Digital%20Photography%20with%20Flash%20and%20No-Flash%20Image%20Pairs

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Digital Photography with Flash and No-Flash Image
Pairs

• Gabriela Martínez
• Processamento de Imagem
• IMPA

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Red eyes Detection

• The idea here is to compute the "red" difference
  in both images and keep the extreme points.
• Here the challenge becomes which color space to
  use.

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Red eyes Detection

• RGB - ineffective since RGB is correlated with
  luminosity
• HSV - ineffective because redness difference is
  split among S and V
• YCrCb - ok

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Red eyes Detection

• First we segment the "chrominance" difference
  image using a low threshold. This gives a binary
  image of a few probable blobs that could be
  considered as red-eye.
• The next step is to only select the blobs which
  pass the high threshold. We obtain a rather
  robust classification.

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Red eyes Detection

• CIE Lab - effective since a is a luminosity
  independent measure of red
• But if there is another surface that reflects red
  light in the image, we could have troubles.

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Implementation

• Using Matlab's Image Processing Tool box.
• Calculate RFCr-ACr , where F is the flash
  image and A is the ambient image.
• Create detection mask
• Find seed pixels with command find and mark them
  with bwselect function.

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Results
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Results
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Results
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Denoising and Detail Transfer

• Reducing noise in photographic images,
  long-standing problem.
• Classical solution Bilateral Filter proposed by
  Tomasi and Manduchi 1998.

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Denoising and Detail Transfer

• Bilateral filter average together pixels
  spatiually near and have similar intensity
  values.
• Ap(1/k(p))sum(gd(p'-p)gr(Ap-Ap')Ap')
• k(p)sum(gd(p'-p)gr(Ap-Ap'))
• gd, gr are Gaussians with width controlled sigd
  (geometric closeness), sigr (intensity range)

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Denoising and Detail Transfer

• Joint Bilateral filter Relies on the flash
  image as an estimator of the ambient image.
• Ap(1/k(p))sum(gd(p'-p)gr(Fp-Fp')Ap')
• k(p)sum(gd(p'-p)gr(Fp-Fp'))
• gd, gr are Gaussians with width controlled sigd
  (geometric closeness), sigr (intensity range)

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Algorithm

• Bilateral Filter calcule A_base, F_base
• Calcule F_detail(F0.02)/(F_base0.02)
• Joint Bilateral Filter calcule A_nr
• Calcule shadow mask diff(F,A) lttshadow
• Result (1-M)A_nrF_detailMA_base

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Results
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Results
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Results
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Results
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Results
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Results
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References

• PETSCHNIGG.,G., Digital Photography with Flash
  and No-Flash Image Pairs. ACM 2004
• GONZALEZ.,R., Digital Image Processing using
  MATLAB. Editorial Prentice Hall.
• http//graphics.standford.edu/georgp/vision.htm
• Bilateral Filtering for Gray and Color Images.
• http//homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_C
  OPIES/MANDUCHI1/Bilateral_Filtering.html