Halftone
A halftone is a photographic-like image formed by a pattern of discrete-sized dots to create the illusion of a true photograph or continuous tone image. Dots in conventional halftone vary size to give the illusion of darker or lighter shades.
Left: Halftone dots.
Right: How the human eye would see this sort of arrangement from a sufficient distance.
Screen Ruling (LPI)
The resolution of a halftone screen is measured in lines per inch (lpi). This is the number of lines of dots in one inch, measured parallel with the screen's angle.
CMYK color model
The CMYK color model (aka process color, four color) is a printing process as well as a subtractive color model used in offset color printing. CMYK refers to the four inks used in some color printing: cyan, magenta, yellow, and key (black).
Typical four colour inks in offset printing: cyan, magenta, yellow, and key (black)
Combination of the CMY “primaries” at full strength results in the “secondary” mixtures: red, green, and blue. Mixing CMY results in a dark brownish gray color.
Dot Gain
Printed materials in offset lithography and some other forms of printing look darker than intended because of this phenomenon. Dot gain occurs because halftone dots grow in area between the original printing film and the final printed result.
Proofs
Proofs are the last opportunity to evaluate graphics and structure prior to printing. Proofs can be made using a wide range of imaging technologies and papers. They not only illustrate color and graphics but show final size, text and image placement on the package.
Digital Proof - A digital proof is a color prepress proofing method where a job is printed from a digital file using a computer printer. Digital proof is often less expensive and with shorter lag time than press proof, It also gives a good approximation of what the actual printed piece will look like.
Press Proof - A press proof is a sample of printing that involves running a proof with printing press, plates and inks on actual paper for checking purpose. It is the most accurate way to preview the output of a commercial print job in terms of images, tone, colors and impositions. The colors approved by the customer in the proof are expected to be rendered identically in the finished job.
Die-line
A die-line is a full size drawn image matching the cutting die, hence the name "die line". It is drawn on a transparent polyester film or in a electronic file that provides accurate measurements for the final cut structure. Press and die-cut operators use these to determine print to sheet and cut to sheet positioning.
