What is image?

An image is a visual representation of something. In information technology, the term has several usages:

1) An image is a picture that has been created or copied and stored in electronic form. An image can be described in terms of vector graphics or raster graphics. An image stored in raster form is sometimes called a bitmap. An image map is a file containing information that associates different locations on a specified image with hypertext links.

Common image file formats online include:

  • JPEG : Joint Photographic Experts Group (pronounced JAY-peg) is a graphic image file produced according to a standard from the Joint Photographic Experts Group, an ISO/IEC group of experts that develops and maintains standards for a suite of compression algorithms for computer image files. JPEGs usually have a .jpg file extension.

  • GIF : Graphics Interchange Format (pronounced JIF by many, including its designer; pronounced GIF with a hard G by many others) stands for Graphics Interchange Format. The GIF uses the 2D raster data type and is encoded in binary. GIF files ordinarily have the .gif extension.

  • GIF89a is an animated GIF image, formatted according to GIF Version 89a. One of the chief advantage format is the ability to create an animated image that can be played after transmitting to a viewer page that moves - for example, a twirling icon or a banner with a hand that waves or letters that magically get larger. A GIF89a can also be specified for interlaced GIF presentation.

  • PNG : Portable Network Graphics (pronounced ping ) is a Portable Network Graphics) is a file format for image compression that was designed to provide a number of improvements over the GIF format. Like a GIF, a PNG file is compressed in lossless fashion (meaning all image information is restored when the file is decompressed during viewing). Files typically have a .png extension.

    PNG can be used for:

    • Photos with line art, such as drawings, illustrations and comics.
    • Photos or scans of text, such as handwritten letters or newspaper articles.
    • Charts, logos, graphs, architectural plans and blueprints.
    • Anything with text, such as page layouts made in Photoshop or InDesign then saved as images.

  • SVG : Scalable Vector Graphics is Scalable Vector Graphics, the description of an image as an application of XML. Any program such as a browser that recognizes XML can display the image using the information provided in the SVG format. Scalability means that the file can be viewed on a computer display of any size and resolution, whether the small screen of a smartphone or a large widescreen display in a PC. Files usually have .svg extension.

  • TIFF : Tag Image File Format is a common format for exchanging raster graphics (bitmap) images between application programs, including those used for scanner images. A TIFF file can be identified as a file with a .tiff or ".tif" file name suffix.

2) A disk image is a copy of the entire contents of a storage device, such as a hard drive or DVD. The disk image represents the content exactly as it is on the original storage device, including both data and structure information.

3) Another use of the term image is for a section of random access memory (RAM) that has been copied to another memory or storage location.

Bitmap

A bit map (often spelled "bitmap") defines a display space and the color for each pixel or "bit" in the display space. A Graphics Interchange Format and a JPEG are examples of graphic image file types that contain bit maps.

A bit map does not need to contain a bit of color-coded information for each pixel on every row. It only needs to contain information indicating a new color as the display scans along a row. Thus, an image with much solid color will tend to require a small bit map.

Because a bit map uses a fixed or raster graphics method of specifying an image, the image cannot be immediately rescaled by a user without losing definition. A vector graphics graphic image, however, is designed to be quickly rescaled. Typically, an image is created using vector graphics and then, when the artist is satisfied with the image, it is converted to (or saved as) a raster graphic file or bit map.