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A CMOS Image Sensor with Analog Gamma Correction using a Nonlinear Single Slope ADC  

Ham Seog-Heon (Dept. Electrical and Electronic Engineering, Yonsei Univ.)
Han Gunhee (Dept. Electrical and Electronic Engineering, Yonsei Univ.)
Publication Information
Journal of the Institute of Electronics Engineers of Korea SD / v.43, no.1, 2006 , pp. 65-70 More about this Journal
Abstract
An image sensor has limited dynamic range while the human eye has logarithmic response over wide range of light intensity. Although the sensor gain can be set high to identify details in darker area on the image, this results in saturation in brighter area. The gamma correction is essential to fit the human eye response. However, the digital gamma correction degrades image quality especially for darker area on the image due to the limited ADC resolution and the dynamic range. This Paper proposes a CMOS image sensor (CIS) with a nonlinear analog-to-digital converter (AU) which performs analog gamma correction. The CIS with the proposed nonlinear analog-to-digital conversion scheme was fabricated with a $0.35{\mu}m$ CMOS process. The analog gamma correction using the proposed nonlinear ADC CIS provides the 2.2dB peak-signal-to-noise-ratio(PSM) improved image qualify than conventional digital gamma correction. The PSNR of the image obtain from the digital gamma correction is 25.6dB while it is 27.8dB for analog gamma correction. The PSNR improvement over digital gamma correction is about $28.8\%$.
Keywords
CMOS image sensor; Gamma correction; Nonlinear analog-to-digital converter; Single-slope ADC;
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