Appendix B : Glossary

 

Algorithm

A sequence of instructions that defines a method of solving a problem.

Bit

A binary digit: a zero or one.

Bitmap

A grid of pixels used to generate an image.

Blue

A primary color of light in the RGB color model.

Brightness

An attribute of color according to which an area looks more or less light.

Byte

Eight bits.

Channels

The individual color or grayscale components of an image. A gray scale has just one channel, whereas an RGB image has three channels, one each for red, green and blue components.

Color Cast

An overall color imbalance in an image, sometimes limited to a specific tonal range.

Color Correction

Altering the tonal properties of an image to optimize its appearance.

Color Model

A coordinate system used to numerically describe colors such as CIELAB, RGB, and CMYK.

Color Space

A specific variant of a color model, with a defined color gamut. For example, the RGB color model encompasses a number of color spaces including Adobe RGB, Color Match RGB and sRGB.

Color Temperature

The temperature in degrees Kelvin (K) of a theoretical black box, heated to produce a certain color light.

Contrast

The tonal range between the lightest and darkest points in an image. Also the tonal difference between two parts of an image.

Cropping

Removing unwanted portions in an image to reduce the size of the image.

Cyan

One of the subtractive primaries used in color printing devices. Cyan ink absorbs red light and reflects green and blue light.

Digital

Any system in which information is stored as discrete numerical values.

Digitize

To convert analog signals or other continuous quantities into discrete digital values.

Dynamic range

The difference between the minimum and maximum values that can be attained in any system.

EXIF

EXIF stands for Exchangeable Image File Format. EXIF is a variation of JPEG, used by almost all digital cameras to record extra interchange information to image files as they are taken.

GIF

Graphics Interchange Format, a widely used file format for images and graphics, particularly for the Web.

Grayscale

An evenly graduated series of tones from black to white and containing no color.

Halftone

An image that has been photographically or digitally transformed into an array of dots in order to be printed.

Highlight

The brightest part of an image, especially the brightest part that still retains distinct details.

Histogram

A graph of tonal contents of an image from highlights to shadows, with the height of the graph indicating the number of pixels at each brightness level.

 

Hue

The name of a color such as blue, green or orange. Also, the property of color that corresponds to wavelength.

JPEG

Joint Photographic Experts Group, a standard technology for compressing image files.

K

See Kelvin.

Kelvin

A unit of measure used for color temperature, based on the centigrade scale extended down to absolute zero (0K or -273.1C).

Lightness

The property of a color that distinguishes white from gray or black.

Megabyte

A million bytes; a thousand kilobytes.

Midtones

The middle part of the tonal range of an image, between the quarter tones and the three-quarter tones.

Photo Contents

File attachments, Windows Applications and Web-based Content are encrypted into images. Photo Content can be executed and viewed in PhotoViz.

Photo Messages

Secret or hidden text messages encrypted into an image. Photo messages can be personalized i.e. only registered users can access the messages. A Registration Photo is used to register users.

PNG

PNG is an extensible file format for the lossless, portable, well-compressed storage of raster images. PNG provides a patent-free replacement for GIF and can also replace many common uses of TIFF. Indexed-color, grayscale, and true color images are supported, plus an optional alpha channel for transparency. Sample depths range from 1 to 16 bits per component.

Pixel

A picture element the smallest area that can be sampled or addressed by a digital device or system.

Quartertones

The tonal areas between the highlights and midtones.

Registration Photo

This image enables the viewer to read all future photo messages from the sender.

Resample

Changing the size of an image file by altering its resolution. Sampling down reduces files size, and involves minimal data loss. Sampling up increases file size and relies on interpolation, a process in which the software makes up pixel values based on the colors of surrounding pixels. This always results in a loss of detail.

Resolution

The smallest sample size that a digital device can detect or produce.

RGB

The red, green blue color model used in color photographic film, monitors, scanners, digital cameras and film recorders.

Saturation

The strength or purity of a color, sometimes called chroma. Saturation represents the colorfulness of an area, judged in proportion to its brightness.

Shadow

The darkest part of an image containing significant visible detail.

Sharpening

The process of increasing the appearance of detail in an image by artificially exaggerating contrast differences around edges.

Three-quarters tones

The tonal range between the midtones and the shadows.

TIFF

Tag Image File Format, widely used file format developed at Aldus and now controlled by Adobe Systems. TIFF files are used for black and white, grayscale, RGB and CMYK images.

White balance

The process of adjusting the RGB signals in a device such as a monitor to make it produce a neutral white.

White point

The color temperature at which a monitor combines red, green and blue phosphors to create pure white.