Patent Application
20170180587
The present invention is directed to systems and methods for optimizing the calibration position when calibrating a document scanning system using either a single calibration target (strip) or a dual calibration target (strip) to account for illumination profile and sensor differences during document handler scanning and platen scanning.
A document handler, also known as Constant Velocity Transport (CVT) device, draws individual sheets from a stack of sheets and sequentially allows the image on each sheet to be scanned by an optical module. The above differences must be periodically compensated for in order to ensure consistent imaging over time. One common source of long-term performance variation over time can be attributed to platen and CVT scanning, due to illumination intensity changes (depth of illumination) and sensor changes. The process of periodic compensation is referred to as calibration. The position on the calibration strip of the calibration function is important but difficult to determine on the calibration strip, especially for an internal second side scanner. The teachings hereof are directed to scanner calibration using a calibration strip.
What is disclosed is an apparatus and method for optimizing the calibration position when calibrating an optical module of a document scanning device. In one embodiment, the present method involves using imaging sensors of an optical module of a document scanning device to obtain an image scan of a calibration strip (as described herein) on a surface of a platen on which a sheet to be scanned is placed. The calibration strip has a first vertical line at a first distance from a right edge of the strip. The second vertical line has at a second distance from a left edge of the strip. A horizontal line is between the first and second vertical lines. A slope of the horizontal line is non-zero. As disclosed herein further, the image scan of the calibration strip is to calibrate the optical module. Features and advantages of the above-described system and method will become readily apparent from the following detailed description and accompanying drawings.
The foregoing and other features and advantages of the subject matter disclosed herein will be made apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:
What is disclosed is an apparatus and method for optimizing the calibration position when calibrating an optical module of a document scanning device. One of ordinary skill in this art would be readily familiar with various aspects of document scanning devices, as are generally known, including document handlers, scan heads, platens, and the like, including methods for performing calibration of a document scanning device.
An “image”, as used herein, refers to a spatial pattern of physical light comprised of known colors of the light spectrum which are visible by the human eye. When reduced to capture or rendering, the image generally comprises a plurality of colored pixels.
A “document sheet” or simply “sheet” refers to an image that has been rendered onto a media substrate such as paper. A sheet can be, for example, a page, a book, a magazine, plots, charts, graphs, photos, and the like. The substrate comprising the sheet may be paper, plastic, fabric, or other image-bearing media.
An “image scan” refers to either a digital representation of a document sheet which has been scanned by the scanner bar, or a hardcopy print of the scanned document sheet.
An “optical module” refers to a portion of the scanning device used to capture and process an image scan of a document sheet. The optical module typically comprises an imaging sensor and an illuminator source mounted on a moveable carriage. Various aspects of the optical module reside in the scanning case, i.e., an area beneath the platen which is traversed by the movable carriage. In various embodiment, the optical module further comprises image processing circuitry, memory, and one or more processors executing machine readable program instructions for performing various aspects of the teachings hereof.
A “scanner bar” also referred to as a “scan head” has an array or equivalent hardware comprising a plurality of imaging sensors that convert reflected light into digital signals. A document scanning device may have more than one scan head. Various aspects of the scan head reside in an area referred to as the scanning case. The scanner bar performs either platen scanning or document handler scanning.
“Platen scanning” refers to a scanning operation wherein the scan head obtains an image scan of a sheet resting on the main platen. In platen scanning, the sheet on the platen remains stationary while the scan head is moved beneath the main platen to capture an image of the face of a document sheet resting thereon. The calibration strip associated with the main platen is called the platen calibration strip.
“Document handler scanning” refers to a scanning operating wherein the scan head obtains an image scan of a sheet which is passing through a scanning window or smaller platen (of adjacent to the main platen). In document handler scanning, the scan head remains stationary while the document handler moves the sheet being scanned along a path of a paper transport or feed mechanisms. The calibration strip associated with the document handler is call the document handler calibration strip.
A “calibration strip”, in one embodiment, is shown in
A “document scanning device” or “document scanner” is a device which, in its broadest sense, comprises a scanner bar that optically scans a media and converts the scanned image to a digitized format and a document handler that transports sheets of paper through the scanning device. Common scanning devices include specialized image receptors mounted on a carriage which move beneath a light-transmissive platen and scan a sheet manually placed on top of the platen or scan a sheet being transported by a document handler. An opaque cover is lowered over the sheet on the platen to exclude ambient light. Thereafter, a carriage moves the scan head over to a calibration strip located inside the scanner case, generally defined as an area beneath the platen. The scan head captures an image scan of the calibration strip. The image is analyzed to obtain measurements which, in turn, are used to calibrate the optical module. Once calibrated, the scan head which generally comprises an array of imaging sensors and light sources mounted on a carriage moves to a start of an imaging area and proceeds to move across the pane beneath the platen while imaging sensors detect the light reflected from the face of the document sheet laying on the platen. The sensors of the scan head may be charge-coupled devices (CCDs) or Contact Image Sensors (CISs). CCD-type scanners typically contain three rows of sensors with red, green, and blue filters and a light source for illumination. CIS-type scanners typically consist of a monochromatic photodiode array and red, green, and blue LEDs for illumination. Transparent images placed on the platen may require special accessories that illuminate them from an upper side. Circuitry in the scanning device creates an image of the document sheet.
Reference is now being made to
The document handler 200 sits atop a main body 201 of the scanner or copier. The document handler is movable relative to the main body, typically by a pivot or hinge-like mechanism (not shown) at the back of the scanner. When the document handler is moved away from the main body, a light-transmissive platen 202 is exposed so a user can place a single sheet thereon to have an image thereof recorded. The platen has a top surface and a bottom surface. When the document handler is in a closed position, a platen backing 203 is in contact with the top surface of the platen and faces downward. Beneath the platen in the scanning area is a scanner bar 204. Mounted on the scanner bar is an illumination source 205 and imaging sensors 206 arranged so that light emitted by illumination source is reflected by the face of the document sheet on top of the platen. The reflected light is recorded by the imaging sensors. The imaging sensors include photosensitive receptors connected to image processing circuitry (not shown) to record and manipulate the image data to obtain an image scan. When a single sheet or other item is desired to be scanned, the scanner bar is caused to move, as shown, relative to the platen to obtain an image scan of that sheet. Alternatively, the imaging sensors 206 are stationary within main body 201 but can selectively record an image on scanning window 207 (a smaller platen) or by the action of an arrangement of one or more movable mirrors or lenses (not shown).
Output analog signals from the imaging sensors are conditioned and converted to digital signals and sent to a controller 208 for further processing or storage. Processor 210 converts the digital signals to output signals 209 and normalizes and further processes the signals as required to enable the device to store and handle the image data in the form required to carry out the scanning task. The processor may also provides enhancements and changes to the signals such as filtering, thresholding, screening, cropping, scaling, and the like, as are desired or as needed. The controller also comprises a memory 211 for storing machine readable program instructions (software), machine operating data, and the scanned image currently being processed, and may further have computer-readable media (not shown) for off-loading the image data. Machine readable program instructions cause the controller, operating alone or in conjunction with the processor 210 to generate signals 212 to control the scanner bar 204, to store and generate calibration values, and to perform other functions know to those in the art.
Sheets placed in tray 213 are drawn one at a time via path 214 by motors (not shown), driving the rollers along the path past the scanner bar and ultimately to output tray 216. If the device is capable of operating in a duplex mode, i.e., sequentially scanning a first one side and then a second side of a sheet, the sheet is effectively inverted and passed through duplexing path 217 for scanning of the second side, or optionally with a second side scanning device 215. In document handler scanning, the scanner bar remains stationary relative to the main body while successive sheets are transported through path 214. When there is no sheet passing through the document handler, the scanner bar sees a backer bar 218 within the document handler. The backer bar may be in the form of a rotatable roll which facilitates transport of a sheet through the document handler. In a practical implementation of a scanner such as is shown in
In this embodiment, there is as first calibration strip 105 (platen calibration strip) and optionally a second calibration strip 110 (document handler calibration strip) for the second side scanning module 215 in a single pass configuration. The first calibration strip is read by scanner bar 204 through the main platen. The scanning device of
The calibration strips should be placed in areas of pre-determined reflectivity such as on or beneath the main platen or near the backing surface 203, where an image scan of the calibration strips can be obtained by the scanner bar for calibration purposes.
Reference is now being made to
Distance from a Top Edge in mm:
Width×((Start Pixel)/Length) (1)
Assume the following measurements: width=10, length=6000, and the start pixel=850. Using Eq. (1) with these values, we get: 10*(850/6000)=1.4 mm (at 801 from the edge 800 of
Linear Scanning Area in mm:
Width×(Linear Motion−Start Pixel)/Length (2)
Assume that following measurements: width=10, linear motion=3800, start pixel=850, and length=6000. Using Eq. (2), and plugging in these values, we get: 10*(3800−850)/6000=4.9 mm (at 802 from the edge 800 of
Number of Scan Lines:
The number of scan lines between the start pixel (at 706) to the point of linear motion 708 is 25 lines (at 710).
Reference is now being made to the flow diagram of
At step 902, use imaging sensors of an optical module of a document scanning device to obtain an image scan of a calibration strip. Embodiments of various calibration strips are shown in
At step 904, analyze the image scan to obtain calibration position and speed measurements.
At step 906, calibrate the relative position and speed of the optical module and calibration strip based on the calibration position and speed measurements.
At step 908, a determination is made whether to re-calibrate this device. If so, then flow processing repeats with respect to step 902 wherein the imaging sensors of an optical module of a document scanning device are used to obtain an image scan of a calibration strip. The image scan of the calibration strip is analyzed to obtain calibration position and speed measurements and the relative position and speed of the optical module and calibration strip is calibrated based on those measures. Thereafter, in this embodiment, further processing stops.
It should be understood that the flow diagrams depicted herein are illustrative. One or more of the operations illustrated in the flow diagrams may be performed in a differing order. Other operations may be added, modified, enhanced, or consolidated. Variations thereof are intended to fall within the scope of the appended claims.
One or more aspects of the teachings herein are intended to be incorporated in an article of manufacture which may be shipped, sold, leased, or otherwise provided separately either alone or as part of a product suite or a service. The above-disclosed and other features, functions, or alternatives thereof, may be desirably combined into other different systems or applications. Presently unforeseen or unanticipated alternatives, modifications, variations, or improvements may become apparent and/or subsequently made by those skilled in this art which are also intended to be encompassed by the following claims.
