Lecture 1 - Digital Image Formation

Question 1

What is the main purpose of digital image formation in image analysis and computer vision?

Answer 1

To convert a physical image into a digital format that can be processed and analyzed by computer algorithms.

Question 2

Define “pinhole camera model”.

Answer 2

A pinhole camera model is a simple camera model that represents the camera as a box with a small hole on one side. Light passes through the hole and projects an inverted image on the opposite side of the box.

Question 3

What are the primary components of a digital image formation system?

Answer 3

Light source, object, lens, image sensor, and image processor.

Question 4

Explain the concept of “sampling” in the context of digital image formation.

Answer 4

Sampling is the process of converting a continuous image signal into a discrete signal by measuring the image intensity at regular intervals (pixels).

Question 5

What is “quantization” in image processing?

Answer 5

Quantization is the process of mapping a large set of input values to a smaller set, such as rounding off pixel intensity values to the nearest integer in digital images.

Question 6

Describe the concept of “resolution” in digital imaging.

Answer 6

Resolution refers to the amount of detail an image holds and is typically measured in terms of the number of pixels in an image or the spatial frequency (e.g., dpi - dots per inch).

Question 7

Define “dynamic range” in the context of digital images.

Answer 7

Dynamic range is the ratio between the maximum and minimum measurable light intensities (brightness levels) in an image.

Question 8

What is “bit depth” in digital images?

Answer 8

Bit depth refers to the number of bits used to represent the color or grayscale value of each pixel, determining the range of colors or shades of gray that can be displayed.

Question 9

Explain “color space” in digital imaging.

Answer 9

A color space is a specific organization of colors, which helps in the representation and reproduction of color in both digital and physical formats. Examples include RGB, HSV, and CMYK.

Question 10

What is the purpose of the “gamma correction”?

Answer 10

Gamma correction is used to adjust the brightness of an image to match the nonlinear response of display devices or the human eye.

Question 11

Describe the “camera calibration” process.

Answer 11

Camera calibration is the process of estimating the parameters of the camera model, such as focal length, principal point, and lens distortion, to improve the accuracy of image measurements and reconstructions.

Question 12

What is “lens distortion” and how does it affect digital images?

Answer 12

Lens distortion is an optical aberration where straight lines appear curved in the image. It affects the accuracy of image-based measurements and needs to be corrected for precise image analysis.

Question 13

Write the formula for the pinhole camera model.

Answer 13

Question 14

Provide the formula for the camera intrinsic matrix
K.

Answer 14

Question 15

What is the equation for converting 3D world coordinates to 2D image coordinates using a pinhole camera model?

Answer 15

Question 16

What is the minimum number of points needed to determine all external calibration parameters if all internal parameters are known?

Answer 16

The minimum number of points needed is six.

Question 17

Why is Rayleigh scattering strongly dependent on the frequency of scattered light?

Answer 17

Rayleigh scattering is more effective at shorter wavelengths (higher frequencies), which is why the sky appears blue.

Question 18

Describe the difference between specular and diffuse reflection.

Answer 18

Specular reflection occurs when light reflects off a smooth surface at a single angle, while diffuse reflection occurs when light reflects off a rough surface in multiple directions.

Question 19

How does the refractive index
n depend on the wavelength of light?

Answer 19

The refractive index
𝑛
n varies with the wavelength of light, causing dispersion of light into its constituent colors as in a prism.

Question 20

Explain the significance of Brewster’s angle in polarization.

Answer 20

At Brewster’s angle, light reflected from a surface is perfectly polarized perpendicular to the plane of incidence, resulting in no reflection of light parallel to the plane.