1. Point Processing cs195g: Computational Photography
James Hays, Brown, Fall 2008
Some figures from Alexei Efros, Steve Seitz, and Gonzalez et al.

2. Image Processing image filtering: change range of image g(x) = h(f(x))
image warping: change domain of image
g(x) = f(h(x)) f x f x h

3. Image Processing image filtering: change range of image g(x) = h(f(x))
image warping: change domain of image
g(x) = f(h(x)) f g h

4. Point Processing
The simplest kind of range transformations are these independent of position x,y:
g = t(f)
This is called point processing.
What can they do?
What’s the form of t?
Important: every pixel for himself – spatial information completely lost!

5. Negative

6. Basic Point Processing

7. Log

8. Power-law transformations

9. Image Enhancement

10. Contrast Stretching

11. Image Histograms
Cumulative Histograms
s = T(r)

12. Histogram Equalization

13. Limitations of Point Processing
Q: What happens if I reshuffle all pixels within the image?
A: It’s histogram won’t change. No point processing will be affected…