The primary digital image recording devices are the digital scanner and the digital still camera. In recent years, these devices have become commonplace, leading to a proliferation of digital images. In this chapter, we discuss these devices in detail, focusing on their limitations and variations. In addition, we will discuss hyperspectral imaging, which makes use of more than three bands to obtain information that can be used in multiple illuminant color reproduction and image segmentation and classification.

Scanners

To process images from scanners and digital cameras effectively, it is necessary to understand the transformations that affect these images during recording. There are several approaches to sampling the two-dimensional image. The first scanners used a single sensor and moved the medium in both orthogonal directions. With the advent of the CCD array, it was possible to project a scan line onto the sensor and move the medium (or sensing array) in the direction orthogonal to the linear array. Finally, it is possible to use a 2-D sensor array to sample the medium without movement during the scan. The most common desktop scanners record the image data using a row of sensors. Thus, we will concentrate on that technology.

The “paper moving” designs consist of both sheet-fed and flat-bed scanners. The “sensor moving” designs include hand-held scanners, which require the user to move the instrument across the paper, as well as flat-bed scanners. The primary sensor types are charge-coupled device (CCD) arrays and contact image sensor (CIS) arrays.