An Electronic-Calibration Scheme for Logarithmic CMOS Pixels

Logarithmic cameras have the wide dynamic range required to image natural scenes and encode the important contrast information within the scene. However, the images from these cameras are severely degraded by a fixed pattern noise (FPN). Previous attempts to improve the quality of the images from th...

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Bibliographic Details
Published in:IEEE sensors journal 2006-08, Vol.6 (4), p.950-956
Main Authors: Choubey, B., Aoyoma, S., Otim, S., Joseph, D., Collins, S.
Format: Article
Language:English
Subjects:
Amplification
Cameras
Circuits
CMOS
CMOS image sensors
CMOS imagers
contrast threshold
Degradation
Dynamic range
electronic calibration
fixed pattern noise (FPN)
Gain
gain correction
Humans
Image contrast
Image sensors
Layout
Lighting
logarithmic pixels
model-based calibration
Pixel
Pixels
Studies
subthreshold operation
wide dynamic-range pixels
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Summary:Logarithmic cameras have the wide dynamic range required to image natural scenes and encode the important contrast information within the scene. However, the images from these cameras are severely degraded by a fixed pattern noise (FPN). Previous attempts to improve the quality of the images from these cameras by removing an additive FPN have led to disappointing results. Using an existing model for the response of logarithmic pixels, it is concluded that the residual FPN in these images is caused by gain variations between pixels. In order to reduce the effects of these variations, a readout circuit, which is based upon a differential amplifier, has been used. However, even with this readout circuit, high-quality images will only be obtained if each image is corrected to remove the effects of both gain and offset variations. Measurement results are presented that show that the quality of the output from the logarithmic pixels is significantly improved if an electronic-calibration procedure is used to correct for both types of variations. In fact, with this procedure, the contrast sensitivity of the logarithmic pixels becomes comparable to that of the human eye over five decades of illumination intensity
ISSN:1530-437X
1558-1748
DOI:10.1109/JSEN.2006.877983