Image Processing or enhancement
Image Processing or enhancement
INTRODUCTION
The aim of image processing or enhancement is to improve the interpretability or perception of information in images for human viewers, or to provide `better’ input for other automated image processing techniques of image processing .Image enhancement techniques has two broad categories:
Image Processing notes
1. Spatial domain methods, which operate directly on pixels.
2. Frequency domain method in which operate on the Fourier transform of the image.
Actually there is no general theory for determining good image enhancement , When it comes to the perception of human. It is good! , if it looks good. When image processing or enhancement techniques are used as pre-processing tools for other techniques of image processing , then quantitative measures can be determined which techniques are most appropriate. Apart from geometrical transformations some preliminary grey level adjustments may indicated, for taking into account imperfections in the system of acquisition . This can be done only pixel after pixel, calibrating by the image output with that constant brightness. The space-invariant grey value transformations are done for this contrast range compression, stretching, etc. The critical distribution is the relative frequency of each grey value, the grey value histogram.The fingerprint images are rarely of perfect quality, due to the reasons like skin condition, variations in impression condition , scanning devices or may be for the non-co-operative attitude of that subject. This degraded quality of image can result in a significant number of spurious minutiae being created and genuine minutiae is ignored. The statistics for the reliably a vital step in studying extract the minutiae of fingerprint minutiae that is the feature from images fingerprint . Image enhancement techniques prior to minutiae extraction to obtain a good number of reliable estimates of minutiae locations.
The fingerprint image enhancement’s main objective of is to improve the ridge characteristics of the image, as this ridge carries the information for minutiae extraction of characteristics of features required . For a well defined fingerprint image, the valleys and ridges should alternate the direction of row in the locally constant .It is basically improving the perception of information or interpretability in images for human viewers and providing `better’ input for other automated image techniques for processing .Modify attributes of an image which is the principal objective of image enhancement to make it more suitable for a given task and a specific observer.
In this process, one or more than one attributes of the image are normally modified and the choice of attributes and the way they are modified for the specific to a given task. Observer-specific factors like the human visual system ,moreover the experience of the observer, will may introduce a subjectivity into the choice of image enhancement methods. There exist many techniques that can enhance a digital image except spoiling it. The methods of enhancement or image processing can be divided in to the following categories:
1. Spatial Domain Methods
2. Frequency Domain Methods
In spatial domain techniques we directly deal with the pixels of image . The pixel values can manipulated to achieve that required enhancement. The image is in methods of frequency domain , first transferred in to frequency domain. It means the image processing of Fourier Transform is computed first. All that enhancement operations are performed on the Fourier transform of the image and then the Inverse Fourier transform is performed for getting the resultant imag and These enhancement operations can performed in order to contrast or the distribution of that grey levels , modifing the image brightness. As a consequence the pixel value (intensities) of the output image will be modified according to the transformation function.
IMAGE ENHANCEMENT TECHNIQUES
A. Spatial domain methods
The value of a pixel with coordinates (x, y) in the enhanced image is the result of performing some operation on the pixels in the neighborhood of (x, y) in the input image, F. Neighborhoods can be any shape, but usually they are rectangular.
B. Histogram Equalization
Histogram equalization is a method in image processing of contrast adjustment using the image’s histogram When we want to specify a non-flat resulting histogram, we can use the following steps:
1. Specify the desired histogram g(z)
2. Obtain the transform which would equalize the specified histogram, Tg, and its inverse Tg-1
3. Get the transform which would histogram equalize the original image, s=T[i]
4. Apply the inverse transform Tg-1 on the equalized image, that is z=Tg-1[s]
c. Contrast Stretching
Contrast stretching (often called normalization) is a simple image enhancement technique that attempts to improve the contrast in an image by `stretching’ the range of intensity values it contains to span a desired range of values, e.g. the full range of pixel values that the image type concerned allows.
Q1: What are the categories of Image processing or enhancement techniques?
Ans: Image enhancement techniques has two categories:
1. Spatial domain methods, which operate directly on pixels.
2. Frequency domain method in which operate on the Fourier transform of the image.
Q2: What are the methods of enhancement or image processing?
Ans:The methods of enhancement or image processing can be divided in to the following categories:
1. Spatial Domain Methods
2. Frequency Domain Methods
Q3: What is the aim of image processing or enhancement?
Ans: The aim of image processing or enhancement is to improve the interpretability or perception of information in images for human viewers, or to provide `better’ input for other automated image processing techniques of image processing .
Q4: What is the main objective of fingerprint image enhancement?
Ans:The fingerprint image enhancement’s main objective of is to improve the ridge characteristics of the image, as this ridge carries the information for minutiae extraction of characteristics of features required .
Q5: What is exactly Spatial domain method?
Ans: Spatial domain the value of a pixel with coordinates (x, y) in the enhanced image is the result of performing some operation on the pixels in the neighborhood of (x, y) in the input image, F. Neighborhoods can be any shape, but usually they are rectangular.
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Image processing usually refers to digital image processing, but optical and analog image processing also are possible. This article is about general techniques that apply to all of them.Interested people can refer it for their betterment.