Wide Dynamic Range Image Sensor Research Articles

Mantissa-Exponent-Based Tone Mapping for Wide Dynamic Range Image Sensors

The dynamic range of a scene is defined as the ratio between the maximum and minimum luminance in it. Wide dynamic range (WDR) means this ratio is so large that it exceeds the dynamic range of a traditional image sensor. Nowadays, WDR image sensors enable the capture of WDR scenes. However, the captured WDR image requires an additional tone mapping step to compress the high bit pixel of WDR image to low rate pixel so that it can be displayed on the screen. The tone mapping algorithm is mostly done in an image signal processor or with a specific software application. This brief proposes a tone mapping technique that is suitable for direct processing of the output of a WDR image sensor bitstream. The algorithm acquires statistics on the mantissa and exponent parts of the pixel value and then generates a refined histogram for tone mapping. Experiments that evaluate the image quality and hardware efficiency are carried out. The results indicate that the proposed mantissa exponent-based algorithm provides visually pleasing results and preserves details of the original WDR image better than other similar algorithms. The hardware resources’ efficiency of the algorithm makes the system on chip implementation possible.

5-1 可変しきい値を用いたリニア出力型広ダイナミックレンジ撮像デバイス

5-1 可変しきい値を用いたリニア出力型広ダイナミックレンジ撮像デバイス

Recent trends on wide dynamic range image sensor technology

Recent trends on wide dynamic range image sensor technology

Power-Performance Tradeoffs in Wide Dynamic Range Image Sensors with Multiple Reset Approach

A variety of solutions for widening the dynamic range (DR) of CMOS image sensors have been proposed throughout the years. These solutions can be categorized into different groups according to the principle used for DR widening. One of the methods, which is based on autonomous control over the integration time, was implemented by our group. We proposed the multiple resets algorithm, which was successfully implemented in three generations of WDR image sensors. While achieving the same goal of widening the DR of the sensor, each of the implemented imagers had a different architecture, and therefore presented different performance and power figures. This paper reviews designs of the aforementioned sensors and presents a comprehensive analysis of their power consumption. Power-performance tradeoffs are also discussed. Advantages and disadvantages of each sensor are presented.

1A1-C18 実時間画像処理機能を備えた広ダイナミックレンジイメージセンサ

1A1-C18 実時間画像処理機能を備えた広ダイナミックレンジイメージセンサ

A Dynamic Range Expansion Technique Using Dual Charge Storage in a CMOS APS and Multiple Exposures for Reduced Motion Blur

This paper presents a dynamic range expansion technique for CMOS image sensors using dual charge storage in a pixel and multiple exposures. Each pixel contains two photodiodes, PD1 and PD2 whose sensitivity can be set independently by the accumulation time. The difference of charge accumulation time in both photodiodes can be widely controlled to expand the dynamic range of the sensor. It allows flexible control of the dynamic range since the accumulation time in the PD2 signal is adjustable. The multiple exposure technique used in the sensor reduces the motion blur in the synthesized wide dynamic range image when capturing fast-moving objects. It also reduces the signal-to-noise ratio dip at the switching point of the PD1 signal to the PD2 signals in the synthesized wide dynamic range image. To reduce the read out time, a comparator-controlled selective readout of the PD1 and PD2 signals has been tested. The synthesis of the captured images to produce wide dynamic range image is also described. A wide dynamic range image sensor with 320x240 pixels has been implemented and tested. It is found that the use of 4 exposures in one frame for the short accumulation time signals is sufficient for the reduction of motion blur in the synthesized wide dynamic range image, and the signal-to-noise ratio dipping at the switching point of the PD1 to PD2 signals is reduced by 6 dB using 4 short-time exposures.

Wide Dynamic Range Image Sensor with Polygonal-Line I/O Characteristic Adapted to Brightness Distribution of Objects

We propose a CMOS image sensor that realizes wide dynamic range imaging and nonlinear representation of I/O characteristics. The proposed image sensor controls the integration time for each pixel based on the brightness distribution of objects. The histogram at the end of the integration is estimated from the early intermediate photodiode values that are read out to an external circuit. Using the estimated histogram, the imaging parameters, which control the integration time pixel-by-pixel, are optimized in the external circuit. According to the imaging parameters, the intermediate photodiode value is compared with the threshold and reset to the starting value depending on the comparison result. These processes repeat several times. At the end of the integration, the photodiode value is reconstructed by using the imaging parameters. Then, wide dynamic range images with adapted I/O characteristics are obtained. We have fabricated a prototype with a size of 64 x 64 pixels using a 0.35-μm 2-poly 4-metal CMOS process. In this paper, we explain the principle of the proposed sensor and discuss the system architecture and its operation. The experimental results obtained using the prototype are also presented, and we verify its effectiveness.

A Dynamic Range Expansion Technique Using Dual Charge Storage in a CMOS APS and Multiple Exposures for Reduced Motion Blur

This paper presents a dynamic range expansion technique for CMOS image sensors using dual charge storage in a pixel and multiple exposures. Each pixel contains two photodiodes, PD1 and PD2 whose sensitivity can be set independently by the accumulation time. The difference of charge accumulation time in both photodiodes can be widely controlled to expand the dynamic range of the sensor. It allows flexible control of the dynamic range since the accumulation time in the PD2 signal is adjustable. The multiple exposure technique used in the sensor reduces the motion blur in the synthesized wide dynamic range image when capturing fast-moving objects. It also reduces the signal-to-noise ratio dip at the switching point of the PD1 signal to the PD2 signals in the synthesized wide dynamic range image. To reduce the read out time, a comparator-controlled selective readout of the PD1 and PD2 signals has been tested. The synthesis of the captured images to produce wide dynamic range image is also described. A wide dynamic range image sensor with 320x240 pixels has been implemented and tested. It is found that the use of 4 exposures in one frame for the short accumulation time signals is sufficient for the reduction of motion blur in the synthesized wide dynamic range image, and the signal-to-noise ratio dipping at the switching point of the PD1 to PD2 signals is reduced by 6 dB using 4 short-time exposures.

画素並列リセット判定による広ダイナミックレンジイメージセンサ

Wide dynamic-range image sensors are now used for various applications such as intelligent transport systems and security systems. We propose a new image-sensor that controls the reset timing of the photodiode in each pixel. When a pixel value exceeds a threshold during the integration period, this sensor immediately resets the photodiode and records the number of resets in a memory. By using this sensor, linear-wide dynamic-range images can be obtained.

7-4 A Wide Dynamic Range Image Sensor Integrating Column Parallel A/D Converters with Column FPN Cancellation

7-4 A Wide Dynamic Range Image Sensor Integrating Column Parallel A/D Converters with Column FPN Cancellation

A new active pixel structure with a pinned photodiode for wide dynamic range image sensors

A wide dynamic range CMOS image sensor based on a new active pixel structure with a pinned photodiode is proposed and evaluated with device simulations. The proposed pixel device has a linear and a logarithmic characteristics in low and high illumination region, respectively. The technique of direct detection of photodiode potential leads to a wide logarithmic response compared with the conventional linear-log wide DR image sensor with pinned photo diode.

A study on a evaluation method for wide dynamic range image sensor

A study on a evaluation method for wide dynamic range image sensor