Image Formation

Question 1

Name some types of light sources

Answer 1

1. Direct/ Indirect
2. Point/ Area
3. Natural/ Artifical

Question 2

What type of light is used for thermal imaging

Answer 2

Infrared

Question 3

What is aperture?

Answer 3

The hole in a camera where light is let through

Question 4

What happens to the depth of field when aperture increases

Answer 4

It gets narrower

Question 5

What is the F-Number?

Answer 5

focal length divided by aperture, it describes the depth of field.

Question 6

What is the bayes filter in digital cameras

Answer 6

The Bayes filter is a sampling pattern for capturing color images. The pattern contains twice as many green detectors as blue or red.

Question 7

How do we transform the Bayes pattern to digital images

Answer 7

The colors are interpolated using techniques like nearest neighbor, bilinear, cubic or nonlinear interpolation.

Question 8

Name some representations for 3D rotations

Answer 8

• Rotation matrix (SO(3)), euler angles, axis/angle, quarternions

Question 9

What does it mean that lines and points are dual objects in projective geometry?

Answer 9

They have the same representation

Question 10

Do all projective lines have Euclidean counterparts?

Answer 10

No, lines on the form [0,0,z] do not have euclidian counterparts and are known as lines at infinity

Question 11

How do we find the intersection of two projective lines?

Answer 11

The intersection x, can be calculated as: x = l1 x l2

Question 12

Name two types of radial distortion

Answer 12

Pincushion and barrel distortion

Question 13

What is the circle of confusion?

Answer 13

When a point source in the world illuminates more than one point in the image, the distortion is called circle of confusion

Question 14

Name the different parameters of the cameras intrinsic model

Answer 14

fu, fv = focallength in u and v direction
cu, cv = Optical center coordinates
s = skew parameter, 0 in modern cameras.

Question 15

Describe the pinhole camera model

Answer 15

The pinhole camera lets light through a point aperture (infinitesimal small opening), with a detector behind. This will theoretically result in all objects being in focus, but in practice, no light will pass through and no image is created.

Question 16

Name some different color spaces

Answer 16

RGB, HSI, Lab

Question 17

What is the perspective camera model

Answer 17

u = K*[r, t] * X

Question 18

Describe the lens equation

Answer 18

1/a + 1/b = 1/f.

Question 19

What is the difference of pose and the transform T?

Answer 19

The pose is a general description of one coordinate frame in another frame.
The transform T is a matrix representation of the pose.

Question 20

Name two properties of lines in the projective plane

Answer 20

1. All lines in the projective plane intersect. Parallel lines intersect at infinity. l1 and l2 intersect at x = l1 x l2
2. The line going through x1 and x2 is given by: l = x1 x x2

Question 21

Describe the extrinsic and the intrinsic part of the perspective camera model

Answer 21

intrinsic: K
extrinsic: [R, t]

Question 22

What is a homography in the projective plane?

Answer 22

A homography is a non-singular(one-to-one) linear transformation, unique up to scale. For P2 it is represented by a 3x3 matrix with 8 degrees of freedom.