The paper introduces a novel approach to polarization information encoding using Poincaré sphere (PS) trajectory metasurfaces, which leverages a generalized form of Malus' law (GML) governing 2D projections between arbitrary elliptical polarization pairs across the entire PS. This method significantly expands the encoding dimensionality of polarization information, offering versatile functionalities such as histogram stretching, thresholding, and image encryption within non-orthogonal PS loci. The GML describes a universal projection rule from one arbitrary elliptical polarization to another, allowing for arbitrary modulation mappings and parallel information channels. The modulation trajectory can be engineered using analytic functions or aligned modulation grids, enhancing the flexibility and generality of polarization manipulation. Experimental demonstrations show that the proposed PS trajectory encoding metasurfaces can achieve histogram stretching, thresholding, and dual information channel encryption, providing enhanced security and flexibility in polarization optics applications. This work opens new opportunities for metasurfaces in both quantum and classical regimes, including advanced LC displays, optical computation, and encryption.The paper introduces a novel approach to polarization information encoding using Poincaré sphere (PS) trajectory metasurfaces, which leverages a generalized form of Malus' law (GML) governing 2D projections between arbitrary elliptical polarization pairs across the entire PS. This method significantly expands the encoding dimensionality of polarization information, offering versatile functionalities such as histogram stretching, thresholding, and image encryption within non-orthogonal PS loci. The GML describes a universal projection rule from one arbitrary elliptical polarization to another, allowing for arbitrary modulation mappings and parallel information channels. The modulation trajectory can be engineered using analytic functions or aligned modulation grids, enhancing the flexibility and generality of polarization manipulation. Experimental demonstrations show that the proposed PS trajectory encoding metasurfaces can achieve histogram stretching, thresholding, and dual information channel encryption, providing enhanced security and flexibility in polarization optics applications. This work opens new opportunities for metasurfaces in both quantum and classical regimes, including advanced LC displays, optical computation, and encryption.