PDF is a print-oriented format. It is designed to provide a high level of verisimilitude and device-independence when it comes to printing and display on computer screens. As part of its design, each page has information that defines the size of the ‘page’ when it is printed out at ‘100%’. Printer drivers and viewing systems may scale the page up or down to fit a given piece of paper or screen size, but the scaling factor is entirely dependent on the relative size of the page and screen. Ideally, a screen used for display is at least as large as the page size, so that it can be displayed at the size the designer intended.
Since many PDFs that we find for download are formatted for Letter/A4-sized paper, or perhaps reproduce a physical book that is 9”x7”, the only way to display a full page is to scale the image down. For some eyes, that makes the text too small to read comfortably. Displaying a page in landscape mode allows the scaling factor to be less severe, but displays only about 40% of the page at a time, and will still be less than 100% of the original size in general.
Of course PDF page size may be very large (A5/E size for example). These are just too large to be viewed on a Kindle due to memory and performance requirements.
Increase the Contrast Level
I have found that small type often becomes more readable if you bump the contrast level to the ‘darker’ setting. This setting is saved on a per-document basis, so when opening a PDF for the first time, try this out to see if it helps.
Cropping helps a bit
PDF cropping tools
PDF improvements Amazon should consider
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| 'default' Contrast |
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| 'darker' Contrast |
Cropping helps a bit
Kindle auto-crops margin whitespace in fit-to-page (portrait) and fit-to-width (landscape) zoom modes, partially remediating the size mismatch. But many PDF documents have headers and footers that display a chapter or section title, and page numbers, thus allowing fit-to-page zoom to make the text slightly larger. Given that this information is quite often redundant, distracting, or unnecessary (Kindle displays the PDF page labels in the reading progress bar), better use of Kindle’s limited screen ‘real estate’ can be achieved by cropping the margins, headers and footers. This can achieve another reduction in the size mismatch; in some cases quite significantly. It will also improve the efficiency of the other zoom modes (100%, 150%, 200%, 300%) since these don’t crop whitespace. Sometimes even a relatively small improvement can be significant.
Finally, cropping can be a useful preliminary for conversion to a reflowable format such as .mobi or .epub, when the conversion program does not otherwise filter these out of the resulting text stream. (I will cover the perils of PDF file conversion in a future article.)
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| Before cropping |
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| After cropping |
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| Before cropping |
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| After cropping |
PDF cropping tools
There are a number of free and commercial tools that can crop PDFs to improve the small-screen reading experience:
- Briss (search mobileread.com forums for ‘briss’) - Java/cross platform application. Can create multiple crops on the same page (e.g. to deal with 2-column PDFs)
- PDF Scissors - uses ‘Java web start’ technology and internet connection, and requires Java run-time
- OS X Preview app (comes with Mac OS X)
- Adobe Acrobat (powerful, but expensive unless you already need it for some other purpose)
Note that some PDFs are designed with asymmetric margin space, corresponding to a ‘binding edge.’ Thus the margins may be different for ‘left’ and ‘right’ hand pages. For purposes of Kindle display it is usually not necessary to establish different cropping boundaries for left and right pages, just use boundaries that trim as much whitespace as you can without clipping off anything on either side. Kindle will trim the rest of the white space as it displays each page in fit-to-screen or fit-to-width zoom modes.
PDF improvements Amazon should consider
Most ereaders provide at least a basic level of PDF viewing support, and Kindle’s is by no means the best in its class. Some of the features I’d like to see Amazon copy to bring it to parity are:
- PDF reflow - PDF Reflow attempts to detect a text stream on each page and allows the user to select a larger text size to make it more readable. However, whether a given PDF file lends itself to reflow is very much a case-by-case question. Ideally, the PDF reading order of the text elements is properly delineated, and accessibility tagging applied (these steps are also critical for successful conversion to a reflowable format). Since it is very difficult (if not impractical) to automate tagging, tagging must be done manually, and the vast majority of PDFs are created without it. Still, it is ‘worth a try’ because it does work adequately in many cases, and most other readers support it.
- PDF link support - PDF links provide a convenient way to jump to the location of Table of Contents entries, to referenced footnotes, endnotes, or web sites. Kindle does not support this functionality, which is a critical navigation tool for technical documents of many kinds. Lacking this feature, many PDFs are far more difficult to navigate than they would otherwise be.
- PDF compatible annotations - annotations made to PDF files can only be interpreted by Kindle devices. Since annotated PDF files are often important or convenient for participating in workflows, it would be better if annotations were stored in the PDF file’s annotation layer, instead of in a proprietary sidecar file. The contents of a PDF’s annotation layer is displayed on Kindle, however there is no way to view - much less edit - the text inside a ‘sticky note’ or one attached to a highlight. Again, it would be useful to at least be able to view these on Kindle (for example, by clicking on them with the 5way controller).
- 4-panel zoom mode. Many academic and technical papers use a 2-column format. On a small screen like Kindle’s, these would be best viewed by dividing the page into quadrants with a little overlap between top and bottom quadrants, and displaying them in the order upper-left, lower-left, upper-right, lower-right. Sony Reader has this mode.
- finer-grained control over zoom level. The preset zoom levels are often not ‘just right’ for the material being viewed. It would be nice to be able to adjust zoom level in finer increments, e.g 10% or even 1%.
