In his article, Book Scanners: A Short Report about the Minolta PS7000 and the BookEye (META e-news, November 2001), Günter Mühlberger successfully articulates four difficulties in handling bound material in top-down scanning operations. He explains that:
The magnitude of such difficulties is multiplied in the case of top-down scanning tightly bound, oversize materials. Given these more problematic materials, we at the University of Iowa Libraries Preservation Department have been exploring fore edge registration hand-cradling (henceforth referred to as FER hand-cradling) as an alternative to conventional methods for our top-down scanner, which normally calls for a 180° book opening and gutter registration. This alternative emphasizes the important role of hand-manipulation, and perhaps suggests a greater versatility of mid-range scanners such as the Minolta PS7000. Although this method was developed using the Minolta PS7000 in conjunction with Elan GMK's PPP (Precise Page Positioning) image processing software, the method may be adaptable to a variety of scanning operations. In this article, I hope to outline the procedure for the FER hand-cradling method, contrast it to more conventional methods for top-down scanning, and consider how it addresses the difficulties well articulated by Mühlberger.
The Minolta PS7000 is intended to scan a book in right-reading mode, with the head of the book aligned against the back gauge, and centered on the scan table with gutter registration (Fig. 1, b & c). In FER hand-cradling the book is placed on the scan table in a landscape orientation with the fore edge against the back gauge (instead of the head against the back gauge) (Fig. 2 &3, f). Thus, while the scan still moves from the operator's left to right, it is now reading a single page from head to tail. This orientation permits non-damaging production paging at little more than a 90° opening and is particularly suited for tightly bound, oversize materials. This fore edge orientation also seems well suited to the Minolta's lighting array (e.g. page cockling seems less disruptive to the scan).
Since the book's fore edge is against the back gauge, the book orientation for recto page scanning differs from that of verso page scanning. For efficiency, accuracy, and preservation purposes the scanning is implemented in a "two-pass" process: all recto pages are scanned in one series, and the verso pages are scanned in a second series. Proper page sequencing is maintained by using a scanner interface that allows for incremental page/file numbering by 2 (e.g. 1, 3, 5, 7, for recto and 2, 4, 6, 8 etc. for verso). As pages are scanned, the recto and verso scan series are saved respectively in two separate directories. (The reason for separate directories is explained below).
Hand-cradling during the recto pass requires the back cover of the book to rest on the scan table with the head carefully aligned to the left edge of the scan field (Fig. 2a). The individual pages are lifted from the text block to the front cover, which is held vertically at an approximate 100-110 degree angle, depending on the natural opening of the book (Fig. 2b).
Hand-cradling during the verso pass requires that the front cover of the book rest on the scan table with the head carefully aligned the right edge of the scan field (Fig. 3a). As the text block is held perpendicular to the scan table, individual pages are dropped from the vertical position to the horizontal plane of the scan field (Fig. 3b).
In FER hand-cradling, the scan operator becomes a new kind of book reader, who must develop an awareness of the book beyond the text and page sequence, and learn to read its structure and function, anticipating its movement and needs. Each aspect of this hand-cradling process relies upon the skill of the operator, who exercises a very delicate control with her hand-held support and finger paging, and administers consistent placement of the book on the scan table.
Because book scanning is a re-imposition of a book, the operator must give consideration to the three-dimensional aspect of the book; that is, the position of the book along the x-, y-, and z-axes. In conventional top-down scanning, the x-axis aligns with the head & tail, the y-axis with the fore edge, and the z-axis with the height of the text block (at the page opening). In FER scanning, the x-axis aligns with the fore edge, the y-axis with the head & tail, and the z-axis with the height of the book within the depth of field.
To ensure consistent alignment of each scanned page to the next along the x- and y-axis, the orientation of the page on the scan table requires that the head of the book be registered consistently to scan table guidelines and that the fore edge of the book be aligned against the back gauge.
To ensure clean image capture in the z-axis, the operator must exercise a constant awareness of the overhanging sweep (Fig. 2a & 3a, g) as she progresses through the book. If the book's open angle is too slight, the sweep of the pages held vertically can interfere with the capture of the page to be scanned. A subtle increase in the book's open angle will alleviate the overhanging sweep, which would otherwise block text on the page being scanned. If the cockling of a page surface interferes with a successful capture, the operator can reduce this effect by smoothing the page surface and by adjusting the open angle at which the book is held. Very subtle manipulations can induce flatness in the page surface. The operator must also be aware of the scanner's depth of field, periodically adjusting it based on the book's height to achieve the clearest focus.
Following the scanning process, the individual image files are rotated 90 degrees, to reposition them to right-reading orientation, and rejoined as a spread. All recto page images will require a clockwise rotation, and all verso images a counter-clockwise rotation. Because the recto and verso pages have been saved in separate directories, the clockwise and counter-clockwise rotations are easily executed.
The FER hand-cradling method differs from the conventional handling method in a number of ways. For one, it relies primarily on the operator to adjust and finesse the book's opening with each scan. This seemingly intensive handling is, however, quite automatic and intuitive. The handheld support is more natural and less arbitrary than the wedge cradle accessories for 110°-120° openings. Secondly, scanning is not completed sequentially in recto-verso page order, as that would require an exceptional amount of handling on the part of the operator, and unnecessary wear on the book. The "two-pass" process minimizes the handling of the book, thereby preserving the book to a greater degree. Thirdly, FER hand-cradling introduces additional considerations for image processing. The variance in recto and verso book orientations requires an additional step in image processing in that two sets of images must be rotated electronically to restore the individual scanned pages to right reading orientation and sequence. The image rotation may pose additional considerations regarding the pitch of the raw images in relation to one another as well as possible variances in edge clean up. This image processing is minimized, however, if the operator maintains a consistent placement of the book's head on the scan table. Regardless, these additional considerations have not added significantly—if at all—to the time required for scanning and processing such a book.
The FER hand-cradling method responds in part to the problems articulated by Mühlberger:
FER hand-cradling is a dynamic, responsive, and adaptable technique, which can accommodate a wide variety of binding methods. The action of the book joints and spine are clearly visible to the operator.
FER hand-cradling affords the operator a higher-level of control regarding individual page behavior. Subtle changes to the angle at which the book is held open can influence and subdue the lay of the page, offering a flatter page for a higher quality scan.
Likewise, the dynamic movement of the book is under greater control in at least two ways. For one, the ever-changing thickness of the book on the z-axis is more regulated, offering a flatter plane than that in conventional handling, where a page may introduce a variety of heights due to a deep gutter and high sweep. Secondly, because the alignment is determined by the book cover's fore edge (which does not shift significantly as the operator progresses through the book) rather than the centerline of the book gutter (which does shift as one moves through the book), the operator has greater control of page position, and page shift within the scan field is greatly reduced.
Finally, because the hand-cradling of the operator regulates the book opening, books with a modest opening are candidates for scanning.
In conclusion, we believe that the method of fore edge registration hand-cradling suggests an authentic role for preservation in the context of book imaging. It offers better image capture of problematic materials with less risk to the book, as well as greater options to smaller departments with limited resources. While it does require a well-trained operator, it does not call for additional expense. Likewise, on average, the time involved in FER hand-cradle scanning is no greater than that in conventional top-down scanning. While our method was developed using the Minolta PS7000 top-down scanner, it can potentially be used with a variety of top-down scanners. Thus, this method may be of particular interest to operators of the BookEye, the Minolta PS3000 and PS7000.
Chapman, Stephen. "Book Scanners and Cradles: Links to Products and Reviews." RLG DigiNews, Volume 6, Number 4, August 15, 2002. http://www.rlg.org/preserv/diginews/diginews6-4.html#chapman
Mühlberger, Günter. "Book Scanners: A Short Report about the Minolta PS7000 and the BookEye." META e-news, Number 3, November 2001. http://heds.herts.ac.uk/METAe/issue03.htm
Illustractions courtesy Gary Frost
a. Scan Table|
b. Back Guage
c. Centered Gutter Registration
d. 3-d Axis
e. Page Sweep
f. Fore Edge Registration
g. Overhanging Sweep
h. Left Edge of Scan Field
i. Page Lift in Recto scan
j. Right Edge of Scan Field
k. Page Drop in Verso scan