Application Analysis of Color Proofing (I)

For the printing process, it is impossible to accurately reproduce the colors that the natural world can see, the colors captured by the camera, or the colors seen on the computer screen. Because of the limitations and variability in color reproduction, color proofing is often used to simulate and predict the ultimate appearance of a print. Color proofs are an essential tool for communication and quality control used by artists, producers, customers, and printers. Their role is to preview image features during color reproduction. Today, with the diversification of proofing systems and available technologies, it is important to understand the process used and the reasons for its use. It is a very correct proof for the designer and may not be suitable for the printing staff.

The proofing techniques available on the market today have changed dramatically in their ability to simulate and predict the color of printed proofs. In order to accurately simulate colors, the specific properties of color proofs are very important. These properties include color, density, dot gain, and image resolution. Most valuable proofing systems approach these property features in a stable and predictable manner. Therefore, you must use the same set of specifications when you make your proofs to prevent unrealistic effects. Various industry associations in the world have now established proofing specifications for specific printing processes.

Proofing a job often starts with the computer screen in the design process. In the printing workflow, color proofs may exist in the form of digital or analog copy. A qualified proof can be output on a digital proofing device, or it can be color proofed from a color separation film in a conventional manner, in the form of a superimposed polyester coated film, or in the form of a single overprint. Because each type of proof has a different use, accuracy, and cost level, it is not surprising that the printing operation uses different proofing systems to do the proofing to suit their workflow.

(a) Soft Proofing (Screen Proofing)

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Soft proofing proofs display image effects on the display screen to predict the color and content of the image when printed. The display color gamut of the display screen is very different from the printing process, so this proofing form is an inaccurate color communication tool. The main reason is that the computer display uses the RGB color light mixture method to display the image's effect, which is in accordance with the color light additive theory; and the print proofs use the yellow, magenta, and cyan three-color inks to superimpose on the paper to meet the color reduction. theory.

Ambient lighting conditions around the monitor are important for accurate color estimation. Ideally, the display we use should be in a wall of neutral gray with no reflections on the surface of the display. Unrelated colors that can be seen by any operator around the display, including the operator's clothing, can affect color vision.

If we use the display to proof any part of the job, we often need to calibrate our monitor. The color gamut of the display will change over time due to the lifetime of the electron gun, phosphor, and environmental factors. The use of screen calibration (setting screen gamma and white point) can help maintain more stable color reproduction. In addition, by characterization of the display and the printing process, the color gamut of the screen can be forcibly changed to be closer to a given offset printing process. In the absence of other proofing forms, this situation can help minimize the difference between the screen and the final proofs to reduce disagreements and minimize the waste of time and materials. In the color management chapter, we can learn more about this.

(2) Position proofing positions Proofing proofs are obtained from color separation films or digital files and are basically used to detect the composition of a job. These proofs are used to detect content, registration, color bursts, and spot color locations. Position proofs include continuous sample proofs, blue line proofs, and laminated proofs for photo effects. Digital proofing systems that can only be used to display colors without having the ability to accurately predict press print results can also be used for location proofing. These systems generally have the advantages of speed and cost.

(3) Contract Proofing The name of the proofing form has already demonstrated its role in the process of color communication. A proof sheet can be a digital proof from a digital file, a camera-based offline proof from a color separation sheet, or a print proof on a printing press. A copy of the same sheet must be accepted, must comply with the printing industry recommended operating specifications, and do not have to consider making it use what kind of technology.

The most useful combination of the same sheet is also called the final proof sheet, which simulates and predicts the appearance of the printed image (a sample sheet obtained from a digital file or a set of film separation sheets). The same sheet provides a color range that falls within the copying range of the printing press. Keep in mind that the printing process of two sheetfed presses in the same facility may be somewhat different, and the presses are also changing during the printing of the job. Once proofs have been accepted, it is a yardstick for users to print.

* Simultaneous simulation of the same sheet and the same sheet is the customer-recognized copy effect from the same set of color separation sheets used in the printing plate. First, the halftone image on the color separation film is made by the camera and copied onto the pre-colored material of the separate proofing material. Then, different color layers are superimposed on the paper by registration to produce a single-sheet proof product.

Many proofing manufacturers offer a choice of primary colors and receiving materials to accommodate combinations of different ink color, density, dot gain, and some spot color printing specifications. The stability of the simulation proofs lies in the regular and precise calibration of the proofing system and the use of the COLOR BAR or exposure control tool on each proof. Samples should have a cover page stating the name of the product used for proofing.