Google has been promoting the use of WebP, the still image derivative of its WebM video codec. Mozilla has also been looking at the issue, but the open source browser organization has come up with a different conclusion: we don’t need a new image format, we just need to make better JPEGs.
To that end, the group has released its own JPEG compression library, mozjpeg 2.0, which reduces file sizes by around five percent compared to the widely used libjpeg-turbo.
mozjpeg is free and permissively licensed, so Mozilla is hoping that it will see widespread adoption by those creating JPEG images.
As for why Mozilla isn’t interested in WebP even though Google promotes it as superior, it all depends on how you measure image quality. All lossy compression formats contain errors relative to the original image, due to the data that is lost. The thing that makes comparing lossy formats hard is that not all errors are equal; the human visual system is more attuned to some kinds of error and less so to others. For example, it’s more sensitive to errors in brightness than errors in color.
Simple is good, if libjpeg-turbo is working towards better human perception, who needs a new image format?