The Geometry of Noise in Color and Spectral Image Sensors.

Digital images are always affected by noise and the reduction of its impact is an active field of research. Noise due to random photon fall onto the sensor is unavoidable but could be amplified by the camera image processing such as in the color correction step. Color correction is expressed as the combination of a spectral estimation and a computation of color coordinates in a display color space. Then we use geometry to depict raw, spectral and color signals and noise. Geometry is calibrated on the physics of image acquisition and spectral characteristics of the sensor to study the impact of the sensor space metric on noise amplification. Since spectral channels are non-orthogonal, we introduce the contravariant signal to noise ratio for noise evaluation at spectral reconstruction level. Having definitions of signal to noise ratio for each steps of spectral or color reconstruction, we compare performances of different types of sensors (RGB, RGBW, RGBWir, CMY, RYB, RGBC).

Joint electromagnetic and ray-tracing simulations for quad-pixel sensor and computational imaging.

Since Canon released the first dual-pixel autofocus in 2013, this technique has been used in many cameras and smartphones. Quad-pixel sensors, where a microlens covers 2x2 sub-pixels, will be the next development. In this paper we describe the design for such sensors; related wave optics simulations; and results, especially in terms of angular response. Then we propose a new method for mixing wave optics simulations with ray tracing simulations in order to generate physically accurate synthetic images. Those images are useful in a co-design approach by linking the pixel architecture, the main lens design and the computer vision algorithms.

Wavefront sensor architectures fully embedded in an image sensor.

Several architectures of wavefront sensors have been developed since the rise of adaptive optics. In all cases, optical elements are placed in front of image sensors. This makes the sensor quite bulky, expensive, and sensitive to optical misalignment. I propose two novel architectures fully embedded in the image sensor that require no additional optical element. The sensor can be placed directly in the beam to analyze, leading to small, easy to use, and cost-efficient systems. The two architectures are described before testing by simulation of their ability to sense the wavefront distortion and their sensitivity to signal-to-noise ratio.

Uniform illumination and rigorous electromagnetic simulations applied to CMOS image sensors.

This paper describes a new methodology we have developed for the optical simulation of CMOS image sensors. Finite Difference Time Domain (FDTD) software is used to simulate light propagation and diffraction effects throughout the stack of dielectrics layers. With the use of an incoherent summation of plane wave sources and Bloch Periodic Boundary Conditions, this new methodology allows not only the rigorous simulation of a diffuse-like source which reproduces real conditions, but also an important gain of simulation efficiency for 2D or 3D electromagnetic simulations. This paper presents a theoretical demonstration of the methodology as well as simulation results with FDTD software from Lumerical Solutions.