19-11-2012, 04:36 PM
A Survey of Image De-noising Filters
A Survey of Image De-noising Filters.pdf (Size: 272.92 KB / Downloads: 33)
Introduction
Digital image processing is the manipulation of the numeric data
of the digital image for enhancing it to make it suitable for the
further processing according to the specific application needs.
Today, Image Processing systems are very popular due to easy
availability of powerful computers, large size memory devices,
graphics software etc. By doing image processing, corrupted
pictures can be enhanced, medical images clarified, and satellite
photographs improved. Image Processing is a technique to enhance
raw images received from cameras/sensors placed on satellites,
space and aircrafts or pictures taken in normal day-to-day life for
various applications. A digital image is an array of real numbers
represented by a finite number of bits.
Traditional Filters
These include filters which are traditionally used to remove noise
from images. We further divide traditional filters into two classes:
- Spatial domain and transform domain.
Spatial Domain
In spatial domain various filters like mean filter [1], median filter,
all work directly on the input image. It means they directly work
on the pixels of original image. Out of various spatial based filters,
wiener filter [2], gives best performance in case of Gaussian,
Poisson and speckle noise. For impulse noise, median filter [4],
outperforms all other filters. Various enhanced median filters like
weighted median filter [5] are also used for this purpose.
Transform Domain
It is needed when it is necessary to analyze the signal. Here, we
transform the given signal to another domain and do the denoising
procedure there and afterwards inverse of transformation is done
in order to get final output. There are several transforms available
like the Fourier transform, Hilbert transform, wavelet transform,
etc. The Fourier transform is probably the most popular transform.
Among different Fourier transforms [1] fast Fourier Transform
(FFT) is considered the best. However the Fourier transform does
not give high performance in case of image denoising. Wavelet
transform is better for this purpose [3]. Wavelet transform further
provide different methods for removing noise from image which
includes thresholding, non- orthogonal wavelet transform and
coefficient model.
Fuzzy Based Filters
Fuzzy based filters are those filters which include concept of fuzzy
logic in their filtering procedure. Fuzzy based filters can also be
further classified into two categories: fuzzy classical and fully
fuzzy.