HP Z6100ps HP Designjet Z6100 Printer Series - User's Guide - Page 118

Color management Color spaces are only methods of controlling different color-imaging devices. They do not describe colors directly. The same CMYK values, for example, create different colors when sent to different printers that use different inks and paper types. For example, consider a printer that can use indoor inks or outdoor inks. The printer (hardware) is the same, but it has two different color gamuts due to the different chemistry of the inks (dye-based versus pigmented). Furthermore, they need to work with different paper types, as ink interaction with the paper depends on its chemistry. Thus, the colors resulting from given CMYK values depend on the types of inks and papers that you use with a printer. If this is the case using the same printer, you can easily imagine how different results can be obtained with printers using different technologies and therefore using different ink chemistry. The same happens with RGB-controlled devices. For example, imagine that two different monitors from the same manufacturer have their white points at 9600 K and 6500 K, respectively. Their colors are going to be different because they will be related to a different white point reference. The situation varies even more among monitors from different manufacturers. To emulate the standard color temperature of the graphic-arts industry, set the white point of your monitor to 5000 K (also called D50). NOTE: The white point is the brightest neutral color that a device can reproduce or that is present in an image. The human visual system automatically adapts to the content of an image based on its white point. An RGB image, such as an image obtained from a digital camera and edited on a monitor, must first be converted to CMYK before printing. Different devices do not give access to the same color gamuts: some colors that can be shown on a display cannot be matched in print, and vice versa. The following figure illustrates how the human eye perceives a larger range of colors than a typical display or printer. It also shows that the color gamuts in two different types of color-imaging devices do not match each other. 1. All colors 2. Computer monitor gamut 3. CMYK press gamut Some color spaces are not device-dependent, but instead represent how a viewer sees colors, such as CIE Lab or CIECAM02. These color spaces are defined by the CIE (Commission Internationale de l'Éclairage). The advantage of these spaces is that if two objects have the same CIELAB values, they look the same when viewed under the same conditions. Values in these spaces can be obtained from measuring the light emitted or reflected by an object. 106 Chapter 7 Color management