Glossary of Digital Cameras Terms
A
Artefact
Any unwanted attribute, or feature, that degrades the quality of a digital photograph. JPEG compression, for example, may result in artefacts, a common example of which is the appearance of jagged edges on straight lines in an image.
C
CCD
Abbreviation for "Charge Coupled Device"; the most common of the types of image sensor employed by digital cameras in place of traditional camera film. Incident light – that is, the light striking the CCD, in the form of an image – is converted into digital form (a string of "1"s and "0"s) and recorded on digital storage media.
CMOS
Abbreviation for "Complementary Metal Oxide Semiconductor"; the other type of image sensor used by digital cameras. CMOS sensors perform the same basic function as CCD sensors, but employ a positive, and a negative, polarity circuit, only one of which can be "on" at any one time. This means that CMOS sensors use less energy, and operate at lower temperatures than their CCD counterparts. The availability of this type of semiconductor in digital cameras is increasing, although it is still not as widespread as CCD.
Compression
The process of removing redundant data from digital files, so that the amount of data stored, and hence the file size required, is reduced. So-called "lossless" compression techniques remove only redundant data, such that the data can be recreated in its original form, that is, with no loss of detail, or colour, in a photographic image. "Lossy" compression techniques, such as "JPEG" ("Joint Photographic Experts Group"), on the other hand, sacrifice additional data to achieve greater compression ratios. JPEG does, nevertheless, provide an excellent compromise between image quality and file size, in circumstances where files size is important.
D
Digital Zoom
The process of artificially increasing the resolution of an image, using a process known as "interpolation" (see "Interpolation"); interpolation effectively takes a pixel (see "Pixel"), or an area of an image, and makes an educated "guess" at what it would look like at higher resolution. Many digital cameras offer high levels of digital zoom, but deterioration in image quality is increasingly noticeable as the level of digital zoom increases. Superior, "optical" zoom technology, on the other hand, involves the physical movement of the lens assembly – the same process employed for zoom in traditional 35mm film cameras – to augment the data collected by the sensor.
F
FireWire
Otherwise known as "iLink", or "1394"; a high speed serial bus system, in fact, the IEEE1394 standard for connecting peripheral devices and computers. FireWire is one of the fastest peripheral standards ever developed, and can be useful for the transfer of digital images from a digital camera, or camcorder, to a PC. Standard FireWire ports operate at up to 400Mbps ("Mega bits per second") and some devices now support the "1394b" standard, operating at up to 800Mbps.
I
Image Stabilisation
A feature that attempts to compensate for camera shake, or vibration, in hand held photography. Image stabilisation – like zoom – may be either "optical" or "digital". Optical image stabilisation employs vibration sensors and motors to physically move the camera optics to compensate for camera movement. Another method of achieving the same effect is to physically move the camera sensor, as opposed to its lens elements. Digital image stabilisation, on the other hand, is a purely software effect, which again uses "interpolation" (see "Interpolation") to enhance an image, and can result in "artefacting".
Interpolation
A mathematical method of generating missing information. If, for example, an image needs to be magnified, or scaled up, digitally, a missing pixel can be generated by interpolation between the pixels on either side; this process is repeated, over and over again, to produce a new, magnified image.
ISO Film Speed Equivalence
ISO, or "International Organisation for Standardisation" – actually the name of a Swiss organisation responsible for many international standards – is a measure of the sensitivity of traditional camera film; 35mm film photographers, for example, are probably familiar with ISO 100, 200, 400, etc.. An equivalent measurement system exists for digital camera sensors, and digital cameras with higher ISO equivalences allow adjustment of the sensor for low light conditions.
L
LCD
Abbreviation for "Liquid Crystal Display"; uses the behaviour of liquid crystal molecules under an applied voltage to permit, or deny, the passage of light. Many digital cameras provide an LCD screen, which can be positioned at right angles to the camera body, and tilted up or down, thus providing an alternative to the viewfinder in awkward situations. Some digital cameras also have a smaller, electronic viewfinder – also an LCD screen – which simulates a TTL, or "Through The Lens", optical viewfinder.
M
Memory
All digital cameras require some form of digital storage medium, and this is most commonly a removable memory expansion card of some kind; some cameras do, however, have a small amount of integral memory. Flash memory is safe and highly reliable, and can be used over and over again. Some popular flash memory card types include "CompactFlash", "Memory Stick" and "Secure Digital".
P
Pixel
A contraction of the term "picture element"; the smallest, independent element of a digital camera sensor, or a digital photograph produced using that sensor. Each pixel on a camera sensor collects packets of light energy, known as "photons", and converts them into electrical charge. The charge is converted into a voltage, amplified, and passed via an analogue to digital converter, so that the final image can be stored in digital form. The total number of pixels in an image determines the level of detail, and therefore the overall quality, of that image.
R
Resolution
Refers to the total number of pixels, or "megapixels" (Mp) – a megapixel is simply one million pixels – used to capture, or display an image. Resolution is usually quoted as the total number of pixels, or the number of columns and rows of pixels, in the form "640 x 480", "800 x 600", etc.; in either case, the higher the total number, the better.
U
USB
Abbreviation for "Universal Serial Bus"; a fast, "Plug 'n' Play" interface used on many digital cameras to allow the rapid transfer of digital photographs between camera and computer, or camera and printer. USB 1.1 supports a data transfer speed of 12 Mbps – much slower than FireWire, but still much faster than a conventional serial connection, while USB 2.0 supports up to 480 Mbps.
W
White Balance
Also "Auto White Balance", often abbreviated to "AWB"; the process of removing unrealistic colour casts – such as the orange, or blue, hues that can effect photographs taken indoors, or outdoors – so that a subject that is white in reality is rendered as such in a photograph. To be performed effectively, white balance must take into account the "colour temperature" – in other words, the warmth or coolness – of a white light source.
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