How are images stored within a PDF?

Question

The are places that prefer PDF's for printing, and we've also been using PDF as a distributable format that "everyone can open". It's very easy on a mac to save as PDF (or go to "print" and save it as pdf from there) but there are no options presented about how things should be stored.

My question regarding images within pdf:
In what format are images stored within a PDF? Does PDF just wrap around the existing file (embedded) or does it convert it to some other format for storage? Is there any image compression (such as jpeg) or data compression (lzw, zip, etc) applied to the image?

Answer 1

Normally all image content in a PDF is embedded in the file. But PDF allows image data to be stored in external files by the use of external streams or Alternate Images.

Source

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With Some PDF Images Extract you can capture the images from the PDF and save them into many different formats, including JPEG, PNG, TIFF, GIF, and lot more.

Tutorial: Extract images from PDF files to TIFF, JPEG, etc

Answer 2

Wikipedia has a nice writeup on the PDF Image model. It discusses briefly how both vector and raster can be stored. Raster images are typically embedded as 'XObjects' and can compressed using a variety of algorithms (LZW, JPEG, zip)