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Glossary

AE

Auto-exposure.

AF

Auto-focus.

ambient light

In any scene ambient is natural light.

aperture

An opening within the lens that controls how much light reaches the sensor. Apertures come in f-stops , such as f/5.6 or f/22. Each successive f-stop, as the number goes up, decreases the light reaching the sensor by half. Aperture also affects exposure and depth of field . The lower the aperture number, the faster the lens.

Aperture Priority mode

An automatic mode available in most dSLR cameras in which you choose the aperture and the camera chooses the correct shutter speed.

artifacts

Unwelcome visual distortions in an image, such as blooming, chromatic aberrations, noise, and JPEG compression .

aspect ratio

A measurement of the relation between the width and the height of an image. Most digital cameras (along with 35mm cameras) use a 3:2 aspect ratio, though other ratios, such as 4:3 and 16:9, are also found.

blooming

When overexposed pixels affect neighboring pixels, causing a brightening type of distortion.

brightness

The intensity of light shown in an image.

buffer

The camera's onboard memory, available for storing images before the data writes to a memory card.

CCD

Charge Coupled Device, a type of sensor used in dSLR cameras. Light enters the camera and strikes the CCD, and the CCD converts the light into a digital image. In a separate part of the camera, the image undergoes digital-to-analog conversion. CCD sensors are generally more expensive than CMOS sensors.

CMOS

Complementary Metal Oxide Semiconductor, a type of sensor used in dSLR cameras. Cameras with CMOS sensors are generally less expensive than those with CCD sensors. CMOS works in a similar way to CCD, but does more of the computational work at the sensor, rather than in a different part of the camera.

clipping

Image data that is lost due to pushing pixels past their exposure limits, such as shadow clipping and highlight clipping.

contrast

The gradation of tones from darkest to lightest in an image.

continuous shooting speed

How many images per second the camera is capable of capturing.

depth of field

The area of an image measured from the nearest point to the camera to the farthest point away that is in focus. A large depth of field, which is determined by the aperture , means much, if not all, of the image is in focus; small depth of field means only a certain area of the image is in focus.

depth-of-field preview

Closes the aperture down to the selected setting to let you see what areas of your scene will be in focus when you take the picture.

digicam

Point-and-shoot digital camera.

DPI

Dots per inch, a measurement of inkjet printer resolution . The larger the DPI, the higher the resolution of the printed image. Not to be confused with PPI , or pixels per inch.

dSLR

Digital single-lens reflex, a type of digital camera that is the subject of this book. dSLRs are digital versions of 35mm single-lens reflex cameras, the most popular kind of camera used for professional-quality photography.

exposure

The amount of light that the camera allows to reach the sensor, controlled by aperture and shutter speed .

exposure compensation

Used to adjust for dark or bright subjects. Modifies the automatic exposure by adding or subtracting light from the exposure setting.

f-stop

A series of preset apertures , stated in fractures such as f/5.6 and f/8. As the numbers go up, each f-stop reduces the width of the aperture by half.

focal length

Measured in mm (millimeter), the distance from the optical center of the lens to the sensor when the image is "in focus." The shorter the focal length, the larger the field of view.

full-frame sensor

An image sensor on a dSLR camera that is the same size as a frame of 35mm film, or 24mm x 36mm.

grayscale

An image made up solely of black and white tones.

highlights

The lightest pixels in a digital image.

histogram

A graph of the distribution of colors in an image, with the colors graphed horizontally (x-axis) and the amount of each color represented on the y-axis.

hue

What we usually think of as color . A color's hue is that color aspect that makes it different from other colors.

image editor

A program, such as Adobe Photoshop or other proprietary ones that come with most cameras, that allows many aspects of a digital image to be edited.

image sensor

The digital equivalent of film. A sensor collects the photons that pass through the camera and creates an image of pixels from it.

ISO

In film photography, ISO (International Standards Organization) is the rating of the film's speed, such as 100 speed, 400 speed, and so on. The higher the film speed, the more sensitive it is to light, but the grainier the picture will be. dSLR cameras have kept ISO ratings but have applied them to the sensitivity of the sensor. Increasing the ISO setting allows for photography in lower light situations, but again, with grainier results.

JPEG

Joint Photographic Experts Group. JPEG is thought of as a file format for digital images, but is more correctly defined as a method of compression in which data is discarded to make the file smaller.

luminance

A measure of the intensity of light in an image, arrived at by averaging the lowest RGB values and the highest ones.

maximum burst

How many images you can capture before the camera pauses to write the images to a memory card.

megapixel

One million pixels . The more pixels, the higher the potential resolution of a camera.

memory card

A small card used to store the images captured by your camera. Sony Memory Stick, CompactFlash (CF), Secure Digital (SD), and the xD-Picture Card (xD) are all common memory cards.

midtone

A tonal value that lies halfway between an image's shadows and its highlights .

noise

The digital equivalent of grain in film, caused by making the image sensor too sensitive.

PPI

Pixels per inch in a digital image. The higher the PPI, the better the image quality. 300 ppi is a very common resolution that produces high-quality prints. Not to be confused with DPI .

pan

To move the camera sideways to follow a moving object.

photodiode

The element in an image sensor that collects the light and converts it into electrons.

photosite

The union of a pixel and its color filter on an image sensor .

pixel

Short for picture element . A single point in a digital image that is assigned a specific tone and color. Millions of pixels enable smooth transitions of tone and color to produce accurate renditions of an image. The term also refers to points of light on a monitor screen that make up a digital image.

prime lens

A lens with a fixed focal length.

raw

An image format in which no processing is done by the camera; a raw image is a recording of the raw light values that hit the sensor.

recycling time

The amount of time it takes the flash to prepare for a second image.

resolution

The number of pixels in an image measured in PPI

RGB

Red, green, and blue. Digital-imaging systems, such as digital cameras, use combinations of pixels in these three colors to make all other colors.

saturation

A measure of the intensity of color in an image. High saturation means the image has less gray in its tones; low saturation images have a lot of gray.

shadow

The darkest parts of an image.

Shutter Priority mode

An automatic mode available in most dSLR cameras in which you choose the shutter speed and the camera chooses the correct aperture.

shutter speed

The duration that light is allowed to reach the sensor, measured in fractions of a second, such as 1/60. A fast shutter speed means that the shutter, which normally blocks light from reaching the sensor, is opened for a very brief period. Longer shutter speeds leave the shutter open for longer, allowing more light to reach the sensor.

tilt

The movement of the front of the camera as it is angled up and down.

white balance

A variety of settings that allow the camera to compensate for different sources of light illuminating the scene ( daylight , shade , cloudy, twilight, tungsten light, flash, and custom).

zoom lens

A lens with an adjustable focal length covering all ranges.