Image enhancement is considered as one of the most important techniques in image research. The main aim of image enhancement is to enhance the quality and visual appearance of an image, or to provide a better transform representation for future automated image processing. Many images like medical images, satellite, aerial images and also real life photographs suffer from poor and bad contrast and noise. It is necessary to enhance the contrast and remove the noise to increase image quality. One of the most important stages in medical images detection and analysis is Image Enhancement Techniques.
Image enhancement operations improves the clarity of images for human viewing, removing blurring and noise, increasing contrast, and revealing details. The enhancement technique differs from one field to another depending on its objective. The existing techniques of image enhancement can be classified into two categories: Spatial Domain and Frequency Domain Enhancement.
Image Enhancement in Spatial Domain
The term spatial domain refers to the image plane itself and image processing techniques in this category are based on direct manipulation of pixels in an image. Two principal categories of spatial domain processing are Intensity Transformation and Spatial Filtering.
Intensity Transformation or Point Processing operates on single pixels of an image. It is principally used for the purpose of contrast manipulation and image thresholding.
Spatial Filtering or Neighborhood Processing deals with performing operations such as image sharpening by working in a neighborhood of every pixels in an image.
Image Enhancement in Frequency Domain
In frequency domain images first transform to frequency domain using Fourier transformation then apply the enhancement technique in frequency domain and bring back the image in spatial domain by applying the Inverse Fourier Transformation.
Difference Between Spatial Domain and Frequency Domain Image Enhancement Techniques
- The spatial domain methods are those procedures, which operates directly on the individual pixels, composing an image. In frequency domain method we process an image by changing the frequency components in an image.
- Spatial domain processing method involves point processing, mask processing and global processing like histogram processing. Frequency domain processing method includes only global processes.
- Spatial domain image enhancement techniques are gray scale manipulation, histogram equalization, image smoothing and image sharpening. Frequency domain image enhancement techniques are filtering and homomorphic filtering.
- In spatial domain image enhancement, convolution involved which increase the computation cost. frequency domain processing does not required convolution operation.
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