Compressing images without compressing quality

[Paul Smith]

On 6/13/06, Alan M. Evans <ame1 at extratech.com> wrote:
> >  From the description, it sounds vaguely like snake oil to me,
> > especially if they are guaranteeing no information loss. There are
> > things you can do to HTML files (like stripping out extra
> > whitespace), but GIF/JPEG/PNG files are. Only thing I can think of is
> > recompressing PNG files with the highest compression level, but even
> > then, you're not going to save very much space in absolute terms.
>
> I agree about GIF - not much to take out of those. JPEG I'm not certain
> about, but it seems that one could tweak out the compression settings
> and maybe gain something.
>
> But PNG - Many graphics programs toss in heaps of metadata. PNG has many
> chunk types that are not at all necessary to reproduce the graphic
> bitmap data. Also, picking different combinations of compression and
> filter method for the IDAT chunks could result in quite a smaller file.

Thanks to both. I am now wondering whether there is some tool to
automatically crop images. Any suggestions?

Paul