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High-performance imaging using dense arrays of cameras

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yields perspective flyarounds and focal stacks from a single ... Canon 20D digital camera. ordinary microscope. light field microscope. 200 . 2006 Marc Levoy ... – PowerPoint PPT presentation

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Title: High-performance imaging using dense arrays of cameras


1
Light field microscopy
Marc Levoy, Ren Ng, Andrew Adams Matthew
Footer, Mark Horowitz
Stanford Computer Graphics Laboratory
2
Executive summary
  • captures the 4D light field inside a microscope
  • yields perspective flyarounds and focal stacks
    from a single snapshot, but at lower spatial
    resolution
  • focal stack ? deconvolution microscopy ? volume
    data

3
Devices for recording light fields
(using geometrical optics)
  • handheld camera Buehler 2001
  • camera gantry Stanford 2002
  • array of cameras Wilburn 2005
  • plenoptic camera Ng 2005
  • light field microscope (this paper)

4
Light fields at micron scales
  • wave optics must be considered
  • diffraction limits the spatial angular
    resolution
  • most objects are no longer opaque
  • each pixel is a line integral through the object
  • of attenuation
  • or emission
  • can reconstruct 3D structure from these integrals
  • tomography
  • 3D deconvolution

5
Conventional versus plenoptic camera
6
Conventional versus plenoptic camera
7

8
Digital refocusing
S
  • refocusing summing windows extracted from
    several microlenses

9
Example of digital refocusing
10
Refocusing portraits
11
Macrophotography
12
Digitally moving the observer
S
S
  • moving the observer moving the window we
    extract from the microlenses

13
Example of moving the observer
14
Moving backward and forward
15
A light field microscope (LFM)
eyepiece
intermediate image plane
objective
specimen
16
A light field microscope (LFM)
  • 40x / 0.95NA objective
  • ?
  • 0.26µ spot on specimen 40x 10.4µ on sensor
  • ?
  • 2400 spots over 25mm field
  • 1252-micron microlenses
  • ?
  • 200 200 microlenses with12 12 spots per
    microlens

sensor
eyepiece
intermediate image plane
objective
specimen
? reduced lateral resolution on specimen
0.26µ 12 spots 3.1µ
17
A light field microscope (LFM)
sensor
18
Example light field micrograph
  • orange fluorescent crayon
  • mercury-arc source blue dichroic filter
  • 16x / 0.5NA (dry) objective
  • f/20 microlens array
  • 65mm f/2.8 macro lens at 11
  • Canon 20D digital camera

200µ
ordinary microscope
light field microscope
19
The geometry of the light fieldin a microscope
  • microscopes make orthographic views
  • translating the stage in X or Y provides no
    parallax on the specimen
  • out-of-plane features dont shift position when
    they come into focus

objective lenses are telecentric
20
Panning and focusing
panning sequence
focal stack
21
Mouse embryo lung(16x / 0.5NA water immersion)
200µ
pan
focal stack
light field
22
Axial resolution(a.k.a. depth of field)
  • wave term geometrical optics term
  • ordinary microscope (16x/0.4NA (dry), e 0)
  • with microlens array (e 125µ)
  • stopped down to one pixel per microlens

? number of slices in focal stack 12
23
3D reconstruction
  • confocal scanning Minsky 1957
  • shape-from-focus Nayar 1990
  • deconvolution microscopy Agard 1984
  • 4D light field ? digital refocusing ?3D focal
    stack ? deconvolution microscopy ?3D volume
    data

24
3D deconvolution
McNally 1999
focus stack of a point in 3-space is the 3D PSF
of that imaging system
  • object PSF ? focus stack
  • ? object ? PSF ? ? focus stack
  • ? focus stack ? ? PSF ? ? object
  • spectrum contains zeros, due to missing rays
  • imaging noise is amplified by division by zeros
  • reduce by regularization, e.g. smoothing

25
Silkworm mouth(40x / 1.3NA oil immersion)
100µ
slice of focal stack
slice of volume
volume rendering
26
Insect legs(16x / 0.4NA dry)
200µ
27
3D reconstruction (revisited)
  • 4D light field ? digital refocusing ?3D focal
    stack ? deconvolution microscopy ?3D volume
    data
  • 4D light field ? tomographic reconstruction
    ?3D volume data

28
Implications of this equivalence
  • light fields of minimally scattering volumes
    contain only 3D worth of information, not 4D
  • the extra dimension serves to reduce noise, but
    could be re-purposed?

29
Conclusions
  • captures 3D structure of microscopic objects in a
    single snapshot, and at a single instant in time

Calcium fluorescent imaging of zebrafish larvae
optic tectum during changing visual stimula
30
Conclusions
  • captures 3D structure of microscopic objects in a
    single snapshot, and at a single instant in time
  • but...
  • sacrifices spatial resolution to obtain control
    over viewpoint and focus
  • 3D reconstruction fails if specimen is too thick
    or too opaque

31
Future work
  • extending the field of view by correcting
    digitally for objective aberrations

32
Future work
  • extending the field of view by correcting
    digitally for objective aberrations
  • microlenses in the illumination path
  • ? an imaging microscope scatterometer

angular dependence of reflection from single
squid iridophore
33
http//graphics.stanford.edu/projects/lfmicroscope
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