Sunday, April 5, 2009

Digital Image Processing: An Introduction

Digital Image Processing (DIP) is a technique which involves manipulation of digital image to extract information. When satellite images are being manipulated in such manner, this technique is also referred to as satellite image processing.

It involves combination of software-based image processing tools. The whole process of Digital Image Processing can be classified into three parts-

Digital Image Pre-Processing

The raw satellite images may contain variety of errors in their geometry and radiometry (cosmetic appearance). Hence it is important to rectify these images before starting their interpretation. This typically involves the initial processing of raw satellite image for correcting geometric distortions, radiometric corrections & calibration and noise removal from the data. This process is also referred as Image Rectification. Image pre-processing is done before enhancement, manipulation, interpretation and classification of satellite images hence it is called so.

Digital Image Enhancement

Before starting visually interpreting satellite images, some image enhancement techniques are applied to manipulate theme to improve and enhance features. This helps in better interpretation of the images and in segregating one feature type to the other. Image enhancement involves use of a number of statistical and image manipulation functions provided in image processing software. These include contrast enhancement, histogram equalization, density slicing, spatial filtering, image ratio (like RVI, NDVI, TVI etc.), principal components analysis (PCA), colour transformations, image fusion, image stacking eic.

Digital Image classification

It is software–based image classification technique which involves automated information extraction and subsequent classification of multispectral satellite images. These are statistical decision rules which groups pixels in different feature classes. Digital classification techniques are less time consuming than visual techniques. Digital satellite images can be classified digitally using supervised, unsupervised or hybrid type of image classification (these will be discussed in detail in a separate chapter).

Please see INDEX for complete list of topics