1. A method of correcting warping of an acquired image in an MRI system, caused by non-linearities in gradient field profiles of gradient coils, comprising: constructing a distortion map for mapping each location x, y, z in real space to a location x′,y′,z′ in warped space based on deviations from linearity of a magnetic field produced by the gradient coils; wherein image values at x′, y′, z′ are computed directly from k-space data using inverse gridding from uniform to non-uniform sample locations; and wherein (i) k-space data is transformed to uniformly spaced samples in warped space, (ii) image values are computed at the x′, y′, z′ warped space locations using convolution interpolation, and (iii) the computed image values are used to form a real space image.