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Monday, March 26, 2007

Digital Photography Glossary

Check out common terms you need to know for digital imaging

Labels: Learning Center

Bit
The smallest data unit of binary computing, being either 1 or 0. Eight bits make up one byte. (See also Bit-Depth.)

Bit-Depth
Also referred to as color depth, bit-depth determines the maximum number of shades or intensities of colors that can be represented at a time. Camera sensors typically have 12-bits-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 (8 bits x 3 channels = 24 bit-depth). Image file sizes increase dramatically, and not all devices (printers, monitors) will benefit from higher bit-depth. Additionally, some image editing may have limited-or no-capabilities of working beyond 8 bits.

CCD (Charge-Coupled Device)
CMOS (Complementary Metal Oxide Semiconducter)
Two types of sensors used in digital cameras. These sensors are the digital equivalent of film in that, as the light enters the camera through the lens, the light waves are focused on the sensor, recorded electronically and then processed into a digital image. The CCD is the most common electronic image sensor used in digital cameras and is noted for its high quality but also for its extensive power requirements. CMOS is a sensor technology that encompasses all required camera circuits on a single chip. In the early days of digital photography, CMOS sensors were used in low-end digital cameras because they were less expensive to manufacture. However, more recently, because of technological advancements and the low power requirements of CMOS technology, a number of high-resolution, high-quality digital cameras now use CMOS sensors.

Chromatic Aberration
A fringe or outline of any color generated when the lens does not focus all light waves at the same focal point. While a chromatic aberration can be purple, the term "purple fringing"-a purple/blue fringe along high-contrast edges-refers to a separate phenomenon that is generally caused by characteristics of the sensor.

Color Spaces
Every device that produces, measures, or captures color has its own way of reproducing all the colors in the visible spectrum, which is known as its color space. The most common color spaces in digital photography are Adobe RGB 1998 and Adobe sRGB. The former has a broader color gamut (range of colors/tones), while sRGB has a smaller color gamut.

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) can result in visible degradation of image quality, especially when saving the same image as a JPEG multiple times, because some image data is lost in each compression process. Lossless compression (like LZW compression) preserves all image data.

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