Sometimes i work with JPEG files for my web designs. There are occasions where the PNG format is not suitable..
There are several optimization techniques for the PNG format, but I noticed that for the JPEG format, the possibilities are limited, especially if you work on a Mac.
Probably the most elegant solution so far is the selective compression that allows you to precisely control the compression in specific areas of the images. If you combine then the image with JpegOptim and jpegtran from libjpeg (or use imageOptim) you can reduce even more the filesize.
I am still not satisfied by this options. I don't want to buy a license for fireworks only because of the selective jpeg, and I wonder if there's some other image optimization software out there that offers similar features..
On windows you have Jpeg Optimizer..
Is there any tool that you use for your workflows that you can suggest me?
Guetzli specializes in producing high-quality files with nearly imperceptible distortions. It's very, very slow though.
JPEGmini is pretty good at recompressing JPEGs to the lowest still-good quality.
The last two are best combined with lossless ImageOptim (includes MozJPEG/
jpegrescan) for the most efficient JPEG compression I'm aware of.
Ten years ago, this would have been a great question. But in 2011, unless you are sure that a high percentage of site visitors will be on dial-up or similar low-bandwidth connections, the effort put into selective compression doesn't produce enough value to be worth it. The differences in quality and file size are so minimal, and broadband connections so ubiquitous, that you end up saving no more than a few milliseconds in page load times.
Even mobile devices, constrained for the moment by 3G speeds in most places, will not benefit significantly from selective compression.