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Elements of photographic systems

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Chapter 2 Elements of photographic systems Introduction to Remote Sensing Instructor: Dr. Cheng-Chien Liu Department of Earth Science National Cheng-Kung University – PowerPoint PPT presentation

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Title: Elements of photographic systems


1
Chapter 2
  • Elements of photographic systems
  • Introduction to Remote Sensing
  • Instructor Dr. Cheng-Chien Liu
  • Department of Earth Science
  • National Cheng-Kung University
  • Last updated 13 March 2003

2
2.1 Introduction
  • Advantages of aerial photography
  • Improved vantage point
  • Capability to stop action
  • Permanent recording
  • Broadened spectral sensitivity
  • Increased spatial resolution and geometric
    fidelity

3
2.2 Early history of aerial photography
  • 1839 ? photography
  • 1840 ? use of photography for topographic
    surveying
  • 1858 ? aerial photograph (balloon)
  • 1860 ? Fig. 2.1 the earliest existing aerial
    photograph
  • 1882 ? use kite to obtain aerial photograph

4
2.2 Early history of aerial photography (cont.)
  • 1890 ?the first kite aerial photograph
  • 1906 ?Fig 2.2 the world-wide known aerial
    photograph obtained from kite
  • 1890 ? the giant camera 1.4 x 2.4m
  • 1903 ?Airplane
  • 1909 ?Fig 2.3 The first aerial motion picture
  • World War I II ?Military purposes

5
2.3 Basic negative-to-positive photographic
sequence
  • Fig 2.4 generalized cross section of BW
    photographic materials
  • Silver halide grains
  • Gelatin
  • emulsion ? photochemical reaction ? latent image
  • Base (support)
  • Backing

6
2.3 Basic negative-to-positive photographic
sequence (cont.)
  • Fig 2.5 negative-to-positive sequence
  • Negative film exposure reverse geometry tone
  • Paper print enlargement reverse geometry tone
  • Contact printing only reverse tone
  • Most aerial photographic paper prints
  • Diapositives, transparencies

7
2.4 Processing black and white films
  • Five steps
  • Developing developer solution
  • Selective, alkaline reducing agents
  • Molecular ionic state ? pure atomic(black) state
  • Stop bath acidic solution
  • Fixing
  • fixer solution? Remove unexposed silver halide
    grains
  • ? Harden the emulsion and render it chemical
    stable
  • washing ? free of any chemical residues
  • drying ? remove water
  • Air drying or heat drying

8
2.5 Film exposure
  • The simple camera
  • Fig 2.6 comparison between pinhole and simple
    lens cameras
  • Diaphragm ? lens diameter
  • Shutter ? duration of exposure

9
2.5 Film exposure (cont.)
  • Focus
  • Equation of focusing
  • Focal length f
  • object distance o
  • image distance i
  • Depth of field
  • f is fixed, charge o ? change i, there exists a
    limited range of i ? depth of field
  • for aerial photography ? o ? ? ? i ? f

10
2.5 Film exposure (cont.)
  • Exposure
  • equation of exposure
  • Film exposure E (J mm-2)
  • Scene brightness S (J mm-2 s-1)
  • Diameter of lens opening d (mm)
  • Exposure time t (sec)
  • Lens focal length f (mm)

11
2.5 Film exposure (cont.)
  • Aperture setting (f-stop) F f/d
  • F ?? d ? ? E ?
  • For a fixed value of E F?t1/2
  • t ?? stop action, prevent blurring ? the case of
    aerial photography
  • d ?? F ?? useful under low light condition
  • d ?? F ?? depth of field ?
  • Lens speed ? Ff/dmax
  • Example 2.2

12
2.5 Film exposure (cont.)
  • Geometric factors influencing film exposure
  • Extraneous effect
  • those factors influence exposure measurements,
    but have nothing to do with true changes in
    ground cover type or condition
  • Geometric
  • atmospheric

13
2.5 Film exposure (cont.)
  • Geometric factors influencing film exposure
    (cont.)
  • Extraneous effect (cont.)
  • Falloff ? a distance from the image center ?a
    ground scene of spatially uniform reflectance
    does not produce spatially uniform exposure in
    the focal plane.
  • Fig 2.7 factors causing exposure falloff

14
2.5 Film exposure (cont.)
  • Geometric factors influencing film exposure
    (cont.)
  • Vignetting effect
  • internal shadowing resulting from the lens mounts
    and other aperture surfaces within the camera.
    It varies from camera to camera and varies with
    aperture setting for any given camera.
  • Anti-vignetting filter (see 2.11)

15
2.5 Film exposure (cont.)
  • Geometric factors influencing film exposure
    (cont.)
  • Correction model ? radiometric calibration (for
    given F)
  • Photograph a scene of uniform rightness measure
    exposure at various q location identify the
    relationship Eq E0cosnq
  • Modern camera n 1.5 4

16
2.5 Film exposure (cont.)
  • Geometric factors influencing film exposure
    (cont.)
  • Object location
  • Fig 2.8 Sun-object-image angular relationship
  • Solar elevation, azimuth angle, viewing angle
  • Fig 2.9 Geometric effects that cause variations
    in focal plane irradiance
  • differential shading
  • differential scattering
  • specular reflection ?
  • extreme exposure
  • few information
  • should be avoid!

17
2.6 Film density and characteristic curves
  • Radiometric characteristics
  • how a specific film, exposed and processed under
    specific conditions, responds to scene energy of
    varying intensity
  • Important for photographic image analysis
  • Tonal values ? ground phenomenon
  • (darkness) (crop yield)
  • Photograph ? visual records ? many energy
    detectors (silver halide grains)

18
2.6 Film density and characteristic curves (cont.)
  • Film exposure
  • Instantly open ? energy ? reflectance ? exposure
  • Theoretically ? reflectance fn(l)
  • Unit
  • meter-candle-second (MCS) or ergs/cm2
  • MCS is an absolute unit, based on standard
    observer that is defined photometric.
  • We will deal with relative exposures
  • Transmittance

19
2.6 Film density and characteristic curves (cont.)
  • Film exposure (cont.)
  • Opacity O ?1/T
  • Density D ? log(O) ? log (1/T)
  • Transmission densitometer
  • Reflectance densitometer
  • Fig 2.11, Table 2.1
  • BW film ? AgBr
  • Color film ? 3 dye layers ? filter ? max
    absorption
  • D-logE curve
  • Each film has a unique D-logE curve
  • Also called HD curve

20
2.6 Film density and characteristic curves (cont.)
  • Fig 2.13
  • Components of a characteristic curve
  • Gross fog Dmin Dbase Dfog
  • Toe
  • Straight-line portion
  • g ? DD/DlogE
  • g ? contrast ? explain!
  • g ? development t T
  • Shoulder
  • Dmax
  • The range of densities Dmax - Dmin

21
2.6 Film density and characteristic curves (cont.)
  • Film speed
  • The sensitivity of the film to light
  • Speed ?? exposure time ?
  • Speed ?? size of AgBr ?? resolution ?
  • Aerial film speed (AFS)
  • AFS ? 1.5 / E0
  • E0 E(D 0.3 Dmin)
  • Effective aerial film speed
  • Kodak aerial exposure computer

22
2.6 Film density and characteristic curves (cont.)
  • Fig. 2.14
  • Exposure latitude
  • The range of log E that will yield an acceptable
    image on a given film
  • The range of variation from the optimum camera
    exposure setting that can be tolerated without
    excessively degrading the image quality
  • Radiometric resolution
  • The smallest difference in exposure that can be
    detected in a given film analysis
  • Film contrast ?? exposure latitude ?? radiometric
    resolution ?

23
2.6 Film density and characteristic curves (cont.)
  • Densitometer (microdensitometer)
  • Light source
  • Aperture assembly
  • Filter assembly
  • Receiver
  • Electronics
  • Readout / recorder

24
2.6 Film density and characteristic curves (cont.)
  • Types of Densitometer
  • Spot
  • Scanning
  • Flatbed
  • Rotating drum
  • Output of densitometer
  • Analog-to-digital (AD)
  • Digital image
  • D 03
  • DN 0255
  • DIP
  • Fig. 2.17 CCD scanner

25
2.7 Spectral sensitivity of black and white films
  • BW photographs
  • Panchromatic film (Fig 2.18)
  • Infrared-sensitive film (Fig 2.18)
  • Boundary 0.30.9 mm
  • 0.9 mm the photochemical instability of
    emulsion material
  • 0.3 mm
  • Atmosphere absorption scattering
  • Grass lenses absorption ? quartz lenses

26
2.7 Spectral sensitivity of black and white films
  • Application of UV photography in zoological
    research and management. (Fig 2.19)
  • Harp seals on the snow and ice surface
  • Adult harp seals ? dark on both images
  • Infant harp seals ? only be dark on UV image
  • Reliable monitoring of the change in population
    in harp seals.

27
2.7 Spectral sensitivity of black and white films
(cont.)
  • Limited applications of UV photography
  • Mainly due to atmospheric scattering
  • Monitoring oil spills

28
2.8 Color film
  • Advantage of color film ? more discriminable
  • Color-mixing processes
  • Psychophysical mechanisms ? not fully understand
  • We perceive all colors by synthesizing relative
    amounts of just three

29
2.8 Color film (cont.)
  • Additive primaries Blue, Green, Red
  • Blue Green ? Cyan
  • Blue Red ? Magenta
  • Green Red ? Yellow
  • Complementary color choose one primary color
    and mix the others.
  • Color TV ? principle of additive color (human
    eyes)

30
2.8 Color film (cont.)
  • Color photography ? principle of subtractive
    color
  • Cyan dye ? absorb red
  • Magenta dye ? absorb green
  • Yellow dye ? absorb blue
  • The subtractive color-mixing process plate 2b

31
2.8 Color film (cont.)
  • Structure and spectral sensitivity of color film
  • Fig 2.20
  • Blue blocking filter
  • Generalized cross section (Fig 2.20a)
  • Spectral sensitivities of the three dye layers
    (Fig 2.20b)
  • Color formation with color film (Fig 2.21)

32
2.9 Processing color films
  • Color negative films
  • Negative-to-positive sequence
  • Similar to BW negative film
  • Color reversal films
  • Directly produce positive image
  • Color slides
  • Color diapositives, color positive transparencies

33
2.9 Processing color films (cont.)
  • Fig 2.22 color reversal process
  • Expose film
  • First developer
  • Re-expose to white light
  • Color developer
  • Bleach fixer
  • View image

34
2.10 Color infrared film
  • Color of dye developed in any given emulsion
    layer ? (not necessary correspond to) ? color of
    light to which the layer is sensitive
  • Color infrared film
  • 3 emulsion layers
  • 0.70.9 mm
  • False color

35
2.10 Color infrared film (cont.)
  • Fig 2.23 Structure and sensitivity of color
    infrared film
  • Blue blocking filter (yellow filter)
  • Image color ? ground reflectance
  • (nearly equal sensitivity of all layers of the
    film to blue)
  • Improve haze penetration ? reduce Rayleigh
    scatter ? filter out blue light

36
2.10 Color infrared film (cont.)
  • Camouflage detection (CD) film
  • WWII
  • Healthy green vegetation ? red (Plate3)
  • Object painted green ? blue (Plate3)
  • Only when T is extremely high ? IR film can
    record. Otherwise, IR film is responding to
    reflected IR energy that is not directly related
    to T
  • Fig 2.25
  • Plate 4

37
2.11 Filters
  • Filters
  • Transparent (glass or gelatin) materials
  • Absorption or reflection, eliminate or reduce the
    energy
  • reading a film in selected portions of the
    spectrum
  • Place in front of lens
  • Kodak Wratten filter number

38
2.11 Filters (cont.)
  • Absorption filter
  • Often used in film-filter combination
  • E.g. use a UV-transmitting (Wratten 18A) filter
    to discriminate harp seals pups. (Fig 2.19)
  • E.g. use a short wavelength blocking filter (high
    pass) to distinguish between natural grass and
    artificial turf (Fig 2.27)
  • Bandpass filter
  • Fig 2.28 typical transmittance curve for
    bandpass filter.
  • Low pass absorption filters are not available!

39
2.11 Filters (cont.)
  • Interference filters reflect rather than absorb
  • Yellow filter ? panchromatic film ? reduce
    atmospheric haze
  • BW film
  • Yellow filter ? forestry
  • Red or IR-only filter ? delineate water bodies

40
2.11 Filters (cont.)
  • Antivignetting filters
  • Strongly absorbing in central area and
    progressively transparent in circumferential area
  • Usually built into other filters
  • Color-compensation filter ? aging
  • Using filters ? increase exposure
  • Filter factors

41
2.12 Aerial Cameras
  • Four basic types

42
2.12.1 Single-Lens frame cameras
  • Single-lens frame camera
  • Most common camera
  • Photogrammetric mapping purpose
  • High geometric image quality
  • Film format size 230mm
  • Film capacity 240mm x 120m
  • Intervalometer
  • Focal length 90210mm, most widely used 152mm
  • Long focal length 300mm ? high altitude
  • Frame camera lense (measured along image
    diagonal)
  • Normal angle (lt75o)
  • Wide angle (75o100o)
  • Super wide angle(gt100o)

43
2.12.1 Single-Lens frame cameras (cont.)
  • Principal components (Fig 2.31)
  • Lens cone assembly
  • Lens ? bring light rays to focal plane
  • Filter
  • Shutter
  • Diaphragm
  • Body
  • Magazine
  • Supply reel
  • Take up reel
  • Film flattening mechanism
  • Film-advancing mechanism

44
2.12.1 Single-Lens frame cameras (cont.)
  • Principal components (cont.)
  • Image motion compensation
  • Moving the film across the focal plane at a rate
    just equal to the rate of image movement.
  • Fig 2.32 the modular nature of modern aerial
    mapping camera system
  • Fig 2.33 a vertical photograph (mapping camera)
  • Fiducial marks
  • Principal point

45
2.12.1 Single-Lens frame cameras (cont.)
  • Large Format Camera (LFC) (NASA)
  • Orbit altitude
  • Space shuttle, free-flying spacecraft, aircraft
  • Advanced image motion compensation mechanism
  • 305-mm-focal-length lens
  • 230x460-mm image format
  • Space-hardened
  • High resolution (3) low distortion (lt15 mm)
  • Fig 2.36
  • Fig 2.37
  • Fig 2.38

46
2.12.1 Single-Lens frame cameras (cont.)
  • Metric Camera (ESA)
  • Reconnaissance cameras
  • Faithfully record details but not geometric
    fidelity
  • Color-corrected lens ? high quality color
    photographs

47
2.12.2 Multi-lens Frame Cameras
  • Multi-band photographs
  • photographs taken simultaneously from the same
    geometric vantage point but with different
    film-filter combinations.
  • Fig 2.39 multi-lens frame cameras
  • Fig 2.40 example B,G,R, IR
  • Enhance contrast, but to optimize this contrast ?
    choose the film-filter combination

48
2.12.2 Multi-lens Frame Cameras (cont.)
  • Color additive viewers
  • Fig 2.41, 2.42
  • Four projectors aimed at a single viewing screen
  • Four BW multi-band images in a positive
    transparency format
  • Optically superimpose ? color composite images
  • Normally, use 3 projectors
  • True or false color
  • Exotic color display ? enhance discrimination
  • Plate 5 example of color composite

49
2.12.2 Multi-lens Frame Cameras (cont.)
  • Camera filter colors
  • Viewer filter colors
  • Positive transparency-viewer filter combinations
  • DIP
  • Plate 12 six examples of Lansat TM data
  • Multi-band photography use arrays of several
    single-lens frame cameras

50
2.12.3 Strip Cameras
  • Fig 2.44
  • Moving film past a fixed slit in the focal plane
  • Shutter ? continuously open
  • Inherant image motion compensation
  • Width of slit ? determine exposure
  • Designed and good for low altitude and high speed
    military reconnaissance
  • Permits obtainment of very detailed photography

51
2.12.3 Strip Cameras (cont.)
  • Bad for high altitude and moderate speed ?
    distortion
  • Frame cameras improve in lens image motion
    compensation ? Strip Cameras have a very limited
    application.

52
2.12.4 Panoramic Cameras
  • Similar to strip cameras, but rotate the lens or
    a prism to cover ground areas (Fig 2.45)
  • Fig 2.46
  • panoramic distortion and scan positional
    distortion

53
2.12.4 Panoramic Cameras (cont.)
  • Optical bar camera
  • NASA. High altitude. Reconnaissance purpose
  • 610-mm-focal-length lens
  • Total FOV 1200 (?600)
  • Film capacity 2000m
  • Altitude 19800m
  • Ground coverage 34.3km x 2
  • Used extensively for high altitude aerial
    reconnaissance and Apollo missions

54
2.12.4 Panoramic Cameras (cont.)
  • Pro ?
  • broad and detailed view of the ground
  • Con ?
  • lack the geometric fidelity
  • variations of atmospheric effect

55
2.12.4 Panoramic Cameras (cont.)
  • Applications
  • USFS (Plate 9)
  • Forest pest damage detection Plate 9
  • Timber salvage operations
  • EPA
  • Enviro-Pod one vertical camera one
    forward-looking camera
  • Industrial pollutants
  • hazardous waste sites
  • emergency episodes

56
2.13 Electronic imaging
  • Comparison between photographic and electronic
    imaging (Table 2.2)
  • Charge-coupled devices (CCDs) ? wider range
  • Digital signal ? storage, process, transmit.
  • Kodak Professional DCS 200 digital camera
  • Nikon camera body Kodak camera back
  • 1524 x 1012 (9x9 mm)
  • 1/8000 sec
  • 1.5 Million pixels
  • For 35 mm film 2.53 Million pixels
  • Fig 2.49, 2.50

57
2.13 Electronic imaging (cont.)
  • Airborne Data Acquisition and Registration System
    5000 (ADAR System 5000)
  • A multi-spectral digital camera system (4 CCD
    Sensors)
  • 0.0120.3 mm in band width
  • 739 x 478
  • 1/60 1/2000 sec
  • Ground resolution 0.54m per pixel
  • GPS monitoring
  • Plate 6

58
2.13 Electronic imaging (cont.)
  • Pro
  • Rapid turnaround time
  • Images are immediately available computer-ready
  • Higher exposure latitude

59
2.14 Video recording
  • Video recording ? standard analog television
    signals are recorded on magnetic tape or disles
  • Can use various cameras
  • Follow NTSC RS-170 standard
  • Tape format super-VHS, Hi-8, HDTV..etc.
  • Pros
  • Real-time viewing immediately available
  • Inexpensive media
  • Audio track
  • Recorded GPS information

60
2.14 Video recording (cont.)
  • Cons
  • Poor spatial resolution
  • Expensive equipment
  • Cumbersome to index or handle tapes
  • View
  • VCR
  • AD converter ? frame grabber

61
2.14 Video recording (cont.)
  • Applications ? timeliness is required in crop
    inventorying or disease detection
  • Generalized agricultural, rangeland and natural
    resource management
  • Analysis of hazardous waste sites
  • Detection of soil conditions
  • Wild rice mapping
  • Trout stream monitoring
  • Right-of-way monitoring
  • Water quality studies
  • Crop condition assessment

62
2.14 Video recording (cont.)
  • Applications (cont.)
  • Detection of forest insect and disease problems
  • Irrigation mapping
  • Detection of frost damage in citrus groves
  • Fig 2.53 example of 4 CCD array cameras
  • Plate 7 example of video versus photograph
  • Still video cameras
  • Widely used in photojournalism
  • No significant advantage for aerial imaging

63
2.15 Basic geometric characteristics of aerial
photographs
  • Orientation
  • Vertical photographs ? rarely obtainable
  • Tilted photographs
  • Oblique photographs
  • High ? image of the horizon
  • Low

64
2.15 Basic geometric characteristics of aerial
photographs (cont.)
  • Taking vertical aerial photographs
  • Fig 2.55
  • Flight lines (flight strips)
  • nadir line
  • Endlap ? at least 50 to ensure total
    stereoscopic coverage
  • Stereoscopic coverage
  • Stereopairs

65
2.15 Basic geometric characteristics of aerial
photographs (cont.)
  • Taking vertical aerial photographs (cont.)
  • Stereomodel
  • Stereoviewing
  • Intervalometer
  • Stereoscopic overlap area
  • 55 65 overlap ? at least 50 endlap (Fig
    2.56)
  • Air base
  • Base-height ratio ? air base / flying height
  • ??Vertical exaggeration ? (Fig 2.57)

66
2.15 Basic geometric characteristics of aerial
photographs (cont.)
  • Taking vertical aerial photographs (cont.)
  • Sidelap ? at least 30
  • Block of photographs
  • GPS navigation system control
  • Index mosaic (Fig 2.59)

67
2.15 Basic geometric characteristics of aerial
photographs (cont.)
  • Scale of aerial photographs
  • Photograph scale one unit of distance on a
    photograph represents a specific number of units
    of actual ground distance
  • Unit equivalents, representative fractions,
    ratios
  • Example 2.3

68
2.15 Basic geometric characteristics of aerial
photographs (cont.)
  • Scale of aerial photographs (cont.)
  • (Fig 2.60)
  • Photographs taken over terrain of varying
    elevation will exhibit a continuous range of
    scales associated with the variations in terrain
    elevation
  • Example 2.4
  • Example 2.5
  • Average scale

69
2.15 Basic geometric characteristics of aerial
photographs (cont.)
  • Comparative geometry of map vertical aerial
    photograph
  • Map ? orthographic projection ? map position
  • Vertical photograph ? perspective projection ?
    relative horizontal (planimetric)positions
  • Fig 2.61
  • Relief displacement tops of objects are always
    displaced from their bases, this distortion is
  • ? hobject ? 1/H ? radial distance from the
    principal point
  • Aerial photographs ? (not directly) ? map (chap
    4)
  • Ground coverage
  • fn(camera format size, focal length, H)
  • Fig 2.62

70
2.16 Photographic resolution
  • Spatial resolution
  • an expression of the optical quality of an image
    produced by a particular camera system
  • Influenced by
  • Resolving power of film
  • Camera lens
  • Uncompensated image motion
  • Atmospheric condition
  • Film processing condition
  • Fig 2.63 resolving power test chart

71
2.16 Photographic resolution (cont.)
  • Resolving power of the film (lines/mm)
  • The reciprocal of the center-to-center distance
    (mm) of the lines that are just distinguishable
    in the test chart
  • ?? Contrast ?

72
2.16 Photographic resolution (cont.)
  • Modulation transfer function
  • A microdensitometer is used to scan across images
    of a series of square wave test patterns (Fig
    2.64)
  • Spatial frequency ??modulation transfer
    function?
  • Complete curve (Fig 2.65)
  • A trade-off between speed resolution
  • Dynamical spatial resolution of the total system
  • Detection ? recognition ? identification
  • Ground resolution distance

73
2.17 Conclusion
  • Aerial photography
  • Backbone of remote sensing
  • Pros
  • Cons limitations
  • Trend ? digital recording
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