63fb46d6_bster_US___Patent_applications__Description
[Patent application number] 20100142820 [Published] 06-10-2010 [Description] 
3 + 1 LAYER MIXED RASTER CONTENT (MRC) IMAGES HAVING A BLACK TEXT LAYER - A method, system and data structure for providing a 3+1 layer MRC image, including a black text layer. The black text layer includes pixel data corresponding to black text in an image and may be assigned a predetermined value for the color of black. According to one or more embodiments, using thresholding processing along with various morphological operations, the black text layer may be generated.
Xing Li, Webster US - Patent applications