Question

How are digital images saved in computers? Explain in terms of pixels and digital signal processing.

Answer 1

A digital image is a numeric representation, normally binary, of a two-dimensional image. Depending on whether the image resolution is fixed, it may be of vector or raster type. By itself, the term "digital image" usually refers to raster images or bitmapped images (as opposed to vector images).

Raster images have a finite set of digital values, called picture elements or pixels. The digital image contains a fixed number of rows and columns of pixels. Pixels are the smallest individual element in an image, holding antiquated values that represent the brightness of a given color at any specific point.

Typically, the pixels are stored in computer memory as a raster image or raster map, a two-dimensional array of small integers. These values are often transmitted or stored in a compressed form.

Raster images can be created by a variety of input devices and techniques, such as digital cameras, scanners, coordinate-measuring machines, seismographic profiling, airborne radar, and more. They can also be synthesized from arbitrary non-image data, such as mathematical functions or three-dimensional geometric models; the latter being a major sub-area of computer graphics. The field of digital image processing is the study of algorithms for their transformation.

What is a pixel?
A 'pixel' (short for ‘picture element') is a tiny square of colour. Lots of these pixels together can form a digital image.

Each pixel has a specific number and this number tells the computer what colour the pixel should be. The process of digitisation takes an image and turns it into a set of pixels.

How do pixels make up a display?
If you look closely at your computer monitor you will see that the screen is made up of millions of tiny squares.

Each one of those squares is a pixel and each pixel can be one of millions of different colours.

To display an image, the computer tells the monitor to show a particular colour for each of the pixels.

What is a bitmap?
A bitmap is a method for storing images using pixels. It is called a bitmap because it is a 'map' of where the 'bits' of information are stored.

This information is stored as a sequence of numbers defining the colour of each pixel.

In a simple black and white image, a bitmap just needs to know if a pixel is ‘on’ or ‘off’, which can be stored as 1 or 0. In a colour image we need lots of 'bits' (typically 24) to store the colour values of each pixel.

Bitmap is also the name for a common file format for saving images.

Digital signal processing (DSP) is the use of digital processing, such as by computers or more specialized digital signal processors, to perform a wide variety of signal processing operations. The signals processed in this manner are a sequence of numbers that represent samples of a continuous variable in a domain such as time, space, or frequency.

Digital signal processing and analog signal processing are subfields of signal processing. DSP applications include audio and speech processing, sonar, radar and other sensor array processing, spectral density estimation, statistical signal processing, digital image processing, data compression, video coding, audio coding, image compression, signal processing for telecommunications, control systems, biomedical engineering, and seismology, among others.

DSP can involve linear or nonlinear operations. Nonlinear signal processing is closely related to nonlinear system identification and can be implemented in the time, frequency, and spatio-temporal domains.

The application of digital computation to signal processing allows for many advantages over analog processing in many applications, such as error detection and correction in transmission as well as data compression.Digital signal processing is also fundamental to digital technology, such as digital telecommunication and wireless communications. DSP is applicable to both streaming data and static (stored) data