GLOSSARY^201
aspect ratio The ratio of length to width in image sensors, computer displays, television screens, and
photographic prints.
autofocus A lens mechanism that automatically focuses the lens by bouncing an infrared light beam
or sound waves off the subject matter or by measuring the contrast in a scene. Some cameras use a com-
bination of methods.
automatic exposure A camera mode that adjusts both the aperture and shutter speed based on
readings from a light meter.
automatic flash An electronic flash that measures the light reflected from a subject, varying the
duration and intensity of the flash for each exposure.
available light All the natural and artificial light a photographer uses, short of light provided by
flash units. Or as one photographer put it, all the light that’s available.
B
back-lit or back-lighting A setting that illuminates the subject from behind.
banding Areas of color that show no differentiation except to change abruptly from one color inten-
sity to another so that what should be a gradual change of color is marked by noticeable bands of color.
Bayer pattern, Bayer matrix A distribution of red, green, and blue filters on an image sensor
that provides twice as many green filters as red and blue because of the eye’s sensitivity to shades of
green.
bit depth The number of bits—0s and 1s in computer code—used to record, in digital image situa-
tions, the information about the colors or shades of gray in a single pixel, which is the smallest amount
of information in a graphic image. The smaller the bit depth number, the fewer tonal values possible. For
example, a 4-bit image can contain 16 tonal values, but a 24-bit image can contain more than 16 mil-
lion tonal values.
bitmap An image represented by specific values for every dot, or pixel, used to make up the image.
black noise Also known as dark current, it is the signal charge the pixel develops in the absence of
light. This charge is temperature sensitive and is normal in electrical image-sensing devices.
bleeding The color value of one pixel unintentionally appearing in the adjacent pixel or pixels.
blooming The bleeding of signal charge from extremely bright pixels to adjoining pixels, oversaturat-
ing those adjoining pixels. Masks or potential barriers and charge sinks are used to reduce blooming.
BMP file A Windows file type that contains a bitmapped image.
borderless printing A printing technique, offered on some photo printers, that prints photos from
paper’s edge to paper’s edge, without leaving a white border.