Depending on which step in the production process you want to analyze, different categories of proofing will be considered:
Digital Proofs - reveal what is on a computer file. You might want to see digital proofs before making film. You might also want to see a digital proof when going computer to plate (CTP).
Film Proofs - reveal what is on the film that will be used to make plates.
Press Proofs - Press proofs reveal what in on the printing plates.
The following are some examples of proofing in each category:
Desktop Proof (Digital)
A laser print or inkjet printout shows low-resolution contents of computer files or portions of documents, such as photos and charts.
Use a desktop proof to check:
- text and headline type and placement
- keylines or halftone cropping, size and position
- placement of rules, reverses and tints
- crop marks for trims and folds
- production color
Desktop proofs are the most common kind of proof for quick and digital printing. Make sure you do the followings:
- print one copy for the printer and one copy for you
- show exactly how you want the jobs to be printed, collated, folded, trimmed, stapled, drilled or padded
Bluelines (Digital or Film)
Printers make bluelines on photosensitive paper with the same dimensions as the press sheets for print jobs. Operators fold and bind the sheets so you can check crossovers, backups, page sequence and graphic placement.
Use bluelines to check:
- text and headline placement
- halftone cropping, size and position
- placement of rules, reverses and tints
- page sequence
- crossovers and backups
- scores, perforations and drills
- trims, folds, and binding
Most bluelines are contact prints of plate ready film negatives, but some are digital printouts. They serve identical purposes. You may also hear a blueline called a silverprint or dylux.
Overlays (Film)
An overlay proof shows each color on a separate sheet of polyester film. Sheets are laid over each other in register and taped to backing paper. Overlay proofs for four-color process jobs have four pieces of film taped together, one for each process color, from top to bottom, black, cyan, magenta, and yellow.
Overlay proofs are inexpensive to make but have the disadvantage that the overlays themselves have a slight color cast, either yellow or gray. Looking through three or four layers can distort colors and sharpness.
Use an overlay proof to check:
- placement, trapping and register of flat colors
- please color or production four-color
- position of varnish or other coating
Integrals (Film or Digital)
Integral proofs look similar to color photographs or to finished printing done on glossy paper. Printers can match dyes an toners to inks, ensuring the best possible parallel between proof and final printed product. Some integral proofs are on the paper stock specified for the print jobs. Other proofs use proprietary material and substrates.
You car use a desktop printer to make simple integral proofs, but the best come from film or from high-end digital proofers. Digital proofs come from complex machines that require careful calibration for linearization and dot gain compensation. Integral proofs sometimes even look better than the printed product since they do not show dot gain. If made from film adjusted for dot gain, on the other hand, color in integral proofs may look too weak.
Use an integral proof to check:
- image trapping and register of process colors
- match original four-color process
Integral proofs may also be know as Rainbow, Iris, Matchprint, Cromalin, and so forth.
Press Proofs / Press Check
Press proofs come from plates put on press, inked and run on paper specified for the job. Only press proofs show the true effect of dot gain or the way in which the paper color affects ink colors. However, press proofs are costly in both time and money and are becoming less necessary since overlays and integrals are becoming more accurate.
Use press proofs to check:
- wet ink trapping
- trapping and register of process colors
- match product four-color process
- ink density and gray balance
