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02principleofphotographyandimaging-181110150543

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Lecture 2: Principles of
Photography & Imaging
© 2019 Dr. Sarhat M Adam
BSc in civil Engineering
Msc in Geodetic Surveying
PhD in Engineering Surveying & Space Geodesy
Note – Figures and materials in the slides may be the authors own work or
extracted from internet websites, Materials by Duhok or Nottingham
universities staff and their slides, author's own knowledge, or various internet
image sources and books.
Introduction
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Photography, which means “drawing with light,”
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Idea originated long before cameras.
◼
Ancient Arab observed it in their tents.
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Children observe it in their childhood.
d1
Fig01
Introduction
◼
In 1700 , French artist used the idea in the figure for drawing
object.
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In 1839, the French Louis Daguerre made a pinhole box to capture
photograph without an artist.
◼
Many improvements have been made, but the basic principles of
image capturing remained essentially unchanged.
◼
The modern innovation technology of imaging is Digital Camera.
Fundamentals Optics
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Film and digital cameras have lens which depend upon optical
elements.
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Optics has two branches
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Physical Optics
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Lights travel through a transmitting
medium such as air in a series of
electromagnetic waves emanating
from a point source.
◼
Can be visualized as a group of
concentric circles expanding or
radiating away from a light source.
Fig02
Fundamentals Optics
◼
Light wave has frequency, amplitude, and wavelength.
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Frequency: number of waves pass a point in a unit of time.
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Amplitude: height of the crest or depth of the trough.
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Wavelength: distance of full cycle.
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V is velocity, in units m/s
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f: frequency, in cycles/s or hertz
Λ: wavelength, in m
Fig03
light moving at the rate of 2.99792458 × 108 (m/s) in a vacuum.
Fundamentals Optics
◼
Fig04
Bundle of rays emanating from a point source in accordance with
the concept of geometric optics.
Refraction of light rays
Fig05
• n & n′ are refractive index of the 1st & 2nd medium, respectively.
• Angles φ & φ′ are measured from the normal to the incident and
refracted rays, respectively.
Fundamentals Optics
◼
Light rays may change directions by reflection.
◼
When a light ray strikes a highly polished metal mirror, it is
reflected so that the angle of reflection φ′′ = incidence angle φ.
Fig06
(a) First-surface mirror demonstrating the angle of incidence φ and angle of refection
φ′′ (b) back-surfaced mirror.
Lenses
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Simple lens is optical glass with two or one spherical surface.
◼
To gather light rays and bring them to focus at opposite side.
◼
Act like tiny pinhole allows a single light ray from each object
point to pass.
◼
Tiny hole of diameter d1 of the pinhole camera illustrated in F
shape figure produces an inverted image of the object.
◼
When an object is illuminated, each point in the object reflects a
bundle of light rays.
◼
An infinite number of image points, focused in the image plane
Lenses
Fig07
Camera VS Eye
iris
retina
• The iris limits the amounts of light from entering our eyes.
• In camera is represented by diaphragm.
Lenses
◼
The optical axis line joining the centers of curvature of the
spherical surfaces of the lens (points O1 and O2).
◼
R1 and R2 are the radii of the lens Surfaces.
Rays parallel to OA come to focus at F (focal point of the lens).
f is the focal length (F to center of lens).
A plane perpendicular to the optical axis passing through the
focal point is called the plane of infinite focus.
◼
◼
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Fig08
Lenses
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A single ray of light traveling through air (n = 1.0003) enters a
convex glass lens (n′ = 1.52) having a radius of 5.00 centimeters
(cm), as shown in Figure. If the light ray is parallel to and 1.00
cm above the optical axis of the lens, what are the angles of
incidence ϕ and refraction ϕ′ for the air-to-glass interface?
Fig09
Lenses
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Answer
Fig10
Lenses
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Equation 1 defines the relationship between the object distance
(o), the focal length (f), and the image distance (i).
◼
The focal length is a characteristic of the thin lens, and it
specifics the distance at which parallel rays come to a focus.
---------- (1)
Fig11
Object distance=infinity
1/o too small for object at infinity so
Image distance = focal length
https://www.physicsclassroom.com/c
lass/refrn/Lesson-5/ConvergingLenses-Object-Image-Relations
Lenses
◼
Example
Find the image distance for an object distance of 50.0 m and a focal
length of 50.0 cm.
Solution
Thick Lenses
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Former assumption on lenses considered thickness negligible.
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With thick lenses, this assumption is no longer valid.
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Nodal points must be defined for thick lenses.
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Called incident nodal point and the emergent nodal point.
Fig13
Fig12
Aerial Camera with 15
unit lenses
Thick Lenses
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(f) of thick lens is the distance from N′ to this plane of infinite
focus.
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It is impossible for a single lens to produce a perfect image.
◼
Always be somewhat blurred and geometrically distorted.
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The imperfections called aberrations.
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Using of additional lens elements able to correct for aberrations.
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Lens distortions do not degrade image quality but deteriorate the
geometric quality (or positional accuracy) of the image.
◼
They are ether symmetric radial, or decentering.
◼
Both occur if light rays are bent, or change directions.
Lenses
◼
◼
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Angle formed between the camera’s lens and the width of area seen
on the photograph.
f = distance between lens &focal plane
Wide angle lenses (short f) excessively exaggerate displacement of
tall objects best for flat terrain
Single lens Camera
◼
Most important fundamental instrument in Photogrammetry.
◼
Geometry is depicted in fig01 and similar to that of pinhole, fig 07.
◼
The size of aperture (d2) is much larger than a pinhole.
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Object & image distances governed by the lens formula
◼
Pphotographing objects at great distances, the term 1/o approaches
zero and image distance i is then equal to f.
◼
In aerial photography, O is very great with respect to I, therefore
aerial cameras are manufactured with their focus fixed for infinity.
◼
This is accomplished by fixing image distance equal to the focal
length of the camera lens.
Fundamentals Optics
Illuminance
Fundamentals Optics
Shutter & Aperture
◼
illuminance and time of exposure unit is meter candle-seconds
◼
f-stop settings variation made by aperture which controlled by
Diaphragm.
◼
As the diameter of the aperture increases, enabling faster
exposures, DoF become less & lens distortion become more.
◼
To maximize DoF, slow shutter speed and large f-stop setting.
◼
To photograph rapid moving objects, a fast shutter speed is
essential.
◼
If aperture area is doubled, total exposure is doubled.
◼
If shutter time is halved and aperture area is doubled, total
exposure remains unchanged.
Fundamentals Optics
Shutter & Aperture
◼
◼
◼
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Nominal f-stop (1, 1.4, 2.0, 2.8, 4.0, 5.6, 8.0, 11, 16, 22, and 32).
The aperture diameter equals the lens focal length. (f/d)=1.0.
f-1.4 halves the aperture area from that of f-1.
Nominal f-stops listed previously halves the aperture area of the
preceding one.
Fundamentals Optics
Shutter & Aperture
Fundamentals Optics
Shutter & Aperture
Fundamentals Optics
Shutter & Aperture
◼
1.
2.
3.
4.
Digital Camera in addition to manual, has
Fully automatic mode, where both f-stop and shutter speed are
appropriately selected.
Aperture priority mode, where the user inputs a fixed f-stop and the
camera selects the appropriate shutter speed.
Shutter priority mode, where
the user inputs a fixed shutter
speed and the camera selects
the appropriate f-stop.
In “Program” mode, the
camera automatically chooses
the Aperture and the Shutter
Speed based on the amount of
light.
Fundamentals Optics
Shutter & Aperture
Fundamentals Optics
Example
Suppose that a photograph is optimally exposed with an fstop setting of f-4 and a shutter speed of 1/500 s. What is
the correct f-stop setting if shutter speed is changed to
1/1000s?
Solution
Total exposure is the product of diaphragm area and shutter
speed. This product must remain the same for the 1/1000 -s
shutter speed as it was for the 1/500-s shutter speed, or
A1time1=A2time2
◼
◼
Let d1 and d2 be diaphragm diameters for 1/500- and
1/1000 -s shutter times, respectively.
Fundamentals Optics
Example
◼
Then the respective diaphragm areas are
Fundamentals Optics
Digital Images
◼
◼
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Digital image is divided into a fine grid of “picture elements,”
or pixels.
Consists of an array of integers, referred to as digital
numbers (gray level, or degree of darkness).
many thousands or millions of these pixels available in one
image.
Numbers in the range 0 to 255
can be accommodated by 1 byte.
Each 1 byte consists of 8 binary
digits. or bits.
An 8-bit value can store 28, or
256, values.18*11=198 Bytes.
Fundamentals Optics
Digital Images
◼
Discrete sampling , a process in which digital image produced
◼
In this process, small image area (a pixel) is “sensed”
◼
◼
1.
To determine the amount of electromagnetic energy GSD
Discrete Sampling has two fundamental characteristics:
Geometric (Spatial) Resolution
◼
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Physical size of an individual pixel
Smaller pixel sizes corresponding to higher geometric resolution
160*160
80*80
40*40
20*20
10*10
Fundamentals Optics
Digital Images
2.
Radiometric Resolution
1.
Level of quantization
Discrete quantization levels are 256, 32, 8, and 2
8bits, 4bits, 3bits, and 1 bits.
2.
Spectral resolution
Digital Images
2. Spectral resolution
◼ Sun emits electromagnetic energy, entire range called electromagnetic
spectrum.
◼
◼
◼
Electromagnetic energy travels in sinusoidal oscillations called waves.
The velocity of electromagnetic energy in a vacuum is constant. C=Fƛ
Visible spectrum are very composed of only a very small portion.
Fundamentals Optics
Digital Images
2. Spectral resolution
Fundamentals Optics
Digital Images
Example
A 3000-row by 3000-column satellite image has three spectral channels.
If each pixel is represented by 8 bits (1 byte) per channel, how many
bytes of computer memory are required to store the image?
Fundamentals Optics
Lens resolution
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Resolution is important in
photogrammetry
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Resolution or resolving of lens
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Measures by two methods
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Lines/mm and MTF
Fundamentals Optics
Lens DoF
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Object distance that can be accommodated by a lens
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Without deterioration
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Aperture dependent.
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The shorter the focal
◼
The shorter the f, the greater its depth of field.
Camera inner parts
Aperture
Camera inner parts
Fundamentals Optics
two general classifications
1. Metric Camera
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Specifically for photogrammetric applications.
Have fiducial marks built into their focal planes.
Have calibrated CCD arrays, which enable accurate recovery of their
principal points.
Stably constructed and completely calibrated (f, p, &, lens distr. Can
be applied over long period.
Large format cameras (9”*9”)
2. Nonmetric Camera
◼
◼
For low accuracy requirements and budgets.
characterized by
◼
an adjustable principal distance, no film flattening or fiducial marks, lenses with
relatively large distortions, and lens distortion values vary with different focus
settings ((i.e., different principal distances).
Digital image Display
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The colour of any pixel can be represented by 3D coordinates in what is
known as BGR (or RGB) colour space.
If quantified as an 8-bit value, this range from 0 to 255 for R, G, and B.
Digital image Display
◼
◼
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The intensity-hue-saturation (IHS) system, on the other hand, is more
readily understood by humans.
cylindrical coordinates in which the height, angle, and radius represent
intensity, hue, & saturation, respectively.
Axis of the cylinder is the grey line, extends from origin to max RGB.
Digital image Display
◼
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Intensity = brightness & hue = the specific mixture of wavelengths that
define the colour & saturation = the boldness of the colour.
Hue
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