Important Note: This article is part of the series in which TechReport.us discuss theory of Video Stream Matching.
2.1 – What is an Image?
An image is a photograph, line drawing, or text document that has been converted to digitized form, usually by a scanning device. A scanned image is saved in a particular image file format. Typically, an image is displayed in a window that can be sized or moved. Images can also be annotated, e-mailed, faxed, or printed.[1, 2]
The basic two-dimensional image is a monochrome (grayscale) image which has been digitized. Mathematically we can describe image as a two-dimensional light intensity function f(x , y) where x and y are spatial coordinates and the value of f at any point ( x , y) is proportional to the brightness or grey value of the image at that point.
A digitized image is one where spatial and grayscale values have been made discrete. Intensity measured across a regularly spaced grid in x and y directions intensities sampled to 8 bits (256 values).
For computational purposes, we may think of a digital image as a two-dimensional array where x and y index an image point. Each element in the array is called a pixel (picture element).
2.1.1 – Types of Image
There are three basic types of digital image file formats. They are Vector, Raster and Meta format. These will be described below.
2.1.1.1 – Vector Format
An image stored in a vector format is an image defined by mathematically lines, curves, and circles etc, which are stored as mathematical formulas. Compared to raster images only the formulas are stored. This makes the size of the file very small. The images don’t loose focus when you zoom, since the lines are re-rendered.
A vector image gives a very high quality, it requires small storage space and is easy to edit. That’s why you should always try to save your vector images in a vector format. It is not possible to save photos, scanned images etc in a vector format. Examples of vector images are drawings, diagrams and illustrations.
2.1.1.2 – Raster Format
A raster or a bitmap image is that which can be written in terms of two-dimensional function f (x, y) where x and y are the spatial coordinates. Each f (x, y) represents a picture element (pixel). Composed of gray-levels / colors and the locations. The dots create a pattern that forms the image. The pattern will show if you take a very close look at the image. Drawings, photos and images etc, which shall be used in a document, need to be transformed into a digital format. This is done by scanning the image or takes a photo with a digital camera. The image is then stored as a raster file, i.e. dot-pattern image.
2.1.1.3 – Meta Format
An image in Meta format is a combination of both of the two basic formats; vector and raster format. A Meta image can include both vector and raster information. Photos are stored in raster format. In some cases you might want to put describing numbers, text and arrows in these images.
Both text and arrows should be saved as vector information and not as raster to keep the good quality but the photos still needs to be in a raster format. The image below includes both vector and raster information. The storage is done in a Meta format. Examples of meta images are scanned photos in which you want to include describing text.
