Color Separation and Color Models
If you are sending color work to a service bureau or printing shop, either you or the service bureau will need to create color separations. Color separations are necessary because a printing press applies only one color of ink to a sheet of paper at a time. In commercial printing, the process involves splitting colors in a composite image to produce a number of separate grayscale images, one for each primary color in the original. In the case of a CMYK image, four separations must be made—cyan, magenta, yellow and black.
A color separation is created by first isolating each color element in an image. Each color element is then used to create a sheet of film. Each sheet of film is used to apply one color of ink to the sheet of paper. Printing presses produce color using either process colors or spot colors. The number of colors you plan to use will be the main factor in deciding which method to use.
Halftoning and Screening
Color Palettes and Color-Matching Systems
Halftoning and Screening
To understand some of the underlying principles of color separation, read how halftoning and screening can be used to create many colors when you are printing with only a few process colors.
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Printing Color Separations
When you print color separations to file, you can create a print (.PRN) file that includes all separations, only one separation or any combination of separations, depending on the complexity of the image.
Generally, you should be able to save all the color separation information in one .PRN file. However, if the image contains special effects and several color separations (e.g., CMYK plus a number of spot colors), the .PRN file may be unacceptably large. In this case, create a .PRN file for each separation. Include the separation name in the filename for easier file identification. When you print color separations, you can produce a sheet of paper or film even when there is nothing on it (e.g., there may be only yellow and black on a page but the cyan and magenta plates will be printed anyway). Normally you would not do this to avoid wasting costly film, however, there may be instances when you want to create plates that are blank.
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Notes About Color Models
CorelDRAW® provides a number of color models from which you can choose colors. These include RGB, CMY, CMYK, CMYK255, HSB, HLS, Lab and YIQ. If you are printing your work, the CMYK model is recommended. If your work will be displayed solely on screen, use the Red, Green and Blue (RGB) model.
The term “color model” is used in two ways in CorelDRAW.
You can select colors from a variety of different color models (e.g., HSB, CMYK, etc.).
Or, after a color model has been selected, you can edit this color using a “visual selector” in the Uniform Fill dialog box (e.g., HSB – Wheel Based, CMYK – 3D Subtractive, etc.). This visual selector is also sometimes referred to as a color model. CorelDRAW lets you select and apply colors from a variety of different color models. Each model contains slightly different colors, giving you hundreds of colors from which to choose. In addition, you can modify these colors by adjusting their component values. For example, if you want to use a color that appears in the CMYK color model (e.g., red), but the color is not dark enough, you can adjust the color manually using the controls found in the Uniform Fill dialog box.
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Using a Visual Selector
An easy way to pick colors is to use one of the visual selectors to sample colors directly from a color model chart. The layout of the visual selector is based on the number of channels in the color model you choose from the Model list box. In CorelDRAW 6, different controls are displayed depending on the visual selector chosen:
- The single-channel visual selector, used in the grayscale color model, is a vertical slider along a gradation from black (0) to white (255).
- The three-channel visual selector (for the CMY, RGB, HSB, HLS, Lab and YIQ color models) is a square that contains gradients of a color, from black along the bottom to white in the upper left. Pure color is in the upper right with a slider to change the hue of the pure color.
- The four-channel visual selector is used for the CMYK and CMYK 255 color models. In these models, the visual selector becomes a three-dimensional colored cube. Drag the nodes of the cube to select a color using proportional amounts of cyan (at the top), magenta (to the lower left) and yellow (to the lower right) values. The slider to the right of the model controls black (K) values.
Tip: The conversion between color models is regulated by Corel Color Manager. Make sure that you have calibrated your system before you convert bitmaps from one model to another—especially when you are converting to CMYK because this color model is based on the characteristics of an output device (which has a device-dependent color space).
For more information please see Color Management.
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RGB
RGB isplays the colors available for the RGB color model. This model is based on the light primary colors. Use this color model if the drawing will be produced on a radiant device, such as a computer monitor or a television screen, or on a transparent medium such as slides. Modify the level of red, green and blue by clicking and dragging the small square that appears; the vertical slider adjusts color brightness by scaling all current R, G and B values geometrically. R, G and B values range between 0 and 255.
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CMYK
CMYK is a subtractive color model made up of cyan (C), magenta (M), yellow (Y) and black (K). A subtractive color model produces color when light is reflected off an object or surface. The reflected light determines the color that is seen when that object is viewed. For example, a perfectly white surface reflects all wavelengths of light. A black surface absorbs all wavelengths.
The CMYK color model is used in most full-color commercial printing. If your project requires full color (e.g., it contain scans of color photographs), you must use process color. Process color is a method of producing virtually any color using only four ink colors: cyan, magenta, yellow and black. The final colors are produced by mixing percentages of these four inks. Process color requires only four color separations.
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CMY
CMY is a subtractive color model made up of cyan (C), magenta (M) and yellow (Y). Use this color model if the drawing or image will be produced on a CMY device, such as a three-ink printer. C, M and Y values range between 0 and 255. This color model is available only through the Color Roll-Up.
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Spot Color
If your project makes use of only one, two or three colors (including black), you’ll probably use spot colors such as those offered by Pantone. Spot color uses a different ink for each color, and each color requires its own color separation.
If your budget is limited, consider:
- obtaining a two-color look by printing on colored paper and using only one spot color
- using tints (percentages) of spot colors to create shadows or highlights, to give the impression of a broader color range
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Images Containing Process and Spot Colors
Some projects require spot and process colors. For example, a marketing brochure may require a spot color to render the corporate color faithfully and process color to reproduce scans of photographs. Remember, though, that each additional spot color requires extra film, plates and ink, and adds to the cost of printing.
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Hexachrome
Corel now supports a new type of process color, called hexachrome. Hexachrome color uses six different ink colors (cyan, magenta, yellow, black, orange and green) to produce full-color images. Talk to your service bureau about whether you should use hexachrome color.
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Palettes
CorelDRAW allows you to work on different elements of your artwork from different palettes and color models. Ultimately, all colors must be printed with process and spot color inks. Colors defined in the RGB or HSB models are translated automatically into CMYK (process) values. As for spot colors, CorelDRAW lets you convert them to CMYK for printing.
Pay close attention to the number of colors you use, especially if you are importing clipart. Make sure you only use the colors you have chosen (i.e., process color or spot color).
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Color Palettes and Color-Matching Systems
Color Palettes
The term “color palette” is used in two ways in CorelDRAW. First, the onscreen Color Palette found along the bottom of the screen is used to select individual colors. This tool is opened by clicking View, Color Palette and activating one of the color palettes (the second use of the term) found there. Second, a color palette refers to a “fixed” collection of colors displayed on the Color Palette, in the Color Roll-Up and in several other locations.
Some of these palettes are the set of colors in your image, some are a custom set you have created and some are designed to work within the limitations of third-party hardware and software. However, most are based on color-matching systems. Some examples of color palettes include Focoltone, Pantone and TRUMATCH®.
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Color-Matching Systems
A brand name color-matching system ensures that standards are being used when you refer to the colors in your project. Color-matching systems are used for printing in color and can be divided into two main categories: spot and process.
If you are sending files to a service bureau or commercial printer, it is strongly recommended that you buy a printed swatch book from the manufacturer of the color-matching system that your service bureau recommends.
Onscreen colors are approximations of color-matching systems and their accuracy depends on a number of variables, not the least of which are the effects that ambient light can have on your monitor. A swatch book provides a precisely printed patch of each color in the color-matching system. Comparing these colors to the onscreen colors can make the printing process run more smoothly.
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