Statistics of Natural Image Categories
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Statistics of Natural Image Categories Antonio Torralba and Aude Oliva. Network: Computation in Neural Systems , 14(2003) 391-412. Jonathan Huang ([email protected]) 1/30/2006. Spatial Image Signatures.

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Statistics of Natural Image CategoriesAntonio Torralba and Aude Oliva. Network: Computation in Neural Systems, 14(2003) 391-412

Jonathan Huang ([email protected])

1/30/2006


Spatial image signatures
Spatial Image Signatures

Averaged pictures of categories of objects, scenes and objects in scenes, computed with 100 exemplars or more per category. Exemplars were chosen to have the same basic level and viewpoint in regard to an observer. The group objects in scenes (third row) represent examples of the averaged peripheral information around an object centered in the image.


Caltech 101
Caltech 101

  • Object Categories:

    • Airplanes

    • Brain

    • Brontosaurus

    • Chandelier

    • Garfield

    • Kangaroo

    • Octopus

    • Trilobyte

    • Etc…

By Antonio Torralba


100 special moments and conan
100 Special Moments (and Conan)

Conan O’Brien

Little Leaguer

Newlyweds

By Jason Salavon


Power spectra of natural images
Power Spectra of Natural Images

  • Fourier Transform:

  • Magnitude Spectrum:

  • Spectral Signature (for a set of images S):


“Demo”

  • Computing the Spectrum (Matlab):

    • Ifft = abs(fftshift(fft2(I,w,h)));

  • Visualization:

    • imshow(log(Ifft)/max(max(log(Ifft))));

    • colormap(cool);




1 f spectra
1/f Spectra

  • Natural Image Spectra follow a power law!

  • As() is called the Amplitude Scaling Factor

  • 2-() is the Frequency Exponent.  clusters around 0 for natural images.

  • Any guesses on why this law holds?


Main idea of torralba oliva papers
Main Idea of Torralba/Oliva Papers

  • “Statistics of Natural Images vary as a function of the interaction between the observer and the world”!



Spectral signatures
Spectral Signatures

  • Why are Fields, Beaches and Coasts less isotropic than other natural environments?


Scene scale
Scene Scale

  • “The point of view that any given observer adopts on a specific scene is constrained by the volume of the scene.”

  • How does the amount of clutter vary against scene scale in man-made environments? In natural environments?


Pca on natural images
PCA on Natural Images

Top Row: PCA on images

Bottom Row: PCA on power spectra


Openness naturalness
Openness/Naturalness

Projection of images onto the second and third principle components. SPC2 corresponds to “Openness” and SPC3 corresponds to “Naturalness”


Spatially localized statistics
Spatially Localized Statistics

  • Windowed FFT

  • Image statistics become non-stationary as scene scale increases.

Top Row: Man-made environments

Bottom Row: Natural environments


What do images statistics say about depth
What do Images Statistics say about Depth?

V: Vertical

H: Horizontal

O: Oblique


Comparing localized spectral signatures and depth
Comparing Localized Spectral Signatures and Depth

  • With increasing depth comes:

    • An increase in global roughness for man-made structures

    • A decrease in global roughness for natural structures

    • Nonuniformity in spatially localized spectral signatures




An algorithm
An Algorithm

  • First use PCA to reduce dimension

  • Goal: For a vector of features v, estimate

    • Since the man-made and natural cases should be treated separately, we model f(v|art) and f(v|nat) as Gaussians.

    • The joint distribution is modeled as a weighted sum of Gaussians:

      where


Model estimation
Model Estimation

  • Expectation-Maximization

    • E-step:

      • Compute posterior probabilities of the clusters given observed data.

    • M-step:

      • Update cluster parameters, weighting training data by the posterior probabilities from the E-step.

Read Torralba and Oliva: Depth Estimation, IEEE PAMI 2002 for the update equations. They do not all fit on one slide...



F d category
f(D|category)

Distribution of Scene Categories as a function of mean depth.



Context in images
Context in Images

  • Question: How can these small people possibly affect the image statistics in any significant way??



Thank you
Thank You

  • References

    • Torralba and Oliva, Statistics of Natural Image Categories. Network: Computation in Neural Systems 14 (2003) 391-412.

    • Torralba and Oliva, Depth Estimation from Image Structure. IEEE PAMI Vol 14, No. 9 (2002).

    • Oliva and Torralba, Modeling the Shape of the Scene: A Holistic Representation of the Spatial Envelope. IJCV 42(3), 145-175 (2001).

    • Srivastava, Lee, Simoncelli, Zhu, On Advances in Statistical Modeling of Natural Images. JMIV 18:17-33 (2003)

    • Mumford, Pattern Theory: the Mathematics of Perception. ICM 2002. Vol III. 1-3


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