New image file formats keep turning up, taking advantage of advances in compression technology. One of the latest is FLIF, Free Lossless Image Format. It claims to outcompress PNG, lossless JPEG2000, lossless WebP, and lossless BPG. Though it has only a lossless mode, it claims that “FLIF works well on any kind of image, so the end-user does not need to try different algorithms and parameters.”
Its claim to compete with lossy JPEGs is based on its use of progressive downloading; the image is downloaded in something like an interlaced form, but with multiple passes (I’m not clear on the details), so images of a particular desired quality can be included with a URL parameter to specify the desired file size. I’m skeptical about this as a practical approach; it puts the burden of determining quality on someone who may not have created the file.
A discussion on Reddit goes all over the place, as Reddit discussions do, with concerns being expressed about possible patent claims and the GPL license on the reference implementation (with large amounts of misunderstanding of both along with the good points).
It’s still a work in progress, and any new image format faces an uphill battle against both the well-established ones, such as JPEG and PNG, as well as the well-funded ones, like WebP. It’s been a long time since any new still image format has had significant penetration in the browser market. Time will tell.