8 Compression Algorithms to Compress Images in PDF Files
Have you met this situation? When you mail a PDF document to your friend, but it is too large to send? If you met, you can compact the PDF file with Acrobat Distiller. PDF files can be compact, and actually, it's the compaction of images in PDF files. And there are 8 compression algorithms to compress images in PDF files.
CCITT compression can be used for black-and-white images. It is the same compression algorithm that is also used in fax devices. It is lossless meaning it will not affect the quality of your images. Acrobat offers CCITT group 3 or group 4 compression. Everyone seems to agree that CCITT group 4 is preferable. You can leave it switched 'on' all the time.
Flate (or deflate as it is sometimes called) is a rather complex compression algorithm. Read this page to learn more about it.
JBIG2 is an alternative to CCITT compression for monochrome black & white images. It is supported from PDF 1.5 (Acrobat 6) onwards. I haven't seen it used yet, which could be because of some users' feedback that the implementation in Acrobat is much slower than CCITT G4 compression.
JPEG compression is used for color and grayscale images. It is a compression algorithm that can be both lossy and non-lossy. In Acrobat, only lossy JPEG-compression is available. This means that some of the detail of the image is lost by compressing it. The better the compression ratio, the more detail you lose.
This fairly new compression algorithm is supported from PDF version 1.5 (Acrobat 6.0) onwards. You can find more information about the compression algorithm on this page. Even though it is more efficient than JPEG compression, JPEG2000 isn't used that much yet because of its CPU overhead and compatibility issues with older systems.
All text and the operators that are part of a PDF can be compressed using an LZW algorithm. This basic compression can reduce the file size of a PDF to about half the size of an equivalent PostScript file.
RLE stands for Run Length Encoding. It is a lossless algorithm so it will not change the quality of your images. More information about the algorithm can be found on this page. In Acrobat RLE compression can be used for black-and-white images. Most people seem to prefer CCITT compression to RLE because it is more efficient.
The ZIP algorithm is also used in popular PC applications like PKzip, WinZIP or StuffIt. When you select ZIP compression, this does not mean that Acrobat will create a ZIPped file, it will just use the algorithm to compress grayscale or color images.