I scan a lot of documentation for BitSavers. Sometimes the documentation has a limited use of color, such as red text highlighting user input, and so-on. Eventually, scanned documents on bitsavers will be run through an optical character recognition (OCR) program. High resolution bitonal (on or off, single bit per pixel) images work best for the OCR process. However, scanning a document with limited use of color in bitonal form means that the limited color highlighting present in the original document is lost. This can be particularly confusing when the original document mixed highlighted text and black text in the same example. In this blog post, I’ll describe how I scan these documents in a manner that preserves the original limited use of color and also keeps the document ready for OCR.

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Sometimes when I encounter vintage computing documentation, the source material I find is a photocopy of an original manual. Recently, while making one final trip to The Black Hole before it closed for good, I found a photocopied manual for a Tektronix 4953/4954 graphics tablet. The manual included the service information for the tablet. For Tektronix products of this period, the service information includes oversize pages that have schematic diagrams of the electronics. Because the manual was a photocopy, the person who made the copies attempted to get the entire diagram by placing various portions of the oversize sheet on the letter size copy area of the photocopier and making several copies to cover the entire diagram.

As I scanned the photocopied pages for BitSavers, I came to the last few pages and realized that they were pieces of a larger diagram. I used the free Microsoft Research ICE (Image Composite Editor) to process the pieces into a single unified stitched image. In the past I had tried the open source utility hugin, but it was always very tedious and time consuming to stitch together a single image from multiple scans. With hugin, I always had to perform several trial stitches before I had a composite that meshed properly from all my individual scans. With ICE, I simply drag the individual images onto it’s window and within seconds I have a high quality composite that I can save back out for inclusion in the final PDF.

See the results for yourself by looking at the last two pages of the Tektronix 4953/4954 Graphics Tablet Instruction Manual on BitSavers. You’ll notice that there are a few little bits missing around the edges of the individual scans; these are areas that are not present in the original photocopied pages.