1. PNU Machine Vision
Lecture 2a: Cameras
Source: S. Lazebnik

2. Image formation Let’s design a camera
- Idea 1: put a piece of film in front of an object
Do we get a reasonable image?
from Noah Snavely

3. Pinhole camera Add a barrier to block off most of the rays
This reduces blurring
The opening known as the aperture
How does this transform the image?
It gets inverted

4. Camera Obscura
Basic principle known to Mozi ( BC), Aristotle ( BC)
Drawing aid for artists: described by Leonardo da Vinci ( )
Gemma Frisius, 1558
Source: A. Efros

5. Camera Obscura
암실, 주름상자

6. Home-made pinhole camera
Why so
blurry?
Slide by A. Efros

7. Shrinking the aperture
Why not make the aperture as small as possible?
Less light gets through
Diffraction effects...

8. Shrinking the aperture

9. Adding a lens
For different distance
“circle of
confusion”
Not focus in a point
There is a specific distance at which objects are “in focus”
other points project to a “circle of confusion” in the image
Changing the shape of the lens changes this distance

10. Lenses F
focal point
focal point at a distance f beyond the plane of the lens (the focal length)
f is a function of the shape and index of refraction of the lens
Aperture restricts the range of rays
aperture may be on either side of the lens
Lenses are typically spherical (easier to produce)

11. Depth of Field
Slide from Wikipedia

12. Depth of Field Small aperture & diffraction Large aperture
IC is 2.5 mm higher than
the circuit board it is mounted on
Large aperture
Slide from Wikipedia

13. Depth of Field
f / 5.6
f / 32
A smaller aperture increases the range in which the object is approximately in focus
Flower images from Wikipedia

14. Depth of Field
focus on a’

15. Depth of Field

16. Perspective effects

17. Perspective effects
Far away objects appear smaller
Forsyth and Ponce

18. Perspective effects

19. Perspective effects Converge in image on horizon line Image plane
(virtual)
pinhole
Scene

20. The eye The human eye is a camera
Iris: 홍체, 환
Pupil: 동공
Cornea: 각막
Retina: 망막
Cone: 추상체
Rod: 간상체
Note that the retina is curved
The human eye is a camera
Iris - colored annulus with radial muscles
Pupil - the hole (aperture) whose size is controlled by the iris
What’s the “film”?
photoreceptor cells (rods and cones) in the retina

21. Eyes in nature: eyespots to pinhole camera
안 점
20mm under water
planarian
앵무 조개
nautilus

22. Eyes in nature 체액
Evolution of eye
유리질의

23. Before Film was invented
Lens Based Camera Obscura, 1568
Srinivasa Narasimhan’s slide

24. Film camera Still Life, Louis Jaques Mande Daguerre, 1837
Srinivasa Narasimhan’s slide

25. Silicon Image Detector
Shree Nayar’s slide

26. Digital camera A digital camera replaces film with a sensor array
Each cell in the array is a Charge Coupled Device
light-sensitive diode that converts photons to electrons
other variants exist: CMOS is becoming more popular
광 양자,
빛 입자

27. Color = So far, we’ve talked about grayscale images What about color?
Most digital images are comprised of three color channels – red, green, and, blue – which combine to create most of the colors we can see
Why are there three? =

28. Color perception Three types of cones
L response curve
특정 파장이 우리 눈의
3가지 센서에 주는 자극은
강도가 다르다.
서로 다른 3가지 센서 강도가
다른 color을 만들어 낸다.
Three types of cones
but regions overlap
Short (S) corresponds to blue
Medium (M) corresponds to green
Long (L) corresponds to red
Different sensitivities: we are more sensitive to green than red
varies from person to person (and with age)
Colorblindness—deficiency in at least one type of cone
Cone: 추상체(원추세포)
Rod: 간상체

29. Field sequential YungYu Chuang’s slide red-채널 요소만 나옴
(흑백 glass plane에 새김)
r필름
(r만 통과)
입력 scene
YungYu Chuang’s slide

30. Field sequential
연속해서 얻은
primary color를
fusion하면
YungYu Chuang’s slide

31. Field sequential
Picture가 형성됨
YungYu Chuang’s slide

32. Prokudin-Gorskii (early 1900’s)
Lantern
projector
3개의 primary color를 담은
흑백 plate를 필터를 통해
합성시켜주는 장치
YungYu Chuang’s slide

33. Prokudin-Gorskii (early 1910’s)
(러시아 전역의 풍경 수천 장을 남겼음)
Color camera가 없던 시절 r, g, b의 filter 3개만 이용하여 negative image plate를 얻었음. 후에(최근)
Dicromatography라는 color 렌더링 기술을 이용하여 오래 전 사진을 생생하게 얻음.
YungYu Chuang’s slide

34. Color sensing in camera: Prism
Requires three chips and precise alignment
More expensive
CCD(B)
CCD(G)
CCD(R)

35. Color filter array Bayer grid
Estimate missing components from neighboring values (demosaicing)
Why more green?
Human Luminance Sensitivity Function
표시 cell의 감지 안된
Cell은 주위 cell값으로 보간
사람은 green밴드에 가장 민감
Source: Steve Seitz

36. Bayer’s pattern
YungYu Chuang’s slide

37. Foveon X3 sensor
Light penetrates to different depths for different wavelengths
Multilayer CMOS sensor gets 3 different spectral sensitivities
YungYu Chuang’s slide

38. Color filter array
red
green
blue
output
YungYu Chuang’s slide

39. X3 technology
red
green
blue
output
YungYu Chuang’s slide

40. Foveon X3 sensor
Bayer CFA
X3 sensor
YungYu Chuang’s slide

41. Historical context
Pinhole model: Mozi ( BC), Aristotle ( BC)
Principles of optics (including lenses): Alhacen ( )
Camera obscura: Leonardo da Vinci ( ), Johann Zahn ( )
First photo: Joseph Nicephore Niepce (1822)
Daguerréotypes (1839)
Photographic film (Eastman, 1889)
Cinema (Lumière Brothers, 1895)
Color Photography (Lumière Brothers, 1908)
Television (Baird, Farnsworth, Zworykin, 1920s)
First consumer camera with CCD: Sony Mavica (1981)
First fully digital camera: Kodak DCS100 (1990)
Alhacen’s notes
Niepce, “La Table Servie,” 1822
CCD chip