Analysis of Several Problems in Color Management

1. What is a color management system?

A color management system (Color Management System) is a system that converts data decoded by one device (such as scanner's RGB) into another device data (such as a printer's CMYK). In this way, the printed or printed color is the same as the scanned color. It is impossible to achieve very precise color matching, but it should be to make the color of the final print closer to the color of the original. The color management system we usually refer to now usually refers to the management system that adopts the internationally recognized CIE color measurement system.

2. The computer we use usually has an ICC profile. What is it? What can it do?

When you import images from a scanner or digital camera and display them on a monitor or print them from a printer, the ICC profiles help you get the right color reproduction. They define the relationship between your device receiving or transmitting data and a standard color space defined by the ICC and are based on a measurement system defined by the CIE. Therefore, if your scanner, digital camera, monitor, and printer each have a profile, you have a standard color space that you can refer to so that when you get an image from the scanner, the digital camera can display it on the screen. Or you can get the correct color when you print out the image from the printer.

The ICC profile standard is based on ICC specifications and can be found on the website. By following this specification, profiles can be exchanged and correctly interpreted by other users. There are two main types of profiles, which are source (input) profiles and destination (output) profiles, which are primarily composed of data tables with standard color space-related devices defined by the ICC. Various relationships are defined in each property file. Special types of profiles are defined for specific workflow applications.

Your device may also not have a profile. If you do not have a profile that is appropriate for your device, you may be able to create a profile yourself, but this requires appropriate measurement equipment and software. In order to combine profiles, you need to use color management features in your computer (such as Mac ColorSync) or an application (such as Photoshop)

3. Why do the colors of the images displayed on each monitor look different? How do you know what color these images will output to paper in the future?

The color management system will help you solve this problem. The secret of good color management is precisely to determine that each file you send to the printer/RIP has the relevant correct input profile, or is defined in color coding, such as sRGB. Then you must ensure that your output device has a good profile, and when you combine them, you choose the correct color conversion mode. You also want to make sure that all equipment is consistent, and correct it if necessary. All of these you have done well, when you export, you will get the expected high quality. If you do not perform any color management, you will only get a failed result.

To enable you to achieve consistent image color and quality on multiple monitors, you must simultaneously correct the brightness, contrast, and color balance of these monitors, and then generate a profile for each monitor. If you want to "predict" the quality of your printouts, you also need a printer's profile. In order to properly calibrate the display, you need a monitor measuring instrument available from X-Rite, Color Savvy, Alwan Color Expertise, or Gretag-Macbeth. These companies also provide related software for you. Generate a profile. In addition, there are "visual" software packages, such as Adobe Gamma, which can be used to correct displays if you do not have a suitable measurement device.

If you want to make a printer's profile, you need characterization software that can be obtained from Agfa, Fuji, Gretag-Machbeth, Heidelberg, Kodak, or Monaco. You also need to use a spectrophotometer, such as the X-Rite or Gretag-Machbeth spectrophotometer. Characterization software also requires the production of your scanner profile.

Like many input devices, when you change the characterization, you may want to set up an sRGB workflow that allows you to provide this type of data. In order to produce high-quality images from sRGB data, the output device allows you to Select color conversion (in most cases, select the default setting). If your printer does not print well from the sRGB data (depending on whether the driver/RIP is set for it in color conversion), you can get an input profile for converting sRGB data into ICC PCS (profile file connection space). A good printer profile correctly reflects the performance of this printer.

If you follow the above steps correctly, you can get good color quality. However, if you do not work for some time and cost and do not work hard, you may not succeed.

4. When I want to buy a new printer, monitor or CPU with a manufacturer's built-in ICC standard, what brand should I buy? What model?

It is not required that the device must be compatible with ICC, but the application software should be able to drive it. For example, a stand-alone printer or monitor does not easily support ICC profiles unless a software application can drive it. This allows you to define an input profile to match it, so that the conversion can be calculated. Some of the equipment used in the printing industry is usually supplied with such software, but such desktop devices are not cheap. In general, when people want to use ICC profiles, they can use the ICC profiles of such devices in their application software (Photoshop, Quark, etc.).

5. What happens when I purchase software that generates ICC profiles and scan IT8 images and make input profiles.

When an input profile is created with IT8 images, the software of the ICC profile reads the RGB values ​​of the scanned image and the average of many pixels in each color block to produce a single three for each color block in the color standard. The RGB values ​​of the group produce a single triple RGB value for each color patch in the color patch. Then, it finds data files for CIELAB or CIEXYZ values. These color measurements are obtained by measuring each color patch provided by the vendor's color code. (If the IT8 color code is provided with the software, it may be when you install the software. Already loaded, you can also load it yourself).

The software then uses these two sets of data to create mathematical functions that better convert RGB to CIEXYZ or CIEAB defined by the ICC Profile Connection Space (PCS). This math is unique to the software. Mathematical functions are used to define lookup tables that convert RGB to PCS. Therefore, when you scan, this profile converts your RGB to this standard color space, and the output profile converts it to CMYK. The output profile is obtained in a similar way, unless it is an efficiency file obtained from the weekly method, which will be used to measure the CIEXYZ or CIELAB value (usually more) for each color patch in the print color (eg IT8). Multi-color) Convert to print color scale using CMYK value.

6. Who studied ICC specifications?

ICC's English name is Internaiog Color Consortiun, the International Color Consortium. Founded in 1993, the organization is committed to the development of color standards to maintain color consistency in scanners, monitors, printers, and other devices, while software developers and hardware manufacturers work together to maintain multi-energy analysis consistency. The ICC created a format standard for color profile devices for surface device features to serve cross-platform environments.