Black point adjustment based on image background
AssigneeXerox Corporation
InventorsFrancis Tse, Ramesh Nagarajan, Charles E. Farnung
Life of this patent
Estimating the term…
Abstract
A digital scanner or copier is provided that can dynamically adjust the black point of an image to be scanned based on detected background level of the document. A pre-scan acts on a small scanning window near a leading edge of the document to obtain a histogram of grey-level values. From this, the background level of the document can be obtained to determine a white point of the image. Additionally, a black point of the image is originally set to a default offset value. However, an adjustment factor based on the detected white point is used to adjust the default offset value to a value that increases the dynamic range of the output image, while still maintaining solid black for black areas of the image.
Claims19
A method for dynamically adjusting a black point of a scanned document based on detected image background, comprising:
- scanning at least a portion of a document;
- automatically detecting a background of the document to form a white point WP of the image;
- providing a default fixed offset value FOV used as an initial black point BP of the image;
- providing a scaled adjustment factor AF dependent on the detected white point WP;
- providing a scaled black point BP by multiplying the fixed offset value FOV by the scaled offset adjustment factor AF;
- computing a gain G according to the equation G =255/(WP−BP);
- and
- scanning the image and applying the gain G and black point BP to all pixels of the image.
A method for dynamically adjusting a black point of a scanned document based on detected image background, comprising:
- scanning a small portion of a document near a leading edge of the document using a digital scanner;
- automatically detecting a background of the document to form a white point WP of the image;
- providing a default fixed offset value FOV used as an initial black point BP of the image;
- providing a scaled adjustment factor AF dependent on the detected white point WP;
- providing a scaled black point BP by multiplying the fixed offset value FOV by the scaled offset adjustment factor AF;
- computing a gain G according to the equation G=255/(WP−BP);
- and
- applying the gain G and black point BP to all pixels of the image.
A digital scanner capable of dynamically adjusting a black point of an image on a document to be scanned based on a detected background of the image, comprising:
- a scanning unit that can scan the document;
- a histogram generator that generates a histogram from scanned data corresponding to at least a portion of the scanned document;
- a computing unit;
- a fixed offset value FOV stored in memory;
- and
- an offset adjuster that calculates an offset adjustment factor AF based on a detected white point WP of the document,
- wherein the computing unit calculates the white point WP based on the histogram, calculates a black point BP based on the fixed offset value FOV and the detected white point WP, and calculates a gain based on the calculated white point WP and black point BP.
Dependencies are inferred from the claim text.