Photoshop CS3

essential skills: photoshop CS3

Levels We have seen how mixing primary colors of light can create the secondary colors. In the previous illustration, where three colored circles were overlapped, the color in each of the three channels is either ‘on’ or ‘off’. In this way six colors are created from three RGB channels. The three channels can, however, house a greater range of information about color than simply ‘yes’ (fully on) or ‘no’ (fully off) in any one pixel location. Capture devices are capable of measuring ‘ how much ’ color is present in any one given location. In a standard RGB image, 256 different levels of color can be assigned to each pixel location. The channels operate very much like a mixing desk, mixing varying amounts of color from each of the three color channels to create the full color spectrum.

If the three channels are mixed in equal proportions what we see is a series of tonal steps from black (0 in all three channels) to white (255 in all channels).

256 levels of tone are reduced to 30 so the steps can be clearly seen

256 separate tones are sufficient to create a smooth transition from dark to light with no visible steps. If the pixels are sufficiently small when printed out, the viewer of the image cannot see either the individual pixels or the steps in tone, and the illusion of ‘ continuous tone ’ or ‘ photographic quality ’ is achieved.

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