Soft proofing is a concept, which allows reproduction of color as printed by a printer on a display. This would reduce the time required to get the approval from the clients and could help in reduction of wastage of paper and resources required for generation of hard copy proofs.
Previously soft proofing was only used for content purposes. But with the advancement in the band width, digitalization of graphic arts workflow, as well as the need to decrease workflow processing times have led to increase in use of soft proofs even for color critical print jobs. The paper involves the study of a workflow to perform soft proofing. Establishing a platform to achieve remote soft proofing is even more complicated, as the conditions under which the client is going to view the soft proof is uncertain. The paper deals with all the issues and difficulties that need to be taken care of in order to set up an effective soft proofing system.
Introduction of Soft Proofing
The most important goal of Color Management is to make color predictable. In order to achieve this objective, image that is printed should appear as close as possible to what is displayed on the screen.
Rather than printing a test proof and consume paper and ink in order to get the proof approved by the customer, soft proofing is a digital process whereby computer monitor screen can be used to preview things like proper color assignments, overprints, separations, transparency, and similar issues that might cause problems on printing devices.
In order to study the workflow of a soft proofing system thorough understanding of the display device and the printer used is required.
Study of Display Device
Proper monitor calibration is the first step in the process of accurately proofing the image prior to printing. White Points, Black Level, Contrast, Color Saturation, and Hue all play a part in determining the monitor’s ability to reliably portray the image, as it will look once printed. All of these parameters must be in precise balance to each other in order to present an accurate prediction of the final output.
The main goal of calibration and profiling a device is to bring it to a known and predictable state.
There are several ways of calibrating the display device. Some of them use profiling packages that come bundled with the monitor. Some use visual calibrators. For this paper, a standalone instrument-and software bundle was used to calibrate and profile the display device.
Apple Cinema Display was used as the display device, where as GretagMacbeth’s EyeOne Monitor was used to calibrate and profile the device.
GretagMacbeth’s EyeOne Monitor is an emissive spectrophotometer and is hung from the display device. It records the spectral data of all the patches that the monitor displays and uses this data to create a profile for the monitor.
Before proceeding with the actual profiling, some calibrations settings need to be selected. These settings are as follows:
Target white point: Target white point is an important parameter that has to be selected as our eye judges all the colors relative to some neutral baseline that the eye considers white.
It is known that our eye works best when operating in an environment with white point which we are most familiar with (daylight). The two most commonly daylight standards are D50 and D65. In the graphic arts industry, the most common standard viewing conditions is D50. When D50 is selected as the white point of the display, the output of the blue channel has to be limited, which reduces overall brightness and the dynamic range. This makes the monitor to appear too dim, and yellowish. For this reason, D65 is selected as the target white point for the display screen.
Target Gamma: It has been found that gamma of 2.2 produces the smoothest display of gradients, with little or no visible banding.
Once the calibration settings have been figured out, profiling of the display device is started.
The instruction given by the profiling software was followed to create the profile.
Summary of Display ICC Profile created:
Study of an Output Device (printer)
Prior to establishing color predictability in a printer, it must be ensured that the printer is stable. This is to say, that given the same input, the printer should be able to produce same output. To ensure this uniformity, the environmental conditions such as temperature, humidity must be standardized. Once the printer becomes repeatable, then only can its predictability be implemented.
Parameters that can affect the repeatability of the printer are as follows:
- Substrate
- Ink/toner
- Temperature
- Humidity
- RIP settings like screen ruling, screen frequency, printer profiles, etc.
- Other non-assignable causes
The basic steps of creating a profile for an output device, as are follows:
Characterizing of the printer: A test form containing many patches having different colors are printed. The test form contains known digital values of CMYK. It is ensured that no color management is done at the RIP. This is to make sure that the printer is using its full gamut. Moreover no tone reproduction curve must be applied on the RIP.
Before printing the test form, the press needs to conform to some specification which includes aim points and tolerance for solid ink densities and tonal value increase (dot gain) for all the colors (eg ISO 12647-2).
Profiling: Once the test form is printed, profiling software like ProfileMaker can be used to create a profile. A spectrophotometer is used to read the spectral values of all the color patches (1617 patches in IT7.8/4). These are then converted into device independent color space (CIELAB). Look up tables are then created which can be used to convert from CMYK to LAB and LAB to CMYK values. The profile created represents the full gamut of the printer. The instructions on how to create a printer profile are very easy to follow.
The profile is dependent on the substrate. Thus the profile should be created using the substrate, the print of which the display would be simulating.
Moreover other external factors like temperature, humidity and internal factors like colorants, must be consistent, as this is necessary for the repeatability of the printer.
Remote Soft Proofing – Issues, Difficulties, and Future
There is a difference in soft proofing and remote soft proofing. The in-house prepress department does soft proofing. Since it is done in house, all the variables/parameters that can affect the outcome of the soft proof are under control and more importantly standardized. It becomes easy to predict the appearance/color of the image based on the soft proof, as it is always viewed under the exact same condition.
But when it comes to remote soft proofing, since the conditions at the client side is unknown, remote soft proofing really becomes a challenge. Moreover even if the viewing condition at the client side is standardized, there could still be some variability due to some random errors. Moreover along with the PDF of the document, the printer profile needs to be communicated at the client side. Thus if a new printer profile is created and is not communicated, there would some differences between the actual print and the proof. Moreover, the client also needs to have a very expensive calibrated, and profiled monitor (having a gamut at least same as the monitor on the printer’s side or more).
Assuming, that the client has all the right equipments to reproduce the colors on their display, they should also have a facility where they could write comments to approve the document. Some software vendors provide this facility where remote soft proofing is done via a web based portal.
Although all the technologies to carry out soft proofing exists, there are many steps where either the printer or the client can make a mistake which would ultimately result in mismatch between the approved soft proof and the actual print. Since the printer has no idea about the viewing condition at the client side, and if the client does approve the soft proof, there could be a difference between what the printer sees at their department and what the client sees. This difference cannot possibly be communicated.
Soft proofing can only be used for jobs that are printed to standard paper using standard inks. It cannot be used if the substrate used is some special paper having some prominent texture or other physical properties. Even with usage of special inks like metallic inks, since the interaction between the substrate and ink cannot be predicted the remote proofing system would fail.
Conclusion
Establishing an accurate soft proofing system involves satisfying a lot of stringent conditions. Technologies and color management tools are already present using which an effective system can be set up. But these systems have variables, changing any one of them could affect the outcome of a soft proofing system. Thus proper training is required for setting up and using such a system.
With such a system in place, it would be possible to reduce the time required to get the approval from the clients and could help in reduction of wastage of paper and resources required for generation of hard copy proofs. Any number of proofs can be sent to different people, and their approval/comments can be received simultaneously. This would help is reduction of job turn around time both for the printer and the client especially for off shored printing jobs.
Steps involving set up of a soft proofing system are calibration, profiling, and linking of profiles. But all of these steps involve a number of variables. Thus proper communication of each setting is required. Moreover, the printer and the monitor must be stable, repeatable. Only then would it be possible to make them predictable.
There are some limitations of such a system like usage of spot colors, metallic inks, special papers, etc. But for most conventional jobs including ones requiring color accuracy can be proofed digitally. It is also to be understood that 100% match is never possible between the display and print, as they use different technologies to reproduce colors, use different primaries. Even a hard copy proof would not match 100% with the final print.
Since the cost for generating a hard proof is very less compared to huge quantity of the actual print, generally customers want to approve a hard copy rather than a soft copy, since the customers have less faith on soft proofing.
But the mindset of people is slowly changing as they become more and more aware of the technologies. Slowly but steadily the number of jobs that are approved based on only soft proofs are increasing.
So it very important to understand each of steps in establishing a platform to carry out soft proofing and also the functionality of each of the parameters that can affect the output of the soft proofing system.
