Getting started with JBIG-KIT ----------------------------- Markus Kuhn -- 2014-03-27 JBIG-KIT is a portable C library that should work on any platform with an ANSI/ISO C compiler, such as GNU gcc. To get started, compile the demonstration software in pbmtools/ and test it with some of the provided example files. On a Unix system, check Makefile to suit your compiler, then start "make". If libjbig.a and/or libjbig85.a have been produced correctly, then activate the automatic library test suite with "make test", or just start libjbig/tstcodec and libjbig/tstcodec85. If these tests fail, please do let me know. On other operating systems, just link libjbig/jbig.c and libjbig/jbig_ar.c together with any application in which you want to use the full JBIG-KIT library. Likewise, just link libjbig/jbig85.c and libjbig/jbig_ar.c together with any application in which you want to use the simpler variant optimized for fax applications. In subdirectory pbmtools/, you will find the programs pbmtojbg and jbgtopbm. These are two file converters, serving as examples for applications that use the full JBIG-KIT library (jbig.c). After testing them on some of the example JBIG files, you can move these executable files together with their respective man pages (in a UNIX style environment) to the appropriate directories. Options -h and --help will give you short command-line usage summaries. The programs pbmtojbg85 and jbgtopbm85 are very similar, but demonstrate use of the simpler jbig85.c library instead. The subdirectory examples/ contains a few files as raw JBIG data streams (called bi-level image entities (BIE) in the standard). Try jbgtopbm ccitt1.jbg ccitt1.pbm to decompress CCITT test letter #1 into a portable bitmap file, which you can then further convert using Jef Poskanzer's PBM tools <http://www.acme.com/software/pbmplus/>, or view with many popular image file viewers, such as the "display" command from ImageMagick. The ccitt1.jbg image is 1728 x 2376 pixels large and may not fit onto your display screen. However, fortunately, I have stored it in JBIG's "progressive mode" with the following resolution layers: layer 0: 216 x 297 pixel layer 1: 432 x 594 pixel layer 2: 864 x 1188 pixel layer 3: 1728 x 2376 pixel In progressive mode, each layer has twice the resolution of the previous one. Resolution layer 0 encodes all its pixels independent from any other data; all other resolution layers encode only the difference between the previous and the new resolution layer, which requires much less space than encoding resolution layers without referring to the lower layer. By default, the BIE files produced by pbmtojbg will all start with a lowest resolution layer 0 that fits onto a 640 x 480 screen. In order to tell jbgtopbm that you do not want to decode higher resolution layers if they will not fit onto your (say) 1024 x 768 pixel display, simply use jbgtopbm -x 1024 -y 768 ccitt1.jbg ccitt1.pbm You will get a 4 times smaller image, the highest resolution layer that still fits onto your screen. You can also directly pipe the image to another application using standard output, by removing the second file name, e.g. jbgtopbm -x 1024 -y 768 ccitt1.jbg | display In fact, the data in the first quarter of the input file is sufficient to decode the requested resolution: head --bytes=4000 ccitt1.jbg | ../pbmtools/jbgtopbm -x 1024 -y 768 | display Now let's do some compression. With jbgtopbm ccitt1.jbg ccitt1.pbm followed by pbmtojbg ccitt1.pbm test.jbg you produce again the same data stream as ccitt1.jbg. However if you want that the lowest resolution layer is not larger than 70 x 100 pixels ("thumb nail" image), then use pbmtojbg -v -x 100 -y 150 ccitt1.pbm test.jbg Option -v will output some technical data, and will tell you that five incremental resolution layers have been created, in addition to the lowest 54 x 75 pixel large layer 0. Look at the lowest resolution layer in test.jbg with jbgtopbm -x 100 test.jbg | display and you will still be able to clearly recognize the layout and line structure of the page, which the implemented bi-level resolution-reduction algorithm tried to preserve. With pbmtojbg -q ccitt1.pbm test.jbg you can enforce a single resolution layer, which usually requires a slightly less space than progressive encoding. OK, another small exercise. Assume you want to build a document database in which you want to store scanned images in two resolution layers, one for screen previewing and one for laser-printer output. However, you do not want your decision to store images in two resolutions to cause too much additional storage requirement. You decide that 3 resolution layers in JBIG fit your requirement and you want to store layer 0: 432 x 594 pixels in the first file test-low.jbg and the two layers layer 1: 864 x 1188 pixels layer 2: 1728 x 2376 pixels in the second file test-high.jbg. No problem, just call pbmtojbg -d 2 -l 0 -h 0 ccitt1.pbm test-low.jbg pbmtojbg -d 2 -l 1 -h 2 ccitt1.pbm test-high.jbg where option -d specifies the total number of layers and -l/-h select the range of layers written to the output file. You will see that the low and high resolution file together are only 1.6 kB larger than if you had stored only the high-res version directly without progressive mode (option -q). Progressive mode has reduced the additional storage requirement by 50% compared to storing the 3.2 kB low-resolution version independently of the high resolution image. In order to view only the screen version, use jbgtopbm test-low.jbg | display and in order to send the full version to the printer, just concatenate both BIE files like in cat test-low.jbg test-high.jbg | jbgtopbm -m | .... All this functionality, and more, are available as functions in the libjbig C library, which you can link into your application. Just copy the relevant files from libjbig/ into your own source-code directory and adapt your Makefile. In libjbig/jbig.txt, you will find documentation about how to use the full library, while libjbig/jbig85.txt documents the fax variant of the library. The latter lacks progressive encoding, but can instead deal better with images where the height is not yet known at the start of a transmission. Markus