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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

Primarily used for close-up photography, macro refers to a one-to-one or higher magnification of a subject provided by optics (i.e., a macro lens). The focal length of a macro lens determines how close the lens must be to a subject to attain a one-to-one image capture. For example, a 60mm macro lens will require a shorter lens-to-subject distance than a 100mm macro lens.

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. Megapixels, however, are not the only factor that determines image quality. The lens, processing algorithms and other attributes are also critical factors.

Memory Card (Media Card)
A memory card is a digital camera storage medium. Although these cards are available in a number of different formats-SD (Secure Digital), CF (CompactFlash), Memory Stick (with several variations), xD-Picture Card-each camera can accommodate only one (sometimes two) of those formats. All cards come in different capacities, measured in megabytes (i.e., 256 MB) or gigabytes (i.e., 2 GB). Some cards are also designed to facilitate high performance, decreasing the time it takes for the camera to write the image data to the card. Card capacities continue to increase in all formats, although not all cameras may be able to use these large-capacity cards. It's also important to note that, with the exception of MicroDrives (CompactFlash Type II), which have moveable parts like a hard drive, all other media cards are solid-state or flash memory cards and are, therefore, fairly nonvolatile.

The process of defining the light levels in a scene and providing a measurement for a proper exposure value. Popular modes include center-weighted metering (an average of the frame, with emphasis on the center of the image), spot metering (generally 1 to 3 percent of the image), and evaluative or matrix metering (an average of independent areas of the image). Most digital cameras offer at least two-but generally three-of these metering options.

Image artifacts caused by complex variations with color that manifest themselves as grain on an image. Excessive noise, which is most often seen first in shadows, usually results in an objectionable-looking image. High-resolution digital cameras with small image sensors, where more pixels are forced to live in a smaller space and have physically smaller photodiodes are more subject to noise than sensors with larger photodiodes. High ISO (light sensitivity) also generates image noise. Most digital cameras are equipped with some form of noise reduction that is either automatically triggered with high ISOs or long exposures or, in higher-end cameras, can be turned on and off manually. When noise reduction is applied in camera (or via image-editing software), it can result in softened or blurred details to lessen the visibility of the noise.

An image-capture option containing the maximum information available from a sensor without the application of in-camera processing algorithms. This allows photographers to have more control over the final image by processing the image manually in a software program. 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. Image-editing applications like Adobe Photoshop are also capable of opening and processing images shot in RAW.

Camera resolution expressed 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 produce larger prints than lower-resolution files.

The three primary colors of red, green and blue that our eyes perceive as the basis for every other color. When added together equally, they make pure white. Most, but not all, digital photography uses an RGB color space. (See also Color Space.)


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