Realisation d'un systeme de conversion des couleurs pour un capteur d'images CMOS a photodetecteur sans filtre optique

The research team of my supervisor, Mr Yves Audet, work on an innovator CMOS (Complementary Metal-Oxide-Semiconductor) image sensor without optical filter. The CCD (Charge-Coupled Device) and CMOS sensors on the market today are based on photodetectors which are sensitive to the light intensity and not to the wavelength. To make them sensitive to color, color filters are deposited on each photodetector so that each photodetector detects only a specific wavelength. This approach has two major drawbacks. First, the use of the color filter reduces the sensitivity of the sensor as the filter absorbs some of the light intensities. Second, each photodetector detects only one color requiring the use of mathematical extrapolation algorithms to deduce the two missing colors at each pixel from the colors of adjacent pixels.;This research work is a continuity in the development effort of the new sensor. It is to find a method for color conversion from sensor color space to a standard color space. The color conversion is performed using a 3x3 color conversion matrix. A method of calculating this matrix while considering the noise in the image has been identified and implemented as a Matlab GUI. The consideration of noise in the image is essential because of the nature of the sensor for which the conversion matrix can have large coefficients in the diagonal. However, they are responsible for the degradation of noise performance. Subsequently, a digital circuit for color conversion was designed in VHDL. A graphical method for evaluating the spectral response of an image sensor according to the regions of color space was developed. The second part of this work is to develop a demonstration prototype for the new sensor. This prototype was made using a development board based on Altera FPGA coupled with a color touch screen. The FPGA was used to make circuits for monitoring, acquisition and display controlled by a Nios II processor. The demonstration prototype was successfully completed.;The new innovative image sensor overcomes these disadvantages by not requiring the deposit of the color optical filters on the photodetectors. It detects color by using the property of a semiconductor material that the penetration depth of electromagnetic waves varies with wavelength. Using this property, the sensor can detect three colors with each pixel. The new sensor is made entirely in CMOS technology as opposed to a Foveon sensor, a company founded in 2002 and uses the same principle of light absorption in a semiconductor to filter the light according to the wavelength. This sensor is not compatible with CMOS technology because it uses three photodiodes buried vertically into the semiconductor. This makes the realization of this sensor expensive.