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The first of these is RGB color – or Red, Green, Blue.  This is a subtractive color system based on combining light to produce color.  The basic idea is that beams of light in each of three colors, G-G-B, can be combined in various intensities to create a wide range of other colors.  This is how televisions, computer monitors, digital cameras, and low-end scanners produce color – for the obvious reason that these are all light-based devices.  Since computer monitors are most often the first step in digital imaging, RGB is also the default color space for many software applications.

The variations in the intensities of the R-G-B components can be defined mathematically by assigning a range of values from highest to lowest intensity for each.  In this way specific colors can be recreated by using specific values.  In most RGB color systems these values range from 0 to 255 for each component – 0 being the least intense and 255 being the most.  Thus, in a standard RGB color picker 0—0—0 is white and 255—255—255 is black.  All intermediate colors fall in between.  The RGB values for the nearest color to Gannon Maroon is R=137, G=32, B=52 or 137—32—52.  For Gannon gold the nearest value is R=255, G=199 and B=38 or 255—199—38.

RGB is generally the final destination color mode for anything that has a computer monitor as its primary display, such as a Web page.  Although these images do print to color printers, they are not expected to be color accurate and will often exhibit color shifts when printed.  (This is because most color printers operate in a different color mode using process colors, or an additive color system.  See the next section.)  For projects intended to end in print, RGB is generally only an interim mode used as a working space, but ultimately intended for conversion to CMYK.

Even within RGB there are several variations that each have different color gamut.  Image editing applications such as Photoshop allow you to select among these to optimize your results.  Two of the most useful are AdobeRGB and sRGB.  AdobeRGB is a wide-gamut color mode that has been optimized to be more compatible with printing projects and conversion to other modes.  If your project is intended for print, and you need to use RGB images in your workflow, AdobeRGB is a highly recommended option.  sRGB is a narrower gamut mode that is optimized for images that appear on computer monitors.  Microsoft uses sRGB as the default color mode for displays within its operating systems since it represents the color space of an “average Windows monitor.”  Although it may be more limited in gamut, working in a color mode that is indexed to the greatest number of users can be advantageous for achieving predictable results.  sRGB has also gained favor as a proposed standard for an Internet color space.

Another variation of RGB is called Indexed Color.  This is still an RGB mode, but instead of being a full range of colors defined by the range of 0—0—0—to 255—255—255, there are a much more limited number of colors allowed in the image.  A predefined color table included as part of the file controls the range of colors available and every color used in the image is “indexed” to this table.  Color variation can be achieved by dithering, but every pixel must match a color in the table.  Color tables can be set to different sizes and specific colors, providing a way to optimize images.

One of the common color tables is called the “Web-safe” palette.  Both PCs and Macs allow 256 colors in their operating system for 8-bit display settings.  This is a common display setting for monitors.  However, there are only 216 colors that match between the two systems.  The Web-safe palette indexes images to these common colors so that colors will be more consistent across platforms.  These Web-safe colors also have reference codes referred to as hexadecimal numbers.  These codes can be used in building Web pages to assign specific colors to components of the Web page.  For instance, the hexadecimal code for black is “#000000” and the code for white is “#FFFFFF”.  The nearest hexadecimal color for Gannon maroon is “#892034” and for Gannon gold is “#FFC726”.

File formats such as the popular CompuServe GIF use this indexing technique.  The advantage is that by reducing the number of colors to a limited range, file sizes can be greatly decreased through more efficient file compression.  This is highly desirable for the Web.  The disadvantage is that the limited set of colors does not provide the best quality display for many types of images.