vglass wrote:Do you want this info out of curiousity or is there something you want to solve?
In any case jpeg compression is very destructive resulting in a huge (high %) is the image data being lost (it's gone baby gone). Detail is lost but much much worse than that further work in PS or whatever will destroy even more data. By the way jpeg is considered a terminal format meaning an image file is converted to jpeg for the purpose of sending it to a printer or put on the web.
I'm not sure from whence you come with your question so I'm not sure if this info will be useful to you:
Capture and keep the maximum amount of image data because then you can choose to create a jpeg or create a fine art quality print.
To capture and keep the maximum amount of data shoot only RAW.
I
My question comes from this:
Loss-less compression is well known. A zip file compresses a bunch and then decompresses losslessly.
Yes, you can compress an image file using zip and other algorithms and lose nothing upon decompressing with the same codec that compressed it.
Loss-less compression works as a ZIP file does on the principle of redundancy. By collecting hundreds of exactly repeating pixel data within an image and converting them into a simple list of Cartesian coordinates all containing the exact same information. This can save a substantial amount of redundant information and upon decompression lose nothing whatsoever.
See "lossless data compression"
http://en.wikipedia.org/wiki/Lossless_data_compression. See further Huffman encoding.
A jpg compression has two parts. The first part defined by the Joint Photographers Experts Group (JPEG) created by the International Standards Organization (ISO) is lossy. The second part of the compression is not lossy as discussed above in Huffman encoding.
What I would like to knwo is if anyone knows what percentage of a jpg compression is lossy and what percentage is loss-less. It is important to know and I cannot find it withing the ISO papers.