US Navy Magazine Compared in PDF, DjVuRaster and DjVuDigital formats
A review by James Rile, PlanetDjVu, May 25, 2002
The U.S. Navy publishes a monthly magazine called "All Hands". It is available on-line at: http://www.chinfo.navy.mil/navpalib/allhands/ah-top.html
From 1997 through 2001 the magazine was reformatted in HTML for on-line viewing. Starting in 2002, the magazine is offered in PDF format. The PDF magazine issues appear to be the same prepress PDF files used to create the printed version of the magazine, but downsampled for web delivery.
While we applaud the retention of the original print layout for web delivery, which is possible with PDF but not possible with HTML, we see a problem with the file size. A more effective format for web delivery of this magazine would be in the DjVu file format.
There are two methods available for the conversion of PDF files to DjVu files. We will call them DjVuRaster and DjVuDigital. DjVuRaster first makes a single color image of the PDF page, then segments this image into background and foreground layers. It addition to putting text into the foreground layer, this also puts high-contrast regions of the photos into the foreground layer.
DjVuDigital segments the PDF page into background and foreground layers, and does this by analysizing the objects of the PDF page to determine if they should go into the background or foreground layers. With this method, photos go entirely to the background layer. This increased file size slightly , but the page quality is better.
When you look at the DjVuRaster and the DjVuDigital examples, use the Mode buttons in the DjVu plugin to see how it was segmented.
When you compare the performance of either DjVu version to the PDF version, you will see the performance and quality of the DjVu files make them attractive alternatives to the web delivery of color magazines such as "All Hands" from the U.S. Navy.
Note that the DjVuDigital examples were created with the Any2DjVu conversion server sponsored by www.djvu.org. See the home page of PlanetDjVu for a link to Any2DjVu.
October 18, 2002 - Extension to Study
We are extending this study today to show the benefits of PDF size optimization using the CVision compression engine for PDF. This engine analyses each graphic object in the PDF file and then applies optimum compression to it, without unduly degrading the quality of the graphic objects.
Here are the results:
November 26, 2002 - Extension to Study
We are extending this study today to show the benefits of PDF size optimization using the PDF Enhancer product (SPE) from PDF Sages, Inc. This engine analyses each graphic object in the PDF file and then applies optimum compression to it, without unduly degrading the quality of the graphic objects.
Here are the results: