Sensory Information Processing (2)

Introduction of image sensors

Topics

Outline of image sensorsHistory of image sensors

• Cameras and photography• Broadcasting, movie and video• Electronic / digital imaging

Components of image sensors• Optics, imaging device, signal line, capture

Approximation of image sensor• Geometry of the camera

History of photography １８３９ daguerreotype (silver plate) １９００ roll film １９３５ color film １９３２ 35mm film still camera(Leica) １９３０ - ５０ rangefinder cameras １９５０ - ６０ SLR (Single lens reflex)

camera １９６０ - ７０ auto exposure １９７７ autofocus １９９５ digital camera (casio QV-10) ..mainly not for image quality improvement, but

just for convenience

Rangefinder camera （ 1940-1960)

Rangefinder camera (1958, 2000)

finder

Double image

base

line

SLR(1959)

What you see is what you get!

Focusing screen(ground glass)

Electronic / Digital imaging

Difference between film and digital camear is only at imaging device

Ex. Digital SLR / film SLR

What matters for image quality?

For convenience cost Small / light

Do up-to-date cameras have high performance in image quality? 8bit quantization Number of Pixels Cheap, small lens Imaging sensor vs.

film Compression (JPEG)

Lens for aerial survey : Aviogon(1952, design by L. Bertele)

Field of view : 96 degDistortion : under 0.008%

Broadcasting / video

１８８４ mechanical scan TV １８９７ Braun tube １９２５ Invent of TV broadcast １９３０ Invent of imaging tube １９５１ Development of VTR １９５３ NHK started TV broadcast １９６０ Color TV broadcast in Japan １９８５ CCD Video camera for consumer ２０１１ Analog broadcast discontinue

歴史

NHK

I/O of image(side talk)

1843 : prototype of facsimileBoth transmitter / receiver have synchronized pendulum with needle for readout / recording

Imaging tube

Braun tube

Projectors and cameraslens

CCD

lensLCD panel

Light source

Condenser lens

Very similar construction

What is the key for image quality? Camera is generally just a box There is no much variation for CCD or

film Lens is the key for photographYou are already satisfied by the

number of pixels, but not for image For the geometric measurement, the

lens is the key for precisenessMost lens has the distortion around 1-

2%

Camera

CCD driver / Signal processing

DigitalCapture

CCD

lens

What is principal parameter of the lens?What is aberration?

What is the image degradation by lenses?How to select the lenses?

How the image is recorded electrically?What is the artifact of CCD?

How to select the CCD?

Camera

How to drive the CCD?How the color value is recovered?

How the Synchronize and Sampling is performed?

CCD driver / Signal processing

DigitalCapture

CCD

lens

What is the ideal image sensor?

Similar image should be captured for the plane perpendicular to the optical axis No distortion No defocus (blurring)

Pinhole camera

Image is formed through small “pinhole”Pro : There is rigid Geometric relationship

between the subject and imageCon : image is too dark (to slow)

What is the lens?

Collect enough light on the image sensor For measurement, image should be similar

to the pinhole camera as possibleNo distortion, sharp picture

It is impossible by simple single lensNo defocus (trade-off with the speed)

lens Image sensor / film

Ideal lens

The image is similar to the subject Geometric condition

• No distortion• No image unsharpness

Photometric condition• The lightness is uniform

h

aberration

Components of imaging optics

Lens systemMostly ３～１０ elements>20 elements for zoom lens

Aperturedeal the trade-off between light and defocus

Nikkor

Example of the lens

Combination of varied type and shape of the lenses

Why we need many elements?

For correcting monochromatic aberrationThin lens with high index glassThick lens with low index glass

For correcting chromatic aberration

There are some differencesfor aberration even if the focal length is same

White lightF spectrum

(blue)

d spectrum(green)

C spectrum

(red)

Longitudinal chromatic aberration of single lens