Patent ID: 6826309
Filing Date: 2004-11-30
Classification: G06T

Abstract:
A method for prefiltering scanned image pixel data, wherein scanned pixel data is divided into pixel blocks (PIBLs), and steps of the method for prefiltering are applied to the PIBLs, the method of prefiltering a given one of the PIBLs comprising the steps of:filtering the pixels of the given PIBL to create a blurred PIBL; computing the average of the two neighboring pixel values in each direction from each pixel of the blurred PIBL, the average for each direction being referred to as North, South, East and West values respectively; setting a first threshold bit (X_Mask) for each pixel of the blurred PIBL if an absolute value of the East value minus the West value for the respective pixel exceeds a fist threshold (TA); setting the first threshold bit (X_Mask) for each pixel of the blurred PIBL if the first threshold bit for a neighboring pixel to the East or the West has its said first threshold bit set; setting a second threshold bit (Y_Mask) for each pixel of the blurred PIBL if an absolute value of the North value minus the South value for the respective pixel exceeds a second threshold (TB) setting the second threshold bit (Y_Mask) for each pixel of the blurred PIBL if the first threshold bit for a neighboring pixel to the North or the South has its said second threshold bit set; OR-ing together the first threshold bit (X_Mask) and the second threshold bit (Y_Mask) for each pixel of the blurred PIBL and providing a result in a filter control mask bit for each respective pixel of the blurred PIBL; creating a temporary block of pixels by applying a smoothing filter to the given PIBL; and creating an output block by copying a value for a pixel of the final output block from a value of a corresponding pixel from the given PIBL when the control mask bit for the corresponding pixel in the blurred PIBL is set, and copying a value for a pixel of the final output block from a value of a corresponding pixel from the temporary block when the control bit mask forte corresponding pixel in the blurred PIBL is not set.