Visual Servoing

Question 1

Explain how Digital (CCD) cameras work

Answer 1

-The CCD chip is an array of light sensitive picture elements
Parameters:
-iris position and shutter speed regulate amount of light being measured
-camera gain controls amplification of the analogue signal from the CCD chip

Question 2

What are the disadvantages of CCD

Answer 2

-Inconsistent
-Problems with dynamic range in different light conditions
-Extreme illumination is a problem

Question 3

Explain how a CMOS camera works

Answer 3

-Metal oxide semiconductor chip
-Array of pixels, which are measured and amplified individually

Question 4

What are the advantages of CMOS

Answer 4

-Reduced power consumption
-CMOS outperforms CCD

Question 5

What are the 2 methods for implementing colour?

Answer 5

-Using a single chip with a colour filter array
-Using three seperate chips by splitting incoming light into 3 paths (R,B,G)

Question 6

What is a common issue with creating colour images?

Answer 6

Near Infra-red sensitivity
-NIR light can interfere with colour accuracy
-Cameras incorporate infrared filters to mitigate this issue

Question 7

Define focal length

Answer 7

The distance from the lens’s image plane to the focal point (where parallel light rays converge)

Question 8

Explain the effect on images due to a changing focal length

Answer 8

Shorter focal length:
wider fov, more distortion, lees magnification

Longer focal length:
narrower fov, greater magnification and distant objects appear closer

Question 9

What equation can be used to estimate distance to an object

Answer 9

1/f = 1/z + 1/e
f -focal length
z-distance to object
e-distance behind the lens

Question 10

Define voxel

Answer 10

-a specific location of an image in 3D space

Question 11

When the image plane is not on the focal plane, what happens?

Answer 11

a blur circle occurs
The radius of the circle is calculated:
R = Lß/ 2e
-this determines sensitivity

-ß is displacement of image plane from e

Question 12

What does the R value signify as we change the distance from the object?

Answer 12

-As distance increase, the difference between R values decreases
-sensitivity decreases as distance inrceases
-this applies to all visual ranging techniques

Question 13

Define depth from focus

Answer 13

The distance of the image to the lens (z-value)

Question 14

Explain camera focusing in terms of depth from focus

Answer 14

-Moving the lens to different positions to find where the image is the sharpest
-optimal focus allows the camera to determine the depth of objects from their focus position

Question 15

Explain camera focusing in terms of depth from defocus

Answer 15

-compares the amount of defocus(blur) at different focus settings to find distance of object from camera

Question 16

Define the pinhole camera model

Answer 16

-has no lens
-when z&raquo_space;f and z&raquo_space; L the camera is modelled as a pinhole camera
-the image plane is between the object and centre of projection

Question 17

Explain perspective projection

Answer 17

With the 2D image plane (u,v) and the 3D point of the object P(x,y,z) and focal length

f/z = u/x = v/y

Question 18

What are the methods for determining depth?

Answer 18

Stereo vision:
-processes 2 distinct images taken at the same time and assumes the relative pose between the 2 cameras is known
structure from motion - processes 2 images taken with the same/different csmera at different times from unkown positions