Gamma correction is an essential function in every modern display device such as plasma display panel (PDP), cathode ray tube (CRT), organic light emitting diode (OLED) and so on. It controls the overall brightness of an image. Images which are not properly corrected may look either too dark or too bright.

Conventionally, gamma corrections are performed in digital domain. However, the limitations of the analog-to-digital converter (ADC) resolution and dynamic range largely degrade the quality of images, especially for the dark areas in the image. Besides, since the realization of these approaches involves the use of direct lookup tables, conventional methods suffer relatively large memory requirements. The storage requirement increases exponentially if more bits are needed. A...[ Read more ]

Gamma correction is an essential function in every modern display device such as plasma display panel (PDP), cathode ray tube (CRT), organic light emitting diode (OLED) and so on. It controls the overall brightness of an image. Images which are not properly corrected may look either too dark or too bright.

Conventionally, gamma corrections are performed in digital domain. However, the limitations of the analog-to-digital converter (ADC) resolution and dynamic range largely degrade the quality of images, especially for the dark areas in the image. Besides, since the realization of these approaches involves the use of direct lookup tables, conventional methods suffer relatively large memory requirements. The storage requirement increases exponentially if more bits are needed. Although some analog methods are reported to provide improved image quality than conventional ones, they cannot be implemented for high dynamic range applications.

In this work, a high dynamic range complementary metal-oxide-semiconductor (CMOS) image sensor with analog gamma correction scheme is presented. Based on a logarithmic pixel structure, our approach provides a crucial solution for gamma correction in high dynamic applications. Furthermore, the fixed pattern noise (FPN) is eliminated by an area efficient correlated double sampling (CDS) circuit. Finally, a non-linear voltage-controlled-oscillator based analog-to-digital converter (VCO-based ADC) merges the analog gamma correction with AD conversion. In addition, in this research a hot pixel correction technology is proposed and compared to other technologies reported in the literature.

The proposed circuits ware designed and fabricated with AMIS 0.35μm CMOS process. The test results show improved performance compared with digital gamma corrections.