Pre-Press Colour Proofing for Offset Printing

woman checking a printed proof




Proofing is an important part of any print job as it shows the printer and client what the finished job will look like. Providing an accurate proof allows for corrections to be made before going to press, but proofs also have other uses. This article will provide a bit of insight into pre-press colour proofing for offset printing.

What is a Print Proof?

A print proof or pre-press proof is a prototype that provides a representation of what your work will look like when commercially printed using the offset printing method. Your computer screen doesn’t always give a true representation of the finished work, so to send work out and be confident of what you’re going to get back, you’ll need to produce a printed proof.

A proof is the closest thing you’re going to get before seeing the finished product.

Proof Uses

Screen Proofing

Screen proofing is the least accurate of all the proofing methods and should only be used for initial concepts and mock-ups. Remember that there is a big difference in the way colour is reproduced for digital screens and the litho printing process. See my article When to Use the RGB or CMYK Colour Models for more on this.

Digital Proofs

Digital proofs are printed out on paper directly from a computer data file. There are a number of digital printing methods, including:-

  • Thermal transfer
  • Dye Sublimation
  • Laser and ink-jet prints

Digital proofs usually give a reasonable representation of the finished job. You may find however, that because the proof isn’t made on the equipment the printer will use, or from film that will be used, that they are unlikely to be accepted as proofs to work from.

Proofs for Client Approval

A colour proof for a client’s approval needs to be a reasonable representation of the final job. When approved, it becomes a guide for the machine minder to use during makeready. This is when they adjust settings to produce a printed sheet to check against during the print run.

It might be difficult for the machine minder to match, if the proof doesn’t match the printing charcteristics.

Compatibility Proofs

Printers of magazines and other periodicals have another important use for pre-press proofs. They receive material for advertisements from many different sources, made by different processes for reproduction with different inks on different machines and papers.

The printer needs to proof each item for compatibility with his own machine, paper and inks. It is much cheaper to remake material and achieve compatibility before going to press than to discover problems during the print run.

Other Proof Uses

  • Digital bureaus and repro houses use colour proofs to give the client a guide for final printing.
  • Publishers use proofs for checking editorial and advertising colour. These proofs are used as quality guides for printing.
  • Advertising agencies sometimes use them in large quantities for distribution to clients and printers.
  • Newspapers use them for checking advertising.

Press (Machine) Proofs

A press or machine proof is an actual printed sample of how the print job will look when printed on a similar if not identical printing press and conditions. Many people believe press proofing will look exactly like the finished job. This is unfortunately not true as printing presses are different in design and performance. Even presses of the same design may differ in ink transfer.

The variables that affect the printing process include:-

  • The human element
  • Ink – water balance
  • Roller and cylinder pressure
  • Roller and blanket composition and condition
  • Paper and ink

It is almost impossible to reprint a set of printing plates with the same inks and paper and get the same result.

A press proof is therefore no guarantee of the appearance of the finished job, but probably the closest approximation.

Evaluation of Colour Proofs

The main difficulty in evaluating colour proofs is that exact reproductions are impossible. These problems are especially difficult when attempting to match a colour transparency. It is impossible to reproduce the brilliance and tone of a strongly illuminated transparency.

Problems encountered when evaluating proofs

  • The original may have colours that are imposible to reproduce with printing inks.
  • Viewing conditions differ.
  • Personal preferences vary for certain hues of memory colours such as skin, grass, sky and foliage.
  • Colour changes have been made intentionally.

How to Compare Pre-Press Proofs and Press Prints

The final decision still rests on the visual perception of the client, even if every physical measurements is made. This is one of the most difficult aspects in comparing proofs with the printed job.

close up of printer registration mark and color swatches on paper
image by – gratuit

The human eye is a very accurate organ and a precise measuring instrument when used to compare two similar objects under the same conditions. The difficulty comes in that there are no common physical or mathematical units in which to express visual differences with any accuracy.

People usually find it difficult to express the differences they perceive.

The Keys to Success

  1. Print characteristics need to be determined and stabilised.
  2. Implementation of ways and means to control colour proofs.
  3. There must be an understanding of how to compare proofs and print. This area is the most difficult, but some methods may include:-
  • The solid ink densities to be used at specific thicknesses.
  • Colour scales and bars should print so that visually all the overprints of solids and tints have the correct hues and strengths.
  • Overprints of solids have the same relative dot gain as the press print will have.
  • Examinations and comparisons must be made under standard viewing conditions.
  • The client and printer must agree on realistic tolerances.

Wrapping Up

Avoid costly mistakes and discuss acceptable colour proofing methods with your printer before preparing print-ready artwork or sending a job for print. This will ensure that everyone involved in the production process has a reference to what the finished job should look like.

Please feel free to contact us if you need help or advice on proofing for offset printing. Visit our home and services pages for more about us and what we do.

Cimeron Collins

Cimeron Collins

Cimeron is an artist and designer who lives in Edenvale, South Africa. He has more than 30 years experience in the printing and publishing industries.

He is an avid WordPress enthusiast and passionate about learning and experimenting with new developments and technology in website design and development.

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