Page 276 - Fundamentals of Light Microscopy and Electronic Imaging

CHAPTER
14

DIGITAL CCD MICROSCOPY

OVERVIEW

Digital CCD cameras contain a charge-coupled device or CCD, a photon detector that is
divided up into thousands or millions of picture elements or pixels, which store the
information from incident photons comprising the microscope image. A computer dis-
plays the reconstructed image on a monitor. The light-sensitivity, dynamic range, spatial
resolution, and speed of a scientific grade CCD camera are extraordinary. The efficiency
of light collection is so great, that a CCD image, compared to a film image of compara-
ble S/N ratio, would be rated at a film speed of 100,000 ASA. Because they give a lin-
ear response over a large range of light intensities, CCD cameras can function as
imaging spectrophotometers, producing tens to hundreds of times better resolution of
light intensity than video or film cameras. They also have a spatial resolution compara-
ble to film (Figure 14-1). Although scientific grade CCD cameras perform these func-
tions well, they work at slower rates than video cameras ( 1–10 frames/sec at full
resolution), and for this reason, are called slow scan cameras, although recent designs
acquire “full frame” images at close to the video rate of 25 or 30 frames/s. One of the
greatest attractions of the CCD camera is the ability to see the photographic results
instantly, allowing the user to evaluate images and proceed more quickly and efficiently,
without having to develop film or make prints in the darkroom. Digital files can also be
directly incorporated into manuscripts and used for electronic presentations at confer-
ences.
The combination of microscope and CCD camera together with computer with
imaging software defines what is called a digital imaging system (Figure 14-2).
Although these systems are still relatively expensive, their versatility and convenience
have greatly stimulated the use of light microscopy in research (Hiraoka et al. (1987). To
use the equipment properly, training and practice are needed to master several software-
dependent procedures for image acquisition, processing, analysis, display, and printing,
topics that we cover in this and the following two chapters. In this chapter we examine
the principles involved in CCD operation, the parameters the user must consider for
obtaining high quality images, and the criteria that are important for comparing the per-
formance of different CCD cameras.
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