2.1 Basics of Color Image Acquisition

The initial task in the processing and analysis of color images is the acquisition of color image data with the highest quality achievable. The output of an image-acquisition system is an electronic signal that represents the distribution of light energy across the field or the spatial extent of the image. In this chapter, we study the aspects of color image processing involved in a digital still-image-acquisition system (such as a DSC). Still-image cameras are the main sources of color images used in day-to-day practice. Scanners represent another source of still color images, but they will not be considered in this chapter. The general scheme followed by a digital camera is shown in Figure 2.1; each block of this scheme is explained in detail in the following sections.

2.1.1 Color image sensors

The main purpose of the sensors in a camera is to convert the incoming light into electrical or electronic signals that represent the color image at each spatial position within the field of view (FOV). All practical DSCs use either charge-coupled devices (CCDs) or complementary metal-oxide semiconductor (CMOS) sensors in 2D arrays [158]. CCD sensors can attain high signal-to-noise ratios (SNRs), whereas CMOS sensors have the advantage of being fabricated in a single integrated circuit along with other components. In addition, CMOS sensors consume far less power than CCDs due to their higher level of integration. For these reasons, CMOS is usually the chosen technology for miniature cameras, such as those built into cellular phones; however, such cameras offer limited image quality [159]. On the contrary, CCD chips are the most commonly used sensors in consumer and professional cameras.