Adobe Creative Cloud applications, such as InDesign, Illustrator, and Distiller offer the option of compressing image and text files in PDF documents. With the right settings, compression will reduce file size without sacrificing image quality. If you absolutely wish to avoid any chance of image quality being degraded due to compression, uncheck all of the boxes under the Images tab. The drawback of this is the resulting PDF file will be much larger than if some form of compression is used. Compression can be used very safely in PDF documents with little or no image degradation. Read on.
ZIP Compression. ZIP compression works well on images that contain large areas of single colors or repeating patterns. ZIP compression is lossless (no data will be sacrificed) if 4-bit compression is used with 4-bit images and 8-bit compression is used with 8 bit images. ZIP is lossy (data will be sacrificed) if 4-bit compression is used with 8-bit images. While it doesn’t offer tremendous compression with four-color bitmap images, ZIP compression results in no loss of data, so it is a completely safe way to gain some image compression.
JPEG Compression. JPEG compression is always lossy: data will be lost when images are compressed. If files are compressed too far, the images in the PDF file will contain visual artifacts. That may sound ominous, but for many images, JPEG compression can be used with little or no noticeable image degradation. Five levels of JPEG compression can be selected: minimum, low, medium, high, maximum. These options refer to image quality; i.e., minimum is the lowest image quality (most compression), and maximum is the highest image quality (least compression).
JPEG2000 Compression. JPEG2000 is a newer international standard for compressing image data. JPEG2000 is not meant to succeed JPEG but is an entirely new form of compression. JPEG2000 supports alpha channel transparency, 16-bit color, and a lossless compression option. One of six levels of JPEG2000 compression can be chosen: minimum, low, medium, high, maximum, lossless. These options refer to image quality; i.e., minimum is the lowest image quality (most compression), and lossless is the highest image quality (least compression). JPEG2000 Compression is only an option when you save PDF files as Acrobat 6 (PDF1.5) or newer.
Automatic Compression. Automatic compression enables Creative Cloud applications to choose the type of compression based on image content. For images that contain sharp transitions, ZIP compression will be used. For all other types of images, JPEG or JPEG2000 compression will be applied. Automatic compression is the very best choice because you’re getting the very best compression performance based on each individual image on a page or in a document.