The Necessity and Possibility of Soft Proofing with Liquid Crystal Monitor (Part 2)

The 3 ways of LCD

TN mode

At present, the most commonly used is a TN (Twisted Nematic) liquid crystal panel. The majority of laptop personal computers, most of which are 15-inch LCD monitors, use display boards in this way. The 17-inch class of cheap products is also a display board in this way. Applying a voltage to the pixel means that the liquid crystal, which was originally parallel to the plane, turns to have an angle, so that the color and gradation characteristics change. With the use of the viewing angle compensator, the left and right viewing angles are relatively wide, and the top and bottom of the screen are obviously different, so they are not suitable for printing process applications.

VN mode

In the 17-inch wide-angle product line, 19-inch products use VA (Vertical Alignment) display panels. When the voltage is not applied to the pixel (dark) state, the liquid crystal remains close to the vertical plane. Angle, so the dependence of the angle of view is larger. It is based on the fact that the tilt direction of the liquid crystal is complex (multi-domain), and the influence is eliminated. As the viewing angle is expanded, the displacement of chromaticity is suppressed, and the displacement of the gradation characteristic is also present. The level used for printing process uses.

IPS method

In the IPS (In Plane Switching) mode, liquid crystals change their angles on the display plane, and chromaticity and gradation characteristics rarely change due to the viewing angle.

The display panel of this type is generally used in a large-area display panel with an 18-inch or larger size because of its good color reproduction characteristics, and is generally used in the medical image field, and it can be said that the display panel is most suitable for a printing process.

Monitor calibration

The characteristics required for the monitor have been described above, and in order to maintain the accuracy of its characteristics, calibrations need to be performed periodically. In most cases, the monitor is color-measured, and the results are used as a basis to adjust the video output of the personal computer. This is called software calibration. This situation results in a change in the color temperature of white, which is equivalent to reducing the brightness of 1 or 2 in RGB, which is equivalent to reducing the use of 256 tones. The case of changing the value of γ from the original value is also equivalent to selecting and subtracting some of the 256 tones to become a gamma that is close to the target, resulting in the loss of tone. When expressing a smooth hierarchy, there are stairs or lines, or the case of seeing colors, that is, these are the root causes.

For printing process applications that require the correct level of features, like the hardware calibration that allows the monitor's characteristics to meet the required values ​​(for example, white temperature 500K/γ1.8). However, on the LCD monitor, the adjustment of the brightness, due to the RGB common backlight adjustment, cannot be individually adjusted to the maximum brightness of the RGB like the CRT monitor.

In order to solve this problem, more than 10 bits of processing are performed inside the monitor, and it is most effective to reassign RGB individually to an 8-bit 256-order function table.

Application in printing

Since the color reproduction characteristic of the monitor is correct and reliable, it can be used in the printing field for the following applications and has been actually used.

1) Perform image processing on the data taken by a digital camera (photographer)
2) The image processing department of the printing company deals with photographic data processing 3) The monitor for the image display in the scanner input department 4) The DTP operation in the press production department 5) The report for the newspaper The image The image processing for the newspaper office 6 ) For the production of advertising production companies

Not limited to the fields listed above, applications can be considered in areas that require correct color reproducibility and their business and post-processing and quality improvement.

Soft Proofing Practice

As we all know, the printing and publishing industry is popularizing the digitization and printing standards of work processes. All of these are for the purpose of shortening delivery time, reducing unnecessary costs, and stabilizing quality. In the transformation of these tasks, the requirements of the monitor are the extent to which the colors of the printed information content can be accurately reproduced on the monitor screen, and finally all the corrections are implemented on the monitor, namely soft proofing.

As a benefit to the user, as the digitalization of the printing workflow, the DDCP that facilitates color proofing is further evolved, and all corrections can be performed by means of the monitor display, thereby saving the cost of proofing, delivering cost and time, and The stage can also reduce the output for confirmation, and can also save the time spent on the correction after proofing.

The key to achieving this is the use of CMS based on color profiles. In fact, the experiment was performed on the monitor to correct the color reproduction. For the experiment, at least the print data, the sample actually printed out with the data, and the ICC setting file of the printer that printed the sample were required. In order to meet the requirements of these requirements, the standard components of JAPAN COLOR Color Reproduction Printing 2001 are used, and the standard components include all of the above.

Job configuration in Photoshop's color settings: For CMYK, select the JAPAN COLOR 2001 Type 1 setting file.

Job Configuration: Select sRGB for RGB. The setting of the monitor selects the setting file that is generated after the white temperature is 5000K/γ1.8 and the brightness is 80cd/m2, and is set in the system.

Under these conditions, each color mark of the print data was displayed on Photoshop, and the Yxy value was obtained using the CS-1000 manufactured by Minolta, and converted to the Lab value and compared with the original data. Regardless of the brightness component, comparisons were made in the ab plane, but with respect to the colors in the sRGB color gamut, good results were obtained with ⊿E(ab) being within 2 .

According to a variety of prints, this accuracy requirement may be reflected differently, but in general, soft proofing on liquid crystal monitors has reached an ideal level.

Source: China Design Printing Network

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