Monday, March 26, 2007
Digital Photography Glossary
Check out common terms you need to know for digital imaging
Labels: Learning Center
A sloping graph, resembling a mountain range with peaks and valleys, that illustrates the exact range of tones the image sensor has captured for a particular shot. Anything past the left edge of the graph is pure black and anything beyond the right edge is pure white. The height of the graph represents the number of pixels for a given area. Some digital cameras have "live" histograms that are visible on the LCD when taking pictures to help the photographer determine the proper exposure. Other digital cameras have a histogram in the playback mode so the photographer can determine, albeit after-the-fact, if the image was properly exposed. Many image-editing programs use histograms as a visual aid when adjusting image files during post-processing.
Image Stabilization (IS)
Optical image stabilization utilizes gyroscopic sensors within the lens to detect and compensate for motion or "camera shake." Alternatively, some cameras achieve IS by moving the image sensor when camera movement is detected. But not all image stabilization is the same, nor as effective. For example, the latest trend in compact cameras is "image stabilization" that does nothing more than boost the ISO (light sensitivity) to achieve higher shutter to avoid blurry pictures. Unfortunately, this type of "stabilization" is usually compromised by high levels of image noise.
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 but this interpolation often results in degradation of image quality. Image-editing software also interpolates pixels when enlarging an image beyond its core values of pixel count and resolution.
ISO (Light Sensitivity)
The ISO rating is an indication of light sensitivity in digital photography. Sensitivity is increased by amplifying sensor output, which also increases noise output, much like the increased grain in film with higher light sensitivity. ISO levels range from 50 to 6400. The higher the ISO, the less actual light is needed to achieve a good exposure. At the same time, by increasing the ISO number, a higher shutter speed can be achieved, lessening the probability of a blurred image caused by camera shake-but with higher ISOs, often at the expense of higher image-noise levels.
JPEG (Joint Photographic Experts Group)
A common algorithm for the compression of image files. JPEG compression can vary from nearly lossless to highly lossy. All digital cameras are capable of capturing images in JPEG format, and because JPEG is a standard, JPEG image files can be read by all image-processing software. (See also Compression.)
LCD (Liquid Crystal Display)
In photography, Liquid Crystal Displays are typically a 1.5- to 2.5-inch screen comprised of liquid crystals that are stimulated by electric current to act as a viewfinder and/or preview screen of your frame. The LCD on most, but not all, digital SLRs is only used for viewing already-captured images and navigating menus. Technology developed to allow a "live view" on digital SLRs is currently available only on a handful of cameras, but this feature may become more widely implemented in the near future.
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. These formulated glasses correct the path of light rays as they pass through the lens, making all colors in the color spectrum focus at the same point. Lenses constructed with these types of glass eliminate or lessen the occurrence of aberrations and some types of artifacts.
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