Digital Image Processing

Last discussed topics Image Processing Introduction Digital Image Creation Image Types Image File Formats

Agenda Types of digital image processing Brightness Complement Image histogram Image types conversion

General Areas of Image Processing 3 general areas of digital image processing Point Operations Pixel Point Processing Local Operations Pixel Group Processing Global Operations

Basics of Digital Images (review) Digital images are a 2D array of values in rows and columns given by I(r,c)

Point Operations A point operation operates on individual pixels and does not take into account any neighbouring pixel values The same operation occurs on all of the pixels in the image

Point Operation Process I(x,y) Operation x 1.5 O(x,y)

Clipping Clipping results from an operation (any) on an image where the pixel value that result from the operation exceeds the limits of the bit depth of the image eg. in an 8 bit depth image operation = x2, pixel value = 150, new (output) value = 300 is clipped to 255 operation = -50, pixel value = 10, new (output) value = -40 is clipped to 0

Arithmetic operations (Brightness) Simple functions include adding or subtract a constant value to each pixel: Or Multiplying a constant value to each pixel: In order to ensure that the output value ranges from 0 to 255 you have to: Round the output values to an integer values Clipping the output value to ranges from 0 to 255

Adding and subtracting a constant We can test this on the blocks image blocks.tif Original Image

Using multiplication and division Original Image

Complements (Negative) Original Image

Image Histogram a graph indicating the number of times each grey level occurs in the image Provides an indication of distribution of pixels values an indication for image contrast & brightness Can be used to aid in adjustment of image contrast levels and brightness Does not provide any information about what can be perceived within the image, i.e. does not provided any spatial information

Original image with 3 gray levels Image Histogram Cont. Original image with 3 gray levels Digital Image Array Image Histgram

No. of pixels Image Histogram Pixel values Image Histogram: Plot of pixel values v and no of pixels with that value

Image Contrast: - well balanced

High Image Contrast Low Image Contrast

Low Image Contrast Low Image Contrast

How to Convert from Grayscscale to Binary Image Gray Image Binary Image

How to Convert from RGB to Grayscale Image Gray Image RGB Image

How to Convert from RGB to Grayscale Image Solution 1 Solution 2 Choose one of R or G or B to represent the Gray image