jpeg compression ratio

Question

Is there a table that gives the compression ratio of a jpeg image at a given quality?

Something like the table given on the wiki page, except for more values.

A formula could also do the trick.

Bonus: Are the [compression ratio] values on the wiki page roughly true for all images? Does the ratio depend on what the image is and the size of the image?

Purpose of these questions: I am trying to determine the upper bound of the size of a compressed image for a given quality.

Note: I am not looking to make a table myself(I already have). I am looking for other data to check with my own.

Answer 1

The compression you get will depend on what the image is of as well as the size. Obviously a larger image will produce a larger file even if it's of the same scene.

As an example, a random set of photos from my digital camera (a Canon EOS 450) range from 1.8MB to 3.6MB. Another set has even more variation - 1.5MB to 4.6MB.

Answer 2

Browsing Wikipedia a little more led to http://en.wikipedia.org/wiki/Standard_test_image and Kodak's test suite. Although they're a little outdated and small, you could make your own table.

Alternately, pictures of stars and galaxies from NASA.gov should stress the compressor well, being large, almost exclusively composed of tiny speckled detail, and distributed in uncompressed format. In other words, HUBBLE GOTCHOO!