Adaptive illumination correction of scanned images

A digital imaging method for imaging an open book having a book binding, said method comprising:

• scanning the open book to produce scanned image data, said image data containing illumination variations adjacent the book binding;
• extracting illumination data from the scanned image;
• normalizing the illumination variations across the scanned image;
• and
• outputting the normalized image data on a physical media,
• wherein the extracting illumination data step includes obtaining light levels of (i) background portions and (ii) foreground portions of the image;
• wherein the normalizing step includes defining a background illumination distribution and a foreground illumination distribution, from the obtained light levels;
• determining a background low threshold value BL and a background high threshold value BH from each background illumination distribution;
• and determining a foreground low threshold value FL and a foreground high threshold value FH from each foreground illumination distribution;
• calculating reference values for BL, BH, FL, and FH based on a plurality of BL, BH, FL, and FH values determined from regions not adjacent the book binding;
• generating a tone reproduction curve (TRC) corresponding to the calculated reference values of BL, BH, FL, and FH;
• and compensating the scanned image data in accordance with the generated TRC in order to maintain positions of BL, BH, FL, and FH values across the scanned image that are consistent with the corresponding reference values.

A digital imaging method for imaging an open book having a book binding, said method comprising:

• scanning the open book to produce scanned image data, said image data containing illumination variations adjacent the book binding;
• extracting illumination data from the scanned image;
• normalizing the illumination variations across the scanned image;
• and
• outputting the normalized image data on a physical media;
• wherein the extracting illumination data step includes obtaining light levels of (i) background portions and (ii) foreground portions of the image;
• wherein the normalizing step includes calculating an illumination scaling factor g(x) from the average of the upper 10 percent of background light levels;
• and
• scaling the scanned image data i(x, y) according to the relationship:
• i′(x, y)=i(x, y)/g(x).

A xerographic apparatus for reproducing an image representation of a scanned open book, said apparatus comprising:

• a planar imaging platen;
• means for scanning the open book placed on the platen to produce scanned image data, said scanned image data containing illumination variation adjacent a binding of the book;
• means for extracting illumination data from the scanned image data;
• a processor for calculating a plurality of illumination compensation parameters from the extracted illumination data;
• an image processor for compensating the scanned image data for illumination variations;
• an illuminator for transferring an image charge pattern onto a photoreceptor;
• at least one developing station for developing the charge pattern;
• and
• at least one fuser station for fixing a developed image onto a physical media;
• wherein the processor for calculating a plurality of illumination compensation parameters includes means for defining a background illumination distribution and a foreground illumination distribution;
• and means for determining high and low threshold values for the background and foreground illumination distributions;
• wherein the image processor includes means for calculating a illumination compensation factor g(x) and means for scaling the scanned image data i(x, y) according to the relationship i′(x, y)=i(x, y)/g(x).

A method of correcting illumination variation in a scanned image of a non-planar original object, said method comprising:

• scanning at least a portion of the non-planar original object to produce scanned image data;
• acquiring illumination variation data from the scanned image data;
• deriving a plurality of illumination compensation values from the acquired illumination variation data;
• altering the scanned image data in accordance with the illumination compensation values;
• wherein the step of acquiring illumination variation data includes measuring illumination values at a plurality of pixel locations;
• wherein the step of deriving a plurality of illumination compensation values includes calculating a spatially-dependent illumination gain factor g(x) from the measured illumination values;
• and
• wherein the step of altering the scanned image data i(x, y) includes scaling and offsetting the scanned image data according to the relationship i′(x, y)=i(x,y)/g(x)−b(x) and b(x) is a predetermined illumination offset factor.

A xerographic apparatus for reproducing an image representation of a scanned open book, said apparatus comprising:

• a planar imaging platen;
• means for scanning the open book placed on the platen to produce scanned image data, said scanned image data containing illumination variation adjacent a binding of the book;
• means for extracting illumination data from the scanned image data;
• a processor for calculating a plurality of illumination compensation parameters from the extracted illumination data;
• an image processor for compensating the scanned image data for illumination variations;
• an illuminator for transferring an image charge pattern onto a photoreceptor;
• at least one developing station for developing the charge pattern;
• and
• at least one fuser station for fixing a developed image onto a physical media;
• wherein the processor for calculating a plurality of illumination compensation parameters includes means for defining a background illumination distribution and a foreground illumination distribution;
• and means for determining high and low threshold values for the background and foreground illumination distributions;
• and
• wherein the image processor includes means for generating a tone reproduction curve (TRC) corresponding to the determined high and low threshold values for the background and foreground illumination distributions not adjacent the book binding, and means for mapping scanned image data in accordance with the generated TRC.