[Zlib-devel] zlib compression ratio

[Ralf Junker]

I noticed that 7-zip achieves about 7 to 8 percent better compression for *.ZIP files than most deflate algorithms, including zlib (stats quoted from the 7-zip help file):

Archiver            Compressed size  Ratio
7-Zip (zip format)  676284           100%
PKZIP 2.04g -ex     726047           107%
WinZip 7.0 (Max)    731499           108%

What kind of magic does 7-zip use? Couldn't zlib's deflate be imporived to achieve similar ratios?

If such an improved zlib deflate spreads, this would help to make better use of the limited network bandwidth, would it not?

Ralf

>I think we both know that compression speed isn't the bottleneck these
>days.  Home computers, even 5-year-old ones, are ridiculously overpowered,
>and the stuff that gets gzip- or deflate-encoded isn't the bulk of what
>gets downloaded, anyway--already-compressed binary formats are.
>
>No, the reasons for poor web-browsing performance are primarily in the
>network (bandwidth latency, DNS latency, multi-request latency) and in
>the page-design/browser-architecture combo (failure to render until all
>CSS finishes downloading, 2-request limit for simultaneous downloads
>from the same site, unnecessary redirects, poorly compressed images,
>overweight Flash, swapping due to memory leaks, you name it...).  Even
>doubled performance in inflate()--and I don't believe it was anything
>like that, was it?--would not make a noticeable difference in the
>rendering speed of most pages.