FOP has native ability to handle some graphic file formats.

Apache XML Graphics Commons contains codecs for PNG and TIFF access. FOP can use these.

For JDKs 1.4 or higher, FOP provides a wrapper to load images through the JDK's Image I/O API (JSR 015). Image I/O allows to dynamically add additional image codecs. An example of such an add-on library are the JAI Image I/O Tools available from Sun.

Because of licensing issues, the JIMI image library is not included in the FOP distribution. First, download and install it. Then, copy the file "JimiProClasses.zip" from the archive to {fop-install-dir}/lib/jimi-1.0.jar. Please note that FOP binary distributions are compiled with JIMI support, so there is no need for you to build FOP to add the support. If jimi-1.0.jar is installed in the right place, it will automatically be used by FOP, otherwise it will not.

FOP has been compiled with JAI support, but JAI is not included in the FOP distribution. To use it, install JAI, then copy the jai_core.jar and the jai_codec.jar files to {fop-install-dir}/lib. JAI is much faster than JIMI, but is not available for all platforms. See What platforms are supported? on the JAI FAQ page for more details.

Current FOP distributions include a distribution of the Apache Batik version 1.6. It is automatically installed with FOP. Because Batik's API changes frequently, it is highly recommended that you use the version that ships with FOP, at least when running FOP.

Batik must be run in a graphical environment. It uses AWT classes for rendering SVG, which in turn require an X server on Unixish systems. If you run a server without X, or if you can't connect to the X server due to security restrictions or policies (a so-called "headless" environment), SVG rendering will fail.

Here are some workarounds:

• If you are using JDK 1.4, start it with the -Djava.awt.headless=true command line option.
• Install an X server which provides an in-memory framebuffer without actually using a screen device or any display hardware. One example is Xvfb.
• Install a toolkit which emulates AWT without the need for an underlying X server. One example is the PJA toolkit, which is free and comes with detailed installation instructions.

FOP uses Apache Batik for SVG support. This format can be handled as an fo:instream-foreign-object or in a separate file referenced with fo:external-graphic.

The SVG is rendered into PDF by using PDF commands to draw and fill lines and curves. This means that the graphical objects created with this remain as vector graphics. The same applies to PostScript output. For other output formats the SVG graphic will be converted to a bitmap image.

There are a number of SVG things that cannot be converted directly into PDF. Parts of the graphic such as effects, patterns and images are inserted into the PDF as a raster graphic. The resolution of these raster images can be controlled through the "target resolution" setting in the configuration.

Currently transparency is limited in PDF so many svg images that contain effects or graphics with transparent areas may not be displayed correctly.

If possible, Batik will use normal PDF or PostScript text when inserting text. It does this by checking if the text can be drawn normally and the font is supported. This example svg text.svg / text.pdf shows how various types and effects with text are handled. Note that tspan and outlined text are not yet implemented.

Otherwise, text is converted and drawn as a set of shapes by Batik, using the stroking text painter. This means that a typical character will have about 10 curves (each curve consists of at least 20 characters). This can make the output files large and when it is viewed the viewer may not normally draw those fine curves very well (In Adobe Acrobat, turning on "Smooth Line Art" in the preferences will fix this). If the text is inserted into the output file using the inbuilt text commands it will use a single character.

Note that because SVG text can be rendered as either text or a vector graphic, you may need to consider settings in your viewer for both. The Acrobat viewer has both "smooth line art" and "smooth text" settings that may need to be set for SVG images to be displayed nicely on your screen (see Edit / Preferences / Display). This setting will not affect the printing of your document, which should be OK in any case, but will only affect the quality of the screen display.

Currently, SVG images are rendered with the dimensions specified in the SVG file, within the viewport specified in the fo:external-graphic element. For everything to work properly, the two should be equal. The SVG standard leaves this issue as an implementation detail. FOP will probably implement a scaling mechanism in the future.

If you use pixels to specify the size of an SVG graphic the "source resolution" setting in the configuration will be used to determine the size of a pixel. The use of pixels to specify sizes is discouraged as they may be interpreted differently in different environments.

• Soft mask transparency is combined with white so that it looks better on pdf 1.3 viewers but this causes the soft mask to be slightly lighter or darker on pdf 1.4 viewers.
• There is some problem with a gradient inside a pattern causing a PDF error when viewed in acrobat 5.
• Text is not always handled correctly, it may select the wrong font especially if characters have multiple fonts in the font list.
• More PDF text handling could be implemented. It could draw the string using the attributed character iterator to handle tspans and other simple changes of text.
• JPEG images are not inserted directly into the pdf document. This area has not been implemented yet since the appropriate method in batik is static.
• Uniform transparency for images and other svg elements that are converted into a raster graphic are not drawn properly in PDF. The image is opaque.