Light source estimating apparatus and image pickup apparatus

A method for estimating a type of light source, the method comprising:

• calculating a first sensitivity ratio spatial distribution between a signal value of a first color pixel and a signal value of a second color pixel, the ratio being calculated from a first picked-up image picked up with an image sensor under an arbitrary light source, wherein the first color pixel and the second color pixel have color filters having a same spectral characteristic and the first color pixel and the second color pixel have different sensor responses;
• calculating at least one second sensitivity ratio spatial distribution group from a second picked-up image picked up with the image sensor under a known light source;
• estimating a type of the arbitrary light source based on a similarity between the first sensitivity ratio spatial distribution and the at least one second sensitivity ratio spatial distribution group,
• wherein the image sensor has a pixel array in which a plurality of color pixels are arranged in a lattice shape, the first color pixel is a Gr pixel, and the second color pixel is a WG pixel which has a full width at half maximum greater than a full width at half maximum of a function indicating spectral sensitivity characteristics of the Gr pixel.

An image pickup apparatus comprising:

• an image sensor having a first color pixel and a second color pixel, which have different sensor responses;
• and
• a light source estimating apparatus configured to estimate a type of an arbitrary light source from a first picked-up image picked up with the image sensor under the arbitrary light source, wherein the light source estimating apparatus comprises:
• a sensitivity ratio spatial distribution calculating unit configured to calculate a ratio between a signal value of the first color pixel and a signal value of the second color pixel in the first picked-up image to acquire a first sensitivity ratio spatial distribution;
• and
• a similarity determining unit configured to estimate a type of the arbitrary light source based on similarity between a second sensitivity ratio spatial distribution group calculated using a second picked-up image picked up with the image sensor under a known light source and the first sensitivity ratio spatial distribution.