Seeing through Obscure

Glass

Qi Shan, Brian Curless, and Todayoshi Kohno

University of Washington

What is obscure glass?

Obscure glass:

glass with texture relief

Refraction distorts and blurs

the background.

Examples of obscure glass

Examples of obscure glass

Examples of obscure glass

Examples of obscure glass

Camera

Camera

The goal of the project

* =

* = -1

Inverse

Digital approach

Optical approach

-1

. ( )

A linear form

I FL

. =

I F

Rewriting the formation process in a matrix-vector form

Lknown unknown unknown

= one pixel

.

Digital approach

Calibration

Reconstruction

. =

-1

. ( )

Recover from a

single input?

known unknown known

known unknown known

known unknown unknown

Calibration (obtaining F)

Assumption: have access to both sides of the glass.

Calibration process:

1. Place a set of known patterns at the back of the obscure glass;

2. Capture the images through the obscure glass

The number of calibration patterns

For 50x50 kernels, a naïve algorithms needs more than

2,500 image pairs

We assume sparseness of F combined with a multi-

scale optimization

The number of required patterns

◦ 2,500 -> ~100

Experimental procedure:

1) Position camera close to glass.

2) Capture calibration patterns through glass;

estimate F.

3) Remove, then approximately replace camera.

4) Take multiple shots from nearby viewpoints.

5) Compute a result image for each shot

6) Keep best image (nearest to original

viewpoint).

Results

Increase allowed size of kernels

Digital approach

Optical approach

-1

. ( )

Optical approach

Optical approach

Snell’s Law

sin

sin

in out

out in

n

n

in

in

out

out

Snell’s Law

sin,

sin

in outout in

out in

in out

nn n

n

in

out

in

out

Limitations

Digital approach requires:

◦ sparse-kernel glass;

◦ access to both sides for a period of time;

◦ ability to re-position camera reasonably well

Applied substance requires access to the textured

side(s)

Placing substance and/or camera on glass reveals

the observer

Digital approach

Optical approach

Backup slides

Natural image statistics

…

Natural image statistics

…