Page 360 - Fundamentals of Light Microscopy and Electronic Imaging

GLOSSARY 343

entire group of wavelet profiles describes the location of the wavefront at a later time,
t. Huygens’ principle is commonly used to describe the distribution of light energy in
multiple interacting wavefronts as occurs during diffraction and interference. 72
Image analysis. Any number of measurement operations of objects contained in an
image including particle counts; geometrical measurements of length, width, area,
centroid location, and so forth; intensity measurements; contour measurements;
stereology; and many other operations. 283
Image distance and object distance. With respect to the principal planes of a lens, the
image-to-lens and object-to-lens distances, as predicted by the lens equation in geo-
metrical optics. See also Lens equation. 45
Image histogram. A frequency histogram of pixel values comprising an image, with
pixel values shown on the x-axis and the frequency of occurrence on the y-axis.
The histogram allows one to see the relative contributions of dark, gray, and bright
pixels in an image at a glance and is useful for adjusting image brightness and con-
trast. 284
Image processing. The adjustment of an image’s pixel values for purposes of image
correction and measurement (flat-field correction) or display (adjustment of image
brightness and contrast). 283
Immunofluorescence microscopy. A mode of fluorescence microscopy in which a cer-
tain molecular species in a specimen is labeled with a specific fluorescent antibody.
Fluorescence emission from excited antibodies is collected by the objective lens to
form an image of the specimen. Antibodies can be made fluorescent by labeling them
directly with a fluorescent dye (direct immunofluorescence) or with a second fluo-
rescent antibody that recognizes epitopes on the primary antibody (indirect immuno-
fluorescence). 179
Incandescent lamp. A bulb containing an inert gas and metal filament that emits pho-
tons as the filament becomes excited during passage of electric current. The spectrum
of visible wavelengths emitted by the filament shifts to increasingly shorter wave-
lengths as the amount of excitation is increased. The output of incandescent lamps is
very high at red and infrared wavelengths. 29
Index ellipsoid. See Refractive index ellipsoid.
Infinity corrected optics. The latest optical design for microscope objective lenses in
which the specimen is placed at the focal length of the lens. Used by itself, the image
rays emerge from the lens parallel to the optic axis and the image plane is located at
infinity. In practice, a tube lens or Telan lens located in the body of the microscope
acts together with the objective to form an image in the real intermediate image
plane. This optical design relaxes constraints on the manufacture of the objective lens
itself and allows for placement of bulky accessory equipment such as fluorescence
filter cubes in the space between the objective and the tube lens. 50
Integrated histogram. A modified form of an image histogram in which the x-axis
indicates the pixel value and the y-axis indicates the cumulative number of pixels
having a value of x and lower on the x-axis. The edge of the histogram defines a dis-
play function from which one can determine the rate of change in light intensity at
any value of x along the gray scale. Useful for determining the gray-level midpoint
and for determining if LUTs should be linear, exponential, etc. 287
Intensifier silicon-intensifier target (ISIT) camera. A video camera tube used for
low-light imaging applications. An ISIT tube is essentially a SIT tube modified by
the addition of an image intensifier coupled by fiber optics as a first stage of light
amplification. 250