A digital proofing system involves printing each of the subtractive primary color components of the image (cyan, magenta, yellow), and black through the proofing device to create the full color digital proof. A digital proof can cost less than half that of an analog proof and they are produced in much less time. The different types of digital color proofing systems are sublimation, thermal wax, ink-jet, color laser, and laser thermal.

A digital sublimation system is the closest of all digital proofing methods to the analog process. Like the analog process, the transparent colorant is transferred from a sheet or roll (called ribbons) of a clear polyester base, which has been coated with the colorant. The ribbons are brought into contact with a receiver sheet and varying temperatures of heat are used to transfer the colored material in the image area to the receiver sheet. The colorant begins as a solid and then it is heated to become a gas. Once the colorant is placed on the receiver, it cools and becomes a solid again. The same procedure is completed for each color. Most systems can transfer the colorant to the actual printing stock either directly or as an additional step. A digital sublimation system requires little maintenance and provides consistent results.

There are two different types of sublimation proofers: dye and laser. The dye sublimation process uses dyes to create the color on the proof and the heat required in the proofing process is supplied by a thin pointed metal stylus. The laser sublimation process uses pigments to create the color on the proof and a laser is used to provide the heat that is required.

• Dye Sublimation
  
  Dye sublimation proofing systems were the first of the sublimation systems on the market. They utilize a series of thousands of styluses and dye based colorants, which are relatively inexpensive and reasonably fast. They have some disadvantages over other methods. The dye colors that make up the proof will fade with time and may not match the color at the press. Also, the proofs must be viewed under proper lighting conditions and the process has limited resolution.
  
  
• Laser Sublimation
  
  Laser sublimation systems were the first dot oriented digital proofing systems. They are much more expensive and are slower than dye sublimation systems, but the quality has been considered equal to the analog proofing system. Possible negative aspects of the system are that the colors can change over time and the proofs must be viewed under proper lighting conditions.

The most common ink-jet proofing systems in use are drop on demand (DOD) and continuous flow. DOD works by squirting small droplets of ink onto the substrate. A continuous flow system works with a continuous flow of very small droplets of ink directed toward a receptor base mounted on a spinning drum. In locations where color is not needed, the droplets are deflected and captured by a waste collection system.

Since the proofing substrate is much whiter and glossier than most papers, the proofs usually are of better quality than the actual printed piece. To compensate for the difference, some ink-jet systems allow a simulation of the paper to be printed on the proof by printing the paper color along with the rest of the document. Also, some systems are able to print on the same paper that will be used for printing the job on the press.

The ink-jet printers require high-quality coated or glossy paper to provide the highest quality proofs. The paper contains a base layer of paper and a second layer, which has a special coating that accepts ink. The specially coated surface allows the ink to dry instantly during printing to avoid smearing and spreading. The weight of the paper is heavy enough to avoid bleed through and curling and yet allows the paper to be folded and handled like regular printing stock.

Laser printers and copiers use a pre-charged drum or belt that conducts a charge when exposed to light. Toner is magnetically attracted to the appropriate areas of the image and repelled from others. The printer transfers the image to the paper where it is fused by heat and pressure.

Color laser copiers, interfaced with fast and powerful RIPs, are now being used by service bureaus, quick printers, and design shops as a means of producing proofs quickly. They are also used for short-run digital color printing.

The laser thermal imaging proofer is a high-end halftone digital proofing system that uses pigment-based colors to produce exceptionally high quality proofs. The substrate is attached to a drum and an inked donor sheet is place on top of the substrate. An infrared diode laser beam strikes the donor sheet, transferring the colorant from the donor sheet on to the substrate. Laser thermal imaging is one of the most popular types of proofing systems because it gives the closest match to the actual printing process.