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Color Concepts for Simulated Process
The Color Wheel
To discuss the process of making a full color separation for screen printing, it is helpful to think of a color wheel. A color wheel provides a visual description of the way colors blend to create the visible spectrum. The color wheel also demonstrates the components used to discuss and control color.
Hue
In the color wheel shown here, the Hue (color), changes as we move around the edge of the circle. Hue is the most apparent aspect of color, and is what is described by a colors name. This wheel shows how each Hue blends into another Hue around the circle. Hues directly across the wheel are color opposites.
Primary Hues
In printing, the primary hues are Cyan, Magenta and Yellow. Combinations of these three primary colors produce the remaining colors in the color wheel.
Saturation
Saturation is the “colorfulness” or intensity of a color. In this color wheel the saturation is at maximum along the outer edge, and decreases towards the center.
Hue and Saturation in Screen Printing
This graphic shows how a 6 station screen printing press
may represent the colors in this color wheel.
Printing the Value
By adding Black and White inks to our screen printing set up we can represent the Value as well as the Hue and the Saturation.
Color Models and Modes –
Color Models
The screen print color wheel and the Munsell color system are both a kind of color model, describing a way to combine colors to create the visible spectrum. Color models are often designed for particular types of output devices and mediums. For example, RGB is a color model designed for capturing and displaying light. CMYK is a color model used for printing.
Adobe Photoshop and Color Modes
Several color models and are available for working with color in Adobe Photoshop®. These color models are called Modes. To change Modes choose: Image / Mode /
Channels –
Adobe Photoshop’s color channels.
The basic building block for a color mode is the Color Channel. A color mode combines channels to display an images Hue, Saturation and Values. the RGB mode, for example, uses 3 primary color channels; Red, Green and Blue, to represent the spectrum of colors.
• An individual channel represents a single primary or custom color in a Color Model or Mode.
• How a channel displays color is determined by its type and color mode.
A design in the CMYK Mode with only the Cyan and Magenta channels visible.
Multiple channels are combined to create the available spectrum of colors.
Individual channel colors are mixed to create the range of colors available to the color mode. These colors can be represented and adjusted using a single composite channel, or contained separately using spot color channels.
In Adobe Photoshop there are three basic types of channels
•Composite Channels
The main color modes, RGB and CMYK, contain one channel for each color as well as a composite channel that displays the combined color information. the composite channel combines the color channel information based on the type and Working pro le of the color mode. the composite channel can be viewed and edited in the layers palette as a layer, or by editing the individual channels.
•Alpha Channels
Alpha channels are designed to hold transparency information and can be used for saving selections.
Alpha channels can be assigned colors and opacity levels but do not display dot gain settings.
• Spot Color Channels
The Spot color channel is designed to add specific ink colors to the CMYK printing process, or to be used alone when saved in the multi-channel mode. Spot color channels display global Dot gain settings that can be set in the Color Settings menu (See pg 23). Ink Opacity, Hue, Saturation and Value can also be set for each specific channel.
Layers –
Layers are built on the Composite Channels.
Primary color channels in the RGB and CMYK mode are combined to generate a Composite channel that can be accessed from the layers palette.
Multiple layers can be created with the options to control transparency, blending modes and opacity to name a few. Layers are generally used for image adjustments such as masking and touch up as well as for layout and design. When all layers are merged into the background layer the image is said to be flattened.
Layers are generated using the composite channels. Layers allow for transparency, layout and image adjustment, while channels hold the actual color information.
Screen Printing and Channels –
Spot color channel separations
For screen printing, the Spot color channel provides a good approximation of a printed separation. Spot color channels do not generate a Composite channel and are not available in layers. e separation below is printed using three primary colors, as well as a Gray, a Black and a White ink. Each channel represents a single ink
• The three colors; Blue, Red and Yellow, determine the Hue and Saturation of the image.
• The Black, White and Gray print the values and control the shadows and highlights.
Channels on Press
The colors sequence in our channels is the same as the color sequence on press.
Starting from the top of the channels, with successively darker colors below printing later. e exception is the highlight white, which is often printed last.
• Saturation and color placement is controlled by printing halftone dots.
The colors used in a color separation can be customized to meet the needs of the image.
In this color separation, the ink hues only
cover a portion of the spectrum. This
approach tends to narrow the color options, but can create an acceptable print using a limited number of screens.
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