This lecture discusses the principles of color sensors, focusing on the Foveon X3 technology. It begins with an overview of photodiodes and their structures, including the PNP configuration and how it relates to light sensitivity. The instructor explains how the Foveon X3 sensor captures color without traditional color filters by utilizing three layers of pixel sensors, each sensitive to different wavelengths of light. The lecture highlights the advantages of this design, such as capturing red, green, and blue light at every pixel location, compared to conventional sensors that use a Bayer filter. The spectral response of the Foveon sensor is compared to human vision, illustrating the effectiveness of this technology. The discussion also includes the implications of this design on camera specifications, emphasizing how Foveon claims megapixel counts based on its unique pixel structure. The lecture concludes with a comparison of Foveon technology to standard color detection methods, providing insights into its innovative approach to digital imaging.