In an 8-bit RGB image file, each pixel is described with the three basic colors; red, green, and blue, with 8 data bits for each. This allows for 2⁸ = 256 different colors levels for a pixel in each of the three basic colors (2²⁴ for RGB!). Thus, a red pixel can have 256 levels of red. A numerical value of 0 describes a complete absence of red, whereas the value 255 describes the fullest red that can be displayed. At this point a problem is already encountered with relative color definition: given two monitors, it is very unlikely that both will display the color red exactly the same way. For printing, it will be even more complicated. See yourself: take Photoshop and generate a uniform red area with the color values of red 255, green 0, and blue 0. Compare this area with the printed example on the opposite page. Due to the printing and the CMYK color separation, you will notice an obvious color difference, even though these patches have been generated with the exact numbers stated above in RGB mode.

The range of colors that a particular device can reproduce is called its “gamut” or “color space.” Theoretically, you can compare the color gamut of your scanner, monitor, and printer, and from the intersection generate a new color space in which each device would be able to represent every color. However, doing this would greatly underutilize the capabilities of each device. In the example mentioned above with the film scanner, monitor, and printer, the monitor displays fewer colors than the scanner can record. There are also some print colors that the monitor cannot display; but the monitor can also display many colors that the printer cannot handle. Using the smallest common color space would eliminate colors that could be scanned as well as printed. This is the reason that a device-independent color space is used as an interface between devices. However, at the various stages of the workflow, this color space has to be transformed several times. ICC profiles are used to keep the color representation consistent despite the transformations.

In RGB mode, the red tones are defined with explicit color values.

Gamma controls the ratio of input to output signal in a display system (for example, a monitor). In the Windows world, a gamma of 2.2 has become standard; for Mac, it is 1.8. The gamma value controls how the mid-tones of an image file are displayed. The perceived brightness of a monitor depends on this value. For scanning you should use the standard gamma value of the operating system, which will be used later for editing and displaying the images.

For a typical workflow, the first step is to scan the original with a film scanner. The resulting image file will be examined on a monitor. The monitor is the graphical interface for you, the operator. Based on the monitor image, you decide what corrections are needed. Once you are happy with the result, you can save the file with the changes and optionally print it.

Usually the colors in the print will not be identical to the colors on the monitor. This discrepancy is due to the different color models used by the various devices. The monitor works with the RGB color model, whereas the printer works with the CMYK color model. Inevitably, all these differences cause color deviations.

Unfortunately, even with color management these differences cannot be completely eliminated. After all, the monitor can display colors that the printer cannot generate, and vice versa. What color management can do, however, is match most colors, maintain a consistent color representation, and create at least a very good facsimile of the image.