A Glossary of Digital Photography Terms
Sometimes, the phrases, acronyms and strings of numbers or number-letter combinations used to identify photographic hardware or techniques can be daunting to the uninitiated neophyte photographer. We've prepared a list of the basic terms. Have we left any out that you think should be added? Please let us know!
Shorthand term used to describe HD video recorded at 720 horizontal scan lines per inch progressively. Measuring 1280 x 720 (921,000 pixels), 720p video recordings broadcast at 60 frames per second match the highest temporal resolution levels for ATSC and DVB standards.
Also known as “Full-HD,” 1080p is a shorthand term for video recorded at 1920 lines of horizontal resolution and 1080 lines of vertical resolution, and is optimized for 16:9 format playback. The “p” stands for progressive, which means all of the data is contained in each frame as opposed to “interlaced” (i), in which the image data is split between two frames in alternating lines of image data.
Similar to 1080p video, the “i” stands for “interlaced,” which differs 1080p (progressive) video in that each frame contains about twice the data of 1080p video files, which makes them more detailed but also too large for many output applications. Depending on the region in which 1080i is employed the frame rates can be 25, 30 or 60 frames per second.
A distortion of image quality or color rendition in a photographic image caused by optical limitations of the lens used to capture the image. Aberrations commonly show up in the form of halation around contrasty portions of the image or “smearing” of color toward the edges of the frame. Aspheric lens surfaces and advanced lens coatings are often used in more expensive or complex lenses as a means of reducing aberrations.
Image resolution as expressed in horizontal versus vertical pixels (e.g. 1600 x 1200 Pixels is the absolute resolution, and is also expressed as 2.1 Megapixel, having more than 2,000,000 pixels on its sensor).
The A-D Converter converts the analog signal that is emitted from the image sensor into a digital signal.
To import digital image files into a software application for processing or editing purposes. The term is often applied differently within different types of software.
Adobe RGB (Adobe RGB 1998)
A widely accepted color space that encompasses a wider range of color than the more commonly used sRGB color space. Adobe RGB is the preferred color space for images intended for prepress applications.
Aka Continuous Focus, AF Servo, is maintained by partially pressing the camera's shutter release button, which enables you to continuously maintain focus on a moving subject as the subject moves within the frame. Shutter-response times are usually faster in AF Servo since the subject is already in focus.
The process by which smooth curves and lines that run diagonally across the screen of a low-resolution digital file take on a jagged look as opposed to a smooth, natural rendition. Smoothing and anti-aliasing techniques can reduce the effects of aliasing.
AMOLED (Active-Matrix Organic Light Emitting Diode)
AMOLED is an advanced version of an OLED (Organic Light Emitting Diode), which offers better contrast, lower power consumption and a physically narrower profile than OLEDs and LEDs.
Anti Shake (Image Stabilization)
Also known as Image Stabilization (IS), Vibration Reduction (VR), or simply image stabilization, anti-shake technology is a method of reducing the effects of camera movement on the photographic image. Image stabilization can be achieved in the lens or in the camera body. In-camera Image Stabilization is achieved by mounting the camera sensor on a “floating” micro-geared stage that rapidly shifts the sensor in the opposite direction of the camera's movement, which effectively cancels out the image movement.
The alternative method of canceling camera movement is by employing a gyroscopically-driven “floating” element in the rear portion of the lens that rapidly shifts the element in the opposite direction of the camera movement. Needless to say, either process is quite complex and requires extreme high-speed data processing coupled with precision lens/sensor movements in order to achieve the desired effect.
The ultimate benefit of IS technology is that it enables you to handhold a camera three to four shutter-speeds slower than non-IS enabled cameras or lenses.
Note: Although image stabilization is usually a function of the lens, some camera manufacturers, including Pentax and Sony/Minolta feature in-camera image stabilization, which enables sharper handheld shooting with lenses that aren’t IS-enabled.
The adjustable opening—or f-stop—of a lens determines how much light passes through the lens on its way to the film plane, or nowadays, to the surface of the camera's imaging sensor. “Faster” lenses have wider apertures, which in turn allow for faster shutter speeds. The wider the aperture is set, the shallower the depth of field of the image.
Wider apertures allow for selective focus, the ability to isolate your subject from background and foreground within the frame. Conversely, if you stop the lens aperture down to its smallest openings, you increase the depth of field, or the amount of focus from foreground to background. Generally speaking, most lenses display the highest level of resolving power when set to about three stops down from the widest aperture.
Note: The term “highest resolution” does not mean the greatest level of depth of field. It just means what is in focus cannot be rendered any sharper by that particular lens regardless of the image’s depth of field.
A metering mode in which the photographer sets the desired lens aperture (f-stop) and the camera in turn automatically sets the appropriate shutter speed to match the scene being recorded. Portrait photographers usually prefer wider apertures for shallower depth of field (DOF), while landscape photographers prefer smaller apertures, which bring more of the scene into sharper focus. (See Shutter Priority,below)
Aperture priority is a preferred method of maintaining a fixed degree of depth of field while shooting under rapidly changing lighting conditions.
A term used to describe the size of the digital imaging sensors used in almost all compact DSLRs. The name is derived from the APS (Advanced Photo System) film format that was introduced in 1996 for the amateur point-and-shoot market. The APS format is 50% smaller (23.6 x 15.8mm) than a standard 35mm frame (24 x 36mm) and has a 1.5x magnification factor (multiply the focal length x 1.5) for determining the 35mm equivalent focal length of lenses used on APS-C format cameras. APS-C format DSLRs from Nikon, Pentax, Fuji and Sony (Alpha) contain APS-C sized imaging sensors.
Canon's compact DSLRs, which include EOS Rebel-series DSLRs, contain APS-C format imaging sensors that are slightly smaller than competitive compact DSLRs (22.3 x 14.9mm, so the lens factor for these cameras would be 1.6x). It should be noted this slightly smaller size does not affect image quality in relation to the larger APS-C imaging sensors, though it does further reduce the effective AOV of your lenses, i.e., they are slightly more telephoto than their 1.5x brethren.
APS-H format imaging sensors (1.3x) are smaller than full-frame (24 x 36mm) imaging sensors but larger than APS-C (1.5x) imaging sensors. Though currently only available in Canon’s high-speed 1D series (not 1Ds) cameras, APS-H format sensors were also used in Leica’s first digital rangefinder, the M8, as well as Leica’s short-lived add-on digital back for the now-discontinued Leica R reflex camera system.
Artifacts refer to distortions within the image as a result of image compression or interpolation. Artifacts can be seen as light halos around dark areas of an image or as a “blocky” quality in the highlight area of an image. Forms of artifacts include blooming, chromatic aberrations, jaggies, moiré, noise and halation.
There are a number of software applications available that have been designed to diminish or eliminate artifacts from a photograph post-capture.
An abbreviation of the American Standards Association, ASA is the term used to describe the light-sensitivity levels of film and camera imaging sensors. The higher the number, the more sensitive—or faster—the film or sensor is. While traditional cameras don't have a specific ASA rating, most digital camera sensors have native, or basic ISO sensitivities of about 100, which depending on the make and model of your camera, can be extended upwards of 6400, 12800, with many top-tier DSLRs’ ISO sensitivity levels upwards of 100,000-plus. That’s about seven to eight times more sensitive than the human eye.
With few, if any, exceptions lower ratings offer better color, sharpness levels and tonal qualities, as well as less noise and grain. The terms ASA and ISO (International Standards Organization) are interchangeable.
Aspect ratio refers to the shape, or format, of the image produced by a camera. The formula is derived by dividing the width of the image by its height. The aspect ratio of a 35mm image is 3:2. Most computer monitors and digicams have a 4:3 aspect ratio. Many digital cameras offer the option of switching between 4:3, 2:3 or 16:9.
An Aspherical lens surface possesses more than one radius of curvature, which allows for the correction of lens aberrations common in simpler lens designs. Sharper definition towards the edges of an image is the most common benefit of a lens containing aspheric elements.
Almost all digital cameras, including the most basic and most advanced, can record audio to go along with their video-capture abilities. Depending on the make and model of the camera, sound can be recorded in monaural or in stereo using the camera’s built-in microphone(s), or via higher-fidelity mics that plug into the camera’s audio jack. Even for still images, most cameras can record short audio annotations that are embedded into the image file.
The ability of the camera and lens to keep the subject in focus during the exposure. Autofocus can be Continuous, meaning focus is maintained regardless of where it moves within the frame, or Single, meaning the point of focus is locked regardless of where the subject may move.
Average metering takes all of the light values for a given scene—highlights, shadows, and mid-tones—and averages them together to establish a good overall exposure. Average metering is best used for front-lit subjects under average lighting conditions. Backlit subjects tend to be silhouetted when metered in Average mode.
AWB (Auto White Balance)
An in-camera function that automatically adjusts the white balance (color balance) of the scene to a neutral setting regardless of the color characteristics of the ambient light source. (See White Balance, below)
Note: Although AWB generally does an acceptable job of cleaning up the color balance of a scene, there are times when AWB should not be used. Examples of times you should avoid AWB are sunrise and sunset, which would lose their warm qualities if the camera were to be set to AWB. In the case of sunrises and sunsets, the camera should be set to Daylightin order to maintain the warmer qualities that make dawn and dusk so visually inviting.
An optical distortion in which the image bows out of square (like a barrel!). Barrel distortion is usually associated with less expensive wide-angle lenses and digital cameras, and is most apparent in architectural photographs or images containing lines that run parallel to each other in the horizontal or vertical plane.
The ability to scan and process more than one image in a single action. Batch scanning is only recommended if all of the images being scanned or corrected are equal in tonal values.
A bit (binary digit) is the smallest unit of digital information. Eight bits equals one byte. Digital images are often described by the number of bits used to represent each pixel, i.e. a 1-bit image is monochrome; an 8-bit image supports 256 colors or grayscales; while 24 or 32-bit supports an even greater range of color.
A method of storing digital information by mapping out an image bit by bit. The density of the pixels determines how sharp the image resolution will be. Most image files are bitmapped. Bitmap images are compatible with all types of computers.
Term for lack of, or loss of, shadow detail in a photographic image, usually the result of underexposure or images captured by a lower resolution (and less dynamic) imaging sensor. Although lost shadow detail can often be (partially) reclaimed in Photoshop or similar photo editing applications, HDR (High Dynamic Range) imaging, in which two or more bracketed images are sampled and combined into a single image file containing increased levels of shadow, highlight and mid-tone detail has become an increasingly common in-camera solution for retaining both shadow and highlight detail.
The appearance of a bright or colored halo around brighter areas of digital image files. Blooming is caused when a portion of the imaging sensor in a digital camera is exposed to too much light, causing signal “leaks” to the neighboring pixels. (Also see Chromatic Aberration)
Blowout is caused by overexposure, which results in a complete loss of highlight details. With the exception of RAW files captured within two stops of the correct exposure, blown-out highlights are difficult, if not impossible, to correct after the fact.
A bit-mapped file format used by Microsoft Windows. The BMP format supports RGB, indexed-color, grayscale and Bitmap color modes.
An English transliteration of a Japanese word that means “haze” or “blur.” Pronounced boh-keh, it refers to the out-of-focus areas in a photograph with limited depth of field, particularly around, but not limited to, the highlight areas. Bokeh appears as little circles in the unsharp areas. Depending upon the shape of the opening formed by the blades of the lens’s aperture, the circles appear either more or less circular. Good bokeh, which has a more “natural” appearance, is most commonly defined by smoother, round-shaped highlights that blend smoothly into the darker shadow areas, an effect that’s directly attributed to the degree of roundness of the lens aperture.
Bracketing involves taking multiple images of the same scene, usually in 1/3, 1/2 or full-stop increments in order to have a choice of exposure options. Many cameras offer the option of bracketing as a custom function. An advanced application of bracketing is HDR imaging (High Dynamic Range) in which several bracketed images are sampled in camera and selectively combined into a single, optimized image file.
A buffer memory is a temporary “holding area” for image data waiting to be processed in a camera. Buffers enable a camera to continue capturing new image files without having to shut down while previous image files are processed. Printers also make use of buffers, which allow you to queue up several pictures at a time while the printer outputs previously queued-up image files.
The number of consecutive images a digital camera can capture continuously before filling the memory buffer or memory card. In order to capture a burst of images the camera must first be locked into “Burst” mode or “Continuous” mode.
A device that allows you to transfer data directly from a camera's removable memory card to the computer without the need to connect the camera to the computer.
CCD (Charge-Coupled Device)
A semiconductor device that converts optical images into electronic signals. CCDs contain rows and columns of ultra small, light-sensitive mechanisms (pixels) that, when electronically charged and exposed to light, generate electronic pulses that work in conjunction with millions of surrounding pixels to collectively produce a photographic image. CCDs and CMOS (Complementary Metal Oxide Semiconductor) sensors are the dominant technologies for digital imaging.
Aka scanner-type CCD, linear CCDs are long, thin sensors that capture an image by recording a vast number of individual "exposures" while scanning across the picture frame. These are best suited for still subjects and continuous illumination. Linear CCDs are predominantly (if not exclusively) used for technical applications.
Also known as color fringing, chromatic aberration occurs when the collective color wavelengths of an image fail to focus on a common plane. The results of chromatic aberration are most noticeable around the edges of contrasty images, especially toward the edges of the frame. Chromatic aberration is most common on less expensive lenses, although even the best optics can occasionally display lower levels of chromatic aberration under certain conditions.
Another form of chromatic aberration is called “purple fringing,” which are the purple streaks or halos that often appear within images produced by digital cameras. Purple fringing originates from light refracting from the light-gathering micro lenses that cap the sensor's pixels. In backlit scenes, this form of purple fringing is commonly called “blooming.”
CMOS (Complementary Metal Oxide Semiconductor)
A type of Imaging Sensor. CMOS chips are less energy consuming than CCD-type sensors and are the dominant imaging technology used in DSLRs. Though once considered an inferior technology compared to CCD sensors, CMOS sensors have vastly improved and are now the dominant sensor technology.
CMY Color (Cyan, Magenta and Yellow)
These three secondary colors can be combined to recreate all other colors. Like CMYK, CMY is used in printing to create the colors seen in a print, though with less density in the blacks as compared to CMYK color. CMY color is used in some of the least expensive desktop printers.
CMYK Color (Cyan, Magenta, Yellow, Black)
CMYK is the color space used for commercial offset printing. CMYK is also a common working color space for inkjet, laser, dye-sublimation and wax thermal printers.
A codec is an application in a camera or video playback device that encodes or decodes video for recording and playback purposes. Without a codec you cannot record or play video. Codec formats include H.264, MJPEG, MPEG-4 AVC/H.264 and AVCHD.
A process by which the image source (digital camera or scanner), monitor and output (printer) are calibrated to use the same or similar color standard, i.e., Adobe RGB, sRGB, etc). This ensures that the image viewed on the monitor has the same range of colors as the image that is printed, and any adjustments made to the color of the image in the computer are accurately represented when the image is printed.
The number of distinct colors that can be represented by a piece of hardware or software. Color depth is sometimes referred to as bit depth because it is directly related to the number of bits used for each pixel. A 24-bit Digital Camera, for example, has a color depth of 2 (2 bits of color) to the 24th power, resulting in a dynamic range of 16,777,216 colors. Similarly, an inexpensive 8-bit color monitor can only reproduce a total of 256 colors, which is far less than the expansive range of color contained in the digital image files captured by almost all consumer digital cameras.
A system of coordinating and calibrating the color spaces of digital cameras, scanners, monitors and printers to ensure that the color and tonal values of the image you see on the screen match those in the final print image.
A palette is the set of available colors. For a given application, the palette may be only a subset of all the colors that can be physically displayed. For example, many computer systems can display 16-million unique colors, but a given program would use only 256 of them at a time if the display is in 256-color mode. The computer system's palette, therefore, would consist of the 16 million colors, but the program's palette would contain only the 256-color subset.
The range of colors that can be reproduced on a computer monitor or in print. The most commonly used color spaces for digital imaging are the baseline sRGB and wider-gamut Adobe RGB (1998).
Compact Flash Card (CF card)
A popular flash memory device, which is available in a number of storage capacities. Unlike earlier mechanically driven MicroDrives, newer CF cards are solid state, quite stable and are capable of operating under extreme environmental conditions. Once the dominant format for in-camera data storage, CF cards have receded from the spotlight as smaller SD/SDHC/SDXC memory cards have become the card of choice in ever-smaller digital cameras.
A method of reducing the size of a digital image file in order to free up the storage capacity of memory cards and hard drives. Compression technologies are distinguished from each other by whether they remove detail and color from the image. Lossless technologies compress image data without removing detail, while "lossy" technologies compress images by removing some detail.
Joint Photographic Experts Group (JPEG) is a lossy compression format supported by JPEG, PDF and PostScript language file formats. Most video formats are also lossy formats. TIFF files are not, and as such, are far more stable than JPEGs and other lossy file formats.
A linear scale for measuring the color of ambient light with warm (yellow) light measured in lower numbers and cool (blue) light measured in higher numbers. Measured in terms of “degrees Kelvin,”* daylight (midday) is approximately 5600-degrees Kelvin, a candle is approximately 800 degrees, an incandescent lamp is approximately 2800 degrees, a photoflood lamp is 3200 to 3400 degrees, and a midday blue sky is approximately 10,000-degrees Kelvin.
*Named for engineer and physicist Lord Kelvin (William Thomson), who conceived of the thermodynamic temperature scale, in 1848.
A hardware device designed to analyze the color characteristics of a swatch of color.
Dark Current (aka “Noise”)
Pixels collect signal charges in the absence of light over time, which can vary from pixel to pixel. The result is known as dark current, or more commonly, noise.
Depth of Field (DOF)
Literally, the measure of how much of the background and foreground area before and beyond your subject is in focus. Depth of field is increased by stopping the lens down to smaller apertures. Conversely, opening the lens to a wider aperture narrows the depth of field.
Depth of Focus
Depth of focus is the measurement of the area in focus within an image, from the closest point of focus to the furthest point of focus.
Digital Asset Management (DAM)
This is the process of managing tasks and making the decisions regarding the import, export, annotation, cataloguing, storage, retrieval and distribution of digital assets such as image files.
Digital Negative (DNG) is an open raw image format owned by Adobe and used for digital photography. It's based on the TIFF/EP standard format and incorporates the use of metadata.
Unlike an optical zoom, which is an optically lossless function of the camera’s zoom lens, digital zoom takes the central portion of a digital image and crops into it to achieve the effect of a zoom. This means that the existing data is not enhanced or added to, merely displayed at a lower resolution, thereby giving an illusion of an enlarged image.
DSLR (Digital Single Lens Reflex)
A single lens reflex camera that captures digital images.
A printing method where a waxy ink is heated to temperatures high enough for the ink to vaporize and bond with a special receiver paper, resulting in images with continuous tone color. The word sublimation is used because the dye goes straight from being a solid to a gas and completely skips the liquid stage. Dye-sublimation prints are also known as Dye-subs.
Dye-sublimation printers, or "dye-sub" printers, are digital photo printers that, unlike ink jet printers, which spray fine droplets of ink upon the print surface, employ a cellophane ribbon that when heated at extremely high temperatures, momentarily vaporizes as it’s transferred to the print surface. Essentially a three-color process (Cyan, magenta, yellow and a protective over-coating), dye-sub prints are popular among commercial printers for their ability to output durable, high-quality photographic prints quickly and relatively inexpensively.
The range of brightness and tonality reproduced in a digital (or traditional) photographic image. Wider dynamic range translates into greater tonal values (and detail) between the darkest shadows and the brightest highlights.
DPI (Dots per Inch)
Printing term for resolution. Also referred to as PPI (Pixels per Inch) when describing monitor resolution. The higher the PPI/DPI, the higher the resolution of the resulting image will be. For viewing images at magnifications of up to life size on a computer screen, you only need 72 DPI. For offset printing the image must be set to 300 DPI at the desired print size, and for inkjet prints, anywhere from 180 to 360 DPI at the desired print size, and preferably with a number divisible by 3.
Note: DPI settings above 400 can diminish the quality of inkjet output.
The effective pixels of a sensor are a measurement of the number of pixels of a sensor that actively record the photographic image. As an example, a camera might hold a sensor that contains 10.5 megapixels, but an effective pixel count of 10.2 megapixels. The reason for this discrepancy is that digital imaging sensors have to dedicate a certain percentage of available pixels to establish a black reference point. These pixels are usually arranged frame-like, along the edge of the sensor, out of range of the recorded image.
Electronic Viewfinder (EVF)
An electronic viewfinder digitally replicates the field of view of the area captured by the camera lens. While once considered a poor replacement for optical viewfinders, newer EVFs containing a million-plus pixels and faster refresh times have become quite accurate, and in many cases, approach the clarity levels of optical finders. An advantage of EVFs is their ability to display exposure data and grids on demand.
OLED (Organic Light Emitting Diode)
An advanced type of LCD that offers improved contrast, blacker blacks, less power consumption and a thinner profile compared to earlier-generation LCDs.
EXIF (Exchangeable Image File)
Commonly used header format for storing metadata (e.g. camera/lens/exposure information, time/date/, etc.) within digital image files.
The process of sending a file out through a specialized mini-application or plug-in so as to print or compress it. The term is also used to describe the action of saving the data to a specialized file format, i.e. JPEG or GIF.
Exposure is the phenomenon of light striking the surface of film or digital imaging sensor. The exposure is determined by the volume of light passing through the lens aperture (f/stop) combined with the duration of the exposure (shutter speed). The proper exposure, which is best determined using a light meter, can be established in a number of exposure modes including manual, program (automatic), shutter priority and aperture priority.
Adding to or subtracting from the “correct” exposure time indicated by the camera's light meter, which results in a final exposure that is either lighter or darker than the recommended exposure time. Most cameras allow for exposure compensation in 1/2, 1/3, or full-stop increments.
Note: The “correct” exposure is not necessarily the “best” exposure.
A term used to describe the aperture, or diaphragm opening of a lens. F-stops are defined numerically: f1/4, f/5.6, f/22, etc. Larger, or wider apertures, allow more light to enter the lens, which calls for faster shutter speeds. “Faster” (wider) apertures also allow for selective focus (narrow depth of field), while slower (smaller) apertures allow for greater depth of field. Wider apertures are preferable for portraits, while smaller apertures are preferable for landscapes.
Ranging in size from a few inches to about a foot diagonally, field monitors serve as a highly accurate alternative to the smaller viewing screens found on most video cameras and camcorders, assisting with critical focus and exposure calibration. With the advent of video capture using HDSLRs, field monitors have become part and parcel of many HDSLR users’ equipment inventories.
The way an image is saved to a digital camera's memory. JPEG, TIFF and RAW (DNG or other proprietary file formats) are the most common file formats found in digital cameras.
Software programs or data that have been written to read-only memory (ROM). Firmware is a combination of software and hardware. In digital cameras, the firmware is the program that allows the user to activate and control the features of the camera.
Flash sync is used to describe either the connection point where you plug an external electronic flash into your camera (usually a PC port or the camera's hot-shoe), or the fastest shutter speed your camera can “sync” with an external flash. Most DSLRs have top sync speeds of 1/125th to 1/320th-second, although some camera/flash combinations can be synced at speeds of up to 1/15,000th-second.
Focal Length Magnifier
Also known as Magnification Factor or Crop Factor, this term is used to describe the angle of view (AOV) of a lens used on a DSLR in terms of how it would appear on a full-frame 35mm camera. As an example, compact DSLRs contain sensors that are about 50% smaller than a standard 35mm frame. As a result, the effective focal length (or AOV) of a 50mm lens on a compact DSLR would be reduced, or cropped to the equivalent of a 75mm lens. Canon EOS Rebels and other compact Canon DSLRs have a 1.6x magnification factor which would make a 50mm lens effectively an 80mm lens. Similarly, Canon EOS 1D-series DSLRs have a 1.3x magnification factor, which effectively makes a 50mm lens the equivalent of a 65mm lens.
A follow focus is a focus-control mechanism used in filmmaking (with film cameras) and in television production (with professional video cameras). There are now follow-focus units that have been designed for use with HDSLR cameras that are used to capture video footage.
Four Thirds (4/3)
A compact digital camera format designed around a 17.3 x 13mm imaging sensor, which is half the size of full-frame (35mm) imaging sensors. Four Third cameras and lenses are manufactured primarily by Olympus and Panasonic. Lenses for Four Third format cameras are made by Olympus, Panasonic, Sigma and are in the planning stage from Carl Zeiss (as of 2/11). A variation of Four Thirds is Micro Four Thirds, a mirrorless FourThird camera format, which is even smaller than standard FourThird format cameras. The sensors in Four Third and Micro Four Third are identical, but Micro Four Third optics cannot be used on standard Four Third camera bodies, due to their smaller lens mounts.
Fringing, commonly associated with less expensive lenses, describes the “bleeding” of color along the edges of contrasty portions of a digital image. Fringing often shows up as cyan blurring on one side of a contrasty object, complemented by red or magenta blurring on the opposite side of the object.
The brightness curve of the color spectrum as displayed (or reproduced) on a computer monitor, a printer or scanner.
Gain refers to the relationship between the input signal and the output signal of any electronic system. Higher levels of gain amplify the signal, resulting in greater levels of brightness and contrast. Lower levels of gain will darken the image, and soften the contrast. Effectively, gain adjustment affects the sensitivity to light of the CCD or CMOS sensor. In a digital camera, this concept is analogous to the ISO or ASA ratings of silver-halide films.
Graphic Interface designed by CompuServe for using images online. This is a 256-color or 8-bit image.
GPS (Global Positioning System)
A technology used for establishing the location of earth-based objects using coordinates obtained by orbiting satellites. These coordinates can be embedded into the headers of digital images as accurate reference points to where the photograph was taken.
GUI (Graphical User Interface)
Pronounced "GOO-ey." Refers to a program interface that takes advantage of the computer's graphics capabilities to make the program easier to use.
A method of calibrating a digital camera, scanner, printer or monitor using specialized hardware such as colorimeters, densitometers and spectrometers.
A digital single lens reflex camera (DSLR) that can also capture high-definition video. Most current DSLRs are also HDSLRs, making the terms almost interchangeable.
A visual representation of the exposure values of a digital image. Histograms are most commonly illustrated in graph form by displaying the light values of the image's shadows, midtones and highlights as vertical peaks and valleys along a horizontal plane. When viewing a histogram, the shadows are represented on the left side of the graph, highlights on the right side, and midtones in the central portion of the graph.
A “live” accessory shoe, usually located on the top of the camera prism housing, which enables you to mount and trigger an electronic flash or wireless transmitter. Hot shoes can also be used to support external microphones, electronic viewfinders, GPS devices and field monitors.
ICC Profile (International Color Consortium profile)
A universally recognized color-management standard for specifying the color attributes of digital imaging devices (scanners, digital cameras, monitors and printers) in order to maintain accurate color consistency of an image from the point of capture through the output stage.
Image Stabilization (See Anti Shake)
A printing method in which the printer sprays micro-jets of ionized ink at a sheet of paper in droplet sizes as small as 2-picoliters. Magnetized plates in the ink's path direct the ink onto the paper in the desired shapes and patterns to make an image.
Interlaced video is a commonly used video capture technique in which in which the imagery consists of two fields of data captured a frame apart and played back in a manner that reproduces motion in a natural, flicker-free form that takes up less storage capacity than progressively captured video.
ISO (International Standards Organization)
Film speed rating expressed as a number indicating an image sensor’s (or film's) sensitivity to light. The higher the number, the more sensitive and faster the sensor (or film) is. Although traditional cameras don't have a specific ISO rating, digital cameras do as a way to calibrate their sensitivity to light. ISO is equivalent to the older ASA.
Most digital cameras have native (basic) ISO ratings of about 100, but can be “extended” far beyond this base rating in order to capture sharp imagery under lower lighting conditions. When shooting at extended ISO levels, image quality begins to suffer in terms of sharpness levels, noise, contrast and added “graininess.”
Term for the stair-stepped appearance of curved or angled lines in a digital image file. The smaller the pixels and/or the greater their number, the less apparent are the “jaggies.” Jaggies are most common in photographs captured at lower resolving powers and Hello Kitty-type digital cameras.
JPEG (Joint Photographic Experts Group)
The de facto standard for image compression in digital imaging devices. JPEG is a “lossy”' compression format, capable of reducing digital image files to about 5% of their normal size. The results in decompression of the files can cause "blockiness," the "jaggies" or "pixelization" in certain digital images. The greater the compression levels, the more pixelization or "blockiness" that will occur. The greater the pixel count is, the less of a chance there is that pixelization will occur.
1,024 bytes, written KB, is used to refer to the size of files, which relates to the amount of information in a file.
A perceptually linear color space (RGB and CMYK are non-linear color spaces) that utilizes luminance as a means of increasing contrast and color saturation.
Also known as shutter lag, lag time refers to the delay that sometimes occurs between the time the shutter button is pressed and the time the shutter fires. Shutter lag is most prevalent when using less expensive point-and-shoot cameras.
LCD (Liquid Crystal Display)
LCD screens, usually found on the rear of digital cameras, allow you to preview and review photographs you are about to take or have taken. LCDs utilize two sheets of polarizing material with a liquid crystal solution between them. An electric current passed through the liquid causes the crystals to align so light cannot pass through them. Each crystal, therefore, is like a shutter, either allowing light to pass through or blocking the light and producing an image in color or monochrome.
A type of rechargeable battery that was originally developed for use with camcorders and is now used as a power source for most digital still cameras and camcorders.
A data-compression technique that can reduce the detail of a digital image file. Most video compression techniques utilize lossy compression. See non-lossy or lossless.
Used with digital imaging, low-pass filters are integrated into many digital sensors to suppress color ghosting and the effects of infrared light.
Also known as Segmented Metering, Matrix metering takes the total image area and breaks it into sections, which are analyzed by the camera's light meter and compared to the light values of the surrounding sections. The results are then compared to similar lighting situations stored in the camera's memory and a correct exposure is established. This entire process occurs in a few microseconds.
1,024 Kilobytes, written MB, is used to refer to the size of files or media such as hard drives. Refers to the amount of information in a file or how much information can be contained on a memory card, CD or DVD, hard drive or disk.
A megapixel contains 1,000,000 pixels and is the unit of measure used to describe the size of the sensor in a digital camera.
The camera's file-storage medium. Most cameras use flash memory, which is a safe, highly reliable form of storage that doesn't need power to hold the images after they are saved. It won't erase the images unless the user chooses to do so. Some cameras contain a limited quantity of built-in memory, but certainly not enough to capture more than a dozen or so images.
In digital photography, a memory card is a removable device used in digital cameras to store the image information captured by the camera. There are several different types of memory cards available including Compact Flash, SmartMedia, SD/SDHC/SDXC, XD and Memory Stick.
Developed by IBM, micro drives are one of the original types of digital memory cards for digital cameras. Essentially small hard drives, micro drives have given way to solid-state Compact Flash cards, which contain no moving parts, and as such, are far more reliable.
Micro lenses are commonly mounted onto the tops of the light-gathering portion of pixels (a.k.a. photons) and are often angled along the edges of camera sensors in order to capture and redirect light back into the pixel, as a method of reducing light falloff on the edges of the image and redirecting it for image processing.
Patterns formed in portions of a photographic image as a result of confusion between a pattern within the photographic scene and the pattern of pixels within the sensor. Moiré can often be eliminated, or greatly reduced, by moving either closer to or farther from your subject. Higher-resolution imaging sensors tend to be less prone to moiré problems.
NiCad ( Nickel Cadmium )
A type of rechargeable battery, the NiCad battery was one of the first successful rechargeable batteries used in small electronics such as digital cameras.
NiMH ( Nickel-Metal Hydride)
A commonly used rechargeable battery for digital cameras and camcorders. A NiMH battery can have two to three times the capacity of an equivalent size nickel-cadmium battery.
A common bugaboo of JPEG files, noise is the appearance of color artifacts within a digital image. Mostly noticeable in the shadow areas of images captured at higher ISO ratings, the image processors used in many current digital cameras utilize noise-suppression software to minimize the appearance of noise artifacts. Heat build-up due to continuous shooting in hot environments can also cause noise artifacts within digital images. Noise is considered the digital version of grain in film negatives.
A process within a digital camera's image processor in which the artifacts caused by “pushed” ISO ratings or other electrical or heat-related artifacts are suppressed or eliminated in an image.
Non-lossy (aka lossless)
A term that refers to data compression techniques that do not remove image data details in order to achieve compression. This method is generally less effective than lossy methods in terms of reducing file size, but retains the entire original image. See lossy.
A type of memory card that retains data when power is turned off. Camera Memory Cards (Compact Flash, SD, SmartMedia, etc.) use non-volatile memory.
OLED (Organic Light Emitting Diode)
An advanced form of LED that does not require backlighting, the OLED displays denser blacks and higher contrast compared to standard LEDs, and can be manufactured with thinner profiles than standard LEDs.
The physical resolution at which a device can capture an image. The term is used most frequently in reference to optical scanners and digital cameras.
Another name for a zoom lens, which is a lens that enables you to change the magnification ratio, i.e., focal length of the lens by either pushing, pulling or rotating the lens barrel. Unlike variable focal length lenses, zooms are constructed to allow a continuously variable focal length, without disturbing focus.
The result of recording too much light when taking a picture, which results in a light image. In digital imaging, overexposure can usually be corrected to a certain extent by the use of image-editing software, depending upon how overexposed your image is. RAW files offer more latitude than JPEGs and TIFFs for correcting overexposure.
The difference between the image seen by a viewing system and the image recorded by the imaging sensor. In point-and-shoot cameras, as subjects move closer to the lens, the variance increases. Only through-the-lens (TTL) viewing systems avoid parallax error.
PC Card (PCMCIA Card)
PC cards are about the size of a credit card and were developed to be a standard for hardware capability expanding devices. PCMCIA cards provide an easy way to transfer photos from the camera to a notebook or desktop PC. In recent years, PCMCIA have become less common as newer (and smaller) technologies have taken their place.
A standardized connector for connecting and synchronizing external electronic flash units (strobes) to cameras.
The PICT format was originally developed by Apple Computer in the mid-1980s. The PICT format supports RGB files with a single alpha channel, and indexed-color, grayscale and Bitmap files without alpha channels. The PICT format is especially effective at compressing images with large areas of solid color.
Short for picture element, pixels are the tiny components that capture the digital image record in your camera. Pixels are also the individual components that collectively recreate the image captured with your digital camera on a computer monitor. The more pixels there are, the higher the screen or image resolution will be.
The breakup of a digital image file that has been scaled up (enlarged) to a point where the pixels no longer blend together to form a smooth image. Pixelization can also appear in the form of step-like or choppy curves and angled lines (also known as the jaggies). As a rule, the greater the number of pixels there are within an image, the less likely it is that you will see pixelization in the image.
An optical distortion, common in less expensive lenses, where parallel lines on the horizontal or vertical plane bow inward. Pincushion distortion is the opposite of barrel distortion.
PNG (Portable Network Graphics)
Developed as a patent-free alternative to GIF, this format is used for lossless compression for purposes of displaying images on the World Wide Web. Adopted by the WWW consortium as a replacement for GIF, some older versions of Web browsers may not support PNG images.
Racking focus is the technique of directing the attention of the viewer of video footage by shifting the focus of the lens from a subject in the foreground to a subject in the background or vice versa.
Many pro and semi-pro digital cameras have the option of capturing RAW files, which unlike JPEGs, TIFFs, and other file formats contain all of the data captured during the exposure in an unedited format. When processed, RAW files can be adjusted far more extensively than images captured in other imaging formats, and can be saved as JPEGs, TIFFs, etc. The original RAW file remains unaltered and can be reprocessed at any time for other purposes.
Red eye is the term used to describe the reddened pupils of the eyes that sometimes occurs when photographing people or pets with an electronic flash. The red color appears when the pupil of the eye is dilated, usually in a low-light environment when the light of the flash strikes the rear portion of the eye and illuminates the blood vessels there. Red eye can often be avoided by placing the flash further than 6" from the camera lens.
The reason red eye is most common with compact digital cameras is because the flashtube is often adjacent to the lens and enters the pupil of a subject head on. A common pre-capture cure for red eye is to bounce the flash onto an adjacent wall or ceiling, which softens the light and eliminates any red-eye effects.
A method of reducing or eliminating red-eye from flash photographs by using a short burst of light, or pre-flash, to momentarily “stop-down” the pupils of the subject’s eyes prior to the actual flash exposure. Some cameras have a built-in pre-flash that fires several times to coax the pupils into contracting, before making the final flash and image capture. Red-eye can also be eliminated electronically after the fact in many photo-editing programs. Many digital cameras contain software applications that electronically eliminate red eye in camera.
A reflex camera is one that utilizes a mirror system to reflect the light (the image) coming through the lens to a visible screen. The image seen in the camera's viewfinder is the same image that strikes the camera's imaging sensor (or film plane). This system provides the most accurate way to frame and focus. The reflex system avoids the parallax problem that plagues most direct view cameras. Reflex cameras are also called SLRs or DSLRs.
The ability to trip the camera shutter from a distance using a cable release or wireless transmitter / transceiver.
Refers to the number of pixels, both horizontally and vertically, used to either capture an image or display it. The higher the resolution is, the finer the image details will be.
RGB Color (Red Green Blue)
Computers and other digital devices handle color information as shades of red, green and blue. A byte is comprised of 8 bits. A 24-bit digital camera, for example, will have 8 bits per channel and can use a total of 8 ones and zeroes for the red, green and blue channels. This allows for 256 different variations, or 28, or 256 different values for each color.
In HDSLR terms, this is a support and focus system designed especially for capturing video footage with an HDSLR camera. Since the ergonomics of the DSLR camera were not meant for the process of video capture, and HDSLR rig provides the support, focusing and monitoring capabilites that are more inherent in single-purpose video cameras.
Saturation is the depth of the colors within a photographic image. Photographs with deep levels of color are described as being heavily saturated. A photograph with lighter levels of saturation is described as having a muted color palette. A totally desaturated color photograph becomes monotone—or black and white.
SD Card (Secure Digital)
Far smaller than CompactFlash cards (CF), Secure Digital memory cards have enabled camera manufacturers to further reduce the size of digital cameras. They are also commonly found in cell phones, PDAs and other small electronic devices that incorporate removable memory. Newer-generation (and faster) SD cards include SDHC and SDXC memory cards.
A mechanism in the camera that controls the duration of transmission the light that reaches the film or sensor. Leaf-shutter lenses, which include most view camera lenses and many medium-format lenses, contain their own proprietary shutters.
A metering mode in which the shutter speed is fixed and the exposure is controlled by opening or closing the lens aperture. Most modern cameras have step-less shutters that can be triggered to open and close infinitely between the camera's fastest and slowest shutter speeds, i.e. 1/236th-sec, 1/54th-sec, 1/5829th-sec, etc.
The length of time the shutter remains open when the shutter release is activated, most commonly expressed in fractions or multiples of a second.
A camera that utilizes a prism and mirror system to project the image seen by the lens onto a focusing screen located below the prism housing. The image the user sees in the viewfinder is identical to the image being recorded. The advantage of SLRs is that you get to view the exact scene the camera will be recording.
Spot metering is the measurement of very small areas of the total picture area. Older cameras, as well as less-expensive digital cameras, only offer a single, centrally-located measuring point, usually between 1 to 5 degrees in coverage. Many newer cameras offer a selection of 3, 5, 7, 11 or more reference points for selective metering, which enable you to selectively measure important areas of the photograph, including areas that are off-center to the frame. Spot metering is a very effective way to take readings of backlit subjects.
The standard color gamut for Windows operating systems. sRGB is also the “lowest common denominator” for color standards, as it can be reproduced on the least expensive computer screens. Adobe RGB is a wider-gamut color space, and is preferred for those seeking higher accuracy in color rendition.
Storage Card (Memory Card)
A compact memory storage device used to store data captured by a digital camera. Storage card formats include CompactFlash (CF), Secure Digital (SD), xD, SmartMedia, and Memory Sticks.
Small, contact sheet-sized image files used to reference or edit digital images. The images that appear on a camera's LCD are thumbnail images of the larger file.
TIFF (Tagged-Image File Format)
TIFF files are flexible bitmap image files supported by virtually all paint, image editing, and page-layout applications. Also, virtually all desktop scanners can produce TIFF images. This format, which uses the .tif extension, supports CMYK, RGB, Lab, grayscale files with alpha channels and Bitmap files without alpha channels. TIFF also supports LZW compression, a lossless compression format.
A series of photographs captured over a period of time. These images can be captured in variable or set time intervals over the course of seconds, minutes, hours, days, weeks, etc.
Although several more advanced cameras offer the option of custom function time-lapse imaging, most cameras require optional hard wired or remotely operated triggering devices to capture time-lapse imagery.
A term used to describe the quality of color and tone ranging from an image's shadow details through the brightest highlight details, including all of the transitions in between these extreme points. Tonal range can also be described in terms of “gamut.”
TTL (Through The Lens)
TTL refers to a metering system that determines the proper exposure based on measuring the light that strikes the imaging sensor (or film plane) after passing through the camera's lens. TTL readings are usually more accurate than handheld meter readings since all exposure factors, including filtration and any optical peculiarities, are taken into account when determining the final exposure. Many dedicated camera flashes also utilize TTL metering to determine the proper flash exposure.
An “acquire” or import interface, developed as a standard for communications between scanners, imaging devices, digital cameras and the computer software. TWAIN allows you to import (acquire) an image into your software. This is the generally the interface of choice for the Windows platform.
The result of recording too little light when taking a picture, which results in a dark image. In digital imaging, underexposure can usually be corrected to a certain extent by the use of image-editing software, depending upon how underexposed your image is. RAW files offer more latitude than JPEGs and TIFFs for correcting underexposure.
The ability of a digital still camera to capture segments of variable-resolution video intended for use in email or Web pages.
System used for composing and focusing the subject being photographed. Aside from the more traditional rangefinder and reflex viewfinders, many compact digital cameras utilize LCD screens in place of a conventional viewfinder as a method of reducing the size (and number of parts) of the camera. Electronic viewfinders (EVFs) have become increasingly better in recent years and are slowly finding their way into traditional DSLRs.
Darkening of the edges of a photographic image due to the inability of a lens to distribute light evenly to the corners of the frame. While correctable with filtration using on camera, center-weighted neutral density filters, or electronically in Photoshop, it is often valuable as a creative device to direct the eye back to the center of the frame.
Traditionally, a watermark is an image or icon that is embedded into paper for security purposes (American paper currency has a watermark). In digital photography, a watermark refers to information that is embedded in the image data to protect the copyrights of the image.
The camera's ability to correct color cast or tint under different lighting conditions including daylight, indoor, fluorescent lighting and electronic flash. Also known as “WB,” many cameras offer an Auto WB mode that is usually—but not always—pretty accurate.
A small, narrow-profile memory card format designed for use with the smallest digital cameras, PDAs and cell phones that accept additional memory.