Author: Wei-Sheng Liao

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Author Wei-Sheng Liao 0922-769-851 R91049_at_csie.nt
u.edu.tw Presenter Wei-Cheng Lin 0912-808-362 r97
944028_at_ntu.edu.tw
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Classify Traditional Cameras

• By films120 camera?135 camera
• By the path between the imaging and the
  viewfinderSingle Lens Reflex?Twin Lens Reflex

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120 Camera

• Use 120 film or 220 film
• 120 film can take 12 pictures, and 220 film can
  take 24 pictures.
• Each frame has the length 6 cm and variant width

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135 Camera (35mm Camera)

• Use 135 film
• General people use this camera
• 135 film can take 36 pictures.
• Each frame has the length 24 mm and the width 36
  mm

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Why we need so big film?

• Get better resolution
• For instance
• If we enlarge a picture of the 135 film to
  10x15, the length and width of it will be 10
  times larger. In the enlarged picture we will
  find obvious pellets. If we enlarge a picture of
  the 6 cm x 6 cm frame of 120 film to 10x10, the
  length and width of it will be 4.23 times larger.
  The pellets will be less obvious.

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Single Lens Reflex (SLR)

• The paths of imaging and viewing are the same
• This camera is usually able to change lenses, and
  some of them are able to change film boxes

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Single Lens Reflex (continue)
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Twin-Lens Reflex (TLR)

• The paths of imaging and viewing are different
• That is the main distinction between TLR and SLR
• Because of the difference, this camera has
  parallax
• Most of these camera are not able to change
  lenses and film boxes

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Twin-Lens Reflex (continue)
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Parallax

• The positions of the viewfinder and the lenses
  are different, so what can be seen in them are
  different
• Only in TLR, not in SLR
• The distance of object is nearer, the phenomenon
  is more obvious
• In viewfinder, there are emending parallax frame

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Parallax (continue)
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Shutter

• The longer of the opening time, the more amount
  of light.
• Two types
• Leaf Shutter
• Focal Plane Shutter

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Leaf Shutter

• This consists of many blades.
• This may be placed at the inside, or the front or
  the back of the lenses

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Focal Plane Shutter

• This consists of two planes.
• This moves vertically or horizontally.
• This is placed at the front of the film.

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Focus Plane Shutter with Flash
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Depth of Field (DOF)

• If a camera is focused at a specific distance,
  only objects at that exact distance will be
  completely sharp.
• In fact, areas in front of and behind the point
  of focus may be acceptably sharp.
• Depth of field is as the range of distance in
  front of the camera that is in sharp focus.

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Depth of Field (continue)
1/3 in front of and 2/3 behind the point of focus
are acceptably sharp
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Advanced Discussion 1

• Now focal plane is placed at yellow 2
• Imaging at position yellow 1 or 3 will be blurred

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Advanced Discussion 2

• The capability of human eyes to differentiate
  the measure of a color area is limit.
• When the length or width of a area is smaller
  than 0.00357 (1/2800) inch, human eyes will feel
  that is a point.

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The Factor of Depth of Field

• Aperture
• Focal length
• Distance of object

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Aperture
The aperture is larger, the DOF is shorter.
The aperture is smaller, the DOF is longer.
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The Reason

• When the aperture becomes smaller, some light
  will not go through.
• The measure of the area will become smaller.

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Focal Length
Telephoto lenses
Wide-angle lenses
The focal length is longer, the DOF is shorter.
The focal length is shorter, the DOF is longer.
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The Reason
Focal length is shorter.
Focal length is longer.
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Distance of Object
The distance of object is longer, the DOF is
longer.
The distance of object is shorter, the DOF is
shorter.
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The Reason
The distance of the object is shorter
The distance of the object is larger
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Example of DOF
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The Formula of Depth of Field
First, we find hyperfocal distance
f the focal length of lenses A aperture
value c circle of confusion
The formula of depth of field is as following
f the focal length of lenses h hyperfocal
distance s the distance of object
In fact, we can go to following webs to download
programs to help us calculate the depth of
field 1 http//www.tangentsoft.net/ 2
http//www.geocities.com/capecanaveral/Lab/9176/su
mbang.html
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Hyperfocal Distance

• If you focus your lens at its hyperfocal distance
  you will get the greatest depth of field.
• Focus your lens at infinity and the leading edge
  of the area that is in focus is the hyperfocal
  point for that lens.
• Focus on that point instead of infinity and you
  will have the greatest range of focus infinity
  back toward your location

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F-stop

f-stop 1 1 1.4 2 2.8 4 5.6 8 11 16
aperture diameter larger ? ? ? larger ? ? ? larger ? ? ? larger ? ? ? larger ? ? ? ? ? ? smaller ? ? ? smaller ? ? ? smaller ? ? ? smaller ? ? ? smaller ? ? ? smaller
picture brightness picture brightness brighter ? ? ? brighter ? ? ? brighter ? ? ? brighter ? ? ? ? ? ? darker ? ? ? darker ? ? ? darker ? ? ? darker ? ? ? darker ? ? ? darker
condition indoor ? ? ? indoor ? ? ? indoor ? ? ? indoor ? ? ? indoor ? ? ? ? ? ? outdoor ? ? ? outdoor ? ? ? outdoor ? ? ? outdoor ? ? ? outdoor ? ? ? outdoor
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(Hyperfocal Distance)
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Circle of Confusion

• Imagine a perfect white point in an empty black
  room. The point has no height, and no width. If
  you focus an optically perfect lens on that
  point, it forms a perfect point on the film as
  well. If, however, you focus slightly in front of
  or behind the point, the point will image on the
  film as a small blurry circle. If that circle is
  small enough, it will still look like a point
  when enlarged for printing. The "circle of
  confusion" is typically calculated as the largest
  on-film circle that you see as a point.
• When you make an 8 12 print and view it from a
  "normal" viewing distance, typically 2-3 feet.
  Anything larger is seen as a small circle, and is
  therefore perceived as out of focus.

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(continue)

• By the formula of Zeiss, CoC d/1730, where d is
  the length of the diagonal line of the film
• When the film is 24X36mm, the diagonal line is
  43.94mm, CoC is equal 25.4um (43.94 mm / 1730)

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Why Focus?

• We want to take sharp pictures.
• Blurred images are loathsome.
• The only way to take sharp pictures is focus.

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Why Is the Picture Blurred?

• Vibration of the camera
• Object moves suddenly
• Choose the wrong object to focus

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The Hair Move
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Choose The Wrong Object
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A Simple Focus Model for Reference Purposes

• The picture below models a simple optic system.
• v distance from lens to focused image plane
• s distance from lens to current image plane
• p focused image point
• P the blurred image point
• d distance between the focused and current
  image planes s-v
• D height of lens

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(continue)

• R radius of blur (we want to calculate this
  value, and minimize it)
• R is minimized as the focused and current image
  planes come closer and closer to coinciding.
• R (s-v)D / (2v) dD / (2v)

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(continue)

• When the blur radius is less than 0.4 pixels, the
  blurred and focused images are difficult to
  distinguish.

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What Are Focus Measures?

• Focus measures are the algorithms by which we
  determine when an image is "focused.
• Large amplitude difference in focus measure
• The focus measure should vary greatly between
  the point of the true focus plane and the various
  defocused plane.
• Minimum computational complexity
• Speed and easy implementation
• General applicability
• Algorithm should not be limited to only
  special types of images.

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Focus Formula

• a ) Absolute gradient
• b ) Threshold absolute gradient
• c ) Squared gradient

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Focus Formula (continue)

• d) Laplacian
• e) Threshold video signal content
• f) Threshold video signal pixel count

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Focus Formula (continue)

• g) Signal power
• h) Standard deviation
• Normalized standard deviation
• Divide the equation for h) by the mean of
  g(i,j). Division by the mean compensates for
  changes in the average image brightness.

Larger standard deviation higher contrast
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Focus Formula (continue)

• j) Absolute variation
• k) Normalized absolute variation
• Divide the equation for j) by the mean of
  g(i,j).

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Image 1

• Characteristics Low mean brightness corresponds
  to taking photos at low illumination (e.g. at
  night).

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Image 2

• Correspond to taking a photo at normal (brighter)
  condition.

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Image 3

• Characteristics High mean brightness. Correspond
  to taking photos at high illumination (e.g.
  bright daylight)

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Conclusions

• See results of algorithms
• Laplacian is the best algorithm.
• Its drawback is Computational Complexity.
• The solution is Two-stage auto-focus algorithm-
  use Absolute Gradient Method to locate the range
  of focus point before implementing second order
  difference filter method to fine-tune.

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Experiment
1
2
3
4
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Experiment (continue)
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5
7
8
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Our Experiments
Zoom0
Zoom500
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Result 1 (Zoom0)
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Result 2 (Zoom500)
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Focus Screen

• Light through the lens is projected to focus
  screen. People focus by it.
• The disadvantage is in darker situation, we can
  not focus well. We need a lightening device.

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Focus Screen Example
Before focusing
After focusing
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Rangefinder

• When focusing, you only combine the upper and
  lower images such that the two images looked like
  one image by the focusing ring.
• The advantage is even in a darker situation, we
  can focus well.

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Rangefinder Example
S Object
Before focusing
After focusing
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Canon Image Stabilizer System

• With two vibrating gyroscopes to detect vertical
  and horizontal movements, the camera shake is
  detected.
• The corrective optical system is moved in
  parallel with the film plane in accordance with
  the amount of the camera shake, and the light is
  refracted in the appropriate direction to cancel
  the image vibration.
• The correcting effect is about 2 steps in terms
  of shutter speed. With a lens of 300mm focal
  length, the camera shake can be prevented in even
  1/60 second.
• PS It is generally said that a yardstick for
  the shutter speed capable of preventing camera
  shake is a minimum 1 second/focal length of the
  lens.
• The image stabilizer system is effective not only
  for a stationary subject, but also for panning a
  moving subject.

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The Picture of Image Stabilizer System





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Autofocus versus Expert Manual Focus

• Speed AF lt MF
• Convenience AF gt MF
• Result AF lt MF
• Manual focus is not easy.

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Multi-CAM1300Autofocus Sensor Module

• This module incorporates five AF sensors that
  together create a large Wide-Cross Array covering
  the center, left, right, top, and bottom of the
  frame.

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Canon Area AF System

• 45 distance measuring points are arranged
  vertically and horizontally.
• Although the conventional five-point AF
  incorporated five pairs of AF diaphragms to
  correspond to each distance measuring point, it
  was structurally impossible to provide 45 pairs
  of AF diaphragms in the same way
• Use the property of the ellipse

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Viewfinder

• It relieves the batteries of the camera from the
  heavy drain of the LCD screen
• Separate from the lens, commonly referred to as
  an Optical Viewfinder (Direct Viewfinder)
• Through The Lens, commonly referred to as a TTL
  (Through The Lens) Viewfinder
• Electronic Viewfinder, also called an Eye-level
  LCD viewfinder

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The Optical Viewfinder
Parallax error occurs because the lens of the
camera and the viewfinder see the subject from a
slightly different position. Over a long distance
the error is hard to detect but over short
distances, such as when photographing portraits
or macros, the difference in the perspective
becomes magnified and can enormously affect the
composition of a photo. This is why many digital
cameras compensate by turning on the LCD screen
when the macro function is used. The screen shows
the image the sensor is receiving and avoids the
parallax error.
Optical viewfinders cannot display 100 of the
image that will be captured and are commonly
limited to around 85 or less of the actual
frame. This is why TTL (through the lens)
viewfinders were developed.
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The Optical TTL Viewfinder
The different systems used to show the image
originating from the lens vary in their details,
but they generally reflect, or split, the light
coming through the lens and direct some, or all
of it to the viewfinder while the image is being
composed.
The disadvantage of TTL viewfinders is that they
are more expensive to build because of their
complexity. This is why they are more commonly
found on high-end and professional digital
cameras. Furthermore, they commonly require a
small LCD display to indicate focusing and
exposure, adding to their cost.
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The Electronic Viewfinder
The advantages of this type of viewfinder are the
same as for the optical version they show
exactly what will be captured, they are visible
in daylight (by virtue of being recessed behind
an eyecup), indicate aperture, shutter speed,
etc. but, in addition, they can also display the
camera menussomething optical viewfinders cannot
do.
The disadvantages of electronic viewfinders can
be summarized in 3 points they require power
(unlike the optical, or optical TTL viewfinders)
show an overly bright view, just like LCD
screens and are quite coarse in comparison to
optical systems. The latter point may be of
greater importance since these systemsto
dateare unable to show the smaller details in
the frame for instance whether someone's eyes
are open, or partially closed.
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Reference

• Canon Web-Technology
• (http//www.canon.com/technology/optics/index.html
  )
• http//content.edu.tw/vocation/art/ks_hc/htm/conte
  nt/ch17/
• http//www.nikon-image.com/eng/35mm/f100/Product_D
  etails/Features/Autofocus/index.html

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End

• My presentation ends.
• Any question?
• Thanks for everyone!!