Acrobat X’s Image Exports
Acrobat X can export a PDF file to four different image formats: two lossy and two lossless.
Everyone knows JPEG, thanks to the zillions of digital cameras running around loose. This lossy image format produces small files whose image quality can be anything from horrible to very good, depending on the settings you’ve chosen for the compression.
Practically speaking, I find that for most PDF documentstext, line art, or imagesJPEG is perfectly acceptable at Acrobat’s default, medium-quality settings (Figure 8). And the file size reduction can be remarkable. The exported page in Figure 8 amounts to about 3.8MB of data; the JPEG file is just 84KB, about 2 percent of the original data size. (To compare, the TIFF version was 889KB, smaller than the original data, but not in the same league as the JPEG.)
Figure 8 Acrobat produces perfectly useable JPEG images at its default settings. Zooming in on the text in this page (right) doesn’t show any obvious artifacts.
Since JPEG’s compression was designed with color images in mind, you will get the best compression if your PDF file has lots of images in it.
JPEG2000 is an updated version of the JPEG format, sporting more sophisticated compression and viewing capabilities. In fact, I’ve never found any circumstance in which exporting a PDF file to JPEG2000 provides a clear benefit compared to regular JPEG. To the contrary, I find that for PDF files with extensive text areas, JPEG 2000 is more prone to odd, shadowy artifacts, even at its high quality setting (Figure 9). I don’t know if this is intrinsic to JPEG2000 or is specific to Adobe’s implementation, but either way, JPEG2000 seems worth avoiding as an export format.
Figure 9 Exporting a PDF file to JPEG2000 has never yielded anything acceptable for me. This PDF file was exported at JPEG2000’s highest-quality setting, and it still looks as though it has a bad case of cellulite.
TIFF files are about as common in the wild as JPEG files. They are lossless, so they’re going to be exactly as good as the original data, but they will almost always be larger than JPEG and other lossy files. That said, grayscale and monochrome TIFFs can be smaller than a JPEG, though it’s not the way to bet. The monochrome PDF file shown in Figure 10, for example, is exported to a 111KB JPEG and a 57KB TIFF.
Figure 10 This black-and-white PDF file is a best case for the lossless image formats. While the exported JPEG was 111KB in size, the TIFF file was a svelte 57KB, and the PNG was positively anorexic at 20KB. PNG rocks, by the way!
PNG files are commonly used for website images, and I like them. They are very compact and, being lossless, they have exactly the same visual quality as the original image. As an Acrobat export format, PNG is just like TIFF, but with consistently better compression; Figure 10’s PDF file became a 20KB PNG file. The only occasional problem I have with PNG is a human one: some peopleI have a particular print shop in mindare not familiar with PNG, it makes them nervous, and so they insist on TIFFs.