1. Digital Image Processing

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

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

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

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

6. 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

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

8. 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

9. 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

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

11. Using multiplication and division
Original Image

12. Complements (Negative)
Original Image

13. 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

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

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

16. Image Contrast: - well balanced

17. High Image Contrast
Low Image Contrast

18. Low Image Contrast
Low Image Contrast

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

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

21. 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