Digital Image Processing Some Basic Intensity Transformation Function Image Negatives Log Transformation Power-Law (Gamma) Transformation Piecewise-Linear Transformation Functions Histogram Processing Histogram Equalization Histogram Matching Histogram Statistics for Image Enhancement

1. Intensity
Transformation &
Histogram Processing
CSE 514 Image Processing
Deep Chokshi
12001503

2. Outlines
Some Basic Intensity Transformation
Function
Image Negatives
Log Transformation
Power-Law (Gamma) Transformation
Piecewise-Linear Transformation Functions
Histogram Processing
Histogram Equalization
Histogram Matching
Histogram Statistics for Image Enhancement

3. Intensity
Transformation
• Intensity transformation are applied on
images for contrast manipulating or image
thresholding.
• It is also known as Gray level transformation
• Intensity level of image is in range of 0 to
255
𝑆 = 𝑇(𝑟)
Where,
r is the value of pixel before processing
s is the value of pixel after processing
T is Transformation function

4. Image Negatives
• Image negative can be represented as
• 𝑆 = 𝐿 − 1 − 𝑟

6. Log Transformation
• Log Transformation is used to compress
the grey level or expand the grey level
• Log Transformation is represented as
• 𝑆 = 𝑐 log(1 + 𝑟)

7. Power Law (gamma)
Transformation
• Power Law is represent by
𝑠 = 𝑐 𝑟γ
γ > 1  nth power
γ < 1  nth root

8. Piecewise-Linear Transformation
Functions
Contrast
Stretching
Grey level
Slicing
Bit Plane
Slicing

9. Contrast Stretching
• It makes Dark portion Darker and Bright
portion Brighter.
• R1 = S1 & R2 = S2  Linear
Transformation
• R1 = R2 & S1 = 0, S2 = L – 1 
Thresholding

10. Grey Level Slicing
• Highlight specific range of grey levels

11. Bit Plane
Slicing
Top 4 bit have majority of visually
significant data

12. Histogram Processing

13. Histogram Equalization
• Image Enhancement
• Graphical Representation
• Manipulating Contrast & Brightness
• Quality  Normalizing  Histogram  Flat Profile
6 6 7 7 6
5 2 2 3 4
3 3 4 4 5
5 7 3 6 2
7 6 5 5 5
0
1
2
3
4
5
6
0 1 2 3 4 5 6 7
Occurrence of Grey Level

14. Histogram Matching
• Also know as Histogram specification
• Generate procced image

15. Histogram Statistic for Image Enhancement
Grey Level No. of Pixel
(nk)
nk/sum sk sk * 7 Equal Level
0 0 0 0 0 0
1 0 0 0 0 0
2 3 0.12 0.12 0.84 1
3 4 0.16 0.28 1.96 2
4 4 0.16 0.44 3.08 3
5 5 0.2 0.64 4.48 5
6 5 0.2 0.84 5.88 6
7 4 0.16 1 7 7
0
1
2
3
4
5
6
7
8
0 1 2 3 4 5 6 7
Compare with original
0
1
2
3
4
5
6
0 1 2 3 4 5 6 7
Occurrence of Grey Level

16. THANK YOU