1. An image visibility restoration method based on a Fisher's Linear Discriminant-based Dual Dark Channel Prior (FLD-based DDCP), adapted to an image processing apparatus, comprising: receiving a plurality of training images corresponding to a plurality of image sizes and a plurality of classes, wherein each of the classes corresponds to a localized light source; generating a plurality of discriminant patterns from the training images based on a Fisher's Linear Discriminant (FLD) model; receiving an incoming hazy image comprising a plurality of incoming pixels and classifying each of the incoming pixels as either belonging to a localized light region or a non-localized light region according to intensity values of the incoming pixels; partitioning the localized light region into a plurality of patches according to each patch size in associated with the image sizes; determining whether each of the patches belongs to a localized light patch based on the FLD model corresponding to each of the patch sizes and determining a designated patch size among the patch sizes accordingly; determining a set of adaptable chromatic parameters respectively corresponding to each color channel according to the intensity values of the incoming pixels in each of the color channels; determining dual dark channels respectively corresponding to the designated patch size and a small patch size; determining atmospheric light in each of the color channels according to the dark channel corresponding to the designated patch size and determining a transmission map according to the dark channel corresponding to the small patch size; restoring the incoming hazy image in each of the channels according to according to the corresponding set of adaptive chromatic parameters, the corresponding atmospheric light, and the transmission map so as to produce a de-hazed image; and outputting the de-hazed image.