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16421: Vision Sensors

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Wean 5312, T-R 1:30pm 3:00pm. High Dynamic Range Imaging. and Tone Mapping ... Images taken with a fish-eye lens of the sky show the wide range of brightnesses. ... – PowerPoint PPT presentation

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Title: 16421: Vision Sensors


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16421 Vision Sensors
  • Lecture 7 High Dynamic Range Imaging
  • Instructor S. Narasimhan
  • Wean 5312, T-R 130pm 300pm

2
  • High Dynamic Range Imaging
  • and Tone Mapping

3
Paul Debevecs SIGGRAPH Course
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The Problem of Dynamic Range
  • Dynamic Range Range of brightness values
    measurable with a camera

(Hood 1986)
  • Todays Cameras Limited Dynamic Range

High Exposure Image
Low Exposure Image
  • We need about 5-10 million values to store all
    brightnesses around us.
  • But, typical 8-bit cameras provide only 256
    values!!

11
High Dynamic Range Imaging
  • Capture a lot of images with different exposure
    settings.
  • Apply radiometric calibration to each camera.
  • Combine the calibrated images (for example,
    using averaging weighted by exposures).

(Mitsunaga)
(Debevec)
Images taken with a fish-eye lens of the sky show
the wide range of brightnesses.
12
Relationship between Scene and Image Brightness
  • Before light hits the image plane

Scene Radiance L
Image Irradiance E
Lens
Scene
Linear Mapping!
  • After light hits the image plane

Camera Electronics
Image Irradiance E
Measured Pixel Values, I
Non-linear Mapping!
Can we go from measured pixel value, I, to
scene radiance, L?
13
Radiometric Calibration
  • Important preprocessing step for many vision and
    graphics algorithms such as
  • photometric stereo, invariants, de-weathering,
    inverse rendering, image based rendering, etc.
  • Use a color chart with precisely known
    reflectances.

255
?
Pixel Values
g
0
?
0
1
3.1
9.0
19.8
36.2
59.1
90
Irradiance const Reflectance
  • Use more camera exposures to fill up the curve.
  • Method assumes constant lighting on all patches
    and works best when source is
  • far away (example sunlight).
  • Unique inverse exists because g is monotonic and
    smooth for all cameras.

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Greg Ward
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Greg Ward
Greg Ward
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