1. A method comprising: under control of a processing unit configured with executable instructions: partitioning an image into a plurality of image blocks; determining that a screen coding scheme is to be used for a first image block of the plurality of image blocks; computing a distribution of pixel values associated with the first image block; selecting one or more pixel values from the distribution of pixel values as one or more major colors, the one or more major colors corresponding to one or more representative pixel values for a plurality of pixels included in the first image block; assigning one or more first index values to the one or more major colors; assigning one or more second index values to one or more escape pixels included in the first image block, the one or more escape pixels not belonging to the one or more major colors; classifying each pixel of the plurality of pixels into a major color of the one or more major colors or an escape pixel of the one or more escape pixels based on a pixel value of each pixel; converting the pixel value of each pixel into an index value based on which major color or escape pixel the pixel value is classified as; determining correlations among the plurality of pixels of the first image block based on a line-based prediction algorithm and the index value of each pixel, the line-based prediction algorithm comprising at least a horizontal mode, a vertical mode and a normal mode; and encoding the first image block into a code according to the line-based prediction algorithm.