Digital Imaging Vocabulary
Bit Depth - Bit depth quantifies how many unique colors are available in an image’s color
palette in terms of the number of 0’s and 1’s, or “bits.” See also: Dynamic Range
Compression - The reduction of image file size for processing, storage, and transmission.
The quality of the image may be affected by the compression techniques used and the level
of compression applied.
There are two types of compression:
- Lossless compression is a process that reduces the storage space needed for an
image file without loss of data. If an image has undergone lossless compression,
it will be identical to the image before it was compressed.
- Lossy compression is another process that reduces the storage space needed for
an image file, but it discards information. If an image that has undergone lossy
compression is decompressed, it will differ from the image before it was
compressed, even though the difference may be difficult for the human eye to
There are both standard and nonstandard compression techniques available. In general, it is
better to employ a compression technique that is supported by standards, is nonproprietary,
and maintained over time. In selecting a compression technique, it is necessary to consider
the attributes of the original. Some compression techniques are designed to compress text,
others are designed to compress pictures.
Derivative, Surrogate or Access Images - Digital images created from another digital image
through some kind of automated process, usually involving a loss of information. Techniques
used to create derived images include sampling to a lower resolution, using lossy
compression techniques, or altering an image using image processing techniques.
Digital Image - An electronic photograph, made up of a set of picture elements ("pixels").
Each pixel is assigned a tonal value (black, white, a shade of gray, or color) and is
represented digitally in binary code (zeros and ones). The term "image" does not imply solely
visual materials as source material; rather, a digital image is simply a representation of
whatever is being captured, whether it be manuscripts, text, photographs, maps, drawings,
blueprints, halftones, musical scores, 3-D objects, etc.
Dots Per Inch or DPI - A measure of resolution used for printed text or images and monitor
Dynamic Range (Bit Depth) - The number of colors or shades of gray that can be represented
by a pixel. The smallest unit of data stored in a computer is called a bit. Dynamic range is a
measurement of the number of bits used to represent each pixel in a digital image. 1 bit or
bitonal means that a pixel can either be black or white. Bitonal imaging is good for black and
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white images, such as line drawings and text. However, scanning in grayscale rather than
bitonal may produce a better looking image. 8 bit color or 8 bit grayscale means that each
pixel can be one of 256 shades of color or one of 256 shades of gray. 24 bit color means
that each pixel can be one of 16.8 million colors. When moving to 48 bit color the available
colors in the display will number 2800 times one trillion. This is an enormous number of
colors. Plus a higher bit resolution can display more shades of gray. With 30 bit color depth,
four times more gray can be represented in the display. Eight times more gray, or even
higher, can be represented by a 36 or 48 color bit-depth display.
File Size - The file size of a digital image is proportional to its resolution. The higher the
resolution, the bigger the file size — file size is different from image size.
Grayscale - A range of shades of gray in an image or the values represented between black
Image Manipulation or Alteration - Making changes (such as tonal adjustments, cropping,
etc.) to a digital image using image editing and processing software such as Adobe
Image size - Describes the actual physical dimensions of an image, not the size it appears
given display device.
JPEG - Joint Photographic Experts Group. A compression algorithm for condensing the size of
image files. JPEGs are helpful in allowing access to full screen image files online because
they require less storage and are therefore quicker to download into a web page.
JPEG-2000 - At its core, JPEG 2000 is an international standard for the compression of still
digital images. JPEG 2000 improves on the compression performance of previous methods
while offering significant new features and capabilities. The format is multi-resolution, which
allows an application to access and decode only the amount of image needed. This allows
the user to quickly view an extremely large JPEG 2000 image almost instantly by retrieving
and decompressing a low resolution, display sized potion of the file. In addition, the format
allows for new access opportunities such as zoom, pan and rotate. JPEG 2000 is still a
lossy, compression technique but may have potential for becoming the file format of choice
for archival master images in the near future.
Master Image - A digital image that is uncompressed and high-quality, therefore, retaining
the best possible color information. It is meant to have lasting utility. Master images are
usually saved in a nonproprietary format and kept off-line in a secure environment. Master
images are of a higher resolution and quality than the digital image delivered to the user onscreen. An archival master accurately represents the original analog item and has an
associated metadata record which provides descriptive, administrative, and technical
information concerning the original and digital items.
Metadata - Data about data, or information provided about a digital object in order to
provide access to that image. Usually includes information about the original object,
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intellectual content of the image, digital representation data, the creation of the digital files,
and security or rights management information.
Optical Resolution - The number of pixels (in both height and width) making up an image, the
more pixels in an image, the higher the resolution, and the higher the resolution of an
image, the greater its clarity and definition (and the larger the file size). Resolution can also
refer to the output device, such as a computer monitor or printer, used to display the image.
Image file resolution is often expressed as a ratio (such as 640x480 pixels), as is monitor
resolution; however, resolution is also expressed in terms of PPI. The assumed universal
monitor resolution for web users is 144 DPI. Image file resolution and output (print or
display) resolution combine to influence the clarity of a digital image when it is viewed.
Pixel - Pixel is short for picture elements, which make up an image, similar to grains in a
photograph or dots in a half-tone. Each pixel can represent a number of different shades or
colors, depending on how much storage space is allocated for it. Pixels per inch refers to
the number of pixels captured in a given inch. When referring to digital capture pixels per
inch (PPI) is the preferred term, as it more accurately describes the digital image.
TIFF - Tagged Image/Interchange File Format a file storage format implemented on a wide
variety of computer systems, usually used for archival or master digital capture.
Document - any object that is not yet digital. For example, a photograph, a book, a
newspaper, a yearbook, a page from a diary, an entire diary, etc. that has not yet been
Digital file - a document that has been scanned or digitized and converted into a computersaved file and is made up of a set of picture elements (pixels). Digital files for the MMP are
saved as TIFF file types.
Digitization - The process of converting analog information into digital format.
Folder - Just like real world folders, folders on your hard drive store files. These files can be
documents, programs, scripts, and any other kind of computer files you can think of. Folders
can also store other folders.
Collection folder - the folder where all of a MMP collection’s digital files and folder hierarchy
are saved. This folder is named the same as the MMP Collection (e.g. Montana Yearbook
Folder hierarchy - how the parent and child folders are structured
Parent folder - a folder created within a collection folder that identifies a document whose
digital files are stored within. May house child folders
Child folder - Child folders are stored in parent folders and can house other child folders and
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