Application Proposal and Technology Exploration of Digital Proofer Simulation Proofing (II)

The establishment and control of the simulation conversion chain

From the perspective of digital workflow, simulation is the color space conversion, and its flow structure is: RGB input color space → simulated color space → proofer color space. It can be seen that its characteristic is that in the conversion from the RGB color space to the color space of the CMYK proofer, a "constrained" color space is inserted, and it is used to describe the color gamut characteristics of various printing and other color reproduction so that the color gamut is comparable. The large proofing effect simulates the appearance of other color reproduction methods with a relatively small field of excellence. For example, according to various color processing software support methods and processing methods for this color process, there are several types of establishment and control.

1. The formation and use of simulation conversion chain based on professional proofing system

Take Best Screenproof as an example. In the dialog box of Figure 3(1), there is a so-called “reference profile” which is used as the simulated color space in the simulation flow, and “paper profile” is used as the proofer color space (actual The basic linear, printer linearity, and total amount of ink corrections are also combined with this paper profile.) It can also be seen from the figure that, for various paper sizes and different output resolutions, manufacturers have given different paper profiles and their supporting basic linearity. The reference profile and its corresponding space conversion algorithm (including single bidirectional) are also set here. The simulation profile includes representative profiles for each space of CMYK, RGB, and L*a*b*.
According to the above simulation method, if it is the simulation of the appearance of various types of printing colors under standard conditions (paper, ink), the “Reference Profile” will be placed in the profile corresponding to the printing process, such as EuroCaleCoated, USWebUnCoated, etc., and “Paper Profile. ” It is necessary to select paper, ink, and built-in or home-made profiles that match the current output. In this way, you can use the fixed simulation process inside Best Screenproof to form a color simulation proof. If you use non-manufacturer-specified paper and ink, the key is to output the paper, ink (and resolution) environment, use Best Screenproof for basic linearization, ink volume settings, and colors such as Profilemaker. With the help of the management software, a homemade paper profile is generated using the colorimeter and IT 8.7 proofs. In addition, the color gamut of the proofing ink should be larger than the printed gamut that is being simulated, otherwise colors outside the gamut will inevitably fail to be simulated.

2. The formation and use of simulation conversion chain based on color management software

Taking ProfileEditor as an example, the formation of the proofing chain can be performed with a well-functioning ProfileEditor. Figure 3(2) shows the software running from the RGB color space (sRGB) to the simulated color space (US WehUncoated) to the proof color space ( A process editing process for Best. It can be seen that the simulation space is used to set the Profile to be simulated such as a printing process, and the latter is to set the Profiler's own profile. It can also set the mapping methods (Relative, Absolute, etc.), and use the screen display to preview the process effects. It can even be improved by editing and editing various parameters such as white point and mapping curve of the output profile. effect. After the determination, it can use the standard ICC Profile, ICC Device link Profile, Photoshop Table format to save the simulation chain, the function is very powerful.

It should be noted here that the color management software generally does not have the control of the proof output, so the simulation profile generated by it must be embedded in the color flow that has specific control over the proof output. Such as the above Best Screenproof proofing process and proofing processes such as Photoshop, CorelDRAW and other universal prepress software.

3. The formation and use of application-based conversion chains

In general prepress software such as Photoshop, CorelDRAW, etc., there are built-in color management process control functions with different functions. In Photoshop, the color management process for proofing paper has only a simple secondary conversion structure based on the PCS (L*a*b*) space, namely RGB→L*a*b*→CMYK. Therefore, if you use Photoshop as a proofing output platform, the key is to obtain or make the composite profile for simulation proofing as described above, and place it in the CMYK Profile setting item of the color management dialog box.

In CorelDRAW, there is a more complex color management flow control as shown in Figure 3(3), which can directly provide the proofer simulation output flow marked with a red line as shown in the figure. It first converts the L*a*b* color values ​​to the CMYK printing color space, and then converts it to the color space of the proofer and outputs it. Therefore, it is not necessary to use other software in advance to create a composite profile, and the key is to obtain the CMYK printout of the simulation and the correct profile of the proofer.

4. Control of mapping methods on the simulation conversion chain

Regardless of the above-mentioned conversion chain, the simulation flow is CMYK (Printing)→L*a*b*→CMYK (Proofing) if the proofing effect of the printing under various printing conditions is simulated according to the standard proofing environment. This process is a process that shifts from a smaller color space to a larger one (a larger proof color space is a prerequisite for simulating various effects). One of the important issues is that the white point (ie paper white) of the CMYK (printing) space must be completely imitated to the proofing effect by using the so-called "absolute" mapping method. For example, if newsprint paper with yellow or grayish-blue newsprint is proofed with standard ink, Absolute is used to transfer newsprint paper whiteness to proofing paper, and other methods (Relative, Sataration, Perceptual) cannot This background color simulation is performed better.