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Compressing images... loss?

 
 
Jeff
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      07-26-2004
I have ~1.5 GB of jpg and tif files, should I compress them when
backing them up or will the compression program compromise the image?

Are there any compression programs anyone likes? (winzip... pkzip...?)

Thanks.
 
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Charles
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      07-26-2004
On 25 Jul 2004 18:37:47 -0700, http://www.velocityreviews.com/forums/(E-Mail Removed) (Jeff) wrote:

>I have ~1.5 GB of jpg and tif files, should I compress them when
>backing them up or will the compression program compromise the image?
>
>Are there any compression programs anyone likes? (winzip... pkzip...?)
>
>Thanks.



Winrar has a large following. No quality lost when using it of
winzip.
--

- Charles
-
-does not play well with others
 
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Ralph Mowery
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      07-26-2004

"Jeff" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
> I have ~1.5 GB of jpg and tif files, should I compress them when
> backing them up or will the compression program compromise the image?
>
> Are there any compression programs anyone likes? (winzip... pkzip...?)


JPG and gif files are already compressed. If you use winzip on them they
will usually be slightly bigger due to the added data winzip will need fo
uncompress the files. You can use the jpg program to reduce the size of a
jpg file but it is a lossey reduction and you will loose some of the image
data.


 
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c0smic
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      07-26-2004
Jeff wrote:

> I have ~1.5 GB of jpg and tif files, should I compress them when
> backing them up or will the compression program compromise the image?
>
> Are there any compression programs anyone likes? (winzip... pkzip...?)
>
> Thanks.


Itís true that compressing JPGs will not save much space. But it will not
harm the file. The restored file will be identical to the original. TIFs
compress nicely, sometimes to a third the original size. If you are backing
folders with different file formats donít worry about it. The files will be
identical to the originals. With a lot of TIFs and a good compression
program like Winrar you might be able to backup 1.5 GB on 3 CDs.

 
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Matt Ion
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      07-26-2004

"Jeff" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
> I have ~1.5 GB of jpg and tif files, should I compress them when
> backing them up or will the compression program compromise the image?
>
> Are there any compression programs anyone likes? (winzip... pkzip...?)


I like WinRAR myself, as it's used widely and also supports ZIP files, plus
can view inside CAB and ISO files.

Regular compression tools, including the compression used by backup
software, is designed to be lossless, so you won't lose any quality.
However, the level of compression depends on repetitive data (a text file of
all one letter will compress a LOT; a text file containing the number PI
will not). Multimedia files in general - audio, video and image - tend to
be extremely random data, and as such will compress very little (1-2% at
best) and in some cases you may even end up with a larger file once you add
in the compressor overhead. Meanwhile, compression does take time to
perform; the higher the compression you set, the longer it takes. It
usually isn't worth the time for the minimal amount of space you save.

About the only way you might see a benefit is to archive numerous images
into one ZIP or RAR file - the more files moved into a solid archive, the
more you save in lost cluster space. But again, the savings would be
minimal until you get a LOT of files in there, and with the cost of storage
and backup space today, it really isn't worth the time it would take.


 
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Tim Smith
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      07-26-2004
On 2004-07-26, Matt Ion <(E-Mail Removed)> wrote:
> Regular compression tools, including the compression used by backup
> software, is designed to be lossless, so you won't lose any quality.
> However, the level of compression depends on repetitive data (a text file
> of all one letter will compress a LOT; a text file containing the number
> PI will not). Multimedia files in general - audio, video and image - tend
> to be extremely random data, and as such will compress very little (1-2%
> at best) and in some cases you may even end up with a larger file once you
> add in the compressor overhead. Meanwhile, compression does take time to


Actually, audio compresses quite well with the right lossless compressor.
FLAC, for example, will typically cut a WAV file in half.

It's more accurate to say that compression depends on *predictable* data,
rather than repetitive data. If an algorithm, given the data up to any
given point in the file, can predict the next byte better than by guessing,
you can turn it into a compression algorithm. The more accurate the
prediction, the better you can compress. Repititive data is predictable, so
compresses well, but other data can be predictable, like audio.

--
--Tim Smith
 
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Ken Weitzel
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      07-26-2004


Tim Smith wrote:
> On 2004-07-26, Matt Ion <(E-Mail Removed)> wrote:
>
>>Regular compression tools, including the compression used by backup
>>software, is designed to be lossless, so you won't lose any quality.
>>However, the level of compression depends on repetitive data (a text file
>>of all one letter will compress a LOT; a text file containing the number
>>PI will not). Multimedia files in general - audio, video and image - tend
>>to be extremely random data, and as such will compress very little (1-2%
>>at best) and in some cases you may even end up with a larger file once you
>>add in the compressor overhead. Meanwhile, compression does take time to

>
>
> Actually, audio compresses quite well with the right lossless compressor.
> FLAC, for example, will typically cut a WAV file in half.
>
> It's more accurate to say that compression depends on *predictable* data,
> rather than repetitive data. If an algorithm, given the data up to any
> given point in the file, can predict the next byte better than by guessing,
> you can turn it into a compression algorithm. The more accurate the
> prediction, the better you can compress. Repititive data is predictable, so
> compresses well, but other data can be predictable, like audio.
>



Predictable data?

Ken

 
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chris French
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      07-26-2004
In message <cf%Mc.114562$ek5.110689@pd7tw2no>, Matt Ion
<(E-Mail Removed)> writes
>
>"Jeff" <(E-Mail Removed)> wrote in message
>news:(E-Mail Removed). com...
>> I have ~1.5 GB of jpg and tif files, should I compress them when
>> backing them up or will the compression program compromise the image?
>>
>> Are there any compression programs anyone likes? (winzip... pkzip...?)

>
>I like WinRAR myself, as it's used widely and also supports ZIP files, plus
>can view inside CAB and ISO files.


I usually use 7-Zip, which is free, though I usually stick tot he zip
format
--
Chris French

 
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David J Taylor
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      07-26-2004
Jeff wrote:
> I have ~1.5 GB of jpg and tif files, should I compress them when
> backing them up or will the compression program compromise the image?
>
> Are there any compression programs anyone likes? (winzip... pkzip...?)
>
> Thanks.


Don't compress the images further (e.g. by using more JPEG compression).
Either accept that you will need to backup onto three CDs, or buy yourself
a DVD writer. I would not recommend putting all the images into one large
Zip file, as if that file becomes corrupt, all the images may be lost.
It's also possible that you may not be able to read a proprietary backup
format in the future, so stick with a straight copy.

Cheers,
David


 
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Matt Ion
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      07-26-2004
"Tim Smith" <(E-Mail Removed)> wrote in message
newsC%Mc.16483$(E-Mail Removed) link.net...
> On 2004-07-26, Matt Ion <(E-Mail Removed)> wrote:
> > Regular compression tools, including the compression used by backup
> > software, is designed to be lossless, so you won't lose any quality.
> > However, the level of compression depends on repetitive data (a text

file
> > of all one letter will compress a LOT; a text file containing the number
> > PI will not). Multimedia files in general - audio, video and image -

tend
> > to be extremely random data, and as such will compress very little (1-2%
> > at best) and in some cases you may even end up with a larger file once

you
> > add in the compressor overhead. Meanwhile, compression does take time

to
>
> Actually, audio compresses quite well with the right lossless compressor.
> FLAC, for example, will typically cut a WAV file in half.


Granted, although that's not a "standard" compression tool. Plus, the
original post asked about "backing up", from which I got the impression he
was using backup software like Veritas or something.

> It's more accurate to say that compression depends on *predictable* data,


Good point...

> rather than repetitive data. If an algorithm, given the data up to any
> given point in the file, can predict the next byte better than by

guessing,
> you can turn it into a compression algorithm. The more accurate the
> prediction, the better you can compress. Repititive data is predictable,

so
> compresses well, but other data can be predictable, like audio.


This is true. And again, depends on the algorithm. Those like ZIP and RAR
and whatever is used by various backup programs are designed to be more
general-pupose, and generally assume that most computer files will be text
and text-based (word processor, spreadsheet, etc.), or program files of some
sort. For other file types, sometimes an algorithm designed specifically
for that file's structure is more effective.


 
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