Image sensor equipped with additional group of selectively transmissive filters for illuminant estimation, and associated illuminant estimation method

An image sensor, comprising:

• a two dimensional array of pixel elements, arranged to receive light energy of incident light and to convert the received light energy into electrical signals;
• a color filter array, superimposed on and in registration with the two dimensional array of pixel elements, the color filter array comprising:
• a first group of selectively transmissive filters, arranged to selectively transmit spectral energy in M colors of the visible spectrum, wherein M is a positive integer that is larger than two;
• and
• a second group of selectively transmissive filters, arranged to selectively transmit spectral energy in N colors of the visible spectrum, wherein any selectively transmissive filter of the first and the second groups of selectively transmissive filters is arranged to transmit spectral energy in one specific color of the visible spectrum, and N is a positive integer that is larger than M;
• and
• a digital circuit, coupled to the two dimensional array of pixel elements, configured to generate a plurality of output signals for pixel elements within the two dimensional array of pixel elements, wherein at least one portion of the output signals carries pixel data representing an image of a scene;
• wherein the image of the scene corresponds to raw image data of pixel elements corresponding to the first group of selectively transmissive filters, and correction of the image is performed according to information derived from pixel elements corresponding to the second group of selectively transmissive filters;
• and
• the digital circuit operates according to an illuminant estimation method for the image sensor, the color filter array comprises a multi-band color filter array (CFA), and the illuminant estimation method comprises the steps of:
• determining a plurality of spectral ratio vectors associated with a plurality of pre-defined light sources, respectively;
• receiving a series of multi-band CFA pixel data from the image sensor;
• computing a mean value for each spectral channel of a plurality of spectral channels and converting mean values respectively corresponding to the plurality of spectral channels into vector elements of a current spectral ratio vector;
• comparing the current spectral ratio vector with the spectral ratio vectors of the pre-defined light sources and computing a norm of the current spectral ratio vector and each of the spectral ratio vectors of the pre-defined light sources, to determine a specific pre-defined light source whose spectral ratio vector is closest to the current spectral ratio vector within the plurality of pre-defined light sources;
• and
• outputting a detection result indicating the specific pre-defined light source whose spectral ratio vector is closest to the current spectral ratio vector within the plurality of pre-defined light sources.