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Chapter 2

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. 2.1 Introduction. Advantages of aerial photography Improved vantage point

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Chapter 2

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  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 B&W 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  F=f/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 • B&W film  AgBr • Color film  3 dye layers  filter  max absorption • D-logE curve • Each film has a unique D-logE curve • Also called H&D 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: 0~3 • DN: 0~255 • DIP • Fig. 2.17: CCD scanner

  25. 2.7 Spectral sensitivity of black and white films • B&W photographs • Panchromatic film (Fig 2.18) • Infrared-sensitive film (Fig 2.18) • Boundary : 0.3~0.9 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 B&W 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 • 0.7~0.9 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 • B&W 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 capacity240mm x 120m • Intervalometer • Focal length : 90~210mm,most widely used: 152mm • Long focal length: 300mm  high altitude • Frame camera lense (measured along image diagonal) • Normal angle (<75o) • Wide angle (75o~100o) • Super wide angle(>100o)

  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 (<15 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 B&W 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

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