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Appendix A. Glossary

Appendix A. Glossary

1-bit image

An image composed of pixels that are either black or white. Called 1-bit (or single-bit) because only one bit of information is required for each pixel.

8-bit image

An image that uses 8 bits of data for each pixel. Because you can count from 0 to 255, a pixel can be any one of 256 different colors.

24-bit image

An image that uses 24 bits of data for each pixel. Because you can count from 0 to roughly 16-and-a-half million, a pixel can be any one of 16.5 million colors.

32-bit image

An image that uses 24 bits of data to store the color of each pixel and an additional eight 8 bits of data to store the opacity of each pixel. This transparency information is called an alpha channel.

35 mm equivalency

What a lens would be equivalent to in terms of a standard 35 mm SLR camera. Used as a standard for discussing the field of view and magnification power of a lens. In 35 mm equivalency, lenses over 50 mm are tele-photo, whereas lenses below 50 mm are wide-angle or fisheye.


Irregularities in a piece of glass that cause light to be focused incorrectly. Aberrations produce artifacts and anomalies in images.

acquire plug-in

A special type of plug-in that allows for communication between your image-editing application and your digital camera.

action-safe area

The area of a video image that will most likely be visible on any video monitor. Essential action should be kept within the action-safe area, because action that falls outside might be cropped by the viewer’s screen. See title safe.

active autofocus

An autofocus mechanism that achieves focus by transmitting something into the scene, usually infrared light or sonar.

adaptive editing control

An adjustment that allows you to alter the shadow and highlight tones in your image. Adaptive editing adjustments analyze your image to determine exactly which tones are shadows and highlights, rather than simply altering all pixels that have a given color value.


Light mixes together in an additive process whereby, as colors are mixed, they get brighter; that is, light is added as the colors are mixed. Additive colors eventually produce white. Red, green, and blue are the primary additive colors that can be used to create all other colors.

adjustment layers

Let you apply Levels, Curves, and many other image-correction functions as a layer, allowing you to remove or adjust the effect at any time.


The stair-stepping patterns that can appear along the edges of diagonal lines in an image.

alpha channel

Extra information stored about the pixels in an image. Alpha channels are used to store transparency information. This information can serve as a mask for compositing or applying effects.


As regards photography, light in the real world travels in a continuous wave. To record those continuous analog waves, your digital camera must first convert them into a series of numbers, or digits.


An opening that is used to control the amount of light passing through the lens of a camera. Typically constructed as an expanding and contracting iris.

aperture priority

A shooting mode on a camera. Aperture priority lets you define the camera’s aperture. The camera will then calculate a corresponding shutter speed based on its light metering.


Advanced Photography System. A fairly new format of film and cameras.


Image degradations caused by image-processing operations. Compressing an image, for example, often results in the creation of many image-compression artifacts. Different image-processing tasks create different types of artifacts.


A measure of film speed. See also ISO.

aspect ratio

The ratio of an image’s length to its width. Most computer screens and digital cameras shoot images that have an aspect ratio of 4:3. 35 mm film and some digital cameras shoot in a 3:2 aspect ratio.


A lens that contains some elements that are not perfect hemispheres. These non-spherical elements are used to correct certain types of aberrations.


Some cameras include special functions that cause them to automatically shoot a series of bracketed images when you press the shutter release.

autofocus-assist lamp

See focus-assist lamp.

automatic exposure

A feature that will automatically calculate the appropriate shutter speed, aperture, and sometimes ISO at the time you take a picture.


In a medium- or large-format camera, the film is held in the back of the camera. The back can be removed and replaced with other backs, including digital backs.

barrel distortion

A type of distortion caused by a lens. Causes the edges of an image to bow outward. Most prevalent in wide-angle and fisheye lenses. See also pincushion distortion.

Bayer pattern

The most common color filter array. A pattern of red, green, and blue filters that can be laid over the photosites of an image sensor and used to calculate the true color of every pixel in the sensor.

bicubic interpolation

A method of interpolation used in a resampling process. Usually the best interpolation choice when you scale an image.

bilinear interpolation

A method of interpolation used in a resampling process.

bit depth

A measure of the number of bits stored for each pixel in an image. Images with higher bit depths contain greater numbers of colors. Also known as color depth.

black and white

In the film world, “black and white” is used to refer to images that lack color; that is, images that are composed of only shades of gray. In the digital world, it’s usually better to refer to such images as “grayscale” because your computer is also capable of creating images composed only of black and white pixels.

blending mode

A setting that determines how the pixels in composited layers blend together. Also known as transfer mode.


A flaring, smearing artifact in a digital photo caused by a photosite on the camera’s CCD getting overcharged. The extra charge spills into the neighboring photosites and creates the artifact.


The quality of the defocused area in an image with shallow depth of field. A better lens will produce smoother, more diffuse bokeh.

boot time

How quickly (or slowly, depending on the camera) the camera will be ready to shoot after powering up.


The process of shooting additional frames of an image, each over- or underexposed. By intelligently bracketing your shots, you stand a better chance of getting the image you want.

bulb mode

A special shutter mode that opens the shutter for as long as you hold down the shutter release button.


See drive.


The white highlight that appears in people’s eyes.


Charge-coupled device, the image sensor used in most digital cameras.

center-weight metering

A light-metering system similar to matrix metering, but that lends more analytical weight to the center of the image.


One component of a color image. Different channels of color are combined to produce a full-color image. For example, red, green, and blue channels are combined by your monitor or digital camera to create a full-color picture. Also known as color channel.

chromatic aberrations

Color artifacts caused by the inability of a lens to evenly focus all frequencies of light. Usually appears as colored fringes around high-contrast areas in a scene. See also purple fringing.


Color information.

chrominance noise

One of the two types of noise that can occur in a digital image. Luminance noise appears as brightly colored specks—usually red, green, purple, or blue—in an image. As with chrominance noise, luminance noise gets worse at higher ISOs, and you’ll most often find it in the shadowy areas of your image.


When highlights or shadows suddenly cut off to completely white or black in an image, rather than fading smoothly.


See Rubber Stamp.


Complementary Metal Oxide Semiconductor. A type of image sensor. Not yet widely used, but offers the promise of better image quality, lower cost, and lower power consumption than a CCD.


See color management system.


Cyan, magenta, yellow, and black, the primary subtractive colors that are used by a printing process to create all other colors. Although cyan, magenta, and yellow are subtractive primaries, it is impossible to create perfectly pure pigments. Therefore, black ink must be added to create true blacks and darker colors.


Special chemicals applied to a lens that serve to reduce flares and reflection.

color calibration

The process of calibrating your input and output devices, as well as your monitor, so that color is accurately displayed on each.

color channel

See channel.

color depth

See bit depth.

color filter array

The colored filters that are placed over the photosites on an image sensor. Because image sensors can only “see” in grayscale, a color filter array is required for them to capture color information.

color gamut

The range of colors that can be described by a particular color model. Also known as gamut or color space.

color management system (CMS)

A set of software components that work together to compensate for the differences in your monitor, printer, and scanner so that your images appear as accurately as possible on your display.

color matching engine

The software component of a color matching system that performs the translations from one color space to another.

color model

A method of representing color. RGB, CMYK, and L*a*b are all color models, and each takes a different approach to representing color. See also color gamut.

color space

See color gamut.

color temperature

Different lights shine at different temperatures, measured in degrees Kelvin (°K). Each temperature has a different color quality.


A type of reusable, removable storage. The most common form of storage used in digital cameras.


The process of layering images on top of each other to create composite images. Compositing is used for everything from creating simple collages to performing complex image correction and adjustment.

continuous mode

See drive.

continuous autofocus

An autofocus mechanism that constantly refocuses as new objects move into its focusing zone.

continuous tone

A printed image that is made up of continuous areas of printed color. Photographic film prints are continuous tone. Ink-jet printers, laser printers, and offset presses use printing methods that don’t print continuous tone. If you look closely at a print from one of these devices, you can see that it is made up of small patterns of dots.

contrast detection

An autofocus mechanism that determines focus by measuring contrast in a scene. The mechanism assumes that maximum contrast means sharpest focus. Contrast detection is a method of passive autofocus.

contrast filters

Filters that you can add to the end of a lens to increase contrast in an image.

contrast ratios

The ratio of the darkest to lightest tones in an image. The higher the ratio, the more contrast there is in the image.


Cathode ray tube.

dark frame subtraction

A method of reducing noise in long-exposure digital photos.


The interpolation process that a CCD uses to calculate color. The color of any individual pixel is determined by analyzing the color of the surrounding pixels.

depth of field

A measure of the area of an image that is in focus. Measured as depth from the focal point of the image.

destructive effects

Filters that actually modify the pixels in your image. Unlike nondestructive effects, there’s no easy way to go back and change a destructive effect’s settings, or undo its effects if you change your mind about it later.

device-dependent color space

A color space that represents colors as combinations of other colors. RGB and CMYK are device-dependent color spaces, because accurate color representation in these spaces is dependent on the quality of your primary colors.

device-independent color space

A color space (such as L*a*b color) that records what a color actually looks like, rather than how it is made.

device profile

A description of the color qualities of a particular device, such as a printer, scanner, digital camera, or monitor. Also known as profile or ICC profile.

digital photography

In this book, the term digital photography is used to refer to images shot with a digital camera.

digital zoom

A feature on many digital cameras that creates a fake zoom by capturing the center of an image and blowing it up to full image size.


The process of converting something into numbers (digits). In a digital camera, an image sensor captures an image that is then converted into numbers, or digitized.


An optical control that lets you adjust the viewfinder on a camera to compensate for nearsightedness.


The process of reducing the size of an image by throwing out data.


Dots per inch, a measure of resolution.


A special shooting mode for shooting a sequence of images in rapid succession. Also known as burst or continuous.


A sealable, waterproof bag that will keep your camera dry, even if it gets submerged.

dual-axis focusing zone

An autofocus mechanism that measures contrast along both horizontal and vertical axes.

dynamic range

The range of colors that a device can represent. A digital camera with larger dynamic range can capture and store more colors, resulting in truer, smoother images.

effective pixel count

The actual number of pixels that are used on an image sensor. In many digital cameras, some of the pixels on the camera’s sensor are masked away or ignored.

electron gun

The image on a CRT screen or television screen is created by three electron guns that paint the screen with three different streams of electrons. Separate guns are provided for the red, green, and blue components of a color image.

electronic TTL viewfinder

An eyepiece viewfinder that uses a tiny LCD screen instead of normal optics, and looks through the lens. (This is the same mechanism you’ll find on most video camcorders.)


One individual lens. Most camera lenses are composed of many different elements.


The light-sensitive chemical coating on the surface of a piece of film.


Exchangeable Image File. A digital image file format used by most digital cameras. Notable because it includes special header information where all of an image’s parameters (shutter speed, aperture, and so on) are stored.


The combination of aperture, shutter speed, and ISO settings that determines how much light will be recorded at the focal plane.

exposure compensation

A mechanism for adjusting the exposure on your camera that is independent of any particular exposure parameter. In other words, rather than specifically changing the aperture or shutter speed, you can simply use exposure compensation to over-or underexpose an image. The camera will calculate the best way to achieve the compensation.

exposure lock

A mechanism that lets you lock the exposure on your camera independently of focus.

external flash sync connection

Allows you to connect an external flash (usually a specific model) to the camera using a small cable.


How quickly an effect changes. For example, a depth-of-field blur might have a quick falloff, meaning that the blur goes from sharp to blurry very quickly.

fast shutter mode

Forces a large aperture to facilitate a fast shutter speed. Sometimes called sports mode.


The process of blurring the edge of a selection to create a smoother blend between an edit and the rest of an image.

fill flash

Allows you to force the flash to fire to provide a slight fill light. Also known as force flash.


A quaint nineteenth-century analog technology for recording images. Requires lots of-many hazardous chemicals, a lot of patience, and doesn’t offer cool features such as Levels dialog boxes or Rubber Stamp tools. Not for the impatient. Does have the advantage that the recording and storage mediums are included in the same package.

filter factor

Most lens filters are documented with a filter factor, which will inform you of the exposure compensation (in stops) required when you use that filter.


Either colored plastics or glass that you can attach to the end of your camera’s lens to achieve certain effects, or special effects that you can apply to your image in your image-editing program. See also plug-ins.


A type of serial connection provided by many computers and digital cameras. Can be used for transferring images between camera and computer. Much faster than USB. Also called IEEE-1394 or i.Link.


An extremely wide-angle lens that creates spherical views.

flash exposure compensation

A control that allows you to increase or decrease the intensity of your camera’s flash. Usually measured in stops.

flash memory

A form of nonvolatile, erasable memory. Used in digital cameras in the form of special memory cards.

focal length

The distance, usually measured in millimeters, between the lens and the focal plane in a camera.

focal length multiplier

Many digital SLRs use an image sensor that is smaller than a piece of 35 mm film. If you attach a lens to one of these cameras, its 35 mm equivalency will be multiplied by the focal length multiplier. For example, if your digital SLR has a focal length multiplier of 1.6x, a 50 mm lens mounted on your camera will have an effective focal length of 80 mm.

focal plane

The point onto which a camera focuses an image. In a film camera, there is a piece of film sitting on the focal plane. In a digital camera, a CCD sits on the focal plane.

focus-assist lamp

A small lamp on the front of the camera that the camera can use to assist autofocusing. Also known as an autofocus-assist lamp.

focus ring

The ring on a lens that allows you to manually focus the lens. Most smaller digital cameras lack focus rings, which can make them difficult to manually focus.

focus tracking

An autofocus mode provided by some cameras that can track a moving object within the frame and keep it in focus. Sometimes called servo focus.

focusing spot

See focusing zone.

focusing zone

An area in the camera’s field of view in which the camera can measure focus. Most cameras only have one focusing zone. The camera will focus on the object in this zone. Some cameras have multiple zones.

force flash

See fill flash.


Sometimes synonymous with stop, more specifically a measure of the size of the aperture on a camera. F-stop values are the ratio of the focal length of the lens to diameter of the aperture.


The midpoint (between black and white) in a tonal range.

gamma correction

The process of correcting the midpoint in an image, without altering the black or white point.


See color gamut.


Thin pieces of plastic that are usually placed in front of lights to create colored lighting effects.


Dream on.


An image composed entirely of shades of gray, rather than color. (Basically, a fancy name for “black and white.”)


Multiple elements cemented together in a lens.


A process used for printing photos that begins by shooting a photo of an image through a special halftone screen. The resulting photo gets broken down by the screen into a pattern of dots that can be easily printed using a single ink. Your computer can generate halftone output from a laser printer, allowing you to skip the photographic halftoning step.

hardware calibration

Special devices that measure the color of an output device. The data gathered by the device is then used to create a color profile of the device. This profile is, in turn, used by color management software to ensure accurate color output.


A graph of the distribution of tones within an image.

hot shoe

A mount for attaching an external flash to a camera.

ICC profiles

See device profile.


Sony’s name for FireWire.


The official name for FireWire.

image buffering

The capability of a camera to temporarily store images in an internal memory buffer before writing them out to a memory card. A large image buffer facilitates the rapid shooting of multiple frames, because the camera doesn’t have to stop shooting to offload images to storage.

image stabilization

Some telephoto camera lenses offer special optics that can stabilize the tiny shakes and jitters that can be caused by your hand.


The process of calculating missing data in an image based on data that is already there.


A mechanism that can expand and contract to create circular apertures to control the amount of light passing through a lens.


A measure of a film’s “speed” or light sensitivity. The higher the ISO, the more sensitive the film. The sensitivity of digital camera sensors is also rated using the ISO scale.


Joint Photographic Experts Group. More commonly, the name of a popular lossy image compression scheme.

L*a*b color

See Lab color.

Lab color

A color model created by the Commission Internationale de l’Éclairage. Lab color describes colors as they actually appear, rather than by how they are made. As such, Lab color makes a great reference space for performing color management and calibration.


How far colors in an image can be pushed or pulled.


Liquid crystal display.

lens flares

Bright color artifacts produced in a lens by reflections within the lens itself.

line screen frequency

The density of the screen that is used in a halftoning process. A screen with more density yields an image with smoother tones and more detail.


Lithium Ion. A type of rechargeable battery.

linear array

A digital camera mechanism that uses a single row of sensors that makes three separate filtered passes over the imaging sensors to create a full-color image.


Indicates that a particular process does not result in any loss of quality.


Indicates that a particular process results in loss of quality.


Brightness information.

luminance noise

One of the two types of noise that can occur in a digital image. Luminance noise appears as brightly colored specks, usually without a color in an image. As with chrominance noise, luminance noise gets worse at higher ISOs, and you’ll most often find it in the shadowy areas of your image. Of the two types of noise, luminance noise is the least annoying, because it can look a lot like grain.


A special type of lens used for photographing objects at extremely close distances.

manual mode

A shooting mode on a camera that allows you to set both the aperture and shutter speed, giving you full control over the camera’s exposure.

matrix meter

A light meter that analyzes many different areas of your scene to determine proper exposure.


A million pixels. Usually used as a measure of the resolution of a digital camera’s sensor.

Memory Stick

A type of reusable, removable storage developed by Sony, not yet adopted by any other camera vendors.


The process of measuring light with a light meter (or by eye) so as to determine proper exposure for a shot.


A property of inks that can cause a print to exhibit color shift when viewed under different types of light. All inks have metameric properties. In desktop inkjet printers, it’s usually just pigment-based inks that exhibit metameric shift.


A tiny hard drive that fits in a Type II CompactFlash slot on a camera. Note that a camera usually has to be approved for use with a MicroDrive.

mirror lockup

The capability to lock a camera’s mirror into the “up” position to reduce vibration when shooting long-exposure images. Some higher-end cameras also provide a lockup feature to aid in cleaning the camera’s sensor.

multiple array

A digital camera mechanism that uses three separate CCDs for capturing a color image, one each for red, green, and blue.

multisegment meter

See matrix meter.

multispot focus

An autofocus mechanism on a camera that can focus on one of several different places within an image.

nearest neighbor

A method of interpolation used in a resampling process.

neutral density filter

A filter that cuts down on the light entering your camera’s lens, without altering the color of the light. Enables you to use wider apertures or faster shutter speeds in bright light.


Nickel Cadmium. A type of rechargeable battery. Not recommended for use in a digital camera.


Nickel Metal Hydride. A type of rechargeable battery.

nodal point

The optical center of a camera’s lens.


The bane of all digital photographers. Noise appears in an image as very fine-grained patterns of multicolored pixels in an area. Shadow areas are particularly susceptible to noise, as are images shot in low light. Noise is very different looking than the grain found in film photos. Unfortunately, it’s also far less attractive.

nondestructive editing

A piece of editing software that doesn’t alter your original image data when you perform an edit. Nondestructive editing systems work by maintaining a list of edits that get applied to your original image data in real time, anytime the image needs to be displayed, printed, or output. Because the edits are kept separate from the image data, you can change or alter the edits at any time. Apple Aperture, Adobe Photoshop Lightroom, and Nikon Capture NX are all examples of nondestructive editors. In Photoshop, Smart Objects and Adjustment Layers provide nondestructive editing capabilities.

normal lens

A lens that has a field of view that is equivalent to the field of view of the human eye. Roughly 50 mm.


An image that was exposed for too long. As an image becomes more overexposed, it gets brighter and brighter. Highlights and light-colored areas wash out to completely white.


The easiest way to understand parallax is simply to hold your index finger in front of your face and close one eye. Now close the other eye and you’ll perceive that your finger has jumped sideways. As you can see, at close distances, even a change of view as small as the distance between your eyes can create a very different perspective on your subject. A camera that uses one lens for framing and another for shooting faces the same problems. Parallax is not a problem at longer ranges, because the parallax shift is imperceptible.

passive autofocus

An autofocus mechanism that achieves focus by analyzing the camera’s view of the scene.

PC card adapter

A special adapter that lets you insert a storage card from your camera into the PC card slot of your computer.

PC cards

Small, credit–card–sized peripheral cards that can be inserted into a PC card slot on a laptop computer, or into a special PC card drive on a desktop computer. PC card adapters are available for most types of digital camera media, allowing you to insert media directly into your PC card slot.


See PC cards.

phase detection

See phase difference.

phase difference

An autofocus mechanism that uses measurements taken through different parts of the camera’s lens to determine focus. Also known as phase detection.


A tiny electrode that sits on the surface of an image sensor. There is one photosite for each pixel on a sensor.

picture elements

The smallest area of color information that can be displayed on a computer monitor. Also, the smallest area of color information that can be detected by a digital imaging sensor. Also known as pixels.

pincushion distortion

A type of distortion caused by a lens. Causes the edges of an image to bow inward. Most prevalent in telephoto lenses. See also barrel distortion.


See picture elements.

pixel mapping

A feature included on some digital cameras. When activated, the camera examines all of the pixels on the camera’s image sensor and creates a map of which ones are bad. It then excludes these pixels from all color calculations. The pixel map is stored and used for all shots until you execute the pixel mapping again. Some cameras lose their pixel maps when you change the camera’s batteries.


Sometimes, the individual pixels in an image can become visible, a process called pixellation.


Special bits of code, usually effects or image-processing filters that can be added to your image-editing application. Most plug-ins conform to the Photoshop plug-in standard.


Special filters that can be fitted onto the end of a lens. Polarizers allow light that is polarized only in a particular direction to enter your lens. Polarizers can completely remove distracting reflections from water, glass, or other shiny surfaces. Polarizers can also be used to increase the contrast in skies and clouds.


Reduction of the number of tones in an image. As a particular tonal range gets posterized, it will appear more “flat.”


Pixels per inch, a measure of resolution.


The process of autofocusing, metering, and white balancing that occurs when you press your camera’s shutter-release button halfway.

prefocus time

How long it takes a camera to perform its prefocus steps (autofocus, metering, and white balance).

prime lens

A lens with a fixed focal length.


See device profile.

proportional zoom control

A zoom control whose rate of zoom changes depending on how far you push or pull the control.


A marketing term for a camera that sits somewhere between the professional and consumer market.

purple fringing

A color artifact specific to digital cameras with resolutions greater than 2 megapixels. Appears in an image around the edges of high-contrast objects, usually shot with wide-angle lenses. Usually confined to the edges of the screen. See also chromatic aberrations.


In JPEG compression, the process of averaging the colors in one 64-pixel square area.


The process of assigning a numeric value to a sample. Part of the digitizing process.


A viewfinder mechanism on a camera. A fixed-focus or zoom lens is used for imaging, whereas a separate optical viewfinder is used for framing your shot.

raw converter

A program that can process raw files from a digital camera into a regular bitmapped, full-color image. A raw converter must include special profile information to process the files from any given camera, as there is currently no accepted standard for raw images.

raw data

Pixel data that comes directly from the CCD with no further processing. Processing is usually performed later using special software. Raw files offer quality equivalent to an uncompressed image, but require much less space.

read-out register

The mechanism that reads the signals from each row of photosites on an image sensor. The read-out register amplifies the signals from the photosites and sends them to the camera’s analog-to-digital converter.


Exposure parameters have a reciprocal relationship so that different combinations of parameters produce the same exposure. For example, setting your camera to a shutter speed of 1/250th of a second at f8 is the same as setting it to 1/125th at f16.


A type of wide-angle lens that includes corrective elements that prevent barrel distortion.


The time it takes a camera to reset itself and prepare to shoot another shot.

red-eye reduction

A special flash mode that attempts to prevent red-eye by firing a short initial flash to close down the pupils in your subject’s eyes.


When the flash from a camera bounces off a subject’s eyes and back into the camera’s lens, the subject will appear to have bright red eyes. Most prevalent in cameras where the flash is very close to the lens.


When primary color channels are positioned over each other so that a full-color image is produced, the images are said to be “in registration.”


The process of slowing and bending light using a transparent substance such as air, water, glass, or plastic.

refresh rate

How often the image on a camera’s LCD viewfinder is redrawn. An LCD with a higher refresh rate will produce an image with smoother motion.


The process of computing new pixel information when resizing a document in your image-editing application. If you are resizing upward, the resampling process will generate new pixels. If you are resizing downward, the resampling process will discard pixels.


In a monitor or digital camera, the number of pixels that fit into a given space. Usually measured in pixels per inch (ppi) or dots per inch (dpi). In a printer, the number of printer dots that fit into a given space, usually measured in dots per inch (dpi).


Red, green, and blue, the additive primary colors that are used by your computer monitor and digital camera to produce all other colors.


The process of analyzing something to determine its content. A digital camera samples light to determine how much, and what color the light is, at any given point in a scene.


A characteristic of color. Colors that are more saturated are typically “deeper” in hue and often darker. As saturation increases, hue shifts slightly.


Small Computer System Interface. An older, high-speed computer interface for attaching hard drives, scanners, and other peripherals.

servo focus

See focus tracking.


The process of using software to increase sharpness in a digital image. Sharpening can happen inside a digital camera or through post-processing on your computer.


A mechanism that sits in front of the focal plane in a camera and can open and close to expose the image sensor or film to light. Many digital cameras do not have physical shutters, but instead mimic shutter functionality by simply activating and deactivating their image sensors to record an image. Cameras that do have shutters typically use a two-curtain mechanism. The first curtain begins to slide across the focal plane to create a gap. It is followed usually very quickly by a second shutter that closes the gap. As the gap passes across, the entire CCD is exposed.

shutter lag

A delay between the time you press the shutter release button on a camera and the time it actually shoots a picture.

shutter priority

A shooting mode on a camera. Shutter priority lets you define the camera’s shutter speed. The camera will then calculate a corresponding aperture based on its light metering.

shutter speed

The length of time it takes for the shutter in a camera to completely expose the focal plane.

single array system

A digital camera mechanism that uses a single image sensor for imaging. Sometimes called a “striped array.”

single lens reflex

A camera whose viewfinder looks through the same lens that your camera uses to make its exposure. Also known as SLR.

single-axis focusing zone

An autofocus mechanism that measures contrast along a single axis only, usually horizontal.

slow-sync mode

A special flash mode that combines a flash with a slow shutter speed to create images that contain both still and motion-blurred objects.


See single lens reflex.


A type of reusable, removable storage.

soft proof

An on-screen proof of a color document.

specular highlights

The bright white glints and reflections that occur on very shiny surfaces and on the edges of objects.

spot meter

A light meter that measures a very narrow circle of the scene.


An RGB color space defined by Microsoft and Hewlett-Packard. It is intended to represent the colors available on a typical color monitor. A little too small for digital photography work.

step-up ring

An adapter that attaches to the end of a lens and allows for the addition of filters or other lens attachments. Serves to change the thread size of the lens.


The process of joining and blending individual images to create a panoramic image.


A measure of the light that is passing through a camera’s lens to the focal plane. Every doubling of light either through changes in aperture, shutter speed, or ISO is one stop. See also f-stop.

striped array

See single array system.


Ink mixes together in a subtractive process whereby as colors are mixed together-together, they get darker; that is, light is subtracted as the colors are mixed. Subtractive colors eventually produce black. Cyan, magenta, and yellow are the primary subtractive colors that can be used to create all other colors.


A lens with a focal length that is longer than normal. As a lens gets more telephoto, its field of view decreases.


See Thin Film Transistor.

Thin Film Transistor

A technology used to create LCD screens. Typically used for the LCD viewfinder/monitors included on the backs of many digital cameras.

three-shot array

A digital camera mechanism that uses three single arrays, one each for red, green, and blue.

through the lens

See TTL.

title safe

A guide similar to the action-safe area. The title-safe area is slightly smaller.

transfer mode

See blending mode.

trilinear array

A digital camera mechanism that uses three linear arrays stacked on top of each other to create a full-color image in a single pass over the image sensor.


When a camera system, be it the viewfinder, white-balance system, light meter, or autofocus, views the scene through the same lens that exposes the sensor, that system is said to be a through the lens or TTL system. A viewfinder mechanism that looks through the same lens that is used to focus the image onto the focal plane. Short for through the lens.


An image that was not exposed enough. In an underexposed image, dark or shadow areas turn to completely black.


The process of enlarging an image by calculating (interpolating) new data.


Universal Serial Bus. A type of serial connection provided by many computers and digital cameras. Can be used for transferring images between camera and computer.

VGA resolution

640 × 480 pixels.

Video LUT Animation

A feature available in some versions of Photoshop that allows for real-time, on-screen viewing of color corrections and changes.

video RAM

The memory in a computer that is used for displaying images on-screen. The more video RAM, the larger your images can be, and the greater the bit depth they can have. Also known as VRAM.


A darkening of the image around the edges.

virtual reality movie

See VR movie.

VR movie

A digital movie that lets you pan and tilt in real time to explore and navigate a virtual space.

wavelet compression

A new fractal-based compression scheme. Converts your image from a series of raster dots into a collection of tiny fractal curves.

white balance

A color calibration used by a camera. Once a camera knows how to accurately represent white, it can represent all other colors. Because white can look different under different types of light, a camera needs to be told what white is, a process called white balancing.


A lens with a focal length that is shorter than normal. As a lens gets more wide-angled, its field of view increases.

XGA resolution

800 × 600 pixels.

zone system

A method of calculating exposure.

zoom lens

A lens with a variable focal length.


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