Abstract: Apparatus and methods for de-screening an image signal utilizing a bank of filters to provide several increasingly blurred versions of the original image signal is disclosed. At any given time, one or more of the blurred versions are created, on a pixel-by-pixel basis. The outputs from a selected pair of blurred signals are then blended together to create a variable blending output that can vary smoothly from no blurring to maximum blurring in a smooth and continuous manner. In addition, the apparatus and methods provide enhanced text and line art by using a variable un-sharp masking mechanism with independent post-blur sharpening control, and detect and enhance neutral (no-color) output pixels.

Abstract: Methods and systems include a dependent min-max module the receives image data and generates a dependent Min value and a dependent Max value within a window around a pixel of interest. A dynamic threshold module, based on the dependent Min and Max values, generates continuity data and enhanced data suitable for identifying, for example, blobs.

Abstract: A method and a system for separating an image signal into a set of image planes. The system comprises a min-max module, a dynamic threshold module and a separation module. The min-max module receives the image signal, searches for a minimum and maximum within at least one window centered on a current pixel in the image signal. The dynamic threshold module computes, for the window, based on the respective minimum and maximum received from the min-max module and the current pixel, a respective indicator representing the distance and direction of the current pixel relative to a respective threshold plane, and outputs a control signal based on the indicator. The separation module separates the image signal into the set of image planes in accordance with the control signal by including a representation of the current pixel in at least one of the image planes.

Abstract: A Statistics Module (STS) is disclosed for collecting essential statistics about an image content for the purpose of applying various image enhancement operations such as page background removal and automatic neutral detection to determine if the page is gray or colored. The Statistics Module uses the blurred signal BLR from a De-Screen Module in order to eliminate some of the scanner noise. The output is a special 3D color histogram array.

Abstract: A method and a system for computing the function value of an input node based on function values of known nodes. A database of known nodes and their corresponding function values is formed. The known nodes are located such that a distance between any two adjacent known nodes is an integer power-of-two number. The database is searched for a first node such that the input node is located between the first node and an adjacent second node. The difference &dgr; between the input node and the first node is computed. Then &dgr; is shifted to the right by k positions, k being the logarithm in base 2 of the distance between the first and second nodes. The input node function value is computed by combining the first node function value with the product of the shifted &dgr; and the difference between the function values of the second and first nodes. When used in MRC context, the above method and system is applied to each of the color MRC planes individually, instead of the merged output.

Abstract: A method and a system for dynamically thresholding an image signal. The system comprises a computing block. The computing block receives the image signal and a minimum and a maximum within each of a set of windows centered on the current pixel in the image signal, and computes, for each of the windows, based on the current pixel and the respective minimum and maximum, a respective indicator representing the distance and direction of the current pixel relative to a respective threshold plane, and outputs a control signal based on the indicators.

Abstract: A method of generating a binary Sel plane for image compression is disclosed. The method first generates a 2 bit gray selector (GraySel). This 2 bit selector is then processed in a second stage to produce a binary Sel decision which minimizes the compression noise evident in the reconstructed image. The method used here to generate the 2 bit GraySel applies a set of prioritized rules over a small 3×3 window that is well suited for segmenting synthetic, PDL generated images that are typically free of scanner noise. The method not only marks the proper sense of the selector when it is known, but also include a 3rd state that indicates that the selector decision is weak or unknown. This weak decision can then be optimized in the second stage process based on strong edges information in the neighborhood.

Abstract: A foreground erosion method is used to meet thin (but unbroken) text requirements using linear YCC segmentation. The method uses a fixed value subtracted from a gray selector signal, thereby thinning/eroding the foreground. In cases where the pixel would be converted from foreground to background, this is only done if a neighborhood test verifies that the thinning won't result in broken lines. The foreground erosion method attempts to match a couple of templates wherein if a match is found, then the adjustment is performed.

Abstract: An efficient method and system for eliminating halftone screens from scanned documents while preserving the quality and sharpness of text and line-art is disclosed. The method and system utilizes one or more independent channels with different sensitivities (e.g., Max, High, and Low) to provide high quality frequency and magnitude estimation. The most sensitive channel (Max) derives the frequency estimate, and the remaining channels (e.g., High and Low) are combined to create the screen magnitude. The Max channel is the most sensitive and will usually report the existence of frequencies even when the screen is very weak. Therefore, the screen frequency must be additionally qualified by the screen magnitude. The screen magnitude can be interpreted as the level of confidence that the local neighborhood represents half-toned data.

Abstract: A method for improving mixed raster compression segmentation utilizes a second stage of a process to generate the MRC Selector plane by operating on a multibit selector (GraySel) signal which is produced by a first stage process. The first stage methods used to generated the GraySel can be PDL or scan oriented. The binary Selector signal produced by the second stage minimizes the compression noise evident in the reconstructed image. This second stage processing relies on knowing the size of the JPEG minimum coded unit (MCU) which will be used to compress the segmented Foreground and Background planes. The idea is to move false (soft) edges away from the real (hard) edges by as large a distance as possible up to the point where they fall off the boundary of the MCU block. Thus a soft edge which occurs between two hard edges is either eliminated or repositioned to the midpoint and a soft edge between a hard edge and the MCU boundary is moved to the boundary.

Abstract: A method and system for de-screening an image signal utilizing a bank of filters to provide several increasingly blurred versions of the original image signal is disclosed. At any given time, only two of these blurred versions are created, on a pixel-by-pixel basis. The outputs from the selected pair of blurred signals are then blended together to create a variable blending output that can vary smoothly from no blurring to maximum blurring in a smooth and continuous manner. In addition, the method provides the capability to enhance text and line art by using a variable un-sharp masking mechanism with independent post-blur sharpening control, and the capability to detect and enhance neutral (no-color) output pixels.

Abstract: A Gamut Enhance Module (GME) is disclosed for applying 3 independent Tone Reproduction Curves (TRC) to each of the color components of an input image. The implementation is done via three independent and fully programmable 1D lookup tables. The input to the Gamut Enhance Module is the output DSS from a Scaling Module (SCL), representing a scaled and de-screened version of the source image. The output is a gamut-mapped signal GME. The GME unit includes special logic to neutralize (set to gray) or preserve input colors.

Abstract: A method and a system for computing the function value of an input node based on function values of known nodes. A database of known nodes and their corresponding function values is formed. The known nodes are located such that a distance between any two adjacent known nodes is an integer power-of-two number. The database is searched for a first node such that the input node is located between the first node and an adjacent second node. The difference &dgr; between the input node and the first node is computed. Then &dgr; is shifted to the right by k positions, k being the logarithm in base 2 of the distance between the first and second nodes. The input node function value is computed by combining the first node function value with the product of the shifted &dgr; and the difference between the function values of the second and first nodes. When used in MRC context, the above method and system is applied to each of the color MRC planes individually, instead of the merged output.

Abstract: A method and a system for separating an image signal into a set of image planes in accordance with a control signal. The system comprises a selector module, an edge processing module and a foreground/background separation module. The selector module receives the control signal and produces a selector signal. The edge processing module receives the selector signal and produces a decision signal.

Abstract: A method and a system for de-screening an image signal. The system comprises a filter bank, a control module and a blend module. The filter bank filters the image signal and produces a set of filter output signals. The control module generates at least one control signal based on the image signal and some of the filter output signals. The blend module dynamically blends the filter output signals in accordance with the control signal to produce a de-screened output signal.

Abstract: A method and a system for dynamically thresholding an image signal. The system comprises a computing block. The computing block receives the image signal and a minimum and a maximum within each of a set of windows centered on the current pixel in the image signal, and computes, for each of the windows, based on the current pixel and the respective minimum and maximum, a respective indicator representing the distance and direction of the current pixel relative to a respective threshold plane, and outputs a control signal based on the indicators.

Abstract: A method and a system for separating an image signal into a set of image planes. The system comprises a min-max module, a dynamic threshold module and a separation module. The min-max module receives the image signal, searches for a minimum and maximum within at least one window centered on a current pixel in the image signal. The dynamic threshold module computes, for the window, based on the respective minimum and maximum received from the min-max module and the current pixel, a respective indicator representing the distance and direction of the current pixel relative to a respective threshold plane, and outputs a control signal based on the indicator. The separation module separates the image signal into the set of image planes in accordance with the control signal by including a representation of the current pixel in at least one of the image planes.

Abstract: A method and a system for separating an image signal into a set of image planes in accordance with a control signal. The system comprises a selector module, an edge processing module and a foreground/background separation module. The selector module receives the control signal and produces a selector signal. The edge processing module receives the selector signal and produces a decision signal. The foreground/background separation module receives the image signal and the decision signal, and outputs a foreground signal and a background signal, a representation of the current pixel of the image signal being included in at least one of the foreground signal and the background signal in accordance with the decision signal.

Abstract: A method and a system for controlling de-screening of documents. The control system is included in a de-screening system including a bank of filters. The filter bank receives an image signal and produces a set of filter output signals. The control system comprises a contrast module, a halftone estimate module and a pixel control module. The contrast module receives a filter output signal from a filter having a large filter span and produces a contrast signal. The halftone estimate module receives the image signal and a filter output signal from a filter having a small filter span and produces an estimated frequency signal and a halftone weight signal. Based on the contrast signal, the estimated frequency signal and the halftone weight signal, the pixel control module produces a control signal which includes information regarding which of the filter output signals are to be blended and the proportion of blending.

Abstract: Pixel blocks of an input image are type classified based on an analysis of pixel values for each respective pixel block. A discrete cosine transform (DCT) is performed on the pixel values of each pixel block, and a quantization modification process thresholds and/or quantizes the resulting DCT coefficients based on the type classification of the respective pixel block. Once the coefficients are modified in this way and encoded, the resulting data can be decoded and dequantized in compliance with the standard JPEG sequential mode data syntax in order to construct a perceptually faithful representation of the image, without passing any additional information to the decoder concerning the quantization modification.