Real-time processing of grayscale image data

Abstract

In a digital reproduction system incorporating a single pass scanner, accurate image processing results from processing a subset of grayscale image data. More specifically, scanlines that correspond to the leading edge of a document are stored and processed to detect skew and to obtain an appropriate correction. The lead edge correction is then applied to the entire grayscale image. Accordingly, the present systems and methods eliminate skew from grayscale images in real-time. The corrected image is rendered to binary and stored in electronic pre-collation memory and cropping, masking and other image editing operations can be performed on the binary image data before the image is printed.

1 . A method, comprising: 
 providing grayscale image data that represents an original document inside a scan area;    locating grayscale image data that represents at least a lead edge of said original document inside said scan area;    identifying a subset of the grayscale image data that excludes substantially all of said grayscale image data that does not correspond to said lead edge;    generating modified image data corresponding to said grayscale image data; and    displaying said modified image data in a viewable format.    
   
   
       2 . A method in accordance with  claim 1  wherein generating said modified image data further comprises: 
 processing said grayscale image data subset to detect skew in said original document lead edge;    deriving skew corrected grayscale image data pixels based upon said detected skew;    converting said skew corrected image data to an output device format; and    storing said output device formatted image data in a memory.    
   
   
       3 . A method in accordance with  claim 2  wherein spatial coordinates for at least a plurality of skew corrected grayscale image data pixels are derived in real-time.  
   
   
       4 . A method in accordance with  claim 1  further comprising retrieving said output device formatted image data and printing said output device formatted image data on a hardcopy sheet.  
   
   
       5 . A method in accordance with  claim 1  wherein generating said modified image data further comprises: 
 locating grayscale image data that represents at least a second edge of said original document inside said scan area;    converting said grayscale image data to a binary format;    storing said binary formatted image data in a memory;    retrieving said binary formatted image data from said memory;    identifying spatial coordinates for at least one corner of said original document based upon a location of said lead edge and at least one second original document edge;    removing at least a portion of said binary image data that does not correspond to data displayed on said original document; and    printing said binary image data.    
   
   
       6 . A method in accordance with  claim 1 , wherein said grayscale image data represents a continuous tone image captured by a raster input scanner.  
   
   
       7 . A method in accordance with  claim 6 , wherein said grayscale image data subset consists primarily of all of the pixels in the first n scanlines, wherein n is equal to the sine of a maximum skew angle multiplied by a number of pixels of said original document extending in a fast scan direction.  
   
   
       8 . A method in accordance with  claim 6 , wherein said grayscale image data subset consists of all of the pixels in the first 100 scanlines of said grayscale image data.  
   
   
       9 . A method in accordance with  claim 1  wherein said grayscale image data is provided by a raster input scanner.  
   
   
       10 . A method in accordance with  claim 1  further comprising identifying all of the grayscale image data corresponding to all of said original document edges.  
   
   
       11 . A method in accordance with  claim 1  wherein said grayscale image data analysis further comprises analyzing a plurality of image pixel scanlines, with the number of scanlines analyzed being substantially equal to the sine of a maximum skew angle multiplied by the number of pixels extending in a fast scan direction of said original document.  
   
   
       12 . A method in accordance with  claim 1  wherein said grayscale image data analysis further comprises analyzing-the first 100 scanlines of pixels of said grayscale image data.  
   
   
       13 . A method in accordance with  claim 1  wherein said grayscale image modification further comprises eliminating at least a portion of said skew.  
   
   
       14 . A system, comprising: 
 an image processor that receives grayscale image data that represents an image scan and converts it to grayscale image data;    a skew detection module that detects skew in at least one initially scanned line of said image scan by analyzing a grayscale image data subset that excludes substantially all of said grayscale image data that does not correspond to said lead edge;    a skew correction module that generates a skew corrected image data corresponding to said received grayscale image data based upon skew detected in said initially scanned line, with at least a portion of said skew being eliminated from said received grayscale image data in real-time; and    an image rendering module that formats said grayscale image data for use by a digital output device.    
   
   
       15 . A system as claimed in  claim 14  further comprising an image editing module that: (i) retrieves output formatted image data corresponding to said skew corrected grayscale image data from a memory; (ii) receives locations for at least two edges located within said image scan; (iii) derives coordinates for document corners inside said image scan; and (iv) removes output formatted image data that is located outside a border of said document corners.  
   
   
       16 . A system, comprising: 
 an image capture device that generates a digital representation of an input document image;    an image processor that (i) isolates pixels in said grayscale image data that represent a leading edge of an original document bearing said continuous tone image; (ii) analyzes said isolated pixels to detect skew in said original document leading edge; (iii) eliminates skew from substantially all pixels in said grayscale image data and (iv) converts said grayscale image data to an output device format; and    an output device that provides visible reproductions of said output device formatted image data.    
   
   
       17 . A system as claimed in  claim 16 , wherein said image capture device is a raster input scanner.  
   
   
       18 . A system as claimed in  claim 16 , wherein said digital output device is a xerographic digital printer.  
   
   
       19 . A system as claimed in  claim 16  further comprising an image editor that (i) derives the locations of at least one corner of said continuous tone image based upon grayscale image data edges locations received from said image processor and (ii) removes a portion of said output device formatted image data based upon its location relative to said at least one continuous tone image corner.  
   
   
       20 . A system as claimed in  claim 16 , wherein said image processor locates substantially all of the pixels in said grayscale image data that correspond to all of said edges of said original document bearing said continuous tone image.