Out-of-layer pixel generation for a decomposed-image layer

Abstract

Images may be decomposed into separate layers each containing a limited number of types of image element (text, line art, or photographic). Each layer can then be compressed separately with a process that is optimal for the type of image element included in the layer. Images are decomposed into foreground, background, and mask layers. A method is provided for generating the out-of-layer pixels and, as a result, generating a layer having a limited color palette that is to be compressed with a palette based lossless compression method. A plurality of neighboring pixels is identified for each pixel selected from the image. If the neighboring pixels are out-of-layer pixels, the spatially corresponding pixel in the decomposition layer is assigned a default value. If the neighboring pixels include in-layer pixels, the pixel of the decomposition layer spatially corresponding to the selected pixel is assigned the predominant color of the in-layer neighbors. If equal numbers of the neighboring pixels have the same colors then the selected pixel is assigned the value of a predetermined neighbor. If no two neighboring pixels have the same color then the spatially corresponding pixel is assigned the color that is most likely to occur in conjunction with pixels having the colors of the neighboring pixels.