Prepress proofing
[5] If errors are found during the printing process on press, correcting them can prove very costly to one or both parties involved.
The main objective of proofing is to produce either a soft or hard copy of what the final product will look like on press.
These systems produce each of the process colors on a separate sheet of clear film and then register them together to view the final proof.
The Ozalid division of General Aniline and Film (GAF) Corporation created Ozachrome[9] as the first commercial system used in proofing.
Basically, sheets of clear polyester were coated with UV-sensitive pigmented emulsions in the four process colors, cyan, magenta, yellow and black.
The sheets were exposed to the artwork via a carbon arc lamp, washed with water and process chemicals, and then dried.
After the end of World War II, the first commercial system, called Watercote, was introduced by the Direct Reproduction Corporation.
In the early 1960s, several attempts were made to develop electrophotographic proofing processes based on the electrofax principle, using paper coated with zinc oxide in a resistive binder as a photoconductor, along with toners consisting of ink pigments dispersed in liquid isopar.
The electrofax principle was introduced in the United States by RCA, and the use of liquid toners was developed in Australia by Ralph Metcalf and Robert Wright of the Australian government.
By 2003, soft proofing emerged using well-calibrated and profiled computer displays under highly controlled viewing conditions.
This approach continues to gain in popularity due to the much lower cost and lesser production time than producing a hard-copy proof.
The major problem is the difference of color spaces (RGB in monitor and CMYK in print), and this is solved by using ICC profiles for input and output devices.
The use of soft proofs in low end printing has become prevalent in recent years allowing for a time and cost savings where color management is not crucial.
It is further divided into five general classifications [13] Blueprint (originated from conventional platemaking) is a copy printed in one color and used for checking and correcting mistakes in contents, imposition layout and completeness of data.
Performing this proof makes it possible to recognize different raster-dependent effects such as smoothness, grade and range of tonal gradations, and moiré or rosette patterns.
The proof is produced via color donors and thermal transfer (ablation) onto intermediate carriers or onto the substrate used for the print run.
The true proof systems use color foils that are to be processed in separate units (laminators), transferred from intermediate carriers onto production paper and/or laminated, either to protect the proof or to give it the appearance of the surface structure of production paper.
Increasingly, however, printers rely on scientific methods, as it is often more cost-effective to buy the necessary technology than to acquire, train and retain skilled artisans.
[14] Typically, one would align the press with the proof when one is trying to achieve a particular industry specification (i.e. Fogra,[15] GRACoL,[16] SWOP,[17] etc.).
Once optimized, a final set of measurements are made of output samples and this data becomes part of the baseline information.
During calibration, device settings may also be changed to achieve an optimal output process and subsequent color match.
Doing this accurately requires well controlled and repeatable processes (including calibration), in order to ensure that the color profiles continue to represent the devices involved.
This can be very difficult, or impossible to do effectively using inkjet printers, so typically laminate processes such as Kodak APPROVAL or Fuji FINALPROOF are needed, so that the proof can be transferred to the preferred packaging materials.
