corner detection & color segmentation
DESCRIPTION
Corner Detection & Color Segmentation. CSE350/450-011 9 Sep 03. Administration. Clarifications to Homework 1 Questions?. Class Objectives. Linear Algebra Review Review how corners can be extracted from computer images - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Corner Detection & Color Segmentation](https://reader035.vdocuments.us/reader035/viewer/2022062810/56815bbc550346895dc9ba8c/html5/thumbnails/1.jpg)
Corner Detection & Color Segmentation
CSE350/450-0119 Sep 03
![Page 2: Corner Detection & Color Segmentation](https://reader035.vdocuments.us/reader035/viewer/2022062810/56815bbc550346895dc9ba8c/html5/thumbnails/2.jpg)
Administration
• Clarifications to Homework 1 • Questions?
![Page 3: Corner Detection & Color Segmentation](https://reader035.vdocuments.us/reader035/viewer/2022062810/56815bbc550346895dc9ba8c/html5/thumbnails/3.jpg)
Class Objectives
• Linear Algebra Review• Review how corners can be extracted
from computer images• Review how color is represented and
can be segmented in a computer image
![Page 4: Corner Detection & Color Segmentation](https://reader035.vdocuments.us/reader035/viewer/2022062810/56815bbc550346895dc9ba8c/html5/thumbnails/4.jpg)
Supporting References
• “A Tutorial on Linear Algebra” by Professor C. T. Abdallah, University of New Mexico
• Edge & Corner Detection: Introductory Techniques for 3-D Computer Vision, Trucco & Verri, 1998
• CVOnline “Color Image Processing” Lecture Notes• Poynton's Color FAQ
![Page 5: Corner Detection & Color Segmentation](https://reader035.vdocuments.us/reader035/viewer/2022062810/56815bbc550346895dc9ba8c/html5/thumbnails/5.jpg)
Edge Detection ReviewINPUT IMAGE
1) NoiseSmoothing
EDGE IMAGE
2) EdgeEnhancement
Horizontal [-1 0 1]
Vertical [-1 0 1]T
),( yxI
xyxI
),(
yyxI
),(
21
22 ),(),(),(
yyxI
xyxIyxI
“GRADIENT” IMAGE
3)Threshold
16/121242121
![Page 6: Corner Detection & Color Segmentation](https://reader035.vdocuments.us/reader035/viewer/2022062810/56815bbc550346895dc9ba8c/html5/thumbnails/6.jpg)
Linear Algebra Review
![Page 7: Corner Detection & Color Segmentation](https://reader035.vdocuments.us/reader035/viewer/2022062810/56815bbc550346895dc9ba8c/html5/thumbnails/7.jpg)
Corner Detection Motivation
• Corners correspond to point in the both the world and image spaces
• Tracking multiple point across consecutive images allows us to estimate the relative rotation and translation of the camera– Hartley’s 8-point algorithm
• Since the camera moves with our robot, we can infer robot motion “simply” by tracking eight or more corners
![Page 8: Corner Detection & Color Segmentation](https://reader035.vdocuments.us/reader035/viewer/2022062810/56815bbc550346895dc9ba8c/html5/thumbnails/8.jpg)
Corner Detection AlgorithmTrucco & Verri, 1998
61605319185855531513555550131310101011111012121110
yyxII
xyxII yx
),(,),(
1. Compute the image gradients
2. Define a neighborhood size as an area of interest around each pixel
3x3 neighborhood
![Page 9: Corner Detection & Color Segmentation](https://reader035.vdocuments.us/reader035/viewer/2022062810/56815bbc550346895dc9ba8c/html5/thumbnails/9.jpg)
3. For each image pixel (i,j), construct the following matrix from it and its neighborhood values
e.g.
Corner Detection Algorithm (cont’d)
61605319185855531513555550131310101011111012121110
xI
2
2
),(yyx
yxxji III
IIIC
22222
2222)3,3(
5553155550
13101011]1,1[
C
![Page 10: Corner Detection & Color Segmentation](https://reader035.vdocuments.us/reader035/viewer/2022062810/56815bbc550346895dc9ba8c/html5/thumbnails/10.jpg)
3. For each matrix C(i,j), determine the 2 eigenvalues λ(i.j)= [λ1, λ2].4. Construct Λ-image where Λ(i,j)=min(λ(i.j)).5. Threshold Λ-image. Anything greater than threshold is a corner.
Corner Detection Algorithm (cont’d)
ISSUE: The corners obtained will be a function of the threshold !
![Page 11: Corner Detection & Color Segmentation](https://reader035.vdocuments.us/reader035/viewer/2022062810/56815bbc550346895dc9ba8c/html5/thumbnails/11.jpg)
Corner Detection Sample ResultsThreshold=25,000 Threshold=10,000
Threshold=5,000
![Page 12: Corner Detection & Color Segmentation](https://reader035.vdocuments.us/reader035/viewer/2022062810/56815bbc550346895dc9ba8c/html5/thumbnails/12.jpg)
Color Segmentation Motivation
• Computationally inexpensive (relative to other features)
• “Contrived” colors are easy to track • Combines with other features for robust
tracking
![Page 13: Corner Detection & Color Segmentation](https://reader035.vdocuments.us/reader035/viewer/2022062810/56815bbc550346895dc9ba8c/html5/thumbnails/13.jpg)
What is Color?• Color is the perception of light in the visible
region of the spectrum• Wavelengths between 400nm - 700nm• Imagers
– Retina (humans)– CCD/CMOS (cameras)
![Page 14: Corner Detection & Color Segmentation](https://reader035.vdocuments.us/reader035/viewer/2022062810/56815bbc550346895dc9ba8c/html5/thumbnails/14.jpg)
RGB Color Space• Motivated by human visual system
– 3 color receptor cells (rods) in the retina with different spectral response curves• Used in color monitors and most video cameras
![Page 15: Corner Detection & Color Segmentation](https://reader035.vdocuments.us/reader035/viewer/2022062810/56815bbc550346895dc9ba8c/html5/thumbnails/15.jpg)
YCbCr (YUV/YIQ) Color Space
“Greyscale”Y= 0.30*R+0.59*G+0.11*B
BGR
VUY
081.0419.0500.0500.0331.0169.0114.0587.0299.0
• Separates luma (“brightness”) from the chroma (“color”) channels: Y = 0.30*R+0.59*G+0.11*B, Cb = B-Y, Cr=R-Y
• YUV/YIQ are similar variants based upon NTSC/PAL television signals
![Page 16: Corner Detection & Color Segmentation](https://reader035.vdocuments.us/reader035/viewer/2022062810/56815bbc550346895dc9ba8c/html5/thumbnails/16.jpg)
Defining Colors in an RGB Image
Red Green Blue
![Page 17: Corner Detection & Color Segmentation](https://reader035.vdocuments.us/reader035/viewer/2022062810/56815bbc550346895dc9ba8c/html5/thumbnails/17.jpg)
How do we represent a “single” color?
Sample set for orange hat
![Page 18: Corner Detection & Color Segmentation](https://reader035.vdocuments.us/reader035/viewer/2022062810/56815bbc550346895dc9ba8c/html5/thumbnails/18.jpg)
Simple RGB Color Segmentation
)1.1,5.254( )8.14,6.103( )07.6,1.45(
256),(251 yxIR 135),(73 yxIG 58),(32 yxIB
& &
Red Green Blue
SegmentedColor Image
![Page 19: Corner Detection & Color Segmentation](https://reader035.vdocuments.us/reader035/viewer/2022062810/56815bbc550346895dc9ba8c/html5/thumbnails/19.jpg)
Color Tracking Demo