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[OM] Re: file compression

Subject: [OM] Re: file compression
From: "Piers Hemy" <piers@xxxxxxxx>
Date: Mon, 21 Jun 2004 20:52:56 +0100
Agreed entirely Mark.  But I think it's worth underling that if we are
talking about an Uncompressed TIFF, zipping it will save perhaps 30% of the
file size (my quick sample of a 15Mb file!), _which can be recovered after
transmision_.  It may well be that jpeg is more efficient than zip at
graphics file compression, but it's a "fire and forget" method - you can
forget about recovering the original image quality.  

Piers 

-----Original Message-----
From: olympus-owner@xxxxxxxxxx [mailto:olympus-owner@xxxxxxxxxx] On Behalf
Of Mark Marr-Lyon
Sent: 21 June 2004 18:59
To: olympus@xxxxxxxxxx
Subject: [OM] Re: file compression

Zip is a lossless compression algorithm so you won't lose anything, but at
best it'll compress about as well as TIFF/LZW.  It may even do worse, since
I think TIFF compresses the color channels separately but I don't remember
for sure.  However, zipping an image file will only help if the image is
previously uncompressed.  Zipping a compressed TIFF will result in a file
that is probably about the same size or a little larger than the TIFF, while
zipping a JPEG will most likely result in a file that is quite a bit larger
than the original JPEG.  If you need to send a JPEG image to someone on a
phone connection, either reduce the number of pixels in the image, or
increase the amount of compression when you save it, then just send the jpeg
file as an attachment without further zipping.

Mark

On Monday, June 21, 2004, at 10:26AM, Gregg Iverson
<golftooter@xxxxxxxxxxxx> wrote:
>My question concerned the sending of large jpg files over a phone 
>connection.  I am also concerned that the receiving ISP might deny an 
>email that contains a large attachment.  What does a zipped photo lose 
>when it is opened?
>
>Discussions of TIFF, JPG etc. have been covered.  I don't remember 
>anything about  zipped files.
>
>gregg


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