Visual Perception Modeling: Local Operations, Histograms, Point Operations, and Algebraic Operations

1. Outline • Announcements • Projects • Local operations • Histograms • Point operations • Algebraic operations • Applications • Image morphing

2. Announcements • Projects • Based on my programs • Need to get familiar with my programs • Find the database you are interested in on the web • Change my program to get the system work • Tune parameters to improve performance • Based on a paper or your idea • Need to talk to me either this week or next week • Make sure that it is doable during the time framework • Report and in-class presentation Visual Perception Modeling

3. Announcements • Research papers • Need to talk to me on the papers or the subjects you are interested in • Decide on the topics within two weeks • Write a research paper for each topic • Do a presentation in class for each topic Visual Perception Modeling

4. Local Operations • A image can be represented by a matrix • Neighborhood • Local operations • Operations whose output depends only on pixels within a local neighborhood Visual Perception Modeling

5. Neighborhoods • 4-neighborhood • For pixel (i, j) {(i-1, j), (i+1, j), (i, j-1), (i, j+1)} • 8-neighborhood • For pixel (i, j) {(i-1, j), (i+1, j), (i, j-1), (i, j+1) (i-1, j-1), (i+1, j+1), (i+1, j-1), (i-1, j+1)} Visual Perception Modeling

6. Point Operations • A point operation takes a single input image into a single output image in such a way that each output’s pixel value depends only upon the pixel value of the corresponding input pixel • Contrast enhancement • Contrast stretching Visual Perception Modeling

7. Types of Point Operations • Linear point operations • PO = f(PI) = a PI + b • Nonlinear point operations • PO = f(PI) where f is a nonlinear function Visual Perception Modeling

8. Image Histograms • Histogram • The histogram is the function showing, for each possible value, the number of pixels in the image that have that particular value Visual Perception Modeling

9. Multi-dimensional Histograms • A multi-dimensional histogram is a function of several variables • For a color image, we can have a three-dimensional histogram Visual Perception Modeling

10. Point Operations and Histograms • Point operations modifies the histogram in a predictable way Visual Perception Modeling

11. Applications of Point Operations • Histogram equalization • Find a point operation such that the histogram of the resulting image will be a flat histogram • Histogram matching • Find a point operation such that the histogram of the resulting image will match the one of a given image Visual Perception Modeling

12. Algebraic Operations • Algebraic operations are operations that produce an output image which is the pixel-by-pixel sum, difference, product, quotient, or other forms of functions of two input images Visual Perception Modeling

13. Traffic Estimation • Suppose aerial photographs are taken of highway section • To estimate how many cars are there in the section, find the difference between two consecutive images and count the number of white regions Visual Perception Modeling

14. Blue-Screen Editing Visual Perception Modeling