Image Enhancement in Spatial Domain

Abstract

Image enhancement is a process, rather a preprocessing step, through which an original image is made suitable for a specific application. The application may vary from thermal image to X-ray image and accordingly the process of image enhancement would differ. Generally, the effect of image enhancement can be perceived visually. Even to address/handle the regular artifacts due to geometric transformations of images, image enhancement is done in form of image interpolation. The spatial domain refers to the 2D image plane represented in terms of pixel intensities. When the image is enhanced by modifying the pixel intensities directly (not as an effect of some other parameter tuning in a different domain), the method is considered as spatial domain image enhancement methodology. Otherwise, the image can be transformed to some other domain—like one 2D image can be transformed to a 2D frequency domain by discrete Fourier transform (DFT). To achieve an enhanced image, the Fourier coefficients are modified. That family of image enhancement methodologies is considered as frequency domain image enhancement which is discussed in the subsequent chapters. Whatever be the domain of image enhancement (either spatial or frequency domain), by the term image enhancement we mean improvement of the appearance of an image (in all sense including human perception and machine perception) by increasing the dominance of some features, or by decreasing the ambiguity between different regions of the image. In most cases, the enhancement of certain features is achieved at the cost of suppressing few other features.