Page 351 - Fundamentals of Light Microscopy and Electronic Imaging

334 GLOSSARY

required to reach saturation remains the same, binning reduces the exposure time
required to reach a certain signal value by a factor equal to the number of binned pix-
els. However, because there are overall fewer pixels in a binned picture covering a
given area, binning also reduces the spatial resolution. 270
Bioluminescence. An oxidative process resulting in the release of energy as light emis-
sion—for example, firefly luminescence, which requires an enzyme, luciferase, to
catalyze a reaction between the substrate luciferin and molecular oxygen in the pres-
ence of ATP. 181
Birefringence. The double refraction of light in transparent, molecularly ordered mate-
rials caused by the existence of orientation-dependent differences in refractive index.
Also refers to the refractive index difference experienced by a transmitted ray
through such a material. Incident beams of light on a birefringent specimen are split
into O and E rays that can recombine after emergence from the object, giving lin-
early, elliptically, or circularly polarized light. 124, 126
8
Bit. In computer language, a binary digit 1 or 0. An 8 bit image therefore has 2 or 256
12
gray level steps, while a 12 bit image contains 2 or 4096 steps. 262, 284
Bleed-through. In fluorescence microscopy, the transmission of unwanted wavelengths
through a filter designed to block them. Bleed-through occurs when a filter’s design
does not allow complete destructive interference of unwanted wavelengths, when the
angle of incident rays is oblique, when the transmission and emission spectra of fluo-
rescent dyes overlap, and for other reasons. 194, 197
Brewster’s angle. The unique angle formed by an incident ray and the perpendicular to
a reflective dielectric substance such as water or glass (the transmitting medium) at
which the reflected ray is totally linearly polarized. Brewster’s angle is given as
tan n /n , where n and n are the refractive indices of the medium of the incident
i
t
t
i
beam and the transmitting medium, respectively. 121
Bright-field microscopy. A mode of optics employing the basic components of objec-
tive and condenser lenses for the examination of amplitude objects such as stained
histological specimens. 12
Brightness. A qualitative expression for the intensity of light. 55
Byte. In computer language, a unit of information containing 8 bits. 284
Camera control unit (CCU) or camera electronics unit (CEU). The main external
electronics control unit of an electronic imaging system. For video cameras, there is
often a stand-alone unit that is used to adjust gain, offset, and other functions; in
CCD cameras, the controlling circuits are often contained in the camera head and are
operated by software on a computer. 269
CCD. See Charge-coupled device (CCD).
CEU. See Camera control unit (CCU).
Charge-coupled device (CCD). A slab of silicon semiconductor that is divided into an
array of pixels that function as photodiodes in a light-sensitive photodetector. In the
presence of an applied voltage and incident light, the pixels generate and store “pho-
toelectrons” (alternatively, electron holes) resulting from the disruption of silicon
bonds from incident photons. The number of stored “photoelectrons” determines the
amplitude of pixel signals in the displayed image. 236, 260
Chromatic aberration. An aberration of lenses, whereby light waves of different wave-
length are brought to focus at different locations along the optic axis. In the typical
case of a simple thin lens, the focal length is shorter for blue wavelengths than it is
for red ones. 51
Circularly polarized light. A form of polarized light whereby the E vector of the wave
rotates about the axis of propagation of the wave, thus sweeping out a spiral. If the