Page 368 - Fundamentals of Light Microscopy and Electronic Imaging

GLOSSARY 351

Progressive scan cameras. A reference to video cameras and camcorders with interline
CCD detectors. The designation “progressive scan” indicates that the entire image sig-
nal is read off the chip at one time and that images are displayed as a series of complete
frames without interleaving as in the case of conventional broadcast video signals. 268
QE. See Quantum efficiency.
Quantum efficiency (QE). The fraction of input photons that are recorded as signal
counts by a photon detector or imaging device. 182, 272
Quenching. The reduction in fluorescence emission by a fluorochrome due to environ-
mental conditions (solvent type, pH, ionic strength) or to a locally high concentration
of fluorochromes that reduces the efficiency of fluorescence emission. 183
Raster. A zigzag pattern of straight line segments, driven by oscillators, used to scan a
point source over the area covered by a specimen or an image. 208, 236
Raw image or raw frame. In image processing, the name of an image prior to any mod-
ifications or processing. 244, 289
Rayleigh criterion for spatial resolution. The criterion commonly used to define spatial
resolution in a lens-based imaging device. Two point sources of light are considered to
be just barely resolved when the diffraction spot image of one point lies in the first-order
minimum of the diffraction pattern of the second point. In microscopy, the resolution
limit d is defined, d 1.22 λ/(NA objective NA condenser ), where λ is the wavelength of
light and NA is the numerical aperture of the objective lens and of the condenser. 88
Readout noise or read noise. In digital imaging, read noise refers to the noise back-
ground in an image due to the reading of the image and therefore the CCD noise
associated with the transfer of charge packets between pixels, preamplifier noise, and
the digitizer noise from the analogue-to-digital converter. For scientific CCD cam-
eras, the read noise is usually 2–20 electrons/pixel. 273
Readout rate. The rate in frames/s required for pixel transfer, digitization, and storage
or display of an image. 269
Real image. An image that can be viewed when projected on a screen or recorded on a
piece of film. 45
Real intermediate image. The real image focused by the objective lens in the vicinity
of the oculars of the microscope. 2, 3
Red fluorescent protein (RFP). A fluorescent protein from a sea anemone of the genus
Discosoma used as a fluorescent marker to determine the location, concentration,
and dynamics of a protein of interest in cells and tissues. The DNA sequence of RFP
is ligated to the DNA encoding a protein of interest. Cells transfected with the mod-
ified DNA subsequently express fluorescent chimeric proteins in situ. 185
Refraction. The change in direction of propagation (bending) experienced by a beam of
light that passes from a medium of one refractive index into another medium of dif-
ferent refractive index when the direction of propagation is not perpendicular to the
interface of the second medium. 20
Refractive index ellipsoid and wavefront ellipsoid. An ellipsoid is the figure of revo-
lution of an ellipse. When rotated about its major axis, the surface of the ellipsoid is
used to describe the surface wavefront locations of E waves propagating outward
from a central point through a birefringent material. The same kind of figure is used
to describe the orientation and magnitude of the two extreme refractive index values
that exist in birefringent uniaxial crystals and ordered biological materials. 128, 130
Region of interest or ROI. In image processing, the subset of pixels defining the
“active region” of an image, determined by defining xy coordinates or by drawing