Scanners and scanning

The first step in converting paper documents into a digital library collection is to obtain images of all pages of all publications in digital format. The next stage is optical character recognition (OCR), and clean, high-quality images are essential for successful OCR. The digitization process requires a scanner capable of working at a resolution of 300 dpi (dots per inch). Most scanning can be done in black-and-white, but if color illustrations are included they must be scanned with a color scanner. In most cases the covers of the book contain colors and will have to be scanned as a color photographic image.

Scanners

Scanners are available in all price ranges, and all shapes and sizes. They range from $100 for flat-bed scanners to upwards of $50,000 for large industrial scanners from manufacturers such as Bell & Howell.1)There are many websites that offer a wide range of scanners for sale. To locate them, just search for “scanners” in search engines like Google, Altavista, or Yahoo.

The output format of a scanned page is a computer file that is usually stored in TIFF or Bitmap format. Compressed TIFF IV is the best format to use. An average page scanned and converted to this format occupies only 50 Kb, compared to perhaps 2 Mb for the equivalent page in uncompressed Bitmap form.

Low-cost flat-bed scanner

Low-cost flat-bed units are the cheapest and most widely available type of scanner. There are many brands: HP, Agfa, Acer, etc. Prices range from $100 to $300. Both black-and-white and color images can be scanned. The low price allows each computer to have its own scanner.

Disadvantages of these scanners include the medium quality of the result, the slow rate of scanning, unreliability in warm environments, and relatively frequent breakdown. Pages must be scanned manually, one by one. Each page must be positioned carefully on the scanning plate to ensure that it is aligned correctly. Productivity of these scanners is low. Despite manufacturers' claims that each page can be scanned in less than a minute, the fact is that rates exceeding twelve pages per hour are rarely achieved. The scanning process monopolizes the computer on which the work is being performed.

Consequently these scanners are useful only for small jobs with limited numbers of pages—no more than 200 to 400 pages a month on a regular basis, or one-time jobs of up to 1000 or 2000 pages.

Low-end scanner with sheet feeder

Low-end scanners with sheet feeders typically cost between $500 and $1200. Ten to fifty pages can be inserted, scanned and processed at once: thus the operator does not have to attend constantly to the machine. This increases capacity up to 150 to 200 pages per day. These scanners are more robust, and have a larger lifespan before repair—usually in the range 30,000 to 50,000 pages.

A disadvantage is that only one side of the page is scanned at a time—the stack of pages must be reversed and rescanned in order to obtain an image of both sides. This often creates problems because sheet feeders are never without problems and sometimes pages get blocked.

These scanners are useful for up to 1500 to 3000 pages a month.

Color scanners

Any scanning operation invariably involves some color images, so a color scanner will always be required. Generally speaking, less than 5% of any publication contains color images, plus the cover. Thus a low cost flat-bed scanner as described above suffices. It is advisable to select one capable of scanning up to 600 dpi resolution.

Professional duplex scanners

Professional scanners are reliable, heavy-duty machines capable of processing a large volume of pages—typically from 2000 pages to 10,000 pages per day. They have an automatic sheet-feeder tray system that processes batches of about 50 to 200 pages. The best and fastest are duplex machines that scan both sides of the page at once.

Professional duplex scanners require a powerful computer with a hard disk of at least 10 to 20 Gb. Prices range from $5000 to $50,000. For example, the Canon DR-6020 duplex scanner costs $5000 and works with double-sided documents. It has a capacity of about 2000 pages per day and a lifespan of 600,000 to 800,000 pages. Bell & Howell and Fujitsu scanners range from $10,000 to $50,000 and have a lifespan of many millions of pages.

Micro-fiche scanners cost from $15,000 for a semi-manual unit to $80,000 for one that operates fully automatically.

Scanning programs

Every scanner comes with its own software, which means that the program must be installed on the computer that manages the scanner. Some have a computer card that needs to be installed in your computer to speed up the scanning operation.

Preparing the documents

Before being scanned, documents must be properly prepared. Dusty documents must be cleaned, humid documents dried, clips removed, pages unfolded.

The spine of each book should be removed by cutting it off, straight and precisely. Books provided by libraries must often be rebound, and if so you should be particularly careful when removing spines in order to facilitate smooth rebinding.

If there are just a few documents, cutting can be done manually with a ruler and cutters. Be careful with your hands! For more documents, special manual cutting machines are available.

For high volumes—more than 20 documents—we recommend asking a printer or copy-shop if you can use their professional cutting machine. Do not forget to remove metal clips which could damage the cutting blades.

The scanning process

Using software provided with the scanner, a digital image of each paper page is scanned and transformed into a Bitmap or TIFF image. These images should be stored on hard disk with standard filenames. The OCR process starts once some or all of a batch of documents have been scanned. It can be undertaken by the person who operates the scanner, or by someone else.

Typically a scanning resolution of 300 dpi is needed, although sometimes 200 dpi is acceptable.

Quality control

The final goal of scanning is either to OCR the pages to obtain perfect word processor or HTML versions of the publications, or to produce enhanced image files such as PDF image files. In either case the quality of the image is very important. If quality is sub-standard, image files will not look good and will consume more memory. Image quality seriously affects the OCR process: with sub-standard quality, productivity deteriorates by up to 40%. OCR typically represents more than 90% of the total cost, so scanning quality can have a very substantial effect on the final cost.

The quality of the TIFF file can be enhanced by adjusting the scanning process to each type of paper, using settings provided by the scanner software. Relatively transparent kind of paper will require a lighter setting; the contrast must be adjusted depending on the quality of printing, and so on.

First divide the material into batches with similar paper and print qualities. Perform OCR tests on a sample from the first batch to determine the optimal settings. Then scan all material in this batch before proceeding to the next one.

Filename conventions

Give each book or document a job number or unique code, which will become the name of the folder that contains all TIFF images in the document. Depending on the computer system (DOS, Windows, UNIX, LINUX, etc) from 8 characters to 128 characters can be used in a filename. We recommend restricting this unique document identifier to 8 to 16 characters. The first five characters might identify the document, the following letter might contain a language code, and the remaining characters might identify the particular page. For example, the identifier u7548e12.tif might identify the TIFF image of page 12 of a book written in English with code u7548e.

Allocate one directory on the hard disk for scanning jobs, say scanjobs. Then make a subdirectory for each job. Within this make a subdirectory for each publication—say u7548e for the above document. Store all the TIFF images of the publication, including color images, in this folder.

Productivity and resources

You should not underestimate the magnitude of the scanning operation—and particularly the OCR process that follows. It is best to consider scanning and OCR as completely separate activities. The optimal choice from an economic and practical point of view should be madeindividually for each one.

Some points to consider are the investment in scanners and computers that is necessary; the availability of appropriate space and human resources; training the workforce; salary costs; the initial and total number of pages to be scanned; deadlines; and whether documents can be outsourced to third parties.

Scanning costs

An important decision is whether to invest in scanning equipment and perform all scanning oneself, or outsource it to a scanning company. The main considerations are:

  • pressure of time for the scanning job;
  • total number of pages;
  • salary costs of those who perform the scanning.

The people who perform the scanning must be highly motivated, technically skilled, and quality-oriented.

The typical cost of scanning by a professional company is $0.06 per page. To this must be added the cost of shipment, which can be up to $0.03 per page for transport from developing countries to developed countries, and $0.015 per page for transport within countries.

Table <tblref table_table_scanning_cost> estimates the cost of doing it yourself, using various scanner types. Note that all figures are approximate. They are provided as rough guidelines based on the authors' experience. The first three columns concern labor costs. The first is the capacity in pages/month, assuming full-time work. The resources required in person-hours per page is obtained by dividing the number of working hours per month by the pages/month capacity in the second column. It is shown in the second column, which assumes 180 working hours per month.

<tblcaption table_table_scanning_cost|Scanning cost></tblcaption>

Capacity (pages/month) Hours/page (180-hour month) Cost/page (assuming $4/hour) Scanner acquisit- ion Scanner lifespan (pages) Outsourced pages for scanner cost<br/>(at $.06 each)
Flat bed scanner 2,500 0.072 $0.288 $300 7,000 5,000
Scanner with sheet-feeder 8,000 0.0225 $0.09 $800 30,000 13,000
Professional: low-end duplex 40,000 0.0045 $0.018 $6,000 600,000 100,000
Professional: high-end duplex 150,000 0.0012 $0.0048 $50,000 8,000,000 833,000

To determine the price per page, multiply the total hourly salary costs in your situation by the second column of Table <tblref table_table_scanning_cost>.As an example, the third column gives the price of in-house scanning at a salaryrate of $4/hour—not including investment costs.

These calculations assume that the scanner is used for a sufficient volume to justify the investment. The final three columns of Table <tblref table_table_scanning_cost> give more information about the cost of the scanner itself. The first of these shows the acquisition cost of the scanner, and the next gives its expected lifetime. The last shows the number of pages that could be scannedcommercially, at a cost of $0.06/page, for the price of the scanner alone.

Of course, many other factors affect the choice of scanner: availability of funds, need to minimize dependence on others, desire to build local capacity, obligations to libraries to scan books locally and not transport them, and so on.

The above figures give some idea of the volume of pages needed to justify different levels of investment. Rarely will an institute or organization need to scan 800,000 pages. At such levels more complex issues arise—such as maintenance and the possibility of recouping costs by offering scanning services to others—that we will not discuss here.

It is tempting to regard the development of scanning capacity asa commercial venture, particularly in developing countries. But one shouldalways bear in mind that scanning is not a repetitive business. Oncedocuments have been scanned, clients never place new orders for the same documents—no matter how good the relationship with the scanning company. From a commercial point of view, intensive marketing efforts are needed. We do not advise NGOs or other non-profit organizations to venture into this realm without thorough initial trials and a carefully-considered business plan.

In conclusion, if 10,000 to 50,000 pages are to be scanned, one should consider outsourcing the job. A low-end professional scanner costing about $6000 can only be justified if more than 100,000 pages have to be scanned. You might consider banding together with a few other institutions—perhaps NGOs or libraries—to purchase such a scanner.

1) All sums of money mentioned in this document are in US dollars, and were current in 2001.