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Automatic Compensation for Camera Settings Automatic Compensation for Camera Settings for Images Taken under Different Illuminantsfor Images Taken under Different Illuminants
School of Electrical Engineering and Computer Science School of Electrical Engineering and Computer Science Kyungpook National Univ.Kyungpook National Univ.
FourteenthFourteenth Color Imaging ConferenceColor Imaging Conference
20062006
Cheng Lu and Mark S. DrewCheng Lu and Mark S. Drew
22 / 16 / 16
Combination of two images for the same scene under different illumination– Estimating scene illumination
– Enhancing photographs shot for shadow removal
Proposed method– Adjusting parametrically two images to compensate
for the difference in camera setting• Exposure speed, ISO, aperture size, and white balance
– Existing effect of illumination
Solving by using shadow effect
AbstractAbstract
33 / 16 / 16
Work on image pairs taken for the same scene under different illumination– Analysis of the difference image (with flash image and
no-flash image)• Estimating surface reflectance and illumination in the no-flash image
• Enhancing photographs in dark environments and removing red-eye effects
• Removing the ambient shadow from the no-flash image
– Inference of the contribution of the flash • Must be in same camera settings
• Different lighting conditions
Causing changes of camera settings
• Not investigated in this problem
IntroductionIntroduction
44 / 16 / 16
Proposed method– Masking model to describe camera settings
• Assuming additivity and proportionality of the different factors involved
• Using 2nd-order masking model with 9 parameters
– Training phase• Image A ; only one light source, illuminant 1
• Image B ; two light sources, illuminant 1 and illuminant 2
55 / 16 / 16
– An example of images
Fig. 1. (a,b): Ambient-light image A, unscaled, and scaled for display.(c,d): “Both” image B (ambient + flash), unscaled, and scaled.
(a)
(c)
(b)
(d)
66 / 16 / 16
Additivity property– Subtracting the image A from image B
• Taken under illuminant 2 only
– Situation with flash image and no-flash image• Difference image
– Pure flash image
– Disappearance of shadow caused by sunlight
77 / 16 / 16
Consumer-grade cameras settings– Focal length
– Exposure time (shutter speed)
– Aperture (f-number)
– ISO (film speed)
– White balance
Other settings– Fixing the focal length
– Using a tripod
– Using RAW format
Camera Settings and Camera Settings and Image AcquisitionImage Acquisition
88 / 16 / 16
Exposure value (EV)– Sum of Aperture Value (AV) and Time Value (TV)
• AV
• TV
ISO (Film speed)– Measure of a photographic film’s sensitivity to light
– Using 100 and 200
White balance settings– Auto, Daylight, Fluorescent, and Tungsten
TVAVEV
NNAV 22
2 log2log
tTV t 21
2 loglog
Where N ; the f-number
Where t ; the shutter time in seconds
99 / 16 / 16
Goal ; Finding a model – Describing the relation between the difference of the
two images and the camera settings
– Transforming A to A’• Shadows caused by illuminant 1 will be removed in the
difference image B−A’
– ; shadow region, ; out-of-shadow region
A Masking Model for Compensating A Masking Model for Compensating for Camera Settingsfor Camera Settings
s ns
Fig. 2. Ambient-light image A with in-shadow and out-of-shadow regions.
1010 / 16 / 16
– Transforming A to A’ via a 3-coefficient vector M• M ; a coefficient for each color channel
– Using compensation of the camera settings of the two images
– Function of the ratios of exposure value, ISO, and white balance between the two images
,)()(
)()())()(()()(
)(')(')()()(')()(')(
sAnsA
sBnsBM
sAnsAMsBnsBLetsAnsAsBnsB
sAsBnsAnsB
no shadow effect
M is a 3-vector.
1111 / 16 / 16
– 2nd-order masking model • Describing the difference by camera settings
• Proposed originally for characterizing color printers– Using logarithms
– Assuming additivity and proportionality
• The form of the 2nd-order model
A
B
iA
iB
iA
iB
A
B
A
B
A
B
iA
iB
A
B
A
B
iA
iB
A
B
A
B
ii
ii
EVEV
mean
mean
mean
mean
ISOISO
ISOISO
EVEV
mean
mean
ISOISO
EVEV
mean
mean
ISOISO
EVEV
isAnsAsBnsB
ccc
bbb
aaa
iM
loglogloglogloglog
logloglog
logloglog
3..1,loglog
321
2
3
2
2
2
1
321
)()()()(
1212 / 16 / 16
– Difference image
Fig. 3. (a): Pure-flash image (B−A) without compensation(b): With compensation (B-A’)
(a) (b)
1313 / 16 / 16
Experimental imaging environment– Using five lighting sources
• Direct sunlight
• Cloudy daylight
• Tungsten light lamp
• Incandescent lamp
• Xenon flash light
– Using five objects with different colors on five different tablecloths
Experiments and ResultsExperiments and Results
Fig. 4. Experimental imaging environment
1414 / 16 / 16
– Capture of images under five situations• Using direct sunlight as illuminant 1 to create shadows and
adding the flash as illuminant 2
• Using tungsten light as illuminant 1 and adding the flash as illuminant 2
• Using tungsten light as illuminant 1 and adding cloudy daylight as illuminant 2
• Using incandescent light as illuminant 1 and adding the flash as illuminant 2
• Using incandescent light as illuminant 1 and adding cloudy daylight as illuminant 2
1515 / 16 / 16
Examples of the results
Fig. 5,6. Results: (a) images A, (b) image B, (c) image B−A’
(a) (b) (c)
1616 / 16 / 16
Addressing the problem– Compensation for camera settings for image pairs for
the same scene under different lighting conditions
– Difficulty• Difference of the two images
– Composite of camera settings and scene illumination
Proposed method– Simple masking model to describe camera settings
SummarySummary