PowerPoint Presentation
Let’s say we have a sensor…
digital sensor (CCD or CMOS)
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Slide by Ioannis Gkioulekas
… and an object we like to photograph
digital sensor (CCD or CMOS)
real-world object
What would an image taken like this look like?
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Bare-sensor imaging
digital sensor (CCD or CMOS)
real-world object
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Slide by Ioannis Gkioulekas
Bare-sensor imaging
digital sensor (CCD or CMOS)
real-world object
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Slide by Ioannis Gkioulekas
Bare-sensor imaging
digital sensor (CCD or CMOS)
real-world object
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Slide by Ioannis Gkioulekas
Bare-sensor imaging
digital sensor (CCD or CMOS)
real-world object
All scene points contribute to all sensor pixels
What does the image on the sensor look like?
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Slide by Ioannis Gkioulekas
Bare-sensor imaging
All scene points contribute to all sensor pixels
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Slide by Ioannis Gkioulekas
What can we do to make our image look better?
digital sensor (CCD or CMOS)
real-world object
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Slide by Ioannis Gkioulekas
Let’s add something to this scene
digital sensor (CCD or CMOS)
real-world object
barrier (diaphragm)
pinhole (aperture)
What would an image taken like this look like?
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Slide by Ioannis Gkioulekas
Pinhole imaging
digital sensor (CCD or CMOS)
real-world object
most rays are blocked
one makes it through
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Slide by Ioannis Gkioulekas
Pinhole imaging
digital sensor (CCD or CMOS)
real-world object
most rays are blocked
one makes it through
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Slide by Ioannis Gkioulekas
Pinhole imaging
digital sensor (CCD or CMOS)
real-world object
Each scene point contributes to only one sensor pixel
What does the image on the sensor look like?
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Slide by Ioannis Gkioulekas
Pinhole imaging
real-world object
copy of real-world object (inverted and scaled)
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Slide by Ioannis Gkioulekas
Pinhole camera a.k.a. camera obscura
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Slide by Ioannis Gkioulekas
Chinese philosopher Mozi
(470 to 390 BC)
First mention …
First camera …
Greek philosopher Aristotle
(384 to 322 BC)
Pinhole camera a.k.a. camera obscura
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Slide by Ioannis Gkioulekas
Pinhole camera terms
digital sensor (CCD or CMOS)
real-world object
barrier (diaphragm)
pinhole (aperture)
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Slide by Ioannis Gkioulekas
Pinhole camera terms
digital sensor (CCD or CMOS)
real-world object
barrier (diaphragm)
pinhole (aperture)
image plane
camera center (center of projection)
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Slide by Ioannis Gkioulekas
Focal length
real-world object
focal length f
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Slide by Ioannis Gkioulekas
Focal length
real-world object
focal length 0.5 f
What happens as we change the focal length?
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Slide by Ioannis Gkioulekas
Focal length
real-world object
focal length 0.5 f
What happens as we change the focal length?
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Slide by Ioannis Gkioulekas
Focal length
real-world object
focal length 0.5 f
What happens as we change the focal length?
object projection is half the size
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Slide by Ioannis Gkioulekas
Pinhole size
real-world object
pinhole diameter
Ideal pinhole has infinitesimally small size
In practice that is impossible.
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Slide by Ioannis Gkioulekas
Pinhole size
real-world object
pinhole diameter
What happens as we change the pinhole diameter?
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Slide by Ioannis Gkioulekas
Pinhole size
real-world object
What happens as we change the pinhole diameter?
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Slide by Ioannis Gkioulekas
Pinhole size
real-world object
What happens as we change the pinhole diameter?
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Slide by Ioannis Gkioulekas
Pinhole size
real-world object
What happens as we change the pinhole diameter?
object projection becomes blurrier
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Slide by Ioannis Gkioulekas
Pinhole size
real-world object
What happens as we change the pinhole diameter?
pinhole diameter
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Slide by Ioannis Gkioulekas
What about light efficiency?
real-world object
pinhole diameter
focal length f
What is the effect of doubling the pinhole diameter?
What is the effect of doubling the focal length?
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Slide by Ioannis Gkioulekas
What about light efficiency?
real-world object
pinhole diameter
focal length f
2x pinhole diameter → 4x light
2x focal length → ¼x light
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Slide by Ioannis Gkioulekas
Some terminology notes
real-world object
pinhole diameter
focal length f
The “f-number” is the ratio: focal length / pinhole diameter
A “stop” is a change in camera settings that changes amount of light by a factor of 2
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Slide by Ioannis Gkioulekas
What does this image say about the world outside?
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Slide by Ioannis Gkioulekas
Accidental pinhole camera
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Accidental pinhole camera
window is an aperture
projected pattern on the wall
window with smaller gap
upside down
view outside window
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Pinhole camera trade-off
Small (ideal) pinhole:
Image is sharp.
Signal-to-noise ratio is low.
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Slide by Ioannis Gkioulekas
Pinhole camera trade-off
Large pinhole:
Image is blurry.
Signal-to-noise ratio is high.
Can we get best of both worlds?
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Slide by Ioannis Gkioulekas
Almost, by using lenses
Lenses map “bundles” of rays from points on the scene to the sensor.
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Slide by Ioannis Gkioulekas
Free lunch?
Do we lose anything by using a lens?
By using a lens we simultaneously achieve:
Image is sharp.
Signal-to-noise ratio is high.
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Slide by Ioannis Gkioulekas
Defocus
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Slide by Ioannis Gkioulekas
Defocus
objects at a one depth are in focus
objects at all other depths are out of focus
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Slide by Ioannis Gkioulekas
Defocus
objects at one depth are in focus
objects at all other depths are out of focus
circle of confusion (i.e., blur kernel)
Is the circle of confusion constant?
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Slide by Ioannis Gkioulekas
Defocus
objects at one depth are in focus
objects at all other depths are out of focus
circle of confusion (i.e., blur kernel)
How do we change the depth where objects are in focus?
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Slide by Ioannis Gkioulekas
Change of focus for different depths
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Slide by Ioannis Gkioulekas
Beyond Pinholes: Real apertures
Bokeh:
[Rushif – Wikipedia]
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Slide by Ioannis Gkioulekas
Tested.com – https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwjY8a-HoaTSAhVq4YMKHbH3BD0QjhwIBQ&url=http%3A%2F%2Fwww.tested.com%2Ftech%2Fphotography%2F2286-how-your-dslr-camera-lens-aperture-really-works%2F&psig=AFQjCNFN6iKuCOI_uXqBCJEUOudwIPcnMA&ust=1487871868729071
https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwjqtK-toaTSAhUl3YMKHXUZDDsQjhwIBQ&url=http%3A%2F%2Fphotographybyethanparker.com%2Fwordpress%2Ftag%2Fhow-we-see&bvm=bv.147448319,d.amc&psig=AFQjCNHZFgp7e3l2x271qKfospDKWgybvQ&ust=1487871976187207
https://en.wikipedia.org/wiki/Bokeh#/media/File:Christmas_Tree_Lights_Bokeh.jpg
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Eclipse pinhole cameras!
[PetaPixel; https://petapixel.com/2012/05/21/crescent-shaped-projections-through-tree-leaves-during-the-solar-eclipse/
http://www.mreclipse.com/SEphoto/TSE2006/TSE2006galleryA.html]
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So why don’t we see this all the time?
We do, it’s just that the scene being imaged (the sun) is a less distinct shape.
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Eclipse pinhole cameras!
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Aperture shape
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What happens as you take a closer look?
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Slide by Ioannis Gkioulekas
Field of View (Zoom)
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Field of View (Zoom) = Cropping
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f
FOV depends of Focal Length
Smaller FOV = larger Focal Length
f
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From Zisserman & Hartley
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Field of View / Focal Length
Large FOV, small f
Camera close to car
Small FOV, large f
Camera far from the car
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Perspective
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The pinhole camera
real-world object
camera center
image plane
focal length f
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Slide by Ioannis Gkioulekas
The (rearranged) pinhole camera
real-world object
image plane
focal length f
camera center
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Slide by Ioannis Gkioulekas
The 2D view of the (rearranged) pinhole camera
What is the equation for image coordinate x in terms of X?
image plane
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Slide by Ioannis Gkioulekas
The 2D view of the (rearranged) pinhole camera
image plane
magnification changes with depth
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Slide by Ioannis Gkioulekas
Forced perspective
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The Ames room illusion
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The Ames room illusion
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Magnification depends on depth
real-world object
What happens as we change the focal length?
depth Z
depth 2 Z
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Slide by Ioannis Gkioulekas
Magnification depends on focal length
real-world object
focal length f
focal length 2 f
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Slide by Ioannis Gkioulekas
What if…
real-world object
focal length f
focal length 2 f
Set focal length to half
depth 2 Z
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Slide by Ioannis Gkioulekas
What if…
real-world object
Set focal length to half
Set depth to half
depth Z
focal length f
Is this the same image as the one I had at focal length 2f and distance 2Z?
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Slide by Ioannis Gkioulekas
Perspective distortion
long focal length
short focal length
mid focal length
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Perspective distortion
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Shutters
[The Slo-Mo Guys]
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Shutters
[The Slo-Mo Guys]
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Shutters
[The Slo-Mo Guys]
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Sensors: Rolling shutter vs. global shutter
[Reddit – r/educationalgifs – u/Mass1m01973]
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