Abstract: A technique for segmenting an image into text areas and non-text areas in which an image is stored with the following information per pixel: gray scale intensity (4 bits) and an indication of whether the pixel is neutral or color (1 bit). The image, e.g. a scanned RGB image, is converted to 0-15 levels of intensity and has a neutral/color indication bit assigned to each pixel. The technique proceeds in three phases as follows: Tile the image by square blocks, e.g. 6×6 or 8×8 for 600 dpi images, and store information about each block in a buffer; sweep the buffer left to right three tile rows at a time and make a preliminary decision for every tile-block in the middle row; examine the decision made in the previous step in a context block, e.g. a 3×3 block, and make revisions if necessary.

Abstract: An image descreening process first smoothes the image, where smoothing is accomplished by applying a convolution with a low pass filter (LPF) kernel, which is a parameter to the descreening function. Using the smoothed image, a determination is made for each pixel for which pixels around it participate in the modified filter. For a current pixel, a window is considered having the size of the LPF kernel, with the current pixel at the center. A threshold T1 which is given as a parameter, is used to mark the pixels in the current window. Considering a pixel in the window, if for all color components the difference between this pixel value to the center pixel value is less than T1 in absolute value the pixel is marked with a 1. Otherwise, the pixel is marked with a 0. Finally, an adaptive version of the LPF is applied. If the number of pixels marked with a 1 in the window is less than a third of the kernel size, the original pixel value is restored.

Abstract: A method and apparatus for image classification includes a first embodiment, in which halftone detection is performed based on the size of a boundary set between a class of light pixels and a class of dark pixels, and further based upon image information contained within each single image plane (i.e within one color plane). This embodiment of the invention is based upon the distinctive property of images that halftone areas within the image have larger boundary sets than non-halftone areas within the image. A second, equally preferred embodiment of the invention provides a cross color difference correlation technique that is used to detect halftone pixels.