free-view watermarking for free view television alper koz, cevahir Çığla and a.aydın alatan

FREE-VIEW WATERMARKING FOR FREE VIEW TELEVISION

Alper Koz, Cevahir Çığla and A.Aydın Alatan

Outline

Introduction Proposed Watermarking Method Robustness Results for the case of known external calibration. Analysis on the watermark transformations during Light Field

Rendering Proposed solution for unknown external calibration Robustness results Summary and future works

Free View TV

Rendered Video

Cam. 0 Cam. 1(Arbitrary view)

A New Problem: Free-view Video Watermarking

Cam. 0 Cam. 1

METU EEE

METU EEE

METU EEE (?)

Arbitrary View

PROBLEM: How to embed the watermark such that the watermark can be extracted from a generated video for an arbitrary view?

Fundamental Case: One object static scenes

Rendered Image

Cam. 0 Cam. 1Imagery Camera

Light Field Rendering (LFR)

Light field:

Static scene

No occlusion

Lambertian Surfaces

Light Field Rendering

For each desired ray:

- Compute intersection with uv and st plane.

-Take closest ray

Variants:

-Bilinear in uv only

-Bilinear in st only

-Quadrilinear in (u,v,s,t)

Light Field Watermarking

W

W

W

W

Direct Approach: Embed the same watermark into each frame of lightfield slab.

uv plane

(Camera plane)

st plane

(focal plane)

),().,(.),(),( tsWtsHtsItsI uvuvuv

Iuv: Frame corresponds to the camera at (u,v).

Huv: Output image after high pass filtering Iuv.

: Watermark strength.

W: Watermark sequence generated from a Gaussian distribution with zero mean unit variance.

Light Field Watermarking

The watermark is inserted to the off-sheared images rather than embedding directly to camera frames.

Camera plane

Focal plane

Cam. 0 Cam. 2 Cam. 1

The same watermark is embedded to the pixels of different camera frames whose corresponding light rays intersectat the same point in the focal plane.

Camera plane

Focal plane

Cam. 1 Cam. 2

wo w1 w2 w3 w4

Watermark Detection

Rendered watermark

W Wren

Rendered Image

W

IrenHigh pass filtering

Normalized Correlation

Wren

Comparison to a threshold

1/0renI

renren

renren

WI

WI

ˆ

,ˆ

Robustness Results

32x32 camera 256x256 pixels 24 Bits RGB

Camera plane

(2,2,2)

(2,0,2)

(0,-2,2)

(-2,0,2)

(0,0,2)

1

-1

-1

1

z

x

y

Focal plane

Geometry of Buddha Light Field :

Robustness Results

Camera position=[0.5 0 2]; Image plane normal: [0 0 1]; focal length=2 (default);

Rendered image Rendered watermarked image

Robustness Results

Camera position =[2.7 2.7 0]; Rotation: [0 0 0]

Rendered image Rendered watermarked image

Transformation on Watermark Sequence in LFR

Bilinear Interpolation is utilized during LFR

Planar projective transformation between the original and rendered watermark.

Same transformation between imagery camera plane and focal plane.


How to find the projective planar transformation?

Find the points at which object surfaceand focal plane intersect.

Find the matches in the arbitraryview.

Determine the transformation between match pairs.



Utilize two properties of these special points:

Light rays have same intensity Observed at similar coordinates in LF images

Properties are related with Light Fieldparametrization.



Find feature points between rendered and all LF images.

Determine images having higher number of correspondences (four images).

Select feature points at same coordinates with similar intensity values.

Fit a planar transformation model between match pairs.


Apply the transformation to the original watermark.

Normalized correlation between the rendered watermark and the rendered image.

To handle small shidts in pixel locations :

utilize magnitude coefficients of the 2D Fourier transformation of the images

Robustness Results

Summary and future works

A novel problem is introduced, Free-view watermarking. Analyses on watermark transformation are examined.

Known external calibrations. Unknown external calibrations Bilinear interpolation in u-v plane.

Watermark is successfully detected from an aritrary view.

Extension of the algorithm for multiple depths and static scenes

free-view watermarking for free view television alper koz, cevahir Çığla and a.aydın alatan

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