Bit Depth: 8 bit vs 16 bit vs 32 or 64 bit. These refer to the colour information stored in an image. The higher the bit depth of an image, the more colour variations and tones it can contain. The simplest image, a 1 bit image, can only show two colours, black and white. The 1 bit can only store one of two values, 0 (white) and 1 (black). An 8 bit B&W image contains 256 shades. A 16 bit B&W image contains 65,536 shades. The higher the bit depth the larger the file size. 16 bit images fare much better in post processing than 8 bit images.
Chromaticity: The quality of a colour independent of its luminance. The hue and colourfulness of a colour. This term is from colour science. But, for our purposes, we can use it interchangeably with the word “colour.”
Chromaticity Diagram: A map of all the colour visible to an average human as established though many tests run by CIE in 1931.
Colour Management: In digital imaging systems, colour management is the controlled conversion between the colour representations of various devices, such as image scanners, digital cameras, monitors, computer printers, offset presses, and corresponding media. The primary goal of colour management is to obtain a good match across colour devices.
Colour Space: RGB working spaces are mathematical matrices of RGB numerical values which are derived from and bounded by the three primaries, include a white point and Tone Reproduction Curve/Gamma, are plotted in 3 dimensions and are designed to encompass portions of the Spectrum-Locus (a map of all of the colour visible to humans). As such, RGB working spaces accommodate the functionality of RGB capture and output devices. Examples are: ProPhoto RGB, Adobe RGB, sRGB, ECI RGB and many more.
C-Print (Chromogenic Print): Conventional darkroom style colour prints which are now made using digital images and are exposed by LED or Laser Diode.
Dithering: is a technique where tiny dots are printed in patterns in order to create the illusion of tones and colors that cannot be physically reproduced.
D-max: The maximum or greatest density possible in an image made from ink on an inkjet print or silver halides in film and silver based print paper or dyes on a C-print (Chromogenic print).
D-min: The lightest tone before blank paper white.
FWA or OBA stands for Fluorescent Whitening Agents or Optical Brightening Agents. These are chemical compounds which are added to certain papers during the manufacturing process to make them appear whiter in the presence of ultraviolet light. Light in the ultraviolet and violet region (usually 340-370 nm) of the electromagnetic spectrum is absorbed and re-emitted in the blue region. The visual effect is that the paper will appear cooler and whiter. In place of these compounds violet-blue shading dyes are added in paper after bleaching of the pulp. The effects of either fades in time. It may not fade evenly which may present as spotted yellowing.
Gamut: The range of colours which a device can capture or produce.
Giclee: is a term which was invented by Jacque Duchene of Nash Editions in 1992 when ink jet technology was in its infancy. Inkjet had been used primarily as a proofing mechanism with equipment like the Iris Inkjet. Nash Editions tried to use modified versions of the Iris Inkjet to serve the fine art photography market and to compete with traditional photographic print processes. The concept struggled, as acceptance by the fine art photography community was weak due to the reproducibility of the digital print stream which threatened the “Limited Edition” aspects of the photographic print. Duchene felt that the use of the french term “Giclee” would provide a mystique which would mask the actual inkjet/digital functionality. It worked and the word stuck. The approximate english translation of Giclee is “to squirt.” The word is rarely seen in galleries anymore.
Gray Balance Failure: is an effect which occurs when a print appears to have perfect neutral balance under one set of illumination but not under different illumination. It may appear to be neutral under one illumination, greenish under fluorescent or it may have a slight magenta cast under dark incandescent illumination. This effect is often confused with metamerism which is not possible as only one sample is involved.
ICC Profiles: are sets of data that characterize a color input or output device. Each profile is a snapshot of the imaging characteristics and capabilities of the device that was profiled. They are small digital files which contain colour look-up tables particular to each device. When embedded in an image file, they form translation tables which allow each device to effectively communicate with another to provide predictably accurate colour reproduction.
Image Resolution: The number of pixels per inch (ppi) contained within a digital image and which together form the digital image. Optimum resolution to achieve the highest quality in print with our equipment is either 360ppi or 720ppi.
L*A*B* (CIE L*A*B*) is a 3 dimensional colour model or map created by the International Commission on Illumination in 1931. It describes mathematically all colour visible to human beings. The letter “L” denotes the luminance values i.e.neutral tonality from pure white to absolute black. The “A” and “B: represent the colour channels. The “A” axis represents Green (negative values) to Red (positive values). The “B” axis represents Blue (negative values) to Yellow (positive values).
Metamerism: Often confused with metameric failure, metamerism is the phenomenon that makes all colour matches possible. It always involves two colour samples with differing spectral properties which appear to match under one illumination but not another. Sample metamerism is a psychophysical phenomenon commonly defined as the situation when two samples with different spectral curves produce a visual colour match under one light source but fail to do so under another. Observer metamerism describes the phenomenon where two observers see the same sample as having a different colour: the difference between the way our eyes see a colour and the way a camera sees colour is an example of observer metamerism.
Metameric Failure: The inability of 2 colour samples with differing spectral properties to maintain a colour match under different light sources. Often, when people talk of metamerism, they’re really describing metameric failure or gray balance failure which occurs when one colour sample appears different under different lighting conditions.
Metamers: Are colours with different spectral composition that appear to match under one lighting condition but differ in another.
Pixel: An acronym for Picture Element in digital imaging. Pixels are the digital equivalent to silver halide grain from conventional photography.
PPI: Pixels Per Inch as seen in a digital image enlarged on a computer screen
Printer Resolution: The number of dots per inch (dpi) which together form a printed image from a digital file. Optimum resolution for our inkjet printing equipment is 2,880 dpi x 1,440 dpi.
Profile (ICC Profile): a small data set which characterizes the maximum capabilities of a particular input or output device. ICC = International Colour Consortium.
Soft Proofing: is viewing a final print ready image, as translated through a selected printer and paper specific icc profile, on a calibrated display for predictive analysis prior to committing it to ink on paper. This allows the photographer to optimize the image for the print. The final print is the final photograph.
Spectrum (spectral) Locus: The Spectrum-Locus is a 2 dimensional plot of the the results of certain visual stimuli to the brain of the standard human observer which are defined as colours. It is not a mathematical grid or matrix designed to suit the functionality of machines. These are working spaces. Instead, it is a map or record of the average human’s response to a range of frequencies of light which, as visual stimuli, create responses in the brain which are subsequently defined as colours.