Glossary of Acronyms, Digital & Photographic Terms

J

Jaggies
A slang term that accurately describes the saw-tooth like edges of a subject when a small-resolution file is enlarged electronically, revealing the pixel structure of an image. To avoid jaggies, scaling up an image should be done before any sharpening of the image occurs and preferably from an initially adequate resolution original image. Jaggies can also occur when a large wide-angle image is cropped to small detail from part of the image and then printed out in a large print.

Java
A language released by Sun Microsystems in 1995 to enhance the functionality of electronic devices. Pieces of Java code are called applets, and these are most commonly encountered in web browsers executing more complex tasks.

Javascript
JavaScript is a language integrated into HTML documents that runs in a web browser on the website visitor's computer. It is used to populate or generate HTML elements or to make them interractive – such as rollover buttons in a navigation bar. It can also allow the browser to connect to databases and even communicate with other applications. It was invented by Netscape in the mid-1990s. It is different to Java and Microsoft's JScript.

JPEG (Joint Photographic Experts Group)
An international standards body set up to establish image compression standards for varying levels of compression. Current JPEG files show some minor loss of data and introduce artifacts. Each time a JPEG image is saved the quality deteriorates by a small increment.
      JPEG 2000 employs lossless compression options using 30:1 compression ratios, for much higher-speed image transmission at higher quality levels. This format is restricted to a few special software companies and is not a formal ISO image standard, due to patent claims by some companies.

K

Kodak Picture CD
The Picture CD is a consumer-resolution CD format developed by Kodak. Remote photofinishers can access the images over the web for distant friends and family. Maximum file sizes apply, so hi res images, when saved to this format, may restrict the maximum size to which a Picture CD image can be printed at a future time. Typically a KPCD file is suited to 100mm x 150mm prints.

L

LAB Colour
A device-independent colour space that defines a specific colour in terms of lightness (luminance) and 2 other variables related to chrominance, to ensure a uniform image and colour appearance. It closely follows human vision perception.

Layers
Layers are the multiple channels of information stored separately in an image-editing program, which allow effective multiple undo levels for creative photographers working on complex images. Very often a layer will simply be an adjustment channel for colour balance or density changes, depending on the output medium. A masking layer can be used to significantly assist in balancing dark and light areas within the same image to make it printable.

LCD (Liquid Crystal Display)
Common now in large screen home TVs, more common in laptop computers and desktop monitors, these flat-panel devices have replaced CRT (Cathode Ray Tube) glass screens, which consumed up to 10x more power and were very bulky.

LD (Low Dispersion)
Low dispersion glass, found in many Tamron and other leading lens makers’ super- telephoto lenses, that reduce color aberration or the splitting of light into primary colours.

Leopard
The development name for the next generation of Apple OS X operating system, revealed in detail by Apple CEO Steve Jobs at the Apple Worldwide Developers Conference, 2007.

Levels
These are the terms to describe the relative brightness levels of colours in RGB files, or in greyscale images as well. Most image editing programs permit adjustment either as "Auto Levels" or manually with personal input. Controlling the levels of individual tones or colours often makes an unacceptable image print satisfactorily.

Li-ion (Lithium Ion)
Lithium Ion batteries are commonly used in digital cameras and laptop computers. They store large amounts of energy in compact spaces.

Lossless
Lossless compression means that when a file is compressed and then reopened, all the information that was there before compression is retained.
Also see Lossy and LZW.

Lossy
Lossy compression involves a substitution of what was there originally with an equivalent or nearly identical piece of information. This introduced material or information shows as an artifact.

LZW (Lemple-Zif-Welch)
A lossless form of compression supported by TIFF, PDF and GIF image file formats.

M

Masks
When you want to make a change to only part of an image, whether it be a colour change or perhaps selective brightness or contrast changes, creation in an image file of a layered mask allows much more versatility than dealing with the composite RGB file all at once.

Metadata
Embedded data in image files which describes, instructs and/or channels specific components of the file for more consistent control of that image. A newspaper, for example, may employ metadata with a JPEG file that also contains information on the date, day, location, camera used, photographer, event, copyright ownership and other caption material. Such metadata is defined by IPTC information, along with EXIF instructions.
See IPTC and EXIF.

Metamerism
The characteristic of how colours reflect back to the viewer differently under altering light conditions. A four-colour sepia image may appear as a neutrally toned image under incandescent light, but appear quite green under fluorescent or daylight conditions. This first became generally known when Epson introduced their 2000P ultra-long-life pigment-ink inkjet printer, which was very sensitive to the viewing colour temperature. More recent dye-based printers do not tend to exhibit this problem.

Moiré
A pattern of interference resulting in swirls of radiating tonal diffraction and reflections. Moiré effects can be seen when a checked jacket is shown on a TV in which there is interference between the original subject matter and the pattern of the recording or display device.

MPEG (Motion Picture Experts Group)
The motion picture equivalent of JPEG files. A compression system for movie video files, now widely used for accessing video via the Internet. MPEG-2 is the common standard of DVD and digital TV set top boxes. MPEG-4 (.mp4) is the standard for fixed and mobile web. These standards are also adopted by ISO as industry standards worldwide.

N

NEF (Nikon Electronic Format)
Nikon’s proprietary RAW file from digital cameras.

Ni-MH (Nickel-Metal Hydroxide)
Batteries used in early DSLR cameras for longer life than the even earlier and highly toxic NiCd (Nickel Cadmium) batteries. On disposal, neither of these battery types should be sent to landfill but should be handed in at collection centres specialising in the safe disposal of such batteries.

Noise
Any part of a signal which was not part of the original. In digital imaging noise is the introduction of random artifacts not present in the original image. At high ISO settings (above 800) and in low or dark conditions, blue channel noise is especially likely with CCD cameras. Modern DSLR and Compact digital cameras provide noise filtering, especially for night pictures or long exposure.

O

Optical Resolution
The ability of an optical system to resolve or detect details in subjects so they may be recorded or observed. A lens may be described as having 100 lines per millimetre optical resolution at its centre; when suitably magnified, it would be possible to detect 100 distinct strands per millimetre.

ORF (Olympus Raw Format)
The proprietary Raw file format from Olympus.

P

Panorama
A panorama image in digital photography normally describes the combination of multiple images into a single ultra-wide format image. On the internet this can also include virtual reality panoramas, widely used by real-estate sales sites, to enable a virtual walk-through of a prospective house or apartment. Special panorama-making software or functions such as the Image Align new in Adobe Photoshop CS3, is required to seamlessly merge these multiple images.

Paths
A path or clipping path is created usually when you wish to isolate an object in a picture away from the rest of the image and export it with a transparent background. When this is done, and the edges of the 'cut-out' image are suitably anti-aliased and feathered, almost seamless insertions can be made in page-layout and presentation programs. It is something that requires patience. Photoshop provides a handy Help Wizard for those who need this for presentations or desktop publishing work.

PCMCIA (Personal Computer Memory Card International Association)
A PCMCIA, or PC, card is a defined-size 64-pin device that slots into a portable computer. These cards may connect a computer to a network (Network Interface Card), provide fax and modem facilities, act as an extended memory card, or provide the SCSI adapter required to work with some older scanners or CD-writers. Adapters in PCMCIA format are available to permit use of CompactFlash or SmartMedia cards within a PCMCIA slot in a computer. PC cards are available as Type I, II or III and vary in thickness accordingly.

PDF (Portable Document Format)
Created by Adobe, PDF files are platform independent ways of moving high quality documents in compressed form over a network or Intranet or the Internet. PDF files resolve many of the incompatibility problems between Mac and PC. A PDF file is created by Adobe Acrobat Distiller and read by the freely downloadable Adobe Acrobat Reader.

Photo CD
Introduced with great flourish by Eastman Kodak as a consumer product in the early '90s, Kodak Photo CD is nowadays the preferred method of storing and archiving professional images, as well as transferring images to clients in multiple resolutions. Nearly all CD-ROM players supplied with computers today can read a Photo CD.

PIM (Print Image Matching)
A proprietary print algorithm embedded in some cameras, enabling the narrow colour space employed in the capture device, usually SRGB, to be expanded out again to more closely reproduce the original dynamic range and colours of the image captured. The system was developed by EPSON.

Pixel
An electronic picture element. A digital camera contains a sensor, usually a CCD or CMOS, containing millions of picture sensor elements. Each of these capture alternating red, green and blue data which provides data comparable to the original image.

Pixelated
An image file, usually quite a small file, reproduced either on a screen or in a printed form, where the size of the pixels is enlarged so much that one can see the jaggy edges of each pixel in the image. A continuous-tone photograph requires a minimum of 200 pixels per inch in four colours to provide an image that has little or no pixelation, producing a seamless blend between the picture elements in the image. Sometimes pixilation is referred to as "an attack of the jaggies".

Point and Shoot
A term often used to describe compact cameras, either film or digital. Now includes the fixed focal length cameras built into mobile/cell telephones.

Polarising Filter
An optical filter attached to the front of a camera lens, that, when rotated, cuts out reflections and has a tendency to enrich colour saturation. Most effective when used when the light source is at right angles to the subject.

Primary Colours
Otherwise known as additive colours: Red Green and Blue (RGB). In colour printing the three subtractive primary colours are cyan, magenta and yellow (CMY).
See CYMK.

PPI (Pixels per Inch)
The number of picture elements (usually printed) per inch of printed surface.

Compiled, written and updated by John Swainston.
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