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
Slide2The 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)
Slide3Why 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
Slide4Other 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
Slide5Different 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
Slide6Camera 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
Slide7The 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
Slide81st 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
Slide9Bilateral 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
Slide10Improvement: 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
Slide11Not 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
Slide12Detecting 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
Slide13Detecting 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
Slide14There 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
Slide15Unified process
Denoising + detail transfer + masking shadows and specularities
Detail Transfer
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Digital Photography with Flash and No-Flash Image Pairs
Slide16More examples
Detail Transfer
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Digital Photography with Flash and No-Flash Image Pairs
Slide17The 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
Slide18Computing 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
Slide19Example
White Balancing
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Digital Photography with Flash and No-Flash Image Pairs
Estimated ambient light
Computed color
Ambient original
White-balanced
Slide20Combining 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
Slide21Thank you!
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Digital Photography with Flash and No-Flash Image Pairs
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