Reproducing colors accurately

Each piece of equipment you use to create a project has a specific range of colors it can reproduce. This is referred to as a device gamut. For example, a monitor displays a different range of colors, or color gamut, than the color gamut that reproduced on a printing press. It is important that the colors your customer requests are the colors you provide in your final product, be it in a magazine, or a newspaper, or on television or the Internet.

This means that your document might include colors that appear properly on your monitor but can't be reproduced on paper. Different monitors, scanners, printers, and other types of equipment all have slightly different color gamuts. Different color gamuts can occur even between similar models of equipment from the same manufacturer. For colors to be accurately translated from device to device, you need to account for the differences between the color gamuts of each device.

Using a Color management system

A color management system (CMS) can minimize the differences in color gamuts. Without a CMS, each application you use generates its own color profile, this means that your output colors may not be consistent. A CMS:

• provides device profiles (scanner, monitor, printer) to map the color spaces between these devices

• can convert from one color model to another color model (for example, from RGB to CMYK)

• provides accurate on-screen or print previews of colors when printed to allow color corrections

Without color management system, it is not possible to accurately achieve color consistency throughout the publishing process which involves the use of different devices or systems. Enabling color correction causes on-screen colors to look duller than they did before color correction was enabled.

Choosing Color Profiles

Profiles, or ICC Color Profiles, are files in a format defined by the International Color Consortium. They describe the color characteristics of color devices and color spaces. Color management software, such as the software in CorelDRAW, uses ICC profiles to transform colors from device to device, and from one color space to another. Having the right profiles is important to getting good color.

Corel software ships with many pre-defined profiles for scanners, monitors, and printers that you can choose to load into your system. Many device manufacturers have ICC Color Profiles available for you to download. Work with profiles that most closely match the devices you have on your system. When you first install your software, generic device profiles will be selected for you to use.

There are 5 profiles you can set to manage color. Use the Monitor profile when displaying documents to your monitor. Use the Scanner profile when scanning images from a scanner device. Use the Composite Printer profile when printing to a local or networked color printer. Use the Separations Printer profile to define CMYK colors in your documents and when creating color separation for printing. Use the Internal RGB profile to define RGB colors in your documents. Changing any of these profile will influence the colors you see and get from the software.

The quickest approach for setting profiles is to set the Monitor profile to the profile for your monitor, and the Composite Printer profile to the profile for your local printer. If you have a special RGB color space you need to work in, you can change the Internal RGB profile to that color space. If you are scanning and have a profile for your scanner, choose your scanner's profile from the scanner list.

Using Embedded color profiles

Embedded color profiles take into account the different color gamuts that exist and provide cross-platform communication of the different color spaces. A color profile is a description of a device's color handling capabilities and characteristics. An embedded color profile is a color profile, attached to or embedded into a color document. It describes the color space of the colors contained within the document. Corel supports ICC-embedded profiles. This allows the same color profile to be communicated across platforms, and ensures accurate color management throughout the publishing process. Embedded color profiles ensure accurate color reproduction between the input (scanner) and the output (printer) device. The ability to embed ICC profiles into many file formats, including CorelDRAW .CPT and .CDR formats, allows for consistent color spaces between all applications that support ICC profiles. TIFF and .EPS formats are supported by CorelDRAW.

Use Color profiles to correct on-screen colors so each color displays as accurately as possible based on its color values. Color profiles can display colors on screen as they will appear when they are printed. Proper color profiles can also warn you when a selected color is outside your printer's color gamut. Accurate color profiles of your scanner, monitor, and printer make it possible for colors to be corrected so the color you see on the screen matches the color in the final output.

Setting the General color settings

The General color settings page contains several additional controls for color behavior. The first three check boxes let you control how colors from some special palettes are separated when printing to color separations. With the check boxes enabled, colors from these palettes separate into their own individual printing plates.

The next group of check boxes control several functions. Enabling "Show CMYK in percentages" causes the screen display of CMYK values to fall into the range of 0 to 100. Disabling this option causes CMYK values to display within the range 0 to 255. "Map spot colors into CMYK gamut" is a useful option which allows you to avoid making additional color separation plates for any spot colors contained in your document. Spot colors separate into the basic C, M, Y, and K printing plates for the printing process. "Composite printer simulates color output of separations printer" is useful for previewing on a local printer what the document will look like when printed on a printing press as color separations. It does this by using the color profiles of both the local printer and the separations printer.

The "Rendering Intent" drop down list, controls the method the color management system uses when it converts colors between spaces that are different sizes or different gamuts. The problem is what to do with colors in one space that are not part of the other space? How do you pick a color in the smaller space to represent the starting color in the larger space? There are three ways to do this. The Rendering Intent option lets you control the method used.

If you choose Saturation, a matching color is chosen so that the saturation component is maximized. It emphasizes saturation in colors, and may cause noticeable shifts in out-of-gamut colors. This is the best for vector graphics (lines, text, and solid colored objects.)

If you choose Perceptual, a matching color is chosen so that it and all colors that are like it, all have the same relationship to each other in the new color space. There is no abrupt changes between colors, but all colors are somewhat different in the new color space. It shifts all the colors in an image so the range of colors lies within the color gamut. This ensures that the relationship between colors is unchanged. This technique works extremely well for bitmaps and photographic-like images

If you choose Automatic, the application chooses for you on an object-by-object basis: vector objects will use Saturation, and bitmap objects will use Perceptual. Automatic is the default mode.

Calibrating your equipment

It is equally important that you calibrate your devices before working on a project in order to achieve color consistency. Calibration refers to the process of building a profile for your monitor, so its particular color characteristics are captured for use by a color management system. After calibrating your monitor, you know what its color space limits are and what colors you expect it to produce.

Calibrating your monitor

All monitors respond differently to the same electronic information. Two identical monitors from the same manufacturer respond differently and display slightly different colors on screen when provided with the identical color file. This is due to a number of factors such as monitor age, ambient lighting, or monitor settings. To achieve consistent color reproduction, it is recommended that you calibrate your monitor and be aware of factors that can affect your monitor's performance.

The following are recommendations to aid you in achieving accurate color reproduction in your projects.

• Warm up your monitor for up to one hour before beginning calibration.

• Clean your monitor screen before beginning calibration.

• Manually adjust your monitor controls and tape them down so they are not accidentally readjusted after system calibration.

• Calibrate your monitor on a regular basis, especially if it is an older monitor because phosphors fade over time.

• Have consistent lighting. Each type of lighting, fluorescent, incandescent, and natural, will affect the colors you see displayed on your monitor. Avoid natural light as much as possible since this changes constantly throughout the day. Consider having grid diffusers installed over fluorescent lighting.

• Use a neutral background on your monitor and for your work area to avoid influencing your perception of colors.

• Take breaks. Give your eyes a rest throughout your work period. Take the time to look away from your monitor to avoid eye strain and fatigue.

• If you view your work on more then one monitor, make sure they are all set at the same white point.

• Use monitor profile building software to build a profile for your monitor.

Calibrating your scanner

Perform scanner calibration every month or so, depending on use. Scanner bulbs change color with age, affecting the color of your scans. Keep the glass clean to improve scanning quality.

There are several tools available for scanner calibration. All of them use the same basic technique: place a known source image on the scanner, scan the image, and look at the colors recorded. Knowing what the values, the colors should be and comparing them to the colors scanned, build a profile that corrects the scanner to produce the right colors. Refer to the accessories that came with your software or your scanner for more information. After you have made your profile, you set it as your Scanner profile.

Calibrating your printer

Color from printers can vary widely, from day to day, from printer to printer, and from one set of inks or color sheets to another. Colors are influenced by the paper used. Inkjet printers, for example, take a wide variety of papers: plain copy paper, coated paper, glossy paper, and many other types of paper. The interaction between the inks and the paper affects the resulting colors. To insure accurate color, create a profile for each combination of media (inks, paper, etc.), and update the profiles as conditions change. Printers age with time, and this, too, can cause colors to shift. Updating profiles periodically will ensure your printer colors are as accurate as possible.

Given all the warnings above, you can still get decent color behavior from a stock or pre-made color profile for your printer. The general behavior of the printer and inks will be captured in such a profile, and the differences due to age and paper will be ignored.

To make a profile for your printer, use a third party printer or output profile-making tools. You need a device to "read" the colors produced by your printer. There are several profile making tools available that let you scan the printer output on a calibrated scanner. The end result is a printer profile that you can use as your Composite Printer profile.

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