Patent Application
20100225937
It is desirable to reproduce rare or old books or other documents for the use and enjoyment of many viewers. However, rare/old books or other documents are often fragile and could possibly be destroyed if handled roughly (or at all). Thus, when imaging these materials it is often the case that the page being imaged is not or cannot be pressed flat for fear of damaging the page. In addition, even relatively new books having many pages will generally have some curvature along the page surface, which contributes to distortion in the imaged page. Consequently, the captured image will often include warped objects and/or text or warped lines of text.
It is desirable to efficiently and economically reproduce books and/or documents having minimal or no warp in the final product.
The accompanying drawings are included to provide a further understanding of embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and together with the description serve to explain principles of embodiments. Other embodiments and many of the intended advantages of embodiments will be readily appreciated as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts.
In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following Detailed Description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.
It is to be understood that the features of the various exemplary embodiments described herein may be combined with each other, unless specifically noted otherwise.
It is often impractical and/or undesirable to force a page to lie flat when imaging a document for fear of damaging the original document. Moreover, books with many pages will generally have some curvature along the page surface, which ultimately contributes to warp in the imaged page. In addition, other sources of warp include image-aberration(s) arising from lens artifacts that give rise to warp on edges of the captured image.
Embodiments provide a process and a system for correcting warp in objects and/or text of an imaged page. Generally, lines of text are printed in straight parallel lines with the words and the lines separated from adjacent words/lines by white space (or whatever the background is composed of). The system/method for correcting warp on an imaged page described below iteratively measures local deviations away from the expected well ordered text or object on the page by analyzing projection profiles of pixels in the image. If warp is detected, the system/method described below transformatively maps or distorts the warped pixels of the text or object to an appropriate, un-warped baseline.
Embodiments provide a system and a method for determining a projection profile for characters in an imaged page, determining whether warp is present on the page, and correcting the warp by mapping or distorting a warped object or a warped line of text to a reference baseline. Determining the projection profile includes both horizontal and vertical profiling, first to determine the orientation and then to evaluate the projection profiles parallel to the text lines to determine the warp.
In one embodiment, computer 22 includes a monitor 30 and is connected to one or more peripheral devices, such as printer 32. Monitor 30 is configured to enable viewing of the captured image of page 28 or viewing of the corrected image having the warp removed. In one embodiment, the corrected, un-warped image is saved to memory, or printed via printer 32, and/or transmitted to another device through network connection 34.
In one embodiment, computer 22 includes a central processing unit operating a suitable microprocessor and interfaced with a suitable computer bus or other interface(s) including a scanner, display monitor 30, a connection to a network interface, a connection to a printer 32, a connection to a keyboard 36, a connection to a floppy disc drive, a connection to a flash drive, or other suitable connections to computer 22 at 38. Computer 22 includes a main memory such as a random access memory that interfaces with a computer bus to provide random access memory storage for use by the central processing unit when executing stored programs. The central processing unit is configured to load and execute instruction sequences from a disc or portable memory (or from the network connection 34) into main memory and execute stored programs from the main memory. In one embodiment, computer 22 includes read-only memory that is provided for storing invariant instruction sequences such as start-up instruction sequences or basic input/output operating sequences, for example through keyboard 36.
In one embodiment, copy assembly 24 includes one or more lights 40 attached to a stand 42 and a support 44 attached to camera 26. In one embodiment, lights 40 are configured to illuminate one or more pages 28 of the book and support 44 is configured to enable camera 26 to have a selectively adjustable focus.
In one embodiment, non-text regions are segmented from a page before isolation of the text regions. Suitable such document segmentation includes the block segmentation approach of Wahl, Wong, and Casey or the area voronoi diagram approach, or other segmentation methods known in the art. In addition, in some embodiments page skew is identified prior to document segmentation through the use of Hough transforms or other suitable methods known in the art. In the presence of warp, the skew so determine is more likely to be slightly in error. In this case, deskew is employed to increase the efficacy of the dewarp
The presence of greatly differential projection profile behavior in vertical and horizontal directions is indicative of text. Text on a page is characteristically printed in parallel lines. In one embodiment, reference baseline 66 is a linear baseline that is horizontal relative to page 28 such that un-warped lines of text are parallel to baseline 66. The un-warped lines of text have a characteristically uniform projection profile pattern that is identifiable by digital analysis. For example, a projection profile for pixels between two adjacent lines is expected to be formed primarily of background (e.g., white pixels). A projection profile of a cross-section taken laterally through characters of text in line 62 would include multiple peaks corresponding to black pixels in each character of text. In one embodiment, the image processing function of computer 22 includes contrast adjustment and black pixels are those pixels having a pixel value in a range between about 0-25 and white pixels are those pixels having a pixel value between about 240-255. In this regard, thin features, for example text, are defined by gray transitions along the edges of the text or object of interest and appropriately identified and processed as described below.
In one embodiment, iterative processing of projection profiles for text 60 is completed until it is determined where baseline 66 intersects line 62, which indicates where baseline 66 just begins to touch (i.e., is tangent) to pixels of one or more characters of line 62. In the illustrated example, baseline 66 is tangent to line 62 approximately at the word “nibh.” The remaining portion of line 62 is warped with the text of line 62 deviating away from baseline 66. The projection profile across line 62 is sufficiently sensitive to recognize that the line of text underneath line 62 is warped and intersects baseline 66. Embodiments described herein provide a system and a method for quantifying the amount of warp of objects/text present in imaged page 28 and correcting the warp by mapping or transforming the warped object/text onto a baseline 66.
In one embodiment, the reference baseline is determined by evaluating projection profiles for a rasterized image of pixels to determine a first location at which the baseline touches or intercepts a black pixel in the boundary of the object. As described above, some projection profiles are associated with the white pixels in the background of the image between two lines of text, for example. Embodiments described herein provide an iterative process for determining projection profiles for the imaged page, calculating a reference baseline based on the projection profiles, and calculating a deviation away from the reference baseline for other pixels on the boundary of the imaged object/text.
Projection profile 100 is formed as a plot (e.g. a one-dimensional graph where the count at each pixel location across the image is the value of the pixels in the individual projection), which when viewed or “read” from left to right across line 62 creates a graph having local maxima (white background) and local minima (black pixels of text). For example, projection profile 100 includes a segment 102 composed of white background pixels (having the arbitrary value of 0) under the letters “pellentes.” The letter “q” includes a descender (e.g., a tail) that is captured by projection profile 100 as one or more black pixels as indicated at 104. Likewise, the letter “p” includes a descender indicated at 106. In the case of grayscale or color intensity images (e.g., non-binarized images), projection profiles are accumulated in one embodiment based on the amount of blackness. The amount of blackness is determined as the sum over all pixels in the projection of the absolute value of (white-point−pixel gray level). It is to be understood that the space between each letter would also register as background, in which case projection profile 100 would include a local minima for pixel(s) of each letter and a local maxima representing the space between each letter. However, for ease of illustration, the local minima associated with the pixel(s) in the letters have been blended into a single segment. In one embodiment, text is distinguished from the background by employing a moving average to filter the projection profiles with a lobe (e.g., half width) of averaging of approximately 1/40 of an inch.
The projection profile 100 includes a segment 108 that is tangent to the letters “ellentesque, nibh quam sollic.” Thus, segment 108 registers the black pixels in those letters. White space between the word “pellentesque” and the comma is indicated at 110. The black pixel(s) of the comma is indicated at 112 and the space after the comma and before the word “nibh” is indicated at 114. The two spaces between the next three words is also indicated at 114. Segments 116 provide a projection profile oriented at a base of the words “nibh quan sollicitudin.” Thereafter, projection profile 100 diverges away from the black pixels in the text as indicated by segment 118.
Segments 108 and 116 indicate sharp demarcations between black pixels and white pixels, knowledge of which contributes to the determination/location of a reference baseline for the text line 62. In one embodiment, segments such as segments 108, 116 are identified as being tangent to, or just touching, a median height portion of a character of text. Segment 118 indicates a divergence away from black pixels and could represent either the end of the sentence or warp. However, projection profile 100 intersects characters in line 65 as indicated by the local minima at 120, which indicates the presence of black pixels and some level of warp in one or both of lines 62 and 65. In this exemplary manner the structure of projection profile 100 can be employed to determine a reference baseline for line 62 and identify the presence of warp in one or both of text lines 62, 65. The correction of the warp that is identified by projection profile 100 is described below.
Linear line segments of best-fit may or may not have a slope. Linear line segments of best-fit having slope of zero correspond with text that is not warped or with text that has negligible warp (after the page is deskewed as described above). In general terms, linear line segments of best-fit that have a non-zero slope indicate some amount of warp in the line of text (provided the page is not skewed). The warp is corrected by mapping the curve of best-fit (having a non-zero slope) onto the baseline. At 180, the curve of best-fit is evaluated and determined to be quadratic (i.e., of the form Y=ax2+bx+c). Warped text is corrected by mapping the quadratic line of best-fit to the baseline at 182. In other words, if there is a lack of confidence in the quality of the line of best fit, then the actions at 170 move to a quadratic best fit, and if this provides a significantly better fit for the data, there is confidence that warp is present, and the equation Y=ax2+bx+c is used to correct the warp.
In one embodiment, the iterative regression employed in
The warp in line 62 of text is corrected by mapping the deviations calculated as the distance D and the angle A back to baseline 66 in a suitable transformative process. In one embodiment, the mapping is pixel-by-pixel in which the pixel associated with the distance D and the angle A is distorted or mapped to baseline 66 by a distance equal to the distance D and is linearized onto baseline 66 by an amount equal to the angle A. In other embodiments, the warp in line 62 of text is not linear but is associated with a higher order best-fit curve. Warp in line 62 is corrected by mapping the quadratic line of best-fit for warped line 62 onto baseline 66. In one embodiment, the calculated distances D to the first black pixel from the edges of the map are employed to correct warp in line 62 by iteratively mapping pixels in the Y direction and then in the X direction to “flatten” out the distance D toward zero.
Embodiments provide a process and a system for correcting warp in objects and/or text of an imaged page that takes advantage of the notion that un-warped lines of text are typically printed in straight parallel lines with the words and the lines separated from adjacent words/lines by white space. The system/method for correcting warp on an imaged page iteratively measures local deviations away from the expected straight/parallel orientation by forming and analyzing projection profiles of pixels in the image. If warp is detected, the system/method transforms or maps or distorts the warped pixels of the text or object to linear un-warped baseline.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments of un-warping text/objects on an imaged page as described herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.
