Chapter 2 Elements of photographic systems Introduction to Remote Sensing Instructor: Dr....

Chapter 2Chapter 2

Elements of photographic systemsElements of photographic systems

Introduction to Remote SensingInstructor: Dr. Cheng-Chien Liu

Department of Earth Science

National Cheng-Kung University

Last updated: 13 March 2003

2.12.1 Introduction Introduction

Advantages of aerial photographyAdvantages of aerial photography• Improved vantage point

• Capability to stop action

• Permanent recording

• Broadened spectral sensitivity

• Increased spatial resolution and geometric fidelity

2.22.2 Early history of aerial Early history of aerial photographyphotography

• 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

2.22.2 Early history of aerial Early history of aerial photography (cont.)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

2.32.3 Basic negative-to-positive Basic negative-to-positive photographic sequencephotographic sequence

Fig 2.4: generalized cross section of Fig 2.4: generalized cross section of B&W photographic materialsB&W photographic materials• Silver halide grains

• Gelatin

• emulsion photochemical reaction latent image

• Base (support)

• Backing

2.32.3 Basic negative-to-positive Basic negative-to-positive photographic sequence (cont.)photographic sequence (cont.)

Fig 2.5: negative-to-positive sequenceFig 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 printsDiapositives, transparencies

2.4 Processing black and 2.4 Processing black and white filmswhite films

Five stepsFive steps• Developing: developer solution

Selective, alkaline reducing agentsMolecular 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

2.5 Film exposure2.5 Film exposure

The simple cameraThe simple camera• Fig 2.6: comparison between pinhole and

simple lens camerasDiaphragm lens diameterShutter duration of exposure

2.5 Film exposure (cont.)2.5 Film exposure (cont.)

FocusFocus• Equation of focusing

Focal length : fobject distance : oimage distance : i

• Depth of field:f is fixed, charge o change i,

there exists a limited range of i depth of fieldfor aerial photography o i f

oif

111


ExposureExposure• 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)

2

2

4 f

tsdE


Aperture setting (f-stop) : Aperture setting (f-stop) : FF = = ff//dd

• F d E • For a fixed value of E: Ft1/2

t stop action, prevent blurring the case of aerial photography

d F useful under low light conditiond F depth of field Lens speed F=f/dmax

• Example 2.2

22

2

44 F

st

f

tsdE


Geometric factors influencing film Geometric factors influencing film exposureexposure• Extraneous effect

those factors influence exposure measurements, but have nothing to do with true changes in ground cover type or condition

Geometric atmospheric


Geometric factors influencing film Geometric factors influencing film exposure (cont.)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

cos

cos/

cos

dAdA

ff

AA

ally)(theoretic cos4 EE


Geometric factors influencing film Geometric factors influencing film exposure (cont.)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)


Geometric factors influencing film Geometric factors influencing film exposure (cont.)exposure (cont.)• Correction model radiometric calibration

(for given F)Photograph a scene of uniform rightness measure exposure

at various location identify the relationship E = E0cosnModern camera : n = 1.5 ~ 4


Geometric factors influencing film Geometric factors influencing film exposure (cont.)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!

2.6 Film density and characteristic 2.6 Film density and characteristic curvescurves

Radiometric characteristicsRadiometric 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 Photograph visual records visual records many many energy detectors (silver halide grains)energy detectors (silver halide grains)

2.6 Film density and characteristic 2.6 Film density and characteristic curves (cont.)curves (cont.)

Film exposureFilm exposure• Instantly open energy reflectance

exposure

• Theoretically: reflectance & fn()

• 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:lightincident total

throughpassinglight T


Film exposure (cont.)Film exposure (cont.)• Opacity: O 1/T• Density: D log(O) log (1/T)

Transmission densitometerReflectance densitometerFig 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 curveAlso called H&D curve


Fig 2.13 Fig 2.13 • Components of a characteristic curve

• Gross fog: Dmin = Dbase + Dfog

• Toe• Straight-line portion

D/logE contrast explain! development t & T

• Shoulder

• Dmax

The range of densities = Dmax - Dmin


Film speedFilm 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


Fig. 2.14: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 resolutionThe smallest difference in exposure that can be detected in

a given film analysis

• Film contrast exposure latitude radiometric resolution


Densitometer (microdensitometer)Densitometer (microdensitometer)• Light source

• Aperture assembly

• Filter assembly

• Receiver

• Electronics

• Readout / recorder


Types of DensitometerTypes of Densitometer• Spot• Scanning

FlatbedRotating drum

• Output of densitometerAnalog-to-digital (AD)Digital image

D: 0~3 DN: 0~255

DIPDIP Fig. 2.17: CCD scannerFig. 2.17: CCD scanner

2.7 Spectral sensitivity of black and 2.7 Spectral sensitivity of black and white filmswhite films

B&W photographsB&W photographs• Panchromatic film (Fig 2.18)

• Infrared-sensitive film (Fig 2.18)

Boundary : 0.3~0.9 Boundary : 0.3~0.9 mm• 0.9 m : the photochemical instability of

emulsion material

• 0.3 m : Atmosphere absorption & scatteringGrass lenses absorption quartz lenses

2.7 Spectral sensitivity of black and 2.7 Spectral sensitivity of black and white filmswhite films

Application of UV photography in Application of UV photography in zoological research and management. zoological research and management. (Fig 2.19)(Fig 2.19)• Harp seals on the snow and ice surface

Adult harp seals dark on both imagesInfant harp seals only be dark on UV image

• Reliable monitoring of the change in population in harp seals.

2.7 Spectral sensitivity of black and 2.7 Spectral sensitivity of black and white films (cont.)white films (cont.)

Limited applications of UV Limited applications of UV photographyphotography• Mainly due to atmospheric scattering

• Monitoring oil spills

2.8 Color film2.8 Color film

Advantage of color film Advantage of color film more more discriminablediscriminable

Color-mixing processesColor-mixing processes• Psychophysical mechanisms not fully

understand

• We perceive all colors by synthesizing relative amounts of just three

2.8 Color film (cont.)2.8 Color film (cont.)

Additive primaries : Blue, Green, RedAdditive primaries : Blue, Green, Red• Blue + Green Cyan

• Blue + Red Magenta

• Green + Red Yellow

Complementary color : choose one Complementary color : choose one primary color and mix the others.primary color and mix the others.

Color TV Color TV principle of additive color principle of additive color (human eyes)(human eyes)


Color photography Color photography principle of principle of subtractive colorsubtractive color• Cyan dye absorb red

• Magenta dye absorb green

• Yellow dye absorb blue

The subtractive color-mixing process: The subtractive color-mixing process: plate 2bplate 2b


Structure and spectral sensitivity of Structure and spectral sensitivity of color filmcolor 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)

2.9 Processing color films2.9 Processing color films

Color negative filmsColor negative films• Negative-to-positive sequence

• Similar to B&W negative film

Color reversal filmsColor reversal films• Directly produce positive image

• Color slides

• Color diapositives, color positive transparencies

2.9 Processing color films (cont.)2.9 Processing color films (cont.)

Fig 2.22 : color reversal processFig 2.22 : color reversal process• Expose film

• First developer

• Re-expose to white light

• Color developer

• Bleach & fixer

• View image

2.10 Color infrared film2.10 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 filmColor infrared film• 3 emulsion layers

• 0.7~0.9 m

• False color

2.10 Color infrared film (cont.)2.10 Color infrared film (cont.)

Fig 2.23: Structure and sensitivity of Fig 2.23: Structure and sensitivity of color infrared filmcolor 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

2.10 Color infrared film (cont.)2.10 Color infrared film (cont.)

Camouflage detection (CD) filmCamouflage 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 TFig 2.25Plate 4

2.11 Filters2.11 Filters

FiltersFilters• 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 numberKodak Wratten filter number

2.11 Filters (cont.)2.11 Filters (cont.)

Absorption filterAbsorption 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 filterBandpass filter• Fig 2.28: typical transmittance curve for bandpass

filter.• Low pass absorption filters are not available!


Interference filters : reflect rather than Interference filters : reflect rather than absorbabsorb

Yellow filter Yellow filter panchromatic film panchromatic film reduce atmospheric hazereduce atmospheric haze

B&W filmB&W film• Yellow filter forestry

• Red or IR-only filter delineate water bodies


Antivignetting filters:Antivignetting filters:• Strongly absorbing in central area and

progressively transparent in circumferential area

• Usually built into other filters

Color-compensation filter Color-compensation filter agingaging Using filters Using filters increase exposureincrease exposure

• Filter factors

2.12 Aerial Cameras2.12 Aerial Cameras

Four basic types:Four basic types:

2.12.1 Single-Lens frame cameras2.12.1 Single-Lens frame cameras

Single-lens frame cameraSingle-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 : 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)

2.12.1 Single-Lens frame cameras 2.12.1 Single-Lens frame cameras (cont.)(cont.)

Principal components (Fig 2.31) Principal components (Fig 2.31) • Lens cone assembly

Lens bring light rays to focal planeFilterShutterDiaphragm

• Body• Magazine

Supply reelTake up reelFilm flattening mechanismFilm-advancing mechanism


Principal components (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 Fig 2.32: the modular nature of modern aerial mapping camera systemaerial mapping camera system

Fig 2.33: a vertical photograph (mapping Fig 2.33: a vertical photograph (mapping camera)camera)• Fiducial marks• Principal point


Large Format Camera (LFC) (NASA)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 m)• Fig 2.36• Fig 2.37• Fig 2.38


Metric Camera (ESA)Metric Camera (ESA) Reconnaissance camerasReconnaissance cameras

• Faithfully record details but not geometric fidelity

• Color-corrected lens high quality color photographs

2.12.2 Multi-lens Frame Cameras2.12.2 Multi-lens Frame Cameras

Multi-band photographsMulti-band photographsphotographs 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

2.12.2 Multi-lens Frame Cameras 2.12.2 Multi-lens Frame Cameras (cont.)(cont.)

Color additive viewersColor 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

2.12.2 Multi-lens Frame Cameras 2.12.2 Multi-lens Frame Cameras (cont.)(cont.)

Camera filter colorsCamera filter colors Viewer filter colorsViewer filter colors

• Positive transparency-viewer filter combinations

DIPDIP• Plate 12: six examples of Lansat TM data

Multi-band photography use arrays of Multi-band photography use arrays of several single-lens frame camerasseveral single-lens frame cameras

2.12.3 Strip Cameras2.12.3 Strip Cameras

Fig 2.44Fig 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 Designed and good for low altitude and high speed military reconnaissancehigh speed military reconnaissance• Permits obtainment of very detailed

photography

2.12.3 Strip Cameras (cont.)2.12.3 Strip Cameras (cont.)

Bad for high altitude and moderate Bad for high altitude and moderate speed speed distortiondistortion• Frame cameras improve in lens & image

motion compensation Strip Cameras have a very limited application.

2.12.4 Panoramic Cameras2.12.4 Panoramic Cameras

• Similar to strip cameras, but rotate the lens or a prism to cover ground areas (Fig 2.45)

Fig 2.46:Fig 2.46:• panoramic distortion and scan positional

distortion

2.12.4 Panoramic Cameras (cont.)2.12.4 Panoramic Cameras (cont.)

Optical bar cameraOptical 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


Pro Pro • broad and detailed view of the ground

Con Con • lack the geometric fidelity

• variations of atmospheric effect


Applications:Applications:• USFS (Plate 9)

Forest pest damage detection Plate 9Timber salvage operations

• EPAEnviro-Pod : one vertical camera + one forward-looking

cameraIndustrial pollutants

hazardous waste sites

emergency episodes

2.13 Electronic imaging2.13 Electronic imaging

Comparison between photographic and Comparison between photographic and electronic imaging (Table 2.2)electronic imaging (Table 2.2)• Charge-coupled devices (CCDs) wider range• Digital signal storage, process, transmit.

Kodak Professional DCS 200 digital cameraKodak Professional DCS 200 digital camera• Nikon camera body + Kodak camera back• 1524 x 1012 (9x9 m)• 1/8000 sec• 1.5 Million pixels• For 35 mm film 2.5~3 Million pixels• Fig 2.49, 2.50

2.13 Electronic imaging (cont.)2.13 Electronic imaging (cont.)

Airborne Data Acquisition and Registration Airborne Data Acquisition and Registration System 5000 (ADAR System 5000)System 5000 (ADAR System 5000)• A multi-spectral digital camera system (4 CCD

Sensors)• 0.012~0.3 m in band width• 739 x 478• 1/60 ~ 1/2000 sec• Ground resolution: 0.5~4m per pixel• GPS monitoring• Plate 6

2.13 Electronic imaging (cont.)2.13 Electronic imaging (cont.)

Pro:Pro:• Rapid turnaround time

Images are immediately available & computer-ready

• Higher exposure latitude

2.14 Video recording2.14 Video recording

Video recording Video recording standard analog standard analog television signals are recorded on magnetic television signals are recorded on magnetic tape or dislestape or disles• Can use various cameras• Follow NTSC RS-170 standard• Tape format: super-VHS, Hi-8, HDTV..etc.

Pros:Pros:• Real-time viewing & immediately available• Inexpensive media• Audio track• Recorded GPS information

2.14 Video recording (cont.)2.14 Video recording (cont.)

Cons:Cons:• Poor spatial resolution

• Expensive equipment

• Cumbersome to index or handle tapes

View:View:• VCR

• AD converter frame grabber


Applications Applications timeliness is required in timeliness is required in crop inventorying or disease detectioncrop 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


Applications Applications (cont.)(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 camerasFig 2.53 : example of 4 CCD array cameras Plate 7: example of video versus Plate 7: example of video versus

photographphotograph Still video camerasStill video cameras

• Widely used in photojournalism• No significant advantage for aerial imaging

2.15 Basic geometric characteristics 2.15 Basic geometric characteristics of aerial photographsof aerial photographs

OrientationOrientation• Vertical photographs rarely obtainable

• Tilted photographs

• Oblique photographsHigh image of the horizonLow

2.15 Basic geometric characteristics 2.15 Basic geometric characteristics of aerial photographs (cont.)of aerial photographs (cont.)

Taking vertical aerial photographsTaking vertical aerial photographs• Fig 2.55

• Flight lines (flight strips)

• nadir line

• Endlap at least 50% to ensure total stereoscopic coverage

• Stereoscopic coverage

• Stereopairs


Taking vertical 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)


Taking vertical aerial photographs Taking vertical aerial photographs (cont.) (cont.) • Sidelap at least 30%

• Block of photographs

• GPS navigation system control

• Index mosaic (Fig 2.59)


Scale of aerial photographsScale 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

D

dS

distance ground

distance photoscale photo


Scale 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

hH

f

H

f

terrainaboveheight flying

length focal cameraScale

avgavg hH

fS


Comparative geometry of map & vertical Comparative geometry of map & vertical aerial photographaerial photograph• Map orthographic projection map position• Vertical photograph perspective projection

relative horizontal (planimetric)positionsFig 2.61

• Relief displacement: tops of objects are always displaced from their bases, this distortion is hobject 1/H’ radial distance from the principal pointAerial photographs (not directly) map (chap 4)

• Ground coveragefn(camera format size, focal length, H’)Fig 2.62

2.16 Photographic resolution2.16 Photographic resolution

Spatial resolution:Spatial resolution:an expression of the optical quality of an image produced

by a particular camera system

• Influenced byResolving power of filmCamera lensUncompensated image motionAtmospheric conditionFilm processing condition

• Fig 2.63: resolving power test chart

2.16 Photographic resolution (cont.)2.16 Photographic resolution (cont.)

Resolving power of the film (lines/mm)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

2.16 Photographic resolution (cont.)2.16 Photographic resolution (cont.)

Modulation transfer functionModulation 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

resolution system

scale image of reciprocalGRD

2.17 Conclusion2.17 Conclusion

Aerial photographyAerial photography• Backbone of remote sensing

• Pros

• Cons & limitations

Trend Trend digital recordingdigital recording

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