Glossary of Acronyms, Digital & Photographic Terms

D

Despeckle Filter
A filter in Photoshop that can remove annoying screen interference when scanning printed materials. It essentially softens adjacent pixels through a blending process and can remove unwanted electronic patterns from an image which were not visible in the original.

Di, Di II (Digitally Integrated)
Tamron Di lenses have an image circle the covers the diagonal of 35mm film cameras, but they are updated and reformulated for digital photography using new lens coatings to minimise reflections from image sensors, which reflect differently to film. They can be used on both film and digital SLRs. Tamron Di II lenses are formatted only for the APS-sized image sensors of some DSLRs, like the Nikon D200 or Canon EOS 400D, typically about 18x24mm. They are not able to be used on film or large 35mm-film-sized digital sensors, but because their image circle is small they offer the convenience of compactness and light weight.

Digital Zoom
This technique, found in a digital camera or camera phone, shrinks the image capture area to a smaller and smaller area of the image sensor. But in doing so it also reduces the amount of pixels of information available. Its counterpart optical zoom, uses optical changes to zoom a subject closer or further, but uses the entire sensor at all times, ensuring full resolution is maintained.

Disc Drives
The hard disk employed in a computer to store files, available in various different types.
IDE: Integrated Drive Electronics interface or connection method. Now being phased out.
RAID: Redundant Array of Independent Discs – configurable in 5 or more ways, specifically aimed at ensuring data is not lost when one or more of the linked drives in a RAID drive fails. Specially used in data back-up systems, for photo archive storage and for 24-hour continuous operation computers.
SATA: Serial Advanced Technology Attachment – the current and updated IDE drive.
SCSI: Small Computer System Interface – a fast drive for desktop and server-based computers.

Dithering
The simulation of the original colours in an image when the display or output medium has a more restricted palette of colours, such as when converting from RGB to GIF files.

DNG
An Adobe file format aimed at being an Open standard, to overcome the variety of proprietary RAW files formats from each of the camera makers. Essentially designed to be a universally transferable Digital Negative file.

Dodging
Selectively lightening part of a picture. The opposite is called burning in.

Dot Gain
The spreading of the dots of ink that occurs when a print is created. As the ink makes contact with the paper it spreads out and tends to blend with other dots as it changes dimension. Sometimes an image that may appear to be "too sharp" when viewed on a computer screen, may reproduce more smoothly when printed, especially if the print material is absorbent paper, rather than photo quality gloss paper.

dpi (Dots Per Inch)
The number of dots of information reproduced during the print process. Typically a black & white laser printer will produce 600 dots per inch, or 360,000 dots per square inch. The best inkjet colour printers will reproduce 2,880 x 1,440 dpi, or 4.15 million dots per square inch, essentially continuous colour tones.

DPOF (Digital Print Order Format)
Digital cameras are usually compatible with standardised DPOF instructions that can be stored within the metadata in a saved image file, for example on a memory card. This data is then employed by a print device or film laboratory, to improve the quality of print by using the instructions embedded in the file to reproduce it more faithfully. Metadata instructions for printing are included in a file format called EXIFprint.

Drop Shadow
The effect added to type or objects, which simulates a shadow on the surface of the page, adding a 3D effect to the look of printed or projected type, objects or photos.

DSLR (Digital Single Lens Reflex)
A camera with a digital sensor, interchangeable lens capability, providing a bright viewfinder, faster response and usually better noise capability than compact digital cameras or camera phones. An SLR is a non-digital, i.e. film, equivalent.

Duotone
A separation technique when printing black and white images to extract a greater tonal range than is possible in simple greyscale images with 255 shades of grey. A separated range of tones that can either be a black toned channel or a coloured channel for a special effect is added to the original greyscale image. The Duotone effect is available in most image editing programs. Use of a third channel is called Tritone, a fourth channel QuadTone.

DVD (Digital Versatile Disc)
A video disc that either records MPEG-2 format video with Dolby sound or MPEG-2 Audio alone. Up to 4.7GB of data can be stored on either side of the disc. DVD is the most rapidly adopted new entertainment format in Australian history. It is replacing CD-ROM as the preferred method of archiving large image libraries. Multiple variations in format exist:
DVD-R / DVD-RW : The original format, dating to 2001-2. RW means re-recordable. R means recordable, but just once.
Dual Layer: A single-sided disc that takes storage up to 7.95GB.
HD-DVD: High Definition DVD. Currently the most-talked about format of High Definition DVD is Sony’s Blu-ray, found also in Sony PlayStation 3. Capacity up to 25GB on a single sided disc and 50GB on a dual-layer disc.

Dynamic Range
The extremes in range between the darkest point in an image file and the brightest point. In scanners this is sometimes referred to as the D-Max, or the maximum dynamic range. A Nikon film scanner can capture a dynamic range of 4.2. The scale is logarithmic, so 4.2 is much greater than 3.6, for example. A top transparency film produces a dynamic range of just over 4.5, while typical colour negative film is just less than 4.

E

Effective Pixels
Digital cameras employing CCD sensors use part of the sensor for control of the camera, but those pixels are not available to capture image data. In 2000 The Japanese Camera and Imaging Products Association established a standard for ensuring all resolution statements made by manufacturers were comparable and only listed those pixels that contributed to an image, regardless of aspect ratio.

EPS (Electronic PostScript) File
A file that is used by vector-based illustration programs, defining images or text as a series of scalable objects, which can be increased in size without losing apparent sharpness. They include low-res preview images embedded in their header section.

EXIF (Exchangeable Image File)
The file metadata format designed by the Japanese electronics industry to improve interchange of data between devices ensure consistency in reproduction. A subset of EXIF metadata, is Epson's proprietary PIM or PRINT IMAGE MATCHING system JPEG files created in cameras conforming to the EXIF standard include EXIF metadata that can be read by a number of imaging programs.

ExpressCard™
A recent smaller format card used for providing fast telephony or memory capabilities. Found in the latest Apple MacBookPro computers, and on certain phone cards from leading mobile phone service providers. The ExpressCard has succeeded the common PCCIA card of the 1990’s. USB 2.0 and PCI Express® compatible.

F

File Size
The size of a file for a photographic image will vary depending on what captured the image in the first place and the use to which the image file will be put. A 7-megapixel image will save 7 million bytes of red, 7 million of green and 7 million of blue, along with the composite data producing a file size of around 25 MB. A file of this size will produce a photo quality image at 300dpi of 8" x 10" (20x25cm).

FireWire
The high-speed IEEE 1394 standard for file transfer between a computer and other imaging device. It was first developed by the video industry for image capture from a digital video source to a computer hard drive. FireWire is found in some professional digital still cameras to rapidly transfer image files to a computer, where the recorded image can immediately be evaluated and manipulated. It’s also common as a transfer port from external backup drives, such as Maxtor or LaCie.

Firmware
The software instruction programs stored in a computer or digital camera's read-only memory. This memory can be 'flashed' with new instructions if the read-only memory is an EPROM (Erasable Programmable Read-Only Memory). Upgrades to scanners and cameras are often posted on manufacturer's websites to enable owners to gain updated capabilities or to correct for bugs in existing programs.

Fisheye Lens
An ultra-wide angle lens that is not linear and distorts level surfaces into a curved field.

Flash

1. A lighting device, either mounted on the camera or connected to the camera and mounted on a light stand, which illuminates a still picture with a short, brilliant burst of light. Also called a flashgun.
2. The rapid writing to memory cards in such a way that that even when power is removed, the device holds that data. Flash memory cards are available in a number of different formats: CompactFlash, XD, MiniSD, SD (SecureDigital), Sony Memory Stick and MemoryStickPro and MMC formats.
3. A file format for the internet that delivers vector-based graphics and animations in Flash-enabled web browsers. Originally developed by Macromedia, later purchased by Adobe Systems.

FlashPix
Not to be confused with Macromedia Flash files for the Internet, the FlashPix file format was first developed in the 1990s by Live Picture, in cooperation with Kodak, Microsoft and Hewlett-Packard, primarily as a means of delivering resolution-independent scalable images to the Internet. The file opens in a flash, initially as a relatively small file. Only as you click on part of the file does more information get streamed out to allow viewing of more and more information connected with the file. The file format has also been adopted in programs such as Microsoft PictureIt and in several programs from MGI software, the company that purchased Live Picture. After an initial burst, it has declined in popularity.

Flickr
A popular website for publishing and sharing images.

Fractal
A mathematically generated pattern applied to a file, such as an image file, enabling that image to be scaled without any apparent loss of detail when printed. So the term Fractal Image means an image created with such a mathematical process.

FTP (File Transfer Protocol)
Used to establish communication between a computer server containing, typically, driver files for scanners or cameras, and an Internet user some distance away. Once the command line is established and the download commences, a continuous stream of data is transferred. Such transfers are faster than opening a normal file, where the Internet sends packets via a variety of unrelated routes, often causing delay.

Flatten
A modern image editing program employs layers to allow multiple adjustments, permitting recall of earlier actions. But each layer adds lots of extra file size, depending on what that layer is used for. Once an image has been finalised, and there is no need for further adjustment, image editing programs like Photoshop or PaintShop Pro allow the user to combine or "flatten" all the layers into a single composite image. Adobe Illustrator also makes use of layers for composite artwork creation, which can be flattened at the conclusion of the assignment. Once done, however, that's it, no more going back to an earlier layer. A flattened file is much smaller as it has to memorise much less detail.

Sometimes the dynamic range of a digital picture will exceed the dynamic range of a newspaper print system, filling in shadow information and blowing out the highlights. Flattening the image is a term used to describe making the extremes more manageable.

Format
To format a disc, you completely remove all existing data and start with a blank disc. The same goes for a flash-memory card. All information is removed when you format the card. For reliable operation of a camera’s memory card, formatting prior to a session is recommended. A disc can be reformatted more than 1000 times before reliability levels can deteriorate.

Foveon
A company that has developed a unique image sensor that mimics some characteristics of film emulsion in its electronic image sensor. Instead of a lattice structure of RGB sensor elements, a Foveon chip employs three separate layers of all read, all green and all blue sensors, one directly below the other. The challenge is that while there are 3x the number of elements per square inch of sensor area, there is a logarithmically higher level of introduced noise, making high-ISO settings difficult to capture. The advantage is a much reduced tendency to Moiré effects in images like check shirts or jackets.

G

Gamma Curves
Gamma is the relative difference between an input value and an output value. A gamma curve is where that ratio is set up or down the curve. Manual adjustment can be further expanded by changes to the shape of the curve, allowing more gradations in mid-tones and less in highlights. A skilled image editor will be able to extract the maximum tonal detail and suitable contrast from an image by careful adjustment of the gamma settings best suited to the output device, whether it is a monitor or printed material.

Gamut
The extent of colour range available in an electronic image or print. A wide colour gamut means an image with a wide colour range.

Gaussian Blur
A softening blur that uses a symmetrical bell-shaped Guassian distribution to yield its softening effect on an image. Often used to soften blue channel noise in a low light digital file, without appearing to soften the image overall. The phenomenon of standard deviation bell-curves was first described by Karl Gauss, a famous astronomer and mathematician in the late 18th century.

GIF (Graphics Interchange Format)
A Graphics Interchange Format file supporting 256 colours or less. It is especially suited to flat art rendition, and usually less well suited to photos. GIF files are usually employed to ensure rapid downloading of web pages when exact colour rendition is not critical. Very small files that are made up of multiple still pictures can be linked to create an 'animated GIF'.

Gigabyte
A gigabyte is a measure of data equivalent to 1,024 megabytes.

Greyscale
As its name suggests, a greyscale image is an image with varying shades of grey, usually 255 shades, from pure white to pure black, level 0 to level 255 respectively.

H

Halo
When an image is “over-sharpened” a small visible bright line surrounds the sharpened subject in a digital image. An image may appear “soft”, requiring some image sharpening, which literally shifts pixels to define edges and surfaces more distinctly. Oversharpening, however, produces undesirable halo effects around these areas.

HDTV
The Blu-ray HD-DVD 'high-definition television' format of 1,920 x 1,080 pixels resolution. Sometimes referred to as 1080p. This compares to the original 'high-definition' format of regular Australian free-to-air broadcasts of 852x576 pixels (576p), both progressive scan formats.

Highlight
The lightest area in an image. Digital cameras are susceptible to “blown highlights”, a term defining data that is lost through excessive brightness that is not recorded, and therefore blown away!

Histogram
A graphical visualization of the tone structure of a file, enabling one to assess the relative values of darkest and lightest points in a file. Adjustments to the values in a histogram are best illustrated by the changes to levels or tone curve of an image. This feature, found in more advanced cameras, can often be used jointly with a highlight indicator, showing exactly which part of an image has exceeded the maximum brightness value at which image data can be captured.

HTML (HyperText Markup Language)
The core language or code used in producing web pages. Programs such as Microsoft Word or Adobe InDesign, while principally set up for print, can create equivalent documents by converting the text to an HTML- coded file. For cleaner code and smaller files, however, HTML files are best generated by specialist programs like Adobe CS3 and the DreamWeaver application that ships with some versions of this software suite.

HTTP (Hyper Text Transfer Protocol)
The standard that allows Internet users to consistently acquire and exchange data across the internet.

I

ICC (International Colour Consortium)
An ICC profile is standard coding system that enables different devices to talk to each other in a controlled way, so that a device such as a camera can be used with a printer and so long as they are used in connection with their ICC profiles, repeatable colour results can be obtained.

Internal Focusing
Often abbreviated as IF. Found in a camera lens that focuses using elements inside it rather than its front elements, so that a lens does not rotate at the front when focal length is adjusted for focus, and the total physical length of the lens does not change as the elements move back and forth. This is important to preserve the framing of the lens. In non-IF lenses, changing focus can often appear to zoom the lens slightly in or out.

Image Browser
A computer program that enables you to view digital picture files, either to sort them, adjust them or arrange them in albums for viewing in different arrangements. An Image Editor is a more comprehensive program that enables a user to modify colour, tone, brightness etc. and even reformat an image.

Interpolation
A method of growing an image file size from nearby data and estimated the appropriate colour for pixels to be in the newly created, larger image It can also describe any process used in which estimation of colour is employed.

IPTC (International Press and Telecommunications Council)
The International Press and Telecommunications Council metadata standard for embedded data in a saved image file, describing key ownership, event, time, date, location and caption information. This is created by the photographer and employed by a newspaper or publisher to ensure the image is correctly described in publication and can be readily located when stored.

IR Filter
A special filter mounted internally in a digital SLR camera across the image sensor to adjust the colour spectrum of the scene being photographed to those colour frequencies seen by a CCD or CMOS sensor.

Compiled, written and updated by John Swainston.
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