Tech Talk
Explanations of Digital Jargon
Glossary of Terms |
Graphic Image Formats
There are too many formats [1] 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. First thing to learn is that the Mac operating system uses 4 letters in its tags to define files. They are shown here as [ tag]. More importantly Macs do not bother to show you these tags or attach them to a file. In the past the Windows operating system used only three letters in their tags and it can not read a file if it does not have a tag.
Rule 1: Mac operators must always insert file tags on their files when saving them.
List of File Formats
| Tag | Fullname | Defined by |
| BMP | Windows Bit Map | Microsoft |
| EPS | Encapsulated Postscript | Patent owned by Adobe |
| GIF | Graphic Interchange Format | Patent currently own by Unisys |
| JPEG | Joint Photographic Experts Group | ISO standard 10918 |
| PCD | Kodak Photo CD | Patent owned by Kodak |
| PNG | Portable Network Graphics | Internet Committee - W3 |
| Portable Document Format | Patent owned by Adobe | |
| TIFF | 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 ³mapping² 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 monitor¹s or display¹s 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 ³g² 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.
JPEG 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 JPEG file is created by choosing from a range of compression qualities (actually, from one of a suite of compression algorithms). When you create a JPEG or convert an image from another format to a JPEG, 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 JPEG's correct name is JFIF for JPEG File Interchange Format. The digital camera manufacturers developed another version call JPEG 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.
Kodak¹s 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 can keep them in their original format or convert them to a more useful image format, keeping the original files as archives.
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.
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.
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.
Display Technology:
CRT - Cathode-ray tube - Like a TV an electronic discharge is shot at the back of its screen ³excite² 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.
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).
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)..
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.
OS Operating System - A set of programs used to control, assist or supervise all the other programs that run on that computer.
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 Œbit¹ if black and white (monochrome, or 2-colors), equal to one Œbyte¹ (8 bits) for ŒIndexed Color¹ (256 colors), equal to 2 bytes for 16-bit color (ŒThousands of Colors¹) equal to 3 Œbytes¹ (24 bits) for ŒTrue Color¹, or (ŒMillions of Colors) equal to 4 Œbytes¹ (32 bits) for " " + 'alpha' (transparency) channel.
Resolution - For a display device it is the quantity of pixels that the device can display.
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 05 implementation.
Imaging 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 (ŒSystem¹) 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.
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 - 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
This material was originally created by Trudy Levy for the Infopeople Project [http://infopeople.org/], supported by the U.S. Institute of Museum and Library Services under the provisions of the Library Services and Technology Act, administered in California by the State Librarian. Any use of this material should credit the author and funding source.
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