Camera

Question 1

Describe the pinhole camera model.

Answer 1

• Real object
• Virtual image
• Pinhole
• Image plane

Question 2

Main elements of the camera model.

Answer 2

• Optical center
• Image plane
• Optical axis
• Principal point
• Focal length
• Refrence systems (camera and real world)

Draw the model!

Question 3

Why the projection matrix is useful? Derive the first form of the projection matrix.

Answer 3

The projection matrix describes how the 3D world is mapped onto the image plane.

1. Consider the 2D plane and the virtual image
2. Define some ratios: x = f*X/Z
3. Compute Z*[X Y 1]

Question 4

How to map points projected onto the image in pixels.

Answer 4

1. Define conversion factors

2. u = 𝑢0 + 𝑥𝑝/w

Question 5

Camera matrix.

Answer 5

…

Question 6

What are the intrinsic parameters?

Answer 6

𝑘𝑢, 𝑘𝑣, 𝑢0, 𝑣0, f

Question 7

What are the extrinsic parameters?

Answer 7

– 3 for translations
– 3 for rotations

Define the relation between camera and world

Question 8

Describe the thin lens model with a sketch.

Question 9

Give the thin lens equation.

Answer 9

1/d0 + 1/d1 = 1/f

Question 10

What is the effect of adding a barrier in front of the lens?

Answer 10

Reduce the circle of confusion.

Question 11

Define the field of view.

Answer 11

Angle perceived by the camera.

𝜑 = arctan(𝑑/2f) <- doubled

Question 12

Problems of real lenses

Answer 12

Distortion:
– Radial: barrel, pincushion
– Tangential

Chromatic aberration
- Color fringes near the image edges

Question 13

Definition of depth of field.

Answer 13

The depth in which we can neglect the presence of the circle of confusion.