Analog to digital

The act of scanning, be it using a flatbed model or one designed for film stock, involves converting continuous tone images into digital files. Photographs in either print or negative (or slide) form contain a range of subtle tones and colors that blend smoothly into each other. These are referred to as continuous tone images. For instance, in a black and white image it is difficult to see where one shade of gray starts and another one finishes. The effect is a smooth transition from the deepest shadows through to delicate highlights.

Computers are clever machines but they have difficulty handling images in this form. So, in order for the photograph to be used in an image manipulation program like Photoshop or Photoshop Elements, it must be changed to a digital file. The file describes the image as a series

Continuous Tone Image Analog Digital
Figure 11.8 Scanners convert continuous tone images such as prints or negatives into the same pixel-based files that we obtain from digital cameras. In this exaggerated detail you can see how individual areas of tone and colour are digitized.

of discrete colors and tones. When we scan a negative or slide we make this conversion by sampling the picture at regular intervals. At each sample point, a specific color is chosen to represent the hue found in the original. In this way, a grid of colors is put together to form a digital version of the continuous tone original (see Figure 11.8).

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Photoshop Secrets

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