Digital photography terminology and glossary

Photo Glossary

A/V outputs
Audio Video or A/V outputs allow you send an image or recording to a TV for viewing.

AVI
A video movie format clip in Windows. Unlike standards created MPEG, it can need any one of a frankly bewildering number of proprietary variations of AVI Video CODEC’s.

CF Card
Compact Flash cards
Perhaps the most common memory card, it has a capacity as high as 2Gb, or larger.
You can also buy high-speed rate version, useful for sports photography or anywhere else you may want to rapidly take several pictures in succession.

CF Type I are the original solid state 3.3mm high cards.
CF Type II cards and devices are 5mm high and include the IBM/Hitachi Microdrive.

Aperture, F-stop
A camera’s aperture works like the iris of your eye, expanding and contracting to adjust the amount of light which passes through. The smaller the aperture, the less light it admits. It also increases the depth of field as you stop down.

CCD
Charge Coupled Device
A digital camera’s image sensing element which converts light to electrical energy, storing it in digital form in the camera’s memory. CCD size is measured in pixels. Sometimes, you may see two slightly different pixel counts listed for the same camera’s CCD. These numbers represent ‘effective’ pixel count and actual pixel count.

CMOS
Complementary Metal Oxide Semiconductor.
A type of semiconductor that has been, until the introduction of the Canon EOS D30, widely unavailable for digital cameras. CMOS semiconductors use two circuits, negative and positive polarity circuits. Because only one of the circuits can be on at once, CMOS chips are less energy consuming than other chips that utilize simply one type of transistor.

While they use less power, some consider them more prone to problem noise and low temperature failures.

DC lenses
‘Digital Camera’ lens
If you see a lens advertised as ‘DC’ you may notice one or two things straight away. It is clearly smaller, lighter and indeed generally a lot cheaper that a similar regular lenses in the same line. Clearly a win-win situation.
Caveat Preemptor… Let the buyer before. Manufacturers are clean about this, your average spotty shop assistant is another matter…

DC lenses are engineered for specific cameras and specifics sensors.
Here’s a quote from Sigma:

Digital cameras having image sensors larger than APS-C size, and 35mm cameras, should not be used with these lenses. If such cameras are used, severe vignetting in the images may result. The angle of view varies depending on the camera the lens is mounted on.

Depth of Field
The range of sharp focus. Controlled by the focal length and aperture opening of the lens.

Here’s a really neat On-line Depth of Field calculator for you to play with!

‘Effective Megapixel’
‘Actual’ pixels is a simple count of every pixel present on the CCD.
‘Effective’ pixels, however, is a count of all the pixels used to record an image (some pixels on a CCD aren’t used to record picture information) and it’s almost always a tiny bit lower than the ‘actual’ count. Effective pixel count is widely used, because it’s a much more accurate way to assess a camera’s maximum picture capture capability.

Note, some digital cameras might advertise the “interpolated” pixels. For instance Fujifilm’s Super CCD image sensor can capture “effective” pixels of 3.1 megapixels, but it’s software interpolates them up to 6 megapixels. Interpolated images are never, ever as good as the real thing, but if advertised clearly, it’s often a good trade on price. See Interpolation below.

Exposure
The amount of light to which the film or CCD is exposed. This is dictated by the aperture, shutter speed, and sensitivity of the film/CCD.

EXIF
Not a lot of people know this…

When most digital camera store your picture they also save extra information. This can include the basic size of the image, the date and date, the aperture, shutter speed, ISO, and most other camera settings, even the make and model of the camera and lens used.

There are freely available software utilities you can use to view this on your computer and some web based picture software – like Gallery will display this along with the picture.

You can study these camera settings, seeing which created the best results, so you can learn from your experience.

Also, a compatible printer can take note of this info and adjust its settings accordingly to calculate the most accurate, lifelike photo print possible.

Film Speed / Sensitivity
Typically this is 100 ISO / ASA for day to day use, rising to 1600 ISO or higher for low-light conditions such as fireworks shows and rock concerns.
A lower ISO number means that the film needs more light to take a picture than does film with a higher ISO, but with the trade off of graininess or noise and colour saturation.
Digital cameras lacking film as they do will mimic these with ‘sensitivity’ settings. Generally only the more expensive cameras offer this feature.

FireWire, IEEE 1394
Used as a faster alternative to USB by some professional digital cameras and camcorders.
A type of cabling technology for transferring data to and from digital devices at high speed. It was invented by Apple Computer but is now commonly used with Windows and other platforms.
Out of interest Sony, probably for marketing reasons, call it ‘iLink’ for their camcorders.

Focal length
The distance from the rear model plane of a lens to the focus when the lens is focused at the infinity position.
It is the lens’ angle of view, generally bracketed into wide angle, normal or telephoto.
Examples can be 20mm wide angle, 125mm-300mm telephoto zoom.

Note: not all focal lengths are created equal!
For digital camera’s this depends on the size of sensor.
Consider a Sigma 50mm f1.8 standard lens…
      On a Nikon D70 this becomes a 75mm f1.8 – x1.5
      On a Canon EOS 1D this becomes a 65mm f1.8 – x1.3
      On a Canon EOS 20D this becomes a 80mm f1.8 – x1.6

This is great news if you like telephoto pictures as you get a boost with no loss of f-stops. The off-side is taking wide angle pictures becomes a problem. That 20mm is now just a 35mm…

FPS
Frames per second.
This relates to how smooth, or how jerky the playback is. The greater the number of frames the less you notice flickering and stilted movement.
For digital stills it applies to how many photographs you can take in a second.

Interpolation
Especially, it spaces out – redraws – the picture on a bigger canvas and intelligently fills in the gaps with the most appropriately coloured pixel. Naturally, it’s not as good as the real thing, as it can guess wrong, but generally it’s a good trade-off.

JPEG
Joint Photographic Experts Group
A picture file format, typically .jpg through .jpe and .jpeg are common too.

The de facto standard for image compression in digital imaging device, though .TIFF, RAW and proprietary are common options too, usually in conjunction.

Along with .GIF and .PNG, the standard form for images – pictures on the Internet.

LCD
Liquid Crystal Display.

MMC
MultiMedia cards are another type of removable memory card.

Megabyte / Gigabyte
A megabyte (Mb) is a millions ‘bytes’ of information.
A Gigabyte is the equivalent of 1,024Mb’s.
For digital camera purposes you can consider it as a measure of how many pictures you can take. A high quality, 6 megapixel photo is roughly 1.5Mb in size, low quality, 2 megapixel pictures will be perhaps a tenth of that.

Megapixel, Megapixel or Mega Pixel
Simply a 1 million pixel image.
You can multiply the horizontal resolution by the vertical resolution to get the total pixel count:

Consumer cameras are typically 2 to 4 Megapixel, Professional cameras 6 to 14 Megapixel, with large format professional camera upwards of a huge 24 megapixel.
If you have to ask, you can’t afford the latter … add three 0’s and VAT to the pixel size!

Megapixel and printing
Remember, size is relative to resolution!
It might all be pixels but on screen it’s ‘pixels per inch’, printed it is ‘dots per inch’. Even on screen all things aren’t equal, a Windows based PC is 96 dpi, an AppleMac 72 dpi. Printed out, you need to scale thing to perhaps 180 dpi, or 360 dpi for high quality.
Note: This a separate issue from whether the printer is 1440 dpi, or 5670 dpi which relates to the size of the ink droplets used to actually print the pictures.

This is a very rough guide for good quality prints.
The bigger variables are the resolution printed at, the printer and ink used and especially the paper used.

  • 1 Megapixel is 1280 x 960 = 4″ x 6″
  • 2 Megapixel is 1600 x 1200 = 5″ x 7″
  • 3 Megapixel is 2048 x 1536 = 8″ x 10″
  • 4 Megapixel is 2272 x 1704 = 11″ x 14″
  • 5 Megapixel is 2560 x 1920
  • 6 Megapixel is 3008 x 2000
  • 10 Megapixel is 3280 x 3280
  • 24 Megapixel

Naturally, it scales up for 6 Megapixel and up.
LTL Imagery have this great page on this subject is you want to read more.

Memory card
Any one of over a dozen small, storage devices. They come in a bewildering array of sizes and capacities though they are all rectangular. They range from smaller than a postage stamp (and almost as thin) saving a mere 8Mb or less to roughly matchbox size, with sizes up to 4gb and rising all the time. At present I believe ‘Secure Digital’ is the most prevalent.

MicroDrive
MicroDrive storage format.
Developed by IBM, microdrives are extremely small hard disks that can fit in a CompactCard memory slot. Available in capacities of 2Gb or possibly larger.

MiniDV
Strictly for camcorders, MiniDV is the leading digital format. About the size of a matchbox, the tape is very compact and can record up to two hours at 500 lines of resolution. It has the highest resolution and smallest dimensions of all consumer video recording formats.

MPEG
Moving Picture Experts Group.
An standards organization that works with the International Organization for Standardization (ISO) to develop standards for digital audio and video compression.

MPEG’s files are compressed movies that can contain both audio and video. Though they are compressed, MPEG files maintain most of the original quality of the uncompressed movie.

Optical / Digital Zoom
Zoom lenses allow you to close in to your subject or pan right out again without you actually having to move and are constructed to allow a continuously variable focal length, without disturbing focus.

Optical zooms use a combination of lenses to magnify the image prior to being captured by the sensor (or film).
Digital zooms change the presentation of existing image collected by the sensor, augmenting it via interpolation at the cost of quality.
Optical zooms are thus far superior to digital zooms.

PictBridge
Developed by Canon, Fuji, HP, Olympus, Seiko/Epson and Sony, PictBridge is a worldwide standard that allows digital devices to print directly to photo printers and other output devices – no PC is required.

PTP
Picture Transfer Protocol
This was developed by the ‘International Imaging Industry Association’ as a standard for image file transfer. It enables image files to be transferred between a digital still camera and PC via USB without a specific device driver.

Pixel
The pixel is the smallest part of a digitised or Digital Image.
Also used in measuring image size and resolution, i.e., 640 x 480 is the pixel resolution of the (largely obsolete) VGA Monitors.
Most monitors now are 1024 x 768 or better.
Note: pixels are square in computers and rectangular in video

Red-eye
Redeye is the term used to describe the red colour often visible people’s eyes when a picture is taken with a flash. It is caused when the pupil of the eye is dilated – usually in a low light environment – and the light of the flash strikes the retina at the back of the eye, reflecting the light through the wide-open pupil.

It is a common problem when the flash is positioned close to the lens, as it is on many small cameras. Bounced flash (with higher-end flashguns) helps avoid this.

Red-eye Reduction
By firing the flash several times just before exposing a photo, cameras with a redeye reduction feature cause a subject’s pupils to contract, reducing the reflection that causes redeye.

Resolution
The quality of a digital image, largely based on the number of pixels used to create the image. More and smaller pixels adds detail and sharpens edges. The file format comes into play also.

The optical resolution is an absolute number that the camera’s image sensor can physically record.
Mimicking monitors, camera makers often specify the resolution as follows:

  • QVGA (320 x 240)
  • VGA (640 x 480)
  • SVGA (800 x 600)
  • XGA (1024 x 768)
  • UXGA (1600 x 1200)
SD Card
Secure Digital card
Another common memory card with capacities of 1Gb or higher.
Again, you can also buy high-speed rate version, useful for sports photography or anywhere else you may want to rapidly take several pictures in succession.

SmartMedia
Another type of removable memory card used in cameras from several major manufacturers.

TIFF
Tagged Image File Format is the industry standard raster file format, which consists of the image and header information. TIFF is also supported by most desktop publishing and paint programs. TIFF images are detailed and vastly larger in size.

Web browsers do not support TIFF’s.

TFT
Thin-Film Transistor.
A general term for high-quality flat panel displays.
TFT-based displays have a transistor for each pixel on the screen. This allows the electrical current that illuminates the display to be turned on and off at a faster rate, which makes the display brighter and shows motion smoother. LCDs that use TFT technology are called “active-matrix” displays.

USB
Universal Serial Bus.
A standard way of connecting to a computer.
Created to replace the ‘legacy’ PS2 and serial buses of the 80’s and 90’s.

White Balance
A devices ability to see a white subject as white by first adjusting the balance to suit the colour of the ambient light around the subject. It means, for example, indoors under fluorescent lights, it will try to compensate and keep colours natural.

xD Picture Card
A small removable memory card used in some new Olympus and Fujifilm.

Other good Digital Camera glossaries can be found at:

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