An image is a spatial representation of an object, a two-dimensional or three-dimensional scene or another image. Often the images reflect the intensity of lights. Most photographs are called continuous-tone images because the method used to develop the photograph creates the illusion of perfect continuous tone throughout the image.
Images stored and processed by computers, displayed on computer screens, are called digital
Images, though they often look like continuous-tone. This is because they are represented by a matrix of numeric values each representing a quantised intensity values. The smallest element on a digital image is known as a pixel — a picture element.
The word pixel is based on a contraction of pix (“pictures”) and el (for “element”); thus a ‘pixel’ refers to the smallest addressable screen e lement; it is the smallest unit of picture that can be controlled. Each pixel has its own address. The address of a pixel corresponds to its coordinates.
Pixels are normally arranged in a two-dimensional grid, and are often represented using dots or squares. Each pixel is a sample of an original image; more samples typically provide more accurate representations of the original. The intensity of each pixel is variable.
A digital image consists of many picture elements (pixels). The number of pixels that compose a monitors’ image determines the quality of the image (resolution). Higher resolution always yields better quality. A bit-map representation stores the graphic/image data in the same manner that the computer monitor contents are stored in video memory.
3.1.1 DIGITAL IMAGE CREATION
There are many ways to create or get digital images. Some of the most common ways are:
Make an image from scratch with a paint program. A good program will allow you to choose the depth, resolution and size.
Grab an image of a screen. The depth, resolution and size are determined by the screen. Capture an image from a digital camera or a camcorder. The depth, resolution and size are determined by the camera or the camcorder. The popular depth is 24-bit. The commonly used resolution is 320 _ 240, 640 _ 480 and 800 _ 600.
Scan a photograph or a print using a scanner. You can select from a range of different depths and resolution. The choice should be determined by the type of original and the final output form.
Convert from existing digital media— e.g., photo CD . The attribute is determined by the original image.
Synthesize an image from numerical data.
3.1.2 DIGITAL IMAGE PROCESSING
Digital Image Processing is very large area but it contains the following sub-areas:
Image analysis is concerned with techniques for extracting descriptions from images that are necessary for higher-level scene analysis methods.
Image recognition is concerned with the techniques for recovering information about objects in the image. A sub-area is character recognition.
Image enhancement is concerned with the technique to improve the image and to correct some defects, such as, colour and tonal adjustment, transformations, e.g., scale, rotate, Special effects, e.g., texture, stylize, blur, and sharpen etc
SELF ASSESSMENT EXERCISE
Explain some of the ways to create a Digital Image
In this unit you have learnt that Images stored and processed by computers, displayed on computer screens, are called digital Images. You should also have learnt about the different ways to create and process digital images.
We highlighted the difference between an image and a digital image, the ways to create digital images and the different areas in processing.
6.0 TUTOR MARKED ASSIGNMENT
1).List and explain the different areas of digital image processing 2).List at least 4 ways to create a digital image
3). Identify the key feature of a digital image.