Digital Photography with Flash and No-Flash Image Pairs

Digital Photography with Flash and No-Flash Image Pairs Digital Photography with Flash and No-Flash Image Pairs - Start

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Digital Photography with Flash and No-Flash Image Pairs




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Presentations text content in Digital Photography with Flash and No-Flash Image Pairs

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Digital Photography with Flash and No-Flash Image Pairs

By: Georg Petschnigg Maneesh Agrawala Hugues Hoppe Richard Szeliski Michael Cohen Kentaro Toyama, Microsoft CorporationPresented by: Yael AmsterdamerAdvanced Topics in Visual Computing, Spring 2012

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The Dilemma: to Flash or not to flash?

Introduction

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Digital Photography with Flash and No-Flash Image Pairs

Natural lighting

Low signal-to-noise ratio (SNR)

Loss of detailsLonger exposure – motion blur

Harsh, unnatural lightingHigh SNRMore detailsMay cause unwanted artifacts (red eye, shadows, specularities)

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Why not both?

The idea: use the good features of each photo to create a better image

Introduction

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Digital Photography with Flash and No-Flash Image Pairs

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Other works on combining images

Introduction

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Digital Photography with Flash and No-Flash Image Pairs

Different exposures

Panoramic view

Relighting

Current work

handles 2 images with specific characteristics,

Envisioned for camera firmware

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Different Applications

DenoisingDetail transferSide requirement: handling flash induced shadows and specularitiesWhite BalancingContinuous Flash AdjustmentRed Eye Removal

Introduction

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Digital Photography with Flash and No-Flash Image Pairs

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Camera Adjustment to light

A certain amount of light is needed for a photoTaking pictures of a dark sceneIncreasing exposure timeOpening the apertureIncreasing ISO (sensor sensitivity)The problem – high ISO noise affects high-frequency details

Background

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Digital Photography with Flash and No-Flash Image Pairs

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The Input

F – the photo with flashA – the no-flash (ambient) photoComposed of 3 RGB intensity values for each pixelAp – one pixel in ASame camera position, focus, apertureOtherwise, registration is requiredAdjusted ISO and exposure timeUndergo non-linear tone-mapping operations

Background

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Digital Photography with Flash and No-Flash Image Pairs

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1st Application: Denoising

A classic problem in image processingThe target: analytically reduce SNR One type of solution: smoothing filtersBilateral Filter [Tomasi and Manduchi 1998]Fast, non-iterativeAveraging close-by pixelsLow-pass filter, combined withEdge-stopping function

Denoising

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Digital Photography with Flash and No-Flash Image Pairs

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Bilateral filter

However, results still have noise or blur (or both)

Denoising

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Digital Photography with Flash and No-Flash Image Pairs

ambient

flash

Bilateral filter

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Improvement: Joint Bilateral Filter

In the flash image there are much more detailsWhy not use F to find edges?

Denoising

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Digital Photography with Flash and No-Flash Image Pairs

Bilateral filter

Joint Bilateral filter

The difference

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Not all edges are real …

May cause over- or under-blur in joint bilateral filterWe need to eliminate their effect

Denoising

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Digital Photography with Flash and No-Flash Image Pairs

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Detecting shadows

Observation: the pixels in the flash shadow should be similar to the ambient imageNot identical:NoiseInter-reflected flashCompute a shadow maskTake pixel p if is manually adjustedMask is smoothed and dilated

Denoising

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Digital Photography with Flash and No-Flash Image Pairs

Pixels for which we will not use F

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Detecting specularities

Take pixels where sensor input is close to maximum (very bright)Over fixed threshold Create a specularity maskAlso smoothed and dilatedM – the combination of shadow and specularity masksWhere Mp=1, we use ABase. For other pixels we use ANR.

Denoising

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Digital Photography with Flash and No-Flash Image Pairs

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There is so much denoising can do

It cannot add details missing in the ambient imageExist in flash image because of high SNRWe use a quotient image:Multiply with ANR to add the detailsMasked in the same way

Detail Transfer

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Digital Photography with Flash and No-Flash Image Pairs

Bilateral filtered

Reduces the effect of noise in F

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Unified process

Denoising + detail transfer + masking shadows and specularities

Detail Transfer

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Digital Photography with Flash and No-Flash Image Pairs

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More examples

Detail Transfer

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Digital Photography with Flash and No-Flash Image Pairs

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The opposite of preserving the atmosphere

The goal: simulate white light in the sceneWhat color is the light in the scene?Flash image can help us:The difference between F and A is only the flash lightAssume it is proportional to the surface albedoInherent property of the surfaceAssume the surface reflects light in the same color (will not work for plastic, glass…)

White Balancing

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Digital Photography with Flash and No-Flash Image Pairs

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Computing the ambient light

We cancel the color of the surfaceThe average c of Cp(col) for pixels with certain properties is the ambient light colorThen we scale A to cancel the ambient light

White Balancing

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Digital Photography with Flash and No-Flash Image Pairs

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Example

White Balancing

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Digital Photography with Flash and No-Flash Image Pairs

Estimated ambient light

Computed color

Ambient original

White-balanced

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Combining flash and no-flash images

Providing complementary details about the sceneUse for denoising and detail transferUse for white balancingFuture workMore robustnessAutomatization of configuration

Summary

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Digital Photography with Flash and No-Flash Image Pairs

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Thank you!

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