Introduction

Digital image sensors are omnipresent in our everyday lives: cameras, videoconferencing, webcams, and of course in our cell phones (although...). Image sensors account for more than 40% of the sales of optoelectronic components. Between 2002 and 2007, the sales of image sensors increased by 35%. These sales mainly consist in CMOS sensor for the basic cameras for cell phones, and in CCD digital cameras. During the first half of 2007, sales fell by 12% compared with 2006, year during which CMOS sensors permitted to obtain a turnover of 4.2 billion dollars which is 30% better than in 2005. On the all year, CCD and CMOS sensors have decreased by 7% ; this decrease could have been due to the cell phones market that started to stagnate. Now, sales are expected to increase by an average of 14% a year until 2012 owing to the emerging markets: medical imaging, toys, video games, ... and it will reach 13.2 billion dollars in 2012. Between 2007 and 2008, the turnover already went up by 10% from 6.9 billion dollars to 7.6 billion dollars. The sales of CMOS sensors reached 4.4 billion dollars in 2008, which represents an increase of 19%, after the drop of 12% in the turnover in 2007. As for CCD sensors, their sales fell by 1% in 2008 (3.2 billion dollars) whereas they had gone up in 2007.

The sensor market is booming and above all more and more expertise is required to be able to analyse the supply and correctly choose “One's sensor”.

But what are the constraints that have to be taken into account? How to read the technical data and most of all how to evaluate one's needs and performances ??? This lesson recapitulates the different questions in a literal way and tries to provide the reader with an answer or, at best, with a progression enabling you to draw your own conclusions about the relevance of the investment that has to be made. However, must be asked the key question WIWA: : Which Image for Which Application ? We will suppose here that the reader is familiar with the fundamentals of imaging and that the reader will only have to use this knowledge to choose the suitable optics and sensor...

There are several possibilities to digitize an image (Fig.1), by using scanning digitization or using digitization point by point distributed on a surface (these “points” can themselves be miniature images, constituents of the final image). Then, the final resolution of the image would be determined by its size and the number of pixels constituting it, and this depending on the physical size of each pixel. You can also find an image definition no longer expressed in dpi (dot per inch), but in lp/mm (line pairs/mm), knowing that two pixels are needed to generate a line pair...

This module is divided into two parts: “lesson” and “case study”. Somes exercises supplement this presentation of image sensors.