Patent ID: 7649554

Claim:
An image composition method comprising: subjecting a first high-sensitivity image signal generated based on high-sensitivity image outputs from corresponding ones of a plurality of pixel positions in a solid-state imaging element that has imaged a subject, to a first nonlinear conversion, so as to prepare a second high-sensitivity image signal; subjecting a first low-sensitivity image signal generated based on low-sensitivity image outputs from corresponding ones of the plurality of pixel positions, to a second nonlinear conversion, so as to prepare a second low-sensitivity image signal; subjecting the second high-sensitivity image signal and the second low-sensitivity image signal to weight adding at every common pixel position, over the entire range of an incident light exposure level exhibited by each incident light that entered to each of the plurality of pixel positions, so as to produce a composed image signal of the subject; and replacing at least one of the first low-sensitivity image signal and the second low-sensitivity image signal with a third signal in a signal level range in which a linear value of the first high-sensitivity image signal is lower than a predetermined level, wherein the third signal is obtained by subjecting to weighting average a fourth signal and the first low-sensitivity image signal, the fourth signal being provided as [the first high-sensitivity image signal/a sensitivity ratio], wherein the sensitivity ratio=[the first high-sensitivity image signal/the first low-sensitivity image signal at a predetermined exposure time]; wherein, provided that the second high-sensitivity image signal is taken as G H (S H ); the second low-sensitivity image signal is taken as G L (S L ); and the composed image signal is taken as Gc, the weight adding is performed according to a composing expression: Gc=k·G H ( S H )+(1- k )· G L ( S L ) where k is a composite parameter having a value falling within a range of 0≦k≦1.