Truly interesting question and answer about compression

[The_Traveler]

altho that seems like an impossibility

If an image is rotated losslessly, why does the file size change?

 

[Advanced Photo]

altho that seems like an impossibility

If an image is rotated losslessly, why does the file size change?

Data is added to the original to make it reconstruct properly and the data about the orientation is a part of that data. After the first transformation data is added, the following transformations simply alter that same data string and do not add more data to it so the size remains the same after the first transform. JPEG is a symmetrical compression method.
It's interesting, but there is nothing new in any of this, it is just a repeat of what has been said so many times before. JPEG goes back to a process started in 1986 for heavens sake. There is not anything left to learn about the process that hasn't been rehashed a thousand times before.

The JPEG standard (ISO/IEC 10918) was created in 1992 (latest version, 1994) as the result of a process that started in 1986. Though, this standard is generally considered as a single specification, in reality it is composed of four separate parts and an amalgam of coding modes.

Part 1 of JPEG (ISO/IEC 10918-1 | ITU-T Recommendation T.81) specifies the core coding technology and it incorporates many options for encoding photographic images. Part 2 defines the compliance testing. Part 3 defines a set of extensions to the coding technologies of Part 1, and via an amendment the SPIFF file format was introduced. Part 4 focuses on the registration of JPEG profiles, SPIFF profiles, SPIFF tags, SPIFF color spaces, SPIFF compression types, and defines the Registration Authorities. And lastly, Part 5 specifies the JPEG File Interchange Format (JFIF). Without any doubt, it can be stated that JPEG has been one of the most successful multimedia standards defined so far.

This is news though: JPEG - 73rd Meeting - Chengdu, China - JPEG issues a call for proposals on light field coding technologies

As is the development of fractal geometry based image compression algorithms, which will be a better method for keeping fine details intact.

Fractal Image Compression