Understanding color and color models

We usually think of color as a quality inherent in an object — for example a red car or a green frog. But color is really what we see as a result of three factors interacting: light, the object, and the observer. As rays of light hit the object, the object absorbs some light and reflects some light. We see the reflected light and perceive it as color. Different colors reflect light of different wavelengths. Human eyes are able to perceive thousands of colors in the visible spectrum of light.

When you apply ink to paper, the colors we see result from the light that the ink reflects. Computer monitors use emitted light rather than reflected light. The colors we see result from light emitted from the screen.

To describe how color is produced or perceived, we use color models. Computer monitors display colors by producing varying amounts of red, green, and blue light — the RGB color model. Human eyes perceive color by its hue, saturation, and lightness levels — the HSL color model. With Corel PaintShop Pro you can select colors using either the RGB or HSL color model. You can also output images using the CMYK (Cyan, Magenta, Yellow, Black) model, which is used for high-end printing applications.

RGB is the default color model in Corel PaintShop Pro. For information about changing the default color model, see To set Palettes preferences. Corel PaintShop Pro uses your preferred color model (RGB or HSL) whenever color values are displayed. When you select colors from the Color page, you are able to enter RGB or HSL values regardless of your preference setting. The color model used to display color values on-screen has no effect on how colors are printed.

All colors on your computer screen are created by mixing red, green, and blue light in varying proportions and intensities. When these primary colors are mixed in equal proportions, they create yellow, cyan, and magenta. Adding all the colors together creates white.

Each primary color (red, green, and blue) is assigned a value from 0 (none of the color present) to 255 (the color at full strength). For example, pure red is produced by combining a red value of 255, a green value of 0, and a blue value of 0. Yellow is a combination of a red value of 255, a green value of 255, and a blue value of 0. Setting all three values to 255 produces white; setting all three values to 0 produces black. When all three colors are set to the same value, the result is gray.

The HSL model is based on how the human eye perceives color using the characteristics of hue, saturation, and lightness. Each characteristic is assigned a value from 0 to 255. The three characteristics are described as follows:

• Hue — the color reflected from an object, such as red, yellow, or orange. Each hue value is assigned based on its position on the color wheel. On the Color page’s Color wheel, colors are assigned counter-clockwise from the top. Red is at the top (value 0) and as you move around the wheel the colors go through orange, yellow, green, blue, purple, and back to red.

• Saturation — the purity or vividness of the color. Saturation represents the amount of gray in the color, from 0 (entirely gray) to 255 (fully saturated color).

• Lightness — the perceived amount or intensity of light in the color. Lightness ranges from 0 (no light, or black) to 255 (total lightness, or white). At 50 percent lightness, or a value of 128, a color is considered pure. For example, pure red has a hue of 255, a saturation of 255 (100 percent) and a lightness of 128 (50 percent). For pure blue, the hue is 170, saturation is 255 and lightness is 128.

The CMYK model is based on the fact that ink on paper both absorbs and reflects light. As white light strikes the ink, part of the color spectrum is absorbed and part is reflected back to your eyes (resulting in the color you see).

In this model, the primary colors cyan (C), magenta (M), and yellow (Y) combine in varying proportions to produce a variety of colors. When the three colors are combined, they produce black. Because impurities in the ink make it difficult to produce a true black, a fourth color, black (K), is added.

Combining inks in this way is called four-color process printing. It is used by printing services and high-end color printers.

Although you cannot create images in Corel PaintShop Pro using the CMYK model, you can produce color separations that can be printed on CMYK printers. There are two ways to do this: You can split the images into CMYK channels, or you can print color separation pages.

CMYK channels are simply four separate grayscale images that represent the percentage and location of cyan, magenta, yellow, and black in the image. For more information about working with color channels, see Using color channels.

When you print CMYK separations, Corel PaintShop Pro prints a separate grayscale page for each primary color. You can then use these pages as “color plates” when working with a printing service. For more information about CMYK color separations, see Printing CMYK color separations.