1. Image Enhancement via Adaptive Unsharp Masking
By Isha Jha

2. What is Unsharp Masking?
Want to emphasize high frequency contents of an image.
Z(n,m) is a high pass filtered version of image
l controls the level of contrast enhancement
Disadvantages:
Noise in smooth regions
Overshoot artifacts

3. Objective
Increasing dynamics in smooth areas amplifies noise – so no emphasis
High contrast areas already have high local dynamics – Require low enhancement to avoid overshoot
Medium contrast areas require most enhancement

4. Solution -1 4
Use Adaptive Unsharp Masking- l varies according to predefined rules Z

5. Algorithm
Measure of Local Dynamics
g(.)

6. Algorithm cont…
b – positive convergence parameter
m – step size

7. Schematic

8. Results

9. Results cont…

10. Measuring Quality of Enhancement
Desired Behavior given by
e(n,m)=gd(n,m)-gy(n,m)
Look at e2
Cost Function

11. Conclusion
The adaptive approach prevents highlighting of noise in smooth areas
In areas with high contrast it produces medium enhancement to avoid artifacts
Highest enhancement in regions with medium contrast