A distortion of image quality or colour rendition within a photographic image caused by optical limitations of the lens used to produce the image. Aberrations commonly show up in the form of halation around contrasty portions of the image and/or 'smearing' of colour toward the edges of the frame.
Absolute resolution
Image resolution as expressed in horizontal versus vertical pixels. (E.g. 1600x1200 Pixels is the absolute resolution, and is also expressed as 2.1 Megapixel)
Adobe RGB (Adobe RGB 1998)
A widely accepted colour space that encompasses a wider range of colour than the more commonly used sRGB colour space. Adobe RGB is the preferred colour space for images intended for prepress applications.
AF Servo
or. Continuous Focus, AF Servo, is maintained by partially pressing the camera's shutter release button, which enables you to 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.
Ambient light – The natural light in a scene.
Vibration Reduction
Vibration Reduction (VR) or Image Stabilization (IS) anti-shake technology is a method of reducing the effects of camera movement to 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 cancelling 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 hand-hold a camera three to four shutter-speeds slower than non-IS enabled cameras or lenses.
A small, circular opening inside the lens that can change in diameter to control the amount of light reaching the camera's sensor as a picture is taken. The aperture diameter is expressed in f-stops; the lower the number, the larger the aperture. For instance, the aperture opening when set to f/2.8 is larger than at f/11. The aperture and shutter speed together control the total amount of light reaching the sensor. A larger aperture passes more light through to the sensor.
The adjustable opening, or f-stop of a lens, determines how much light passes through the lens as it travels to the film plane, or 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', or the ability to isolate your subject within the frame. Conversely, if you stop the lens aperture down to its smallest openings, you increase the depth-of-field, or how much of the image is in focus. Generally speaking, most lenses display the highest level of resolution when set to about 3 stops down from the widest aperture.
Note- 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 images depth-of-field.
Aperture Priority
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, while landscape photographers prefer smaller apertures, regardless of the lighting conditions. Aperture priority is a preferred method to maintain a fixed degree of depth-of-field while shooting under rapidly changing lighting conditions.
A term used to describe the size of a digital camera sensor with a 1.5x magnification factor. 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 than a standard 35mm frame. All Nikon, Pentax, Fuji , and Sony (Alpha) DSLRs contain APS-C sized imaging sensors. Canon's EOS , 20D, and 30D DSLRs are also described as containing APS-C sized sensors even though their sensors are about 20% smaller (1.6x).
Artefacts refer to distortions within the image as a result of image compression or interpolation. Artefacts can be seen as light halos around dark areas of an image or as 'blockiness' of a highlight area of an image. Forms of artefacts include blooming, chromatic aberrations, 'jaggies', moiré, noise, and halation.
Aspect Ratio
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 digicams offer the choice of 4:3 or 16:9 aspect ratios.
Aspherical surface
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.
Average Metering
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. 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 of the scene to a neutral setting regardless of the ambient light source.
Barrel Distortion
An optical distortion in which the image 'bows' out of square. Barrel distortion is usually associated with less-expensive wide-angle lenses and digicams, and is most apparent in architectural photographs or images containing lines that run parallel to each other in the horizontal or vertical plane.
Blocked Shadows
Term for lack of, or loss of, shadow detail in a photographic image, usually the result of underexposure or lower resolution (and less dynamic) imaging sensor. Can sometimes be partially corrected in Photoshop or similar photo editing applications.
Blowout is caused by overexposure, which results in a complete loss of highlight details. With the exception of RAW files captured within 2-stops of the correct exposure, 'blown' highlights are difficult, if not impossible, to correct after the fact.
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.
Buffer – Memory in the camera that stores digital photos before they are written to the memory card.
Burning – Selectively darkening part of a photo with an image editing program.
Burst Rate
The number of consecutive images a digital camera can capture continuously before filling the buffer memory.
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.
Area CCD
A square or rectangular CCD that can capture an entire image at once, which is essential for dynamic subjects and flash photography.
Linear CCD
A.k.a. scanner-type CCD, these sensors are long and thin, and 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.
CMOS ( Complementary Metal Oxide Semiconductor)
A type of Imaging Sensor. CMOS chips are less energy consuming than CCD Type sensors and are becoming increasingly common in pro DSLRs, most notably in Canon and new Nikon DSLRs.
CMYK Colour ( Cyan, Magenta, Yellow, Black)
The colour model in which all colours are described as combinations of these four colours. Most colour printers (ink-jet, laser, dye-sublimation, Wax thermal) are based on CMYK colour; even if they contain additional colours, i.e. dilute magenta, dilute cyan, red, blue, etc.
Chromatic Aberration
The appearance of a bright or coloured 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 neighbouring pixels.
Contrast – The difference between the darkest and lightest areas in a photo. The greater the difference, the higher the contrast.
Colour Calibration
A process by which the image source (digital camera or scanner), monitor, and output (printer) are matched to use the same or similar colour palette. This insures that the image viewed on the monitor has the same range of colours as the image that is printed, and any adjustments made to the colour of the image in the computer are accurately represented when the image is printed.
Colour Depth
The number of distinct colours that can be represented by a piece of hardware or software. Colour 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 colour depth of 2 to the 24th power (about 16.7 million) colours.
Colour Management
A system of coordinating and calibrating the colour responses of digital cameras (or scanners), monitors, and printers to ensure the colour and tonal values of the image you see on the screen matches the final print image.
Colour Palette
A palette is the set of available colours. For a given application, the palette may be only a subset of all the colours that can be physically displayed. For example, many computer systems can display 16-million unique colours, 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 colours, but the program's palette would contain only the 256-color subset.
Colour Space
The range of colours that can be reproduced on a computer monitor or in print form. The most commonly used colour 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.
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 techniques are distinguished from each other by whether they remove detail and colour from the image. Lossless techniques compress image data without removing detail, while "lossy" techniques compress images by removing some detail.
Joint Photographic Experts Group (JPEG) is a lossy compression technique supported by JPEG, PDF, and PostScript language file formats.
Chromatic Aberration
Also known as colour fringing, chromatic aberration occurs when the collective colour 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 towards 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 digicams. Purple fringing originates from light refracting off of the light-gathering microlenses that cap the sensor's pixels. In backlit scenes, this form of purple fringing is commonly called 'blooming.
Colour Temperature
A linear scale for measuring the colour 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 (mid-day) is approximately 5600-degrees Kelvin, a candle is approximately 800-degrees, an incandescent lamp is approximately 2800-degrees, a photoflood lamp is 3200 - 3400-degrees, and a mid-day blue sky is approximately 60,000-degrees Kelvin.
Dark Current
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 as noise.
Digital Zoom
Unlike an optical zoom, the 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.
Dodging – Selectively lightening part of a photo with an image editing program.
DSLR (Digital Single Lens Reflex)
A digital single lens reflex camera.
A printing method where a waxy ink is heated to temperatures high enough for the ink to vaporize, and is then forced to bond with a special receiver paper. The dye sublimation (dye-sub) printing method produces images with continuous tone colour.
Dynamic Range
The range of brightness and tonality reproduced in a digital (or traditional) photographic image. Wider dynamic range translates into greater tonal values between the darkest shadow details and the brightest highlight details.
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 off-set 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.
Note- DPI settings above 400 can actually diminish the quality of inkjet output.
Effective Pixels
The effective pixels of a sensor are a measurement of the number of pixels of a sensor that actually record the photographic image. As an example a camera might contain a sensor that contains 10.5 megapixels, but an effective pixel count of 10.2 megapixels. The reason for this discrepancy is because 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.
EXIF – Exchangeable Image File: the file format used by most digital cameras. For example, when a typical camera is set to record a JPEG, it's actually recording an EXIF file that uses JPEG compression to compress the photo data within the file.
External flash – A supplementary flash unit that connects to the camera with a cable, or is triggered by the light from the camera's internal flash. Many fun and creative effects can be created with external flash.
Exposure explains how light acts on a photographic material. The lens opening (f-stop or aperture) controls light intensity, while the duration is controlled by the shutter speed. A camera with auto-exposure can automatically control the exposure. The same principle works with digital cameras where film is replaced by the CCD.
Exposure Compensation
Adding to or subtracting from the 'correct' exposure time indicated by the camera's 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 ½, 1/3, or full-stop increments.
A term used to describe the aperture, or opening of a lens. F-stops are defined numerically - f1/4, f5.6, f22, etc. Larger, or wider apertures, allow more light to enter the lens, which results in faster shutter speeds. Faster apertures also allow for selective focus (narrow depth-of-field), while smaller (slower) apertures allow for greater depth-of-field. Wider apertures are preferred for portraits, while smaller apertures are preferred for landscapes.
File format
The way an image is saved to a digital camera's memory. The JPEG format is the most common file format found in digital cameras. Other commonly used formats include Tiff, RAW, PSD, and Bitmap
Fill flash – A flash technique used to brighten deep shadow areas, typically outdoors on sunny days. Some digital cameras include a fill flash mode that forces the flash to fire, even in bright light.
Flash Sync
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 1/125 th to 1/250 th, though some camera/flash combinations can be synced at speeds of up to 1/15,000 th.
Fringing, commonly associated with less-expensive lenses, describes the 'bleeding' of colour along the edges of contrasty portions of a digital image. Fringing often shows up as cyan blurring on one side of a contrasty object complimented by red or magenta blurring on the opposite side of the object.
The brightness curve of the colour spectrum as displayed (or reproduced) on a computer monitor, a printer, or scanner.
Graphic Interface designed by CompuServe for using images online. This is a 256-color or 8 bit image.
One gigabyte is equal to 1,024 megabytes. Gigabyte is often abbreviated as G or GB.
Grayscale – A photo made up of varying tones of black and white. Grayscale is synonymous with black and white.
Highlights – The brightest parts of a photo.
Histogram – A graphic representation of the range of tones from dark to light in a photo. Some digital cameras include a histogram feature that enables a precise check on the exposure of the photo. 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, mid-tones, and highlights as vertical peaks and valleys along a horizontal plane.
Hot Shoe
A 'live' accessory shoe, usually located on the top of the camera prism housing that enables you to mount and trigger an electronic flash or wireless transmitter.
ICC Profile (International Colour Consortium profile)
A universally recognized colour management standard for specifying the colour attributes of digital imaging devices (scanners, digital cameras, monitors and printers) in order to maintain accurate colour consistency of an image from the point of capture through the output stage.
IEEE-1394 interface (FireWire)
A very fast external bus standard that supports data transfer rates of up to 400 Mbps (400 million bits per second). Products supporting the 1394 standard go under different names, depending on the company. Apple, which originally developed the technology, uses the trademarked name FireWire. Other companies use other names, such as i.link and Lynx, to describe their 1394 products. In addition to its high speed, 1394 also supports isochronous data -- delivering data at a guaranteed rate. This makes it ideal for devices that need to transfer high levels of data in real-time, such as video devices.
Image resolution - The number of pixels in a digital photo is commonly referred to as its image resolution.
A printing method where the printer sprays ionized ink at a sheet of paper. Magnetized plates in the ink's path direct the ink onto the paper in the desired shapes and patterns to make an image.
Method used in software to increase the resolution of a digital image. The software adds pixels to an image based on the value of surrounding pixels, thereby increasing its resolution. This method can cause artefacts.
ISO speed(International Standards Organization) A rating of a film's sensitivity to light. Though digital cameras don't use film, they have adopted the same rating system for describing the sensitivity of the camera's imaging sensor. Digital cameras often include a control for adjusting the ISO speed; some will adjust it automatically depending on the lighting conditions, adjusting it upwards as the available light dims. Generally, as ISO speed climbs, image quality drops.
JPEG – A standard for compressing image data developed by the Joint Photographic Experts Group, hence the name JPEG. Strictly speaking, JPEG is not a file format, it's a compression method that is used within a file format, such as the EXIF-JPEG format common to digital cameras. It is referred to as a lossy format, which means some quality is lost in achieving JPEG's high compression rates. Usually, if a high-quality, low-compression JPEG setting is chosen on a digital camera, the loss of quality is not detectable to the eye.
LAB Colour
A perceptually linear colour space (RGB and CMYK are non-linear colour spaces) that utilizes luminance as a means of increasing contrast and colour saturation.
Lag Time
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 actually 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/or review photographs you 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.
A data compression technique that can reduce the detail of a digital image file. Most video compression techniques utilize lossy compression.
Low-Pass Filter
Used with digital imaging, low-pass filters are integrated into many digital sensors to suppress colour ghosting and the effects of infra-red light.
Matrix Metering
Also known as Segmented Metering, Matrix metering takes the total image area and breaks it into sections, which are analysed 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.
1024 Kilobytes, written MB, 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 hard drive or disk.
Megapixel ( 1,000,000 pixels)
Digital Camera resolution is often expressed as Megapixels (e.g. PowerShot G7 - 10-Megapixel Digital Camera)
Memory Card
In Digital Photography, a Memory Card is a removable device used in digital cameras to store the images captured by the camera. There are several different types of memory cards available including Compact Flash, SmartMedia , SD , xD, and Memory Stick.
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 further from your subject. Higher-resolution imaging sensors tend to be less prone to moiré problems.
A common bugaboo of JPEG files, noise is the appearance of colour artefacts 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 artefacts. Heat build-up due to continuous shooting in hot environments can also cause noise artefacts within digital images.
Noise Reduction
A process within a digital camera's image processor in which the artefacts caused by 'pushed' ISO ratings and/or other electrical or heat-related artefacts are suppressed or eliminated in an image
Non-lossy or 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 resulting file size, but retains the entire original image.
Optical Zoom
An optical zoom is made to bring you closer to your subject, without you having to move. Zooms are constructed to allow a continuously variable focal length, without disturbing focus.
Paintshop Pro
An image editing software package created and sold by Corel. A user friendly and cost effective image  editing software used by professional photographers and graphic artists.
Panning – A photography technique in which the camera follows a moving subject. Done correctly, the subject is sharp and clear, while the background is blurred, giving a sense of motion to the photo.
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.
An image editing software package created and sold by Adobe Systems Inc. PhotoShop is the most commonly used image editing software used by professional photographers and graphic artists.
PhotoShop Plug-in
A software application that allows a camera, scanner or printer to work directly with Adobe PhotoShop software.
Picasa is free photo management software that helps you instantly find, edit and share all the photos on your PC. Picasa automatically locates all your photos (even ones you forgot you had) and sorts them into visual folders organized by name, size, or date. You can drag and drop to arrange your folders and make albums to create new groups. Picasa also makes simple editing easy by putting one-click fixes and  effects at your fingertips. Picasa makes easy to share your photos - you can email, upload to an online album, print photos at home, make gift CDs, and even post photos to Blogger.
Short for picture element, Pixels are the tiny components that, working together, capture the digital image record in your camera, and later view on a computer monitor. The more pixels that there are, the higher the screen or image resolution will be.
The ‘break-up’ 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 within an image, the less likely you will see pixelization within an image.
Pincushion Distortion
An optical distortion, common in less expensive lenses, where parallel lines on the horizontal and/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 the 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.
PPI (Pixels-Per-Inch)
Also referred to as DPI (Dots per Inch), the higher the PPI, the higher the image quality of the final print.
RAW Files
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 un-edited 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 colour 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 located in the rear portion of the eye. 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 digicams because the flashtube is often adjacent to the lens.
Red-eye Reduction
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. Red-eye can also be eliminated electronically after-the-fact in many photo-editing programs. Many digicams 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 filmplane). This system provides the most accurate framing and focusing. The reflex system avoids the parallax problem that plagues most direct view cameras. Reflex cameras are also called SLRs, or DSLRs.
Refers to the number of pixels, both horizontally and vertically, used to either capture an image or display it. The higher the resolution, the finer the image details.
RGB Colour ( Red Green Blue)
Computers and other digital devices handle colour information as shades of red, green and blue. A 24-bit digital camera, for example, will have 8 bits per channel in red green and blue, resulting in 256 shades of colour per channel.
Saturation is the depth of the colours within a photographic image. Photographs with deep levels of colour are described as being heavily saturated. A photograph with lighter levels of saturation is described as having a muted colour palate. A totally de-saturated colour 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 digicams. They are also commonly found in cell phones, PDAs, and other small electronic devices that incorporate removable memory.
Digital images are inherently soft due to the nature of pixels and how we perceive the images they collectively produce. Sharpening is a method of adjusting the contrast levels between adjacent pixels to give the appearance of a sharper image. Un-sharp mask is the most common sharpening filter for this purpose.
A mechanism in the camera that controls how much light reaches the film.
Shutter Priority
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. 1/236 th, 1/54 th, 1/5829 th, etc..
Shutter speed
The camera's shutter speed is a measurement of how long its shutter remains open as the picture is taken. The slower the shutter speed, the longer the exposure time. When the shutter speed is set to 1/125 or simply 125, this means that the shutter will be open for exactly 1/125th of one second. The shutter speed and aperture together control the total amount of light reaching the sensor. Some digital cameras have a shutter priority mode that allows you to set the shutter speed to your liking.
SLR (Single-Lens-Reflex)
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.
Spot metering
Spot metering allows for the measurement of smaller areas of the total picture area. Older cameras, as well as less-expensive digicams, 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 off-centre to the frame.
The standard colour gamut for Windows operating systems.
A small version of a photo. Image browsers commonly display thumbnails of photos several or even dozens at a time. In Windows XP's My Pictures, you can view thumbnails of photos in both the Thumbnails and Filmstrip view modes.
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.
Time Lapse
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.
While 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.
Tonal Range
A term used to describe the quality of colour and tone ranging from an image's shadow details through the brightest highlight details, including all of the transitions in between these extreme points.
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 'hand-held' meter readings as 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 in determining the proper flash exposure.
The result of recording too little light when taking a picture, which results in a dark image. In digital imaging, under-exposure can usually be corrected to a certain extent by the use of image editing software. RAW files offer more latitude as compared to JPEGs and TIFFs for correcting over or under-exposure.
Unsharp Mask
The most commonly used 'sharpening' filter in Photoshop.
System used for composing and/or focusing the subject being photographed. Aside from the more traditional rangefinder and reflex viewfinders, many compact digicams utilize LCD screens in place of a conventional viewfinder as a method of reducing the size (and number of parts) of the camera.
Fall-off, or 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 centre-weighted neutral density filters or electronically in Photoshop, it is often used as a creative device to direct the eye back to the centre of the frame.
Traditionally, a watermark is an image or icon that is embedded into paper for security purposes (American paper money 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.
White Balance
The camera's ability to correct colour and/or tint when shooting under different lighting conditions including daylight, indoor, fluorescent lighting as well as electronic flash.
xD Cards
A small, narrow-profile memory card format designed for use with the smallest digicams, PDAs, and cell phones that accept additional memory.
Zoom lens
A lens whose focal length can be continuously adjusted through a fixed range of focal lengths.