Compressing images without compressing quality

[Alan M. Evans]

On Tue, 2006-06-13 at 15:30, Elliot Lee 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.