Pattern Recognition Mrs. Andleeb Y. Khan Lecture 03 BCS-VII

Image enhancement using Point Processing 1.What is point processing? 2.Negative images 3.Thresholding 4.Logarithmic Transforms 5.Power Law Transform 6.Grey Level Slicing 7.Bit Plane Slicing

Image enhancement Goal: To modify an image so that its utilization on a particular application is enhanced. A set of ad hoc tools applicable based on viewer’s specific needs. No general theory on image enhancement exists.

Spatial & frequency domains Two broad categories of image enhancement techniques: Spatial Domain Pixel Processing Grey Level Transformation (Data Independent) Histogram Processing (Data Dependent) Arithmetic Operations Mask-based Processing Frequency Domain Filtering Manipulation of Fourier transform or wavelet transform of an image

Image enhancement

Image histogram  The histogram of an image shows us the distribution of grey levels in the image.  Massively useful in image processing, esp. in segmentation.

Histogram example

Spatial domain image enhancement Most spatial domain enhancement operations can be reduced to the form G(x,y) = T[f(x,y)] Where f(x,y) is the input image, g(x,y) is the processed image and T is some operator defined over some neighbourhood of (x,y)

Spatial domain The operator T can be defined over the set of pixels(x,y) of the image The set of neighborhood N(x,y) of each pixel A set of images f1,f2,f3

From system point of view

Point processing in spatial domain Operation on the set of image-pixels

Mask processing or filter Neighborhood is bigger than 1x1 pixel Use a function of the values of f in a pre-defined neighborhood of (x,y) to determine the value of g at (x,y) The value of the mask coefficients determine the nature of the process Used in techniques: Image Sharpening Image Smoothing

Spatial domain  Operation on the set of neighborhoods N(x,y) of each pixel.

Basic grey level transformation

Negative images

Negative images...

Logarithmic transformation

Power law transformations

Power law transformations...

Power law transformation

Power Law Example....

Gamma Correction

Power Law Grey level transform