Graphic Image Formats

 

There are too many formats for communicating image information to computers and their peripherals to list here, but I will give you the highlights and some interesting and maybe even helpful information about them.

 

List of File Formats

Tag	Full name	Defined
BMP	Windows Bit Map	Microsoft
EPS	Encapsulated Postscript	Patent owned by Adobe
GIF	Graphic Interchange Format	Patent currently own by Unisys
JPG	Joint Photographic Experts Group	ISO standard 10918
PCD	Kodak Photo CD	Patent owned by Kodak
PNG	Portable Network Graphics	Patent owned by Adobe
PDF	Portable Document Format	Patent owned by Adobe
TIF	Tagged Image File Format	Adobe

 

 

 

 

 

 

 

 

 

 

 

 

 

 

BMP: is the MS-Windows standard format for graphic files created within its programs. It is a raster image as it is a “mapping” of each bit of information. Raster imaging is not scaleable as vector imaging is, but it is able to show more subtle variations in color as it does map each pixel. It also makes a larger file size.

 

EPS: is a Vector image and therefore scaleable. Vector images are equations or math formulas, the computer then translates the formulas to the monitor’s or display’s pixels. It is smaller and will show crisper edges.

 

GIF: is the grand daddy of image formats for the web. It originally was DJIF and therefore the soft “g” pronunciation. The LZW compression algorithm used in the GIF format is owned by Unisys, and companies that make products that exploit the algorithm (including the GIF format and PhotoShop) need to license its use from Unisys. There are two versions of the format, 87a and GIF89a. Version 89a (July, 1989) allows for the possibility of an animated GIF, which is a short sequence of images within a single GIF file. A GIF89a can also be specified for interlaced (progressive) GIF presentation.

 

JPG or (Joint Photographic Experts Group), is the ISO/IEC group of experts that develops and maintains standards for a suite of compression algorithms for computer image files. They have released an updated version call JPG 2000 that is slowly being adopted.

 

A JPG file is created by choosing from a range of compression qualities (actually, from one of a suite of compression algorithms). When you create a JPG or convert an image from another format to a JPG, you are asked to specify the quality of image you want. Since the highest quality results in the largest file, you can make a trade-off between image quality and file size.

 

The JPG's correct name is JFIF for JPG File Interchange Format. The digital camera manufacturers developed another version call JPG EXIF. The difference is the metadata information that is stored within the image file. The JFIF stores information about the color profile, while the EXIF stores information about the camera.

 

JPEG 2000: has multiple versions for use, including a lossless version and a “tiling” version that allows for “zooming” into detailed areas of the image file. It also has “extensible headers” which is space to write metadata that then is embedded in the image file. How these headers might be used and how metadata might be standardized in the header is still being developed by both special interests groups and those who set standards.

 

Kodak’s Photo CD uses a proprietary image format called an Imagepak that has its own unique image compression technology and color management. It is very good, but will only be found on Photo CDs. The 4.5 MB files expand to clear accurately colored 18mb files. As with any computer file, you can copy the PCD files from the CD-ROM to a server within your system. If you use this scanning method - usually only provided by photo vendors - you should convert them to a more useful image format, such as TIF. Unfortunately, this excellent file format is rapidly becoming obsolete.

 

PNG: as with the previously mention JPEG 2000 are attempts to create a non-proprietary improved web image format. The move is toward interested compression formulas that do not lose information. It is extensible file format for the loss less, portable, well-compressed storage of raster images. Extensible means you can extend its specifications and develop other versions. Unfortunatelyit is not being as widely accepted.

 

Another extensible format is the TIFF. It utilises a structure that can store image data and attributes of that image. It has been extended into several versions, the most common of which is TIFF-Fx for the fax machine.

 

1 For an example of a still only partial listing of formats see http://www.daubnet.com/formats/index.html

 

Computer Hardware and Software terms

 

Algorithm: A step by step procedure for solving a problem

 

Bit: The smallest unit of computer information, = 0 or 1, a binary digit

 

Byte: a sequence of bits, usually 8, that is used as a unit of storage. The fact it is 8 bits rather than 10 is why 5 megabytes do not equal 5000 kb.

 

Display Technology:

 

CRT: Cathode-ray tube - Like a TV an electronic discharge is shot at the back of its screen “excite” the phosphor coated back of the display. This is the older display technology and so that there are several image display management tools created for it. It does not use the same frequency as a TV though, which is why they are not interchangeable.

 

LCD: Liquid Crystal Display - sometimes referred to as a Thin Film Transistor (TFT) display. A current is sent across two conductors on the grid to control the lighting of each pixel. These are the flat panel monitors which use less space and less electricity, but, as a relatively new technology, the color and other display management systems are in their infancy

 

OLED: Organic Light Emitting Diodes - Newly developed by Kodak it is still only available on cell phones and PDAs. The diodes transmit light when a low current is passed through them.

 

Plasma: This flat panel display uses charged gas and Phosphors to create its display. It is brighter then and LCD panel and has a broad viewing angle. They can be quite large such as in high definition TV.

 

Resolution: For a display device it is the quantity of pixels that the device can display

 

OS: Operating System - A set of programs used to control, assist or supervise all the other programs that run on that computer.

 

RAID: (Redundant Array of Inexpensive Disks). Hard disc arrays enable very fast access to data + Much increased reliability through redundancy (information may be mirrored / striped across several discs. Range from Level 0–5 implementation.

 

Imaging Terms

 

Bit-Depth: the number of "bits" of information about something, in imaging it usually describes color but can also describe sound in audio equipment. Note that each additional bit in a binary number system doubles the possibilities so that a 24-bit process is 2 to the 24th power or 16,777,216 available descriptions of information.

 

Bitonal: a bitonal, a.k.a. black & white or lineart, image consists of pixels that can represent one of two tones.

 

Compression: a process used to reduce image file size. Image-compression algorithms may be either information-preserving, a.k.a. lossless, or non-information-preserving, known as lossy.

 

Image Types

Raster image: is a bit map or grid of x/y coordinates specifying each pixel on a display. It is a large file

 

Vector image: is a representation of a sequence of mathematical statements or sequence of commands the place lines or shapes on the display screen. It is a smaller file than a raster image, details "lines" or edges very well and is scaleable.

 

Pixel: the smallest logical unit of visual information that can be used to build an image. Short for picture element, pixels are the little squares that can be seen by enlarging an image.

equal to one ‘bit’ if black and white (monochrome, or 2-colors),

equal to one ‘byte’ (8 bits) for ‘Indexed Color’ (256 colors),

equal to 2 bytes for 16-bit color (‘Thousands of Colors’)

equal to 3 ‘bytes’ (24 bits) for ‘True Color’, or (‘Millions of Colors)

equal to 4 ‘bytes’ (32 bits) for " " + 'alpha' (transparency) channel

 

Image Processing Terms

 

CLUT: Color Lookup Table (or Palette) a table used to choose which of 256 colors are used in 8-bit, Indexed color. Every computer has a built-in (‘System’) CLUT; else the image has to provide it.

 

Color Space: mathematical model of color as a three dimensional space using color terms as the axis

 

Digital Watermark: A digital watermark is an identification code carrying information about the copyright owner, the creator of the work, authorised consumers and so on. The watermark is invisible and permanently embedded into digital data for copyright protection and for checking if the data has been corrupted. By means of watermarking the work is still accessible, but permanently marked.

 

Dither: The process of electronically arranging spatial clusters on a displayed or printed image. Black & white process used within the printing industry to represent colour or grey tone images. Similar to Half-Toning as used by the newspaper industry.

 

DVD: (Digital Versatile Disc). These are, as yet, an unproven standard. Several variants currently exist – DVD-R, DVD-RAM, DVD-RW, DVD+RW. Backwards compatibility is a key concern currently. Current capacities exceed 9 GB (selected variants only).

 

Dynamic range: The range of information concerning the light to dark values in an image.

 

Greyscale: (8 bit). Usually refers to a continuous tone image (typically 256 shades of grey).

 

Histogram: plot of the number of pixels for each possible grayscale value. A histogram is a graph that shows the distribution of intensities in an image. The horizontal axis represents the full range of tonal values, the vertical axis indicates the number of pixels for each intensity value.

 

Highkey: an image where the histogram is weighted toward the white point, thus resulting in a light image.

 

Lowkey: an image where the histogram is weighted toward the black point, thus resulting in a dark image.

 

Hue: color.

 

Resampling occurs in two forms: down sampling and up sampling. Scanning often occurs at a higher resolution than is necessary and the required resolution is obtained by resampling the image. Aliasing can occur when the image data are downsized. To minimise its effects low-pass filtering can be applied to the image before it is downsized. Up sampling should be avoided because no additional image information can be created.

 

Saturation: the intensity of the color.

 

True color: a.k.a. 24-bit color, is the specification of the color of a pixel on a display screen using a 24-bit value. Each RGB level is represented by the range of decimal numbers from 0 to 255. The total number of available colors is 256 x 256 x 256, or 16,777,216 possible colors.

 

TWAIN: (Scanner driver). Generic device driver that allows the scanned image captured by the scanner to be passed to the host PC. The word TWAIN originates from Kipling's "The Ballad of East and West" - "...and never the twain shall meet...", reflecting the difficulty, at the time, of connecting scanners and personal computers. It was up-cased to TWAIN to make it more distinctive. This led people to believe it was an acronym, and then to a contest to come up with an expansion. None were selected, but the entry "Technology Without An Interesting Name" continues to haunt the standard. (taken from the www.twain.org site)

 

Unsharp masking: an artificial transformation that can make images appear more in focus by exaggerating transitions that have been dulled by scanning.

 

Value: the amount of light to dark in the color.

 

Database and Metadata Terms

 

ASP: (Active Server Pages) Microsoft’s default web scripting environment allows developers to embed commands in web pages using a variety of languages (most commonly VBScript).

 

JSP: is similar to ASP, but uses Java as the programming language.

 

EDMS: (Electronic Document Management System). Term to describe the storage and management (including retrieval) of documents which are input to a computer system via a variety of mechanisms (including scanning device, conventional software products such as Word Processors, faxes, email).

 

ER (entity Relationship) Diagrams: a graphic means of showing all the fields and tables in a database and how they are related.

 

GIS Geospatial Information Systems. Incorporating geographic coordinates as part of the data in text records and in images is becoming increasingly important.

 

GUI: Graphical User Interface; building interfaces that make it easier to use computers in general and also to interface with data in tables.

 

HTML: Hypertext Markup Language is really about the graphic appearance of information on web pages, layout/placement, font size, color attributes, etc.

 

Metadata: Data about data; includes technical, administrative and descriptive data.

 

MySQL: An open source database that provides backend services for many major web sites. It runs on many platforms, including Linux and Windows, integrates nicely with the web scripting languages likes PHP and VBScript/ASP and is robust enough to handle large databases.

 

PHP: The PHP group’s website introduces this freely available (open source) scripting language, which can be embedded into HTML and suggests additional resources.

 

Schema: A roadmap to applying a data standard – like MARC, VRA Core 4.0, etc – within XML

 

SQL: (Standard Query Language) pronounced with “sequel” or S-Q-L. The basis for getting and displaying information from related tables by using programmable commands. Oracle, Microsoft SQL Server, IBM DB/2, IBM Informix, Sybase, OpenBAse, MySQL, PostgreSQL, Firebird, all use SQL, MS Access and Filemaker Pro 7 can connect to SQL tables.

 

XML: Extensible Markup Language is a universal language for sharing data between applications. It encloses data values with tags describing what that information means.

 

XSLT: Extensible Stylesheet Language Transformation is a document that sets up how the data fields in your database export to XML and to specific schema.