A USEFUL GLOSSARY TO HELP YOU DECODE SOME OF DIGITAL’S
TERMINOLOGY
By Leah Bence
As technology continues
to expand, so does the vocabulary describing it. To help you
stay on top of the field, we’ve decided to squeeze in an
occasional glossary page of industry terms for a quick refresher
or maybe even as a first-time explanation. For the first Fundamentals
entry, we’ve zoomed in on digital camera terms.
Aberration
Optical imperfections within a lens that cause distortions in
the image. Most aberrations can be minimized through the use
of corrective elements within a lens design.
APO (Apochromatic) Lenses
that use internal elements to bring all colors of the visible
spectrum to a common point of focus, creating a sharp image,
are referred to as APO lenses.
Bit-Depth Also referred to
as color depth, bit-depth determines the maximum number of colors
that can be represented at a time. Camera sensors typically
have 12-bit-per-channel color (red, green and blue) for a 36-bit
image (which JPEG compression reduces to 8 bits per channel).
Although more bit-depth is preferable, there are diminishing
returns beyond 8 bits per channel. Image file sizes increase
dramatically, and the increase in image quality may not be worth
it for many photographers.
CCD (Charge-Coupled Device)
An electronic image sensor for digital cameras. Most digital
cameras are built around CCD sensors.
CMOS (Complementary Metal Oxide Semiconductor) A sensor technology
that encompasses all required camera circuits on a single chip.
Because a CMOS sensor requires less power and generates less
heat than a CCD-based system, many large, high-resolution digital
cameras use CMOS technology.
Compression The process of
encoding files through an algorithm, which decreases the size
for storage or transmission over the Internet. There are two
types of compression: lossy and lossless. Lossy compression
(JPEG is an example) results in a visible degradation in image
quality because some image data is lost in the compression process.
Lossless compression (like LZW compression) preserves all image
data.
Digital Zoom A simulated zoom
effect that enlarges the image on a portion of the image sensor.
Because fewer pixels are used to capture the image, you end
up with a significantly lower-resolution final image.
Effective Pixels Pixels on
the sensor actually used to capture an image. Often, not all
the pixels on a sensor can be used because: 1) some pixels on
the surrounding edges of a sensor are masked off to determine
a black point; or 2) some cameras, especially compact ones,
have lenses that are unable to cover the entire sensor area.
Interpolation (or Resampling)
Artificially increasing or decreasing the number of pixels in
an image through the use of an algorithm. Some cameras increase
the number of pixels automatically to compensate for digital
zoom.
JPEG (Joint Pictures Expert Group)
A common algorithm for the compression of image files. JPEG
compression can vary from nearly lossless to highly lossy. Because
JPEG is a standard, JPEG image files can be read by all image-processing
software.
LD, ED and UD Glass (Low-Dispersion,
Extra-Low-Dispersion and Ultra-Low-Dispersion Glass)
All these terms refer to a glass type used in lenses. They denote
rare or specially formulated glass that corrects the path of
light rays as they pass through the lens, making all colors
in the color spectrum focus at the same point.
Megapixel (one million pixels)
The number of photodiodes (also known as photosites or pixels)
on an image sensor is expressed in megapixels, which in turn
is the resolution of the device (a camera, scanner, etc.). Most
sensors have one photodiode for each pixel in an image. For
example, a 5-megapixel camera has five million photodiodes.
Noise Image artifacts caused
by statistical variations with color that manifest themselves
as grain on an image. Excessive noise usually results in an
objectionable-looking image. Smaller image sensors with physically
smaller photodiodes are more subject to noise than sensors with
larger photodiodes.
RAW An image-capture option
containing the maximum information available from a sensor.
The format is offered by many high-end compact digital cameras
as well as D-SLRs. Each camera company has its own RAW format
and corresponding software to support the format.
Resolution Camera resolution
ex-pressed in the number of photodiodes (megapixels) on the
image sensor. More megapixels equals higher resolution. It’s
important to note that many factors go into image quality, and
resolution is only one of them. If you have a poor-quality lens
on a high-resolution camera, you’ll get a high-resolution
image of poor quality. Higher-resolution image files can be
enlarged with less interpolation than lower-resolution image
files.
TIFF (Tagged Image File For-mat)
A standard image file format for bitmapped graphics. TIFF files
are uncompressed and, therefore, very large compared to compressed
for-mats. Because TIFF is a standard, TIFF image files can be
read by all image-processing software.
