Lecture 1-Image Theory

Question 1

How does human vision work?

Answer 1

On a logarithmic basis.

Question 2

How is aperture measured?

Answer 2

In f-stops (or T-stops)

Question 3

What are f-stops a multiple of?

And how does the light entering the lens change with each higher f-stop?

Answer 3

1.4142
F 1.4, f 2.0, f 2.8, f 4.0, f 5.6, f 8.0…
Amount of light entering the lens halves, amount of brightness appears to change equally.

Question 4

What is Local Colour Adaptation?

Answer 4

The brain always seeks to establish a base white, surrounding colours are interpreted relative to the base white.

Question 5

What is Brightness Adaptation?

Answer 5

The brightness of a colour can be affected by surrounding colours.

Question 6

What is lateral colour adaptation?

Answer 6

Strong background colours will impact a perceived colour cast on foreground objects.

Question 7

What is simultaneous contrast?

Answer 7

Light colours on light backgrounds can be strengthened by bands of black (and vice versa).

Question 8

What is the RGB model?

Answer 8

Additive model- a means of modelling the mixing of light.
Component colours mix ultimately to white.
used for transmissive recording and reproduction.

Question 9

What is the HSV model?

Answer 9

HUE- perception of a specific wavelength (e.g. Green)
SATURATION- the amount of hue present (chroma level)
VALUE- the brightness (luminance level)
HSV is the most common model for grading.

Question 10

What is the CMY/CMYK model?

Answer 10

Subtractive model, means of modelling the mixing of pigment, component colours ultimately mix to black. Used for opaque reproduction, not used in video or digital recording.

Question 11

What colour space to do Television and video use compared to Film and Digital film, and what is the difference?

Answer 11

TV and video use a linear colour space which has an even distribution of levels based on human perception.
Film and digital film systems use a non-linear colour space which has an uneven distribution of levels based on recording medium.

Question 12

Define Chromaticity:

Answer 12

A means to assess colour independent of luminance.

Question 13

Define Colour temperature:

Answer 13

A measurement of colour from a light source, measured in kelvin units (K)

Question 14

Define White Balance:

Answer 14

White balance refers to the colour temperature considered to represent white for the system.

Question 15

What colour temperature is a 
\: Household lightbulb?
\: Studio tungsten?
\: Photographic daylight?
\: Reproductive daylight?
\: Hazy daylight?

Answer 15

Household lightbulb: 2,800K
Studio tungsten: 3,200K (Tungsten balance)
Photographic daylight: 5,600K (daylight balance)
Reproductive daylight: 6,500K (D65)
Hazy daylight- 8,000K
White balance must be set to ensure proper colour fidelity.

Question 16

At what frame rate do we perceive motion?

Answer 16

About 18 frames per second, slower frame rates appears jerky.
Motion blur creates fluid motion.
Faster shutter speeds require higher frame rates to maintain smooth perception of motion.

Question 17

Film and some digital video systems record images progressively (1080p), what is the difference between progressive and TV’s recording format of interlace (1080i)?

Answer 17

Progressive: each frame is recorded in one exposure/scan/pass.
Interlace: Each frame consists of two fields, each filed records at twice the overall frame rate but only includes half of the visual information. E.g. PAL (25fps) each field is recorded in 1/50th sec.