Understanding color models

You need a precise method to define colors. Color models provide various methods to define colors, each model defining colors through the use of specific color components. There are a range of color models to choose from when creating graphics.

CMYK color model

The CMYK color model uses the following components to define color:

• cyan (C)

• magenta (M)

• yellow (Y)

• black (K)

The cyan, magenta, yellow, and black components are the amounts of cyan, magenta, yellow, and black ink that a CMYK color contains and are measured in percent from 0 to 100.

The CMYK color model, a subtractive color model, is used to produce printed materials. Subtractive color models use reflected light to display color. When you combine cyan, magenta, yellow, and black, so that the value of each component is 100, the result is black. When the value of each component is 0, the result is pure white.

RGB color model

The RGB color model uses the following components to define color:

• red (R)

• green (G)

• blue (B)

The red, green, and blue components are the amounts of red, green, and blue light that an RGB color contains and are measured in values ranging from 0 to 255.

The RGB color model is an additive color model. Additive color models use transmitted light to display color. Monitors use the RGB color model. When you add red light, blue light, and green light together, so that the value of each component is 255, the color white is displayed. When the value of each component is 0, the result is pure black.

HSB color model

The HSB color model uses the following components to define color:

• hue (H)

• saturation (S)

• brightness (B)

Hue describes the pigment of a color and is measured in degrees from 0 to 359 (for example, 0 degrees is red, 60 degrees yellow, 120 degrees green, 180 degrees cyan, 240 degrees blue, and 300 degrees magenta). Saturation describes the vividness or dullness of a color and is measured in percent from 0 to 100 (the higher the percentage, the more vivid the color). Brightness describes the amount of white that the color contains and is measured in percent from 0 to 100 (the higher the percentage, the brighter the color).

Grayscale color model

The grayscale color model defines color by using only one component, lightness, which is measured in values ranging from 0 to 255. Each grayscale color has equal values of the red, green, and blue components of the RGB color model. Changing a color photo to grayscale creates a black-and-white photo.

Understanding color depth

Color depth refers to the maximum number of colors an image can contain. Color depth is determined by the bit depth of an image (the number of binary bits that define the shade or color of each pixel in a bitmap). For example, a pixel with a bit depth of 1 can have two values: black and white. The greater the bit depth, the more colors an image can contain, and the more accurate the color representation is. For example, an 8-bit GIF image can contain up to 256 colors, but a 24-bit JPEG image can contain approximately 16 million colors.

Usually, RGB, grayscale, and CMYK images contain 8 bits of data per color channel. That is why an RGB image is often referred to as 24-bit RGB (8 bits x 3 channels), a grayscale image is referred to as 8-bit grayscale (8 bits x channel), and a CMYK image is referred to as 32-bit CMYK (8 bits x 4 channels).

Regardless of how many colors an image contains, the image display is limited to the highest number of colors supported by the monitor on which it is viewed. For example, an 8-bit monitor can display only up to 256 colors in a 24-bit image.

Choosing advanced color management settings

When you choose color profiles, colors are matched between devices as closely as possible by the color management module (CMM) of the Kodak Color Management System, which is the default CMM. Color management modules are also known as “color matching modules.” You can also use one of the following color matching modules :

• Microsoft Image Color Management (ICM)

• Windows Color System (for Windows Vista users)

• Adobe CMM if it is installed on your computer. To download and install the Adobe CMM, visit the Adobe Web site.

Note that the Microsoft ICM, Windows Color System, and Adobe CMM do not change the color profiles that are used by CorelDRAW. If you want the application to use the same color profiles as those of the selected color management module, you must select the appropriate color profiles in the Color Management dialog box.

Out-of-gamut colors and rendering intents

Color gamut is the range of colors that devices such as monitors or printers can reproduce. Colors that cannot be reproduced by the output device are called out-of-gamut colors. Such colors need to be replaced by colors from the color gamut of the output device. To determine how out-of-gamut colors are replaced, you can choose one of the following rendering intents :

• Absolute colorimetric — rendering intent that lets you simulate the output of one device, such as a CMYK printer, on another device, such as a monitor or inkjet printer. This rendering intent preserves the white point through conversions. For example, to render the bluish white of a source to an output on yellowish-white paper, cyan ink is added to the white areas of the output.

• Automatic — default setting, which uses the Saturation rendering intent for vector graphics and the Perceptual rendering intent for bitmaps.

• Perceptual — rendering intent for images that contain many out-of-gamut colors, such as bitmaps and photos. The overall color appearance is preserved by changing all colors to fit within the color gamut of the output device while preserving the overall color relationships.

• Relative colorimetric — rendering intent for producing proofs on inkjet printers. Because human eyes always adapt to white in the medium that is viewed, this rendering intent maps white in the source to white in the output, so that the white in the output is the white of the paper, not the source. Then, all in-gamut colors are accurately reproduced, and out-of-gamut colors are replaced with the closest reproducible color. This rendering intent preserves more original colors than the Perceptual rendering intent.

• Saturation — rendering intent for vector graphics (lines, text, and solid colored objects), business graphics, and elevation maps. Vivid colors are reproduced by converting saturated colors in the source to saturated colors in the output, but often at the expense of color accuracy

Embedding color profiles

When you import or export graphics, you can embed or attach color profiles. By embedding a color profile, you can ensure color integrity; anyone viewing or printing your work will use the same colors that you used.

Settings for separations and composite printers

There are advanced settings for separations and composite printers. You can link a color profile to a specific printer.

Color management styles

When you use color management styles, you can turn off color management or optimize the color display for different outputs.

Printing to film [image setter]

You can set up a print job to produce negative images. An imagesetter produces images on film that may need to be produced as negatives depending on which printing device you are using. Consult your service bureau or printing shop to determine whether you can produce images on film.

You can specify to print with the emulsion down. Printing with the emulsion down produces a backward image on desktop printers.

To print a negative

1. Click File >> Print.

2. Click the Prepress tab.

3. Enable the Invert check box.

Do not choose negative film if you are printing to a desktop printer

To specify film with the emulsion down

1. Click File Print.

2. Click the Prepress tab.

3. Enable the Mirror check box.