Visual Thought User's Guide
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Chapter 21
Using the Color Chooser
Color Selection Methods
Visual Thought's color chooser allows multiple methods for selecting colors. These are:
HLS Method
The HLS Color Model
The HLS (Hue-Lightness-Saturation) color model was developed to correspond to how people perceive color. It is one of the more intuitive color models for synthesizing colors.
Hue is what we think of as "color," as in the difference between red and blue. or orange and green. Lightness is the amount of white mixed in with the color, as in the difference between red and pink (pink is a lighter shade of red). Saturation is how "deep" the color is; if you take any color, such as green, and imagine "bleeding" all the "green-ness" out until you just have gray, you've just imagined bringing the saturation of that color down to zero.
The HLS color space can be visualized as a double cone, two cones with the wide ends stuck together. Hue changes around the perimeter of the cones. Lightness varies vertically, so the bottom of the cones, if held vertically, is pure black, and the top of the cones is pure white. Finally, the radius of the double cone (from the vertical axis out) represents saturation, with zero saturation at the center.
The advantage of the HLS color model is its intuitiveness. For example, pink can easily be generated by choosing a red hue and a lightness value above 50%.
Using the Color Chooser in HLS Mode
The main components of interest in the color chooser in HLS mode are the color box, the three color sliders, and the color wheel.
The color box shows one or two colors. The top half of the box shows the old color, which is the color of the selected Visual Thought objects at the time you popped up the color chooser. The bottom half shows the current color, which is changed as you manipulate the color chooser. The current color will be applied to the selected Visual Thought objects when you click the OK or Apply buttons.
The hue and saturation bars will appear completely black or white if lightness is at 0% or 100%. Change the lightness to choose a color other than black or white.
The three color sliders change the lightness, hue, and saturation parameters. You can change the values by clicking and dragging the mouse inside the bars, or typing a numerical value in the text fields beside the bars and pressing Tab.
The color wheel shows a horizontal slice of the double cone discussed above. Changing lightness changes which slice of the cone you are looking at. For any particular lightness slice,
RGB Method
The RGB Color Model
The traditional color model is RGB (Red-Green-Blue) because it corresponds directly to the color values used to control your color monitor's output. Although the range of colors you can create with RGB is the same as with HLS, the RGB model is much less intuitive and it poses difficulties for color synthesis. For example, what combination of red, green, and blue gives brown or pink?
The RGB color space is modeled by a three-dimensional cartesian coordinate system, with three mutually perpendicular axes. Red values vary along one axis, green along another, and blue along the third. Each value of R, G, and B can range from 0 to 1. The RGB color space thus forms a color cube.
Using the Color Chooser in RGB Mode
As in HLS mode, there are three main components of interest in the color chooser in RGB mode: the color box, the color sliders, and the large square patch in the upper right corner.
The color sliders control the intensity values of red, green, and blue, and are used like the HLS sliders.
The square color patch at the upper right corner shows a red slice of the RGB color cube. That is, as you vary the red slider, the color patch will display the green-blue plane for that value of red. You can therefore drag around in the color patch to vary the green and blue values for any given value of red.
CMY Method
The CMY color model is the complement of the RGB model, and is as difficult to use to generate screen colors. Unless you will generate color separations for printed output by hand, you should probably not use the CMY model.
Grayscale Method
If you will consistently send your Visual Thought output to a grayscale printer, and you are concerned mostly with the look of the printed output instead of the screen display, you should use the Grayscale method exclusively for choosing colors. Using the Grayscale method will give you the greatest fidelity between screen display and grayscale printed output.
To use the color chooser in Grayscale mode, simply change the value of the Grayscale slider.
Named Colors
There may be times when you need to find an exact X Window System color. In this case, you can switch to using named X11 colors at any time.
Simply choose the Views
Named Colors menu item, and a list will appear with all named X11 colors on your system. Double-click on any of the named colors to make it the current color.
Saved Colors
By default, Visual Thought provides a palette of 16 saved colors for quick access. These are located at the bottom of the color chooser.
To make any of these the current color, double-click on the desired patch. Then click OK or Apply to apply the current color to your selected objects.
To change any of the saved colors, click once on the one you wish to change, so that an asterisk appears on its patch, then choose a new current color using any of the color chooser's methods. Then select the OptionsAdd Saved Color menu choice (from the color chooser menu bar) to replace the saved color with your desired color.
Visual Thought User's Guide
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