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Wavelengths and Colors

Ankit MohanMAS.131/531 Fall 2009

Epsilon over time (Multiple photos)

Prokudin-Gorskii, Sergei Mikhailovich, 1863-1944, photographer.

Congress.

Epsilon over time (Bracketing)

Color wheel used in DLP projectors

Image courtesy of shannonpatrick17 on Flickr.

Epsilon over sensors

3CCD imaging system for color capture

Images: Left © Wikipedia User:Cburnett. Upper right © Wikipedia User:Xingbo.License CC BY-SA. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse.Lower right, public domain image by Dick Lyons.

Epsilon over pixelsBayer Mosaicing for color capture

Images: Wikipedia. © Wikipedia User:Cburnett.License CC BY-SA. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse.

Demosaicing to interpolate a full color, high resolution image

Source: Wikipedia © Wikipedia User:Cburnett. License CC BY-SA. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse.

Color sensing in Digital Cameras

Foveon X3 sensor

Nikon dichroicmirrors

Image: Wikipedia. © Wikipedia User:Anoneditor.License CC BY-SA. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse.

Electromagnetic spectrum

Visible Light: ~400-700 nm wavelength

Source: NASA

Spectroscope[http://en.wikipedia.org/wiki/Spectroscopy]

Images: Left © Wikipedia User:Kkmurray. Right © Wikipedia User:Deglr6328.License CC BY-SA. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse.

Multispectral Imaging

Image removed due to copyright restrictions.

In KlemasRemote Sensing and Geospatial Technologies for Coastal Ecosystem Assessment. Edited by Xiaojun Yang. Springer, 2009.Preview in Google Books.

Multispectral Scanning (data cube)

Diagram removed due to copyright restrictions.

Thermal Imaging[http://www.cas.sc.edu/geog/rslab/551]

Glass is opaque;use Germanium lenses

Set of Thermal Imaging photos removed due to copyright restrictions.

Thermal Imaging

[Pavlidis et al., Nature 2002]

[http://www.falstad.com/thermal]

Two photos removed due to copyright restrictions.

Courtesy of Paul Falstad. Used with permission.

Near Infrared Photography

Four photos removed due to copyright restrictions.

Remote Sensing

Images removed due to copyright restrictions.

UV photography [http://www.naturfotograf.com]Quartz lenses

Six flower photos removed due to copyright restrictions.

CIE 1931 Chromaticity Diagram

B

G

R

Fuji Velvia 50 filmNikon D70 camera

sRGB color space

Fixed color primaries

R = ?

G = ?

B = ?

B

G

R

Outside the Color Gamut

R 0.0

B

G

R

Colorimetric or Photometric mapping

Wide Gamut vs. High Power

B

G

R

400nm 700nm550nm

Wide Color Gamut

Adaptive Color Primaries

Ix400nm 700nm550nm

A B C

Ix

Arbitrary white 1D signal

C

B

A

Pinhole

Object Image

Pinhole Camera

xI

x

I

Pinhole

Object Lens L1

C

B

A

x

I

Pinhole

Object PrismLens L1

C

B

A

x

I

x

Spectral Light Field

Prism

x

Placing a 1D screen in a 2D light-field gives a 1D projection in a direction perpendicular to the screen.

Light-Field

xx

pI

x

I

Screen

Prism

x

pI

x

I

Prism

x

t =Prism

x

II

p

t

x

Lens L2x

I

tS

Prism

Lens L2x

I

x

Prism

tSt

tR

Lens L2x

I

x

Prism

tSt

x

Sensor plane (t=ts)

Ip

tSt

x

Rainbow plane (t=tR)

I

p

All rays of the a given wavelength, from all points in the scene, converge to a

unique point in the R-plane.

tRt

x I

p

Ix400nm 700nm550nm

Ix

Rainbow plane (t=tR)

x I

p

Ix400nm 700nm550nm

Ix

Rainbow plane (t=tR)

x I

p

IR400nm 700nm550nm

Ix

IB400nm 700nm550nm

Rainbow plane (t=tR)

position

Rainbow plane (t=tR)

tRt

x

Mask in the Rainbow plane

x

X

0

1tRt

x

0

Mask in the Rainbow plane

tRt

x

0

Ip

Mask in the Rainbow plane

tRt tS

x

0

Ip

Mask in the Rainbow plane

tRt tS

x

0

Ip

Mask in the Rainbow plane

tRt tS

x

0

0

Ip

Mask in the Rainbow plane

tRt tS

Control the spectralsensitivity of the

sensor by placing an appropriate grayscale masks in the R-plane.

Rainbow plane (t=tR)

tRt tS

C

B

A

PinholeLens L1

Prism orDiffraction Grating

Lens L2 Sensor

R-planemask

Scene

Lens L1

Prism orDiffraction Grating

Lens L2 Sensor

R-planemask

Scene

PinholeLens L1

Prism orDiffraction Grating

Lens L2 Sensor

R-planemask

Scene

Aperture and Lens L1

DiffractionGrating Lens L2 Sensor

R-planemaskLens L1

Mohan, A., R. Raskar, and J. Tumblin. “Agile Spectrum Imaging: Programmable Wavelength Modulation for Cameras and Projectors.” Proceedings of Eurographics 2008.

Agile Spectrum Camera

Test Setup

400nm 700nm550nm

m( )

400nm 700nm550nm

m( )

400nm 700nm550nm

m( )

No Mask Two opaque stripes

One opaque stripe

400nm

m( )

700nm550nm

Mohan et al. Eurographics 2008.

400nm

m( )

700nm550nm

DiffractionGrating Lens L2

R-planemaskLens L1 Screen

Mohan et al. Eurographics 2008.

MetamersWhite Illumination Monochromatic Illumination

Mohan et al. Eurographics 2008.

Traditional three primary projector

Agile-spectrumprojector

Mohan et al. Eurographics 2008.

Traditional three primary projector

time

Py

Adaptive primary projector

time

Py

Deuteranope red/green color blindnessW

hite

ligh

tM

agenta light

Deuteranope simulation

Mohan et al. Eurographics 2008.

Limitations

Relatively coarse control due to crude setup with off-the-shelf components.

Diffraction artifacts.

Small F-number of the objectivelens (we used ~f/16).

Chromatic artifacts in out-of-focus regions for the projector.

Improved designMask instead of pinhole at L1

Better optics (LCD/DMD) and calibration

Future work

ApplicationsAdaptive color primaries

Stereo projector

DiffractionGrating Lens L2 Sensor

R-planemask

Mask and Lens L1

Ix400nm 700nm550nm

Bl Gl RlIx

400nm 700nm550nm

Br Gr Rr

Left eye Right eye

Overlapping Light Fields

B

A x

Prism

(x0, 0)

x

Overlapping Light Fields

B

A x

Prism

x

Diffuse, fronto-parallel case

B

A

Prism

x

x

Blurred Light Fields

B

A x

Prism

x

Convolution of spectral light field with a box filter

C

B

A

PinholeLens L1

Prism

Scene

Pinhole multi-spectral camera

2

1

0

x x

Ligh

t fie

ld c

amer

a

x

C

A

Lens L1Scene

Rainbow multi-spectral camera

x

Ligh

t fie

ld c

amer

a

x

x

x

Linear Variable Interference Filter

C

A

Lens L1Scene

Mask based multi-spectral camera

x

Ligh

t fie

ld c

amer

a

x

x

PrismMask, m( )

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MAS.531 Computational Camera and PhotographyFall 2009

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