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Remote Sensing
Topic 2: Photographic PrinciplesChapter 2: Avery and Berlin
Chapter 2: Lillesand and Keifer
Six Advantages of Aerial Photography Over Ground Observation
Basic B/W Film Photography
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A Simple Camera
1/f = 1/o + 1/i
f = focal length of the camera o = object distancei = image distance note: when o is v.big i = f
ExposureExposure (E) at any point in a photograph is dependent on:
E = sd2t / 4f2
where: s = scene brightness d = diametert= time/shutter speed f = focal length
So how do we control the range of exposure?Diameter of the lens opening (d) is adjusted by setting the aperture or f-stop = f / d
E = st / 4F2
Shorter exposure times prevent blurring/image motion, but require high speed films (grainier)Longer exposure times allow more light, so slower (crisper) films can be used, but may result in blurring
Extraneous EffectsExposure falloff is the result of :
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Effect of Exposure Falloff
Film Density Measurements Film density is a measure of ?
Determined using a _________________?
What are measure of film density used for?
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Characteristic Curves - Contrast
Characteristic Curves - Resolution
Low ContrastLow Slope ()Poorer Radiometric Resolution
High ContrastHigh Slope ()Better Radiometric Resolution
Characteristic Curves – Exp. Lat.
Low Exposure Latitude
High Exposure Latitude
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Characteristic Curves – Film Speed
Slow FilmMore ExposureBetter Spatial Resolution
Fast FilmLess ExposurePoorer Spatial Resolution
B/W Panchromatic Films
B/W Infrared Films
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Panchromatic vs. Infrared Photo
Colour Aerial Films
What are the advantages of colour photography?
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Colour TheoryR, G, B are additive primaries
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Colour TheoryYellow, magenta, and cyan are subtractive primaries
Colour TheoryComplimentary colours are those that produce white light when combined
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How Colour Film WorksColour film is based on the principles of subtractive primary coloursYellow, magenta, and cyan dyes are used to filter differing proportions of blue, green, and red lightThe dyes are introduced into different layers of colour film each containing silver halide crystals modified by organic molecules known as spectral sensitizers The subtractive primaries are used to control the relative proportions of additive primaries reflected back to our eye
How Colour Film WorksWhen developed, yellow, magenta, and cyan dyes are introduced inversely proportional to the amount of blue, green, and red light reflected
Spectral Sensitivity
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How Colour IR Film WorksAssignment of dyes to an emulsion layer is arbitrary
Colour infrared films have same dyes assigned to different portion of EMS
Also called false colour film
Spectral Sensitivity
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How Colour IR Film WorksBlue wavelengths are filtered out of incoming light using a filter placed in front of the camera lensNear infrared cyan dye - controls red reflectance to our eyeRed magenta dye - controls green reflectance to our eyeGreen yellow dye - controls blue reflectance to our eye
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FiltersMade of glass or gelatin
Wavelength selectors
Example yellow filter absorbs blue wavelengths allows green and red to pass through commonly used to reduce haze
High vs. low pass
Reduces exposure, so adjustments necessary
Aerial CamerasWide variety can be used
Hand-held 35 mm SLR camerasHand-held digital camerasSingle lens frame camerasMulti-lens frame cameraStrip CameraPanoramic CameraAnalog and digital video recorders
Single Lens Frame Camera
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Single Lens Frame Camera
Standard 9 in. Vertical Photo
Level
Clock
Altimeter
Number of CameraNumber of PhotoFocal Length
A18658 - 138
Multi-Lens Frame Camera
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Strip Camera
Panoramic Camera
Digital ImagingUtilize an rectangular array of solid-state detectors; either CCDs or CMOSSize of array (# photosites or pixels) determines image resolution
Advantages:Increased spectral and radiometric resolutionAbility to digitally process/analyze imageryLinear response to incident energyCan record GPS positionGreater storage capacity
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Digital ImagingPhotosites are actually colour blindFilter are used to control λdetected at each photositeCalled a Bayer mask
in each 4x4 pixel area 2 green, one red, one blue
Interpolation algorithim is used to fill in the resulting checker board pattern with missing colours
Bayer Mask
Large Format Digital Aerial CamerasGyro- stabilized, computer controlled IMCEight-camera system, 12 bit radiometric res.Four panchromatic bands mosaicked into 14,000 x 8000 (112 Mega pixel) imageOther 4 bands are B, G, R, and NIR at 3000 x 2000 (6 M pixel)