Digital Image Processing

“One picture is worth more than ten thousand words”

Digital Image

A digital image is a representation of a two-dimensional image as a finite set of digital values, called picture elements or pixels. Pixel values typically represent gray levels, colours, heights, opacities etc.

Digital Image Processing

Digital image processing is the use of computer algorithms to perform image processing on digital images. As a subcategory or field of digital signal processing, digital image processing has many advantages over analog image processing. It allows a much wider range of algorithms to be applied to the input data and can avoid problems such as the build-up of noise and signal distortion during processing. Since images are defined over two dimensions (perhaps more) digital image processing may be modeled in the form of multidimensional systems.

Digital image processing focuses on two major tasks-

• Improvement of pictorial information for human interpretation.
• Processing of image data for storage, transmission and representation for autonomous machine perception.

History

Early 1920s

One of the first applications of digital imaging was in the news-

• Paper industry,
• The Bartlane cable picture transmission service,
• Images were transferred by submarine cable between London and New York,
• Pictures were coded for cable transfer and reconstructed at the receiving end on a telegraph printer.

Mid to late 1920s

Improvements to the Bartlane system resulted in higher quality images-

• New reproduction processes based on photographic techniques,
• Increased number of tones in reproduced images.

In 1980s - Today

The use of digital image processing techniques has exploded and they are now used for all kinds of tasks in all kinds of areas-

• Image enhancement/restoration,
• Artistic effects,
• Medical visualization,
• Industrial inspection,
• Law enforcement,
• Human computer interfaces.

Launched in 1990

The Hubble telescope can take images of very distant objects. However, an incorrect mirror made many of Hubble’s images useless Image processing techniques were used to fix this.

Task

Digital image processing allows the use of much more complex algorithms, and hence, can offer both more sophisticated performance at simple tasks, and the implementation of methods which would be impossible by analog means.

In particular, digital image processing is the only practical technology for:

• Classification,
• Feature extraction,
• Pattern recognition,
• Projection,
• Multi-scale signal analysis.

Some techniques which are used in digital image processing include:

• Pixelation,
• Linear filtering,
• Principal components analysis,
• Independent component analysis,
• Hidden Markov models,
• Anisotropic diffusion,
• Partial differential equations,
• Self-organizing maps,
• Neural networks,
• Wavelets.

Key Stages in Digital Image Processing

Steps are followings-

Method to follow

Step 1

Step 2

Step 3

Step 4

Step 5

Step 6

Step 7

Step 8

Step 9

Applications

Digital Camera Images

Digital cameras generally include dedicated digital image processing chips to convert the raw data from the image sensor into a color-corrected image in a standard image file format. Images from digital cameras often receive further processing to improve their quality, a distinct advantage that digital cameras have over film cameras. The digital image processing typically is executed by special software programs that can manipulate the images in many ways.

Many digital cameras also enable viewing of histograms of images, as an aid for the photographer to understand the rendered brightness range of each shot more readily.

Film

Westworld (1973) was the first feature film to use digital image processing to pixellate photography to simulate an android's point of view.

Intelligent Transportation Systems

Digital image processing has a wide applications in intelligent transportation systems, such as automatic number plate recognition and traffic sign recognition.