprimary colors for this gamut; in the case of aCRT, they depend on the colours of the phosphors of the monitor. At each point, the brightest possible RGB color of that chromaticity is shown, resulting in the bright Mach bandstripes corresponding to the edges of the RGB colour cube.

RGB red/green/blue- screen

Duotone- two colours, print with continuos tone.

Spot colour- One or more specially mixed colours.

RGB image- Image view- Gamut reading- to see the image in CMYK

In offset printing, a spot color is any color generated by an ink (pure or mixed) that is printed using a single run.

The widely spread offset-printing process is composed of four spot colors: Cyan, Magenta, Yellow, and Key (black) commonly referred to asCMYK. More advanced processes involve the use of six spot colors (hexachromatic process), which add Orange and Green to the process (termed CMYKOG). The two additional spot colors are added to compensate for the inefficient reproduction of faint tints using CMYK colors only. However, offset technicians around the world use the term spot color to mean any colour generated by a non-standard offset ink; such as metallic, fluorescent, spot varnish, or custom hand-mixed inks.

Specially mixed colours- As apposed to a result of a CYMK or RGB mix.

Mono- One colour, like greyscale (Monochrome)

Hexographic Print- Six colours

Prints different on shiny coated paper than on matte.

At the printers

Commercial print processes

Practical

Technical

Economics

Rotary printing

Planographic

Offset lithography (litho)

Rotogravure (Gravure)

Intaglio

Magazines, flooring, large scale.

Flexography (Flexo)

Relif

Different materials, plastic

Not as good quality

CYMK

Digital printing

Raster image processor

Screen print

PAD printing Transfer a 2D image onto a 3D object

What is good? Presentation

Open publication - Free publishing - More what is good

Lithography

Lithography (Offset Printing)

This is the major plate printing process. It uses thin metal plates with the image and non-image areas essentially on the same plane. There are two basic differences between lithography and other processes; (1) It is based on the fact that oil and water do not mix, and (2) is uses the offset principle in which ink is offset from the plate to a rubber blanket on an intermediate cylinder, and from the blanket to the paper on an impression cylinder.

Gravure

Gravure

Gravure is a type of the intaglio printing process that involves engraving the image onto an image carrier. Gravure printing presses two large print reels of paper together rather than sheets of paper. This type of printing is the fastest and widest printing press in operation.
It is capable of transferring more ink to the paper than other printing processes, and is also noted for its remarkable density range.

A gravure printing press has one designated printing unit for each color, commonly CMYK. While the press is in operation, the engraved cylinder is partially immersed into the ink fountain, filling the recessed cells. As the cylinder rotates, it draws ink out of the fountain with it. Acting as
a squeegee, the doctor blade scrapes the cylinder before it makes contact with the paper removing ink from the non-printing (non-recessed) areas. Next, the paper gets sandwiched between the impression roller and the gravure cylinder. This is where the ink gets transferred from the recessed cells to the paper.

The purpose of the impression roller is to apply force,
by pressing the paper onto the gravure cylinder, ensuring maximum coverage of ink. Then the paper goes through
a dryer because it must be completely dry before going through the next color unit and absorbing another
coat of ink.

Flexography

Flexography is the most common type

of printing used for packaging.

A flex graphic print is made by creating a positive mirrored master of the required image as a 3D relief in
a rubber or polymer material. A measured amount of ink (water-based, rather than oil based) is deposited upon the surface of the printing plate (or printing cylinder) using an engraved anilox roll whose texture holds a specific amount of ink. The print surface then rotates, contacting the print material which transfers the ink.

The flexible printing plate used in the final ink printing stage is light sensitive. A positive is placed over the plate, and is exposed to ultra-violet light. The plate is then ‘washed’ on rotating drum in a tank of Toluene solvent, which removes the layer of material that received the ultra-violet light.

The benefits of flexographic printing are:

• Better resolution and ability to print four color process
  (or more).
• Increased ability to reproduce highlight tonal values.
• Uses a wider range of inks, and can print on
  a variety of different materials.
• Inks have low viscosity to enable faster drying,
  which results in faster production and lower costs.

Production Methods

Rotary Printing

The three main types of rotary printingare Offset lithography (litho), rotogravure (Gravure), Flexography (Flexo)