Luiz Carlos Gouveia

A reconfigurable CMOS pixel for applying tone mapping on high dynamic range images

This paper presents the theoretical foundations and the design of a re-configurable pixel circuit capable of capturing images with a wide dynamic range (WDR) of intensities and presenting it in a format fit to be directly displayed on conventional media with limited ability to display WDR scenes. This pixel provides for a programmable transduction function which enables it to produce any monotonically increasing response. Using this flexibility, intensity compression using tone mapping (TM) can be obtained to directly display scenes for wide dynamic range of intensities on low dynamic range displays. More importantly, the tone mapping operator can be changed on the fly to any desired operator without requiring any change in the pixel circuit. Simulation and test results are presented to show the pixels ability to produce WDR images with over 6 decades of dynamic range and compressed images using TM algorithms such as Reinhards and Dragos.

Design of a silicon cochlea system with biologically faithful response

This paper presents the design and simulation results of a silicon cochlea system that has closely similar behavior as the real cochlea. A cochlea filter-bank based on the improved three-stage filter cascade structure is used to model the frequency decomposition function of the basilar membrane; a filter tuning block is designed to model the adaptive response of the cochlea; besides, an asynchronous event-triggered spike codec is employed as the system interface with bank-end spiking neural networks. As shown in the simulation results, the system has biologically faithful frequency response, impulse response, and active adaptation behavior; also the system outputs multiple band-pass channels of spikes from which the original sound input can be recovered. The proposed silicon cochlea is feasible for analog VLSI implementation so that it not only emulates the way that sounds are preprocessed in human ears but also is able match the compact physical size of a real cochlea.

Advances on CMOS image sensors

Purpose n n n n nThe purpose of this paper is to offer an introduction to the technological advances of the complementary metal–oxide–semiconductor (CMOS) image sensors along the past decades. The authors review some of those technological advances and examine potential disruptive growth directions for CMOS image sensors and proposed ways to achieve them. n n n n nDesign/methodology/approach n n n n nThose advances include breakthroughs on image quality such as resolution, capture speed, light sensitivity and color detection and advances on the computational imaging. n n n n nFindings n n n n nThe current trend is to push the innovation efforts even further, as the market requires even higher resolution, higher speed, lower power consumption and, mainly, lower cost sensors. Although CMOS image sensors are currently used in several different applications from consumer to defense to medical diagnosis, product differentiation is becoming both a requirement and a difficult goal for any image sensor manufacturer. The unique properties of CMOS process allow the integration of several signal processing techniques and are driving the impressive advancement of the computational imaging. n n n n nOriginality/value n n n n nThe authors offer a very comprehensive review of methods, techniques, designs and fabrication of CMOS image sensors that have impacted or will impact the images sensor applications and markets.

On Threshold Comparing Biomorphic Image Sensors

Abstract CMOS image sensors have become the principal image sensors for the vast majority of digital cameras currently in market. The market popular sensor is a typical linear sensor which can capture 3-4 decades of illumination intensity, compared to 6-7 decades captured by the human eye. This has inspired research into biomorphic image sensors for over two decades by various groups leading to a number of adaptive pixels, threshold comparing pixel with neurons like firing mechanism as well as logarithmic pixels utilizing sub-threshold transistors. However, these have met little commercial success, often due to higher temporal and fixed pattern noise as well as limited dynamic range. In the paper, we will present a different approach to threshold comparison pixels, wherein a monotonically increasing reference signal is compared to the photo generated charge. The value at which the two signals intersect is recorded as the pixels response. The monotonically increasing reference signal can be changed at the pixels operation to produce any transduction function from the pixel. The tone mapped reference signal can be used to produce tone mapped responses.

Circuits for high performance complementary metal-oxide-semiconductor (CMOS) image sensors

Complementary metal-oxide-semiconductor (CMOS) image sensors have become the mainstay of imaging technology with applications ranging from low end requirements such as that of toys to high end scientific applications. This has been achieved by several advances including noise reduction, pixel count, capture speed enhancement, global shuttering, power reduction as well as dynamic range improvement. This chapter reviews circuits utilised to provide these improvements in CMOS image sensors.