Take it from me Steve, Power Point files like any other
compressed image file can, and regularly does cause
problems due to 'zippng'. There is certainly nothing wrong
with or the practice of zipping an uncompressed file such
as a text file, or the credentials of the software you
mentioned.
I'd have to see evidence of it to believe it, I'm afraid.
Austin's from Missouri and taught me that "Show Me" thing they do there. ;-)
Better yet, if you have evidence of it, do be certain that Nico Mak of
WinZIP fame hears about it.
To use a compressed file and then compress it again is
called concatination. This causes errors in the file
itself and can seriously degrade the image.
This is certainly true of lossy compression like JPG, but not of lossless
compression like ZIP uses.
As to other
types of files; it is standard practice among
photographers that a jpeg image ( which is a compressed
file )is never compressed again by using a compression
utility.
I was a photographer in a former life and have been working with digital
images since the '80s.
This is the first I've ever heard of this. Again: never using JPG
compression on an image more than once, absolutely! ZIP all you like,
though.
Why ZIPP a PowerPoint file anyway? We know that the file
size does not get smaller, it usually gets bigger. The
Power Point file it's self is a robust format
That would explain all the messages we get here every week about how
PowerPoint suddenly can't read a file it was able to read five minutes
earlier? ;-)
In point of fact, at one time, possibly still, PowerPoint had within its
files a byte count of the file size. If the file's physical size on disk
and the internal byte count didn't match, then PPT would declare the file
corrupt and refuse to open it.
Problem is that with certain forms of telecommunications, data packets are
padded to the nearest packet size boundary with nulls, meaning that the last
packet in the transmitted file stands only a one in PacketSize chance of
being transmitted w/o appended nulls. That works out to anything from 1 in
128 to 1 in 2048 or more. In plain terms: in these cases, transmitting
just the PPT file was almost certain to corrupt it.
ZIP utilities were originally written for telcom users so they don't give a
fig about a few nulls at the end of the file; instead, they happily disgorge
the contents of the ZIP unmolested as long as the zip file itself arrives
uncorrupted. Meaning in turn that at one time the ONLY way of making sure a
PPT file arrived alive was to ZIP it.
