Modelling, calibration and correction of nonlinear illumination-dependent fixed pattern noise in logarithmic CMOS image sensors Dileepan Joseph and Steve Collins Department of Engineering Science University of Oxford,
Dec 31, 2015
Modelling, calibration and correction of nonlinear
illumination-dependent fixed pattern noise in logarithmic
CMOS image sensors
Dileepan Joseph and Steve Collins
Department of Engineering Science
University of Oxford, England
May 21-23, 2001 IMTC, Budapest (IEEE) 2
Outline
• Logarithmic image sensors
• Pixel modelling
• Fixed pattern noise (FPN)
• Sensor calibration
• Image correction
• Summary and conclusions
May 21-23, 2001 IMTC, Budapest (IEEE) 3
Logarithmic image sensors
• CMOS versus CCD image sensors– Electronics placed on same die as pixels– Cost, power consumption, size, weight– Quantum efficiency, yield, price pressure
• Logarithmic versus linear pixels– Continuous sensing, random access– High dynamic range, low bit rate– Resolution, sensitivity, frame rate
May 21-23, 2001 IMTC, Budapest (IEEE) 4
Pixel modelling
• Physical model • Abstract model
y)uncertaint (noise,error
leakage) e(photodiod bias
slope) old(subthreshgain
voltages)(thresholdoffset
response
eilluminanc
ln
c
b
a
y
x
xcbay
May 21-23, 2001 IMTC, Budapest (IEEE) 5
Fixed pattern noise (FPN)
• Offset (aj) variation (1 j N pixels)
• Offset and gain (bj) variation
• Offset, gain and bias (cj) variation
ijij xcbay lnˆ
ijjij xcbay lnˆ
ijjjij xcbay lnˆ
May 21-23, 2001 IMTC, Budapest (IEEE) 6
Sensor calibration
• Calibrate the sensor with images yij of M uniform illuminances xi (e.g. white paper)
• Extract parameters by minimising the mean square error
M
i
N
jijij yy
MNMSE
1 1
2ˆ1
May 21-23, 2001 IMTC, Budapest (IEEE) 7
Sensor calibration cont’d
• Calibration error is 3.9, 1.9 and 0.9 for one, two and three parameter models
• Calibration error versus illuminance differs markedly
M
i
N
jijij yy
DOF 1 1
22 ˆ1
May 21-23, 2001 IMTC, Budapest (IEEE) 8
Image correction
• Left to right: original plus one, two and three parameter FPN corrected images
• Top to bottom: apertures of 1.8, 4, 8 and 16 f-stops
• Inter-scene plus intra-scene dynamic range equals 67 dB
May 21-23, 2001 IMTC, Budapest (IEEE) 9
Image correction cont’d
May 21-23, 2001 IMTC, Budapest (IEEE) 10
Summary and conclusions
• Physical and abstract pixel model– Offset, gain, bias and error
• Parameter variation causes FPN– Calibration with uniform illuminance– Results indicate FPN is nonlinear
• FPN correction is necessary– Digital correction of images– More robust analogue circuits
May 21-23, 2001 IMTC, Budapest (IEEE) 11
Acknowledgements
• Many thanks to the Natural Sciences and Engineering Research Council of Canada and the Engineering and Physical Sciences Research Council of Britain for their generous support.