Compressing images... loss?

Discussion in 'Digital Photography' started by Jeff, Jul 26, 2004.

  1. Jeff

    Jeff Guest

    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.
     
    Jeff, Jul 26, 2004
    #1
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  2. Jeff

    Charles Guest

    On 25 Jul 2004 18:37:47 -0700, (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
     
    Charles, Jul 26, 2004
    #2
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  3. Jeff

    Ralph Mowery Guest

    "Jeff" <> wrote in message
    news:...
    > 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.
     
    Ralph Mowery, Jul 26, 2004
    #3
  4. Jeff

    c0smic Guest

    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.


    It’s 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 don’t 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.
     
    c0smic, Jul 26, 2004
    #4
  5. Jeff

    Matt Ion Guest

    "Jeff" <> wrote in message
    news:...
    > 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.
     
    Matt Ion, Jul 26, 2004
    #5
  6. Jeff

    Tim Smith Guest

    On 2004-07-26, Matt Ion <> 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
     
    Tim Smith, Jul 26, 2004
    #6
  7. Jeff

    Ken Weitzel Guest

    Tim Smith wrote:
    > On 2004-07-26, Matt Ion <> 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
     
    Ken Weitzel, Jul 26, 2004
    #7
  8. Jeff

    chris French Guest

    In message <cf%Mc.114562$ek5.110689@pd7tw2no>, Matt Ion
    <> writes
    >
    >"Jeff" <> wrote in message
    >news:...
    >> 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
     
    chris French, Jul 26, 2004
    #8
  9. 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
     
    David J Taylor, Jul 26, 2004
    #9
  10. Jeff

    Matt Ion Guest

    "Tim Smith" <> wrote in message
    news:pC%Mc.16483$...
    > On 2004-07-26, Matt Ion <> 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.
     
    Matt Ion, Jul 26, 2004
    #10
  11. Jeff

    Matt Ion Guest

    "David J Taylor" <-this-bit.nor-this-part.uk>
    wrote in message news:%e2Nc.8169$...
    > 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.


    Oh, and speaking of DVD writers... in my market at least (Vancouver, BC),
    DVD is by far cheaper per-byte than CD now.

    A CD-RW drive can be had around here starting at CDN$50-$60; CD-RW/DVD-ROM
    combo for about $75, and a 4X DVD+/-RW for a hair over $100 (8X writer for
    about $120-$130), which makes the drive itself very affordable.

    CD-R media can be found as low as $30 for a spindle of 100 (very cheap)
    discs; better quality disks still run about $50-$60/100... or 30-60 cents
    per 700MB disc. Averaging that at 45 cents/disc, you get about 65 cents per
    gigabyte.

    DVD+R and DVD-R media can be had for $25 for a spindle of 25, or $1 per
    4700MB disc... or less than 22 cents per gig.

    Doesn't take long at that rate to offset the cost of the writer.
     
    Matt Ion, Jul 26, 2004
    #11
  12. Jeff

    Martin Brown Guest

    In message <gwZMc.13747$>, Ralph
    Mowery <> writes
    >
    >"Jeff" <> wrote in message
    >news:...
    >> 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.


    Although it is just about possible for a JPEG file to be incompressible
    with ZIP encoding it is more common for them to compress by about 1-5%.
    This is usually not worth the effort. In fact a quick and dirty test for
    badly damaged JPEG files is to see if they will compress by more than
    5%.

    TIFs may well compress by a sufficient margin 30-70% to be worth using
    ZIP. Depending on how tight you are for space this may be worthwhile.

    Regards,
    --
    Martin Brown
     
    Martin Brown, Jul 26, 2004
    #12
  13. Already compressed files, such as jpeg, don't compress well. Think about
    it. If compression worked on _every_ file then run the data through the
    compression program often enough and any data of any complexity could
    eventually be compressed down to half a dozen bytes.

    Needless to say it ain't like that. In fact you can prove with quite simple
    mathematics that for every file which you can compress there must be at
    least one file which would get bigger when subjected to the same compression
    algorithm.

    However the good news is that all general purpose data compression
    applications (eg. ZIP) are lossless. Again, if you think about the
    consequences were it not so, you will realise that they have to be. If what
    you are compressing is a picture then you might not be too upset if it
    expanded to something very close, but not identical, to the original. If it
    was your last five years' accounts, you might be a trifle upset if the
    compression program decided to change a few of the figures.

    To return to your original question, should you compress images before
    archiving? If they are in an already compress format, such as jpeg, then
    no. If they are uncompressed (eg. tiff) then yes. If they are a mixture
    then the only way really to tell is to try compressing them and see if the
    result is bigger or smaller than the sum of the component parts.

    Incidentally, the same argument applies to compressed folders within
    Windows. If you habitually use Windows' compressed folders feature, as I
    do, it is a good idea to make sure you turn it off for those folders where
    you store jpeg images.

    Keith
     
    Keith Sheppard, Jul 26, 2004
    #13
  14. Jeff

    Ron Hunter Guest

    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.


    JPG format is already compressed, and little will gained (space wise)
    with further compression, and the loss has already happened. TIF files
    aren't usually compressed but some compression methods can be applied to
    them, and space savings varies. You can apply a lossless compression,
    such as LZW and gain some space, on some pictures. Winzip and Pkzip
    both do lossless compression.
     
    Ron Hunter, Jul 26, 2004
    #14
  15. Jeff

    Ron Hunter Guest

    c0smic wrote:

    > 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.

    >
    >
    > It’s 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 don’t 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.
    >

    Hummm. 1.5 GB and 3 times 600 MB. Yeah, I should think SO. Grin.
    Probably on two....
     
    Ron Hunter, Jul 26, 2004
    #15
  16. Jeff

    Matt Guest

    On 25 Jul 2004 18:37:47 -0700, (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...?)


    A compression program for DATA of any kind, cannot introduce losses -
    a few bytes out of a documenht, or an exe, and goodnight vienna!

    However, as mentioned in other replies, already compressed data (eg.
    JPG) cannot be comp[ressed further - though there may be a small
    amount of compression in the non-image data segments, and for "solid"
    compression, a small amount from repeat compression of headers that
    are identical from file to file.

    For JPEGs, you can sometimes shrink the further using a "cleaner" that
    discards segments not required for the image - it's possible to have a
    preview stored inside the JPG, for instance. If you don't care about
    EXIF information, you can throw that away, leaving it absent or shrunk
    to the minimum if it cannot be left out.


    I'll throw in a vote for 7-Zip, or its 7Z format that's creeping in to
    more and more programs - a solid format that's on a level with RAR,
    but is open-source - not as ubiquitous as zip - YET!


    You may like to divide them into reasonably sized groups, and add some
    PAR files (using SmartPAR or Quickpar) as this can allow a damaged
    file to be recovered by recalculating it from the available ones ond
    the PAR data - though it's probably easier to make multiple copies
    (store in different places).

    --
    I may be dozzzy, but take the ZZZ's out to mail me
    http://www.junkroom.freeserve.co.uk/jvc2080.htm - 2x2x24 CD-RW troubles

    If you drop a cactus, don't try to catch it!
     
    Matt, Jul 26, 2004
    #16
  17. Jeff

    Kev M. Guest

    There's an article on this at cameratown

    http://www.cameratown.com/guides/tutorial_listing.cfm/hurl/id|78

    Kev.


    "Matt Ion" <> wrote in message news:<cf%Mc.114562$ek5.110689@pd7tw2no>...
    > "Jeff" <> wrote in message
    > news:...
    > > 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.
     
    Kev M., Jul 26, 2004
    #17
  18. This has been interesting discussion concerning compression.

    I have several questions concerning jpeg compression.

    Is there a difference in quality of jpeg images with different
    levels of jpeg compression? What do you lose by using a lower level
    jpeg compression to save the files? You do save disk space but do
    you lose anything else?

    I have a canon powershot and the options are superfine (very large
    files), fine (large files), and normal. I guess the normal has the most
    compression and the superfine has the least compression. Please
    correct me if I'm wrong.

    Thanks for any information. These little manuals are really don't
    explain the differences.

    Thanks

    Alan
     
    Post Replies Here Please, Jul 27, 2004
    #18
  19. Jeff

    Matt Ion Guest

    "Post Replies Here Please" <> wrote in message
    news:...
    > This has been interesting discussion concerning compression.
    >
    > I have several questions concerning jpeg compression.
    >
    > Is there a difference in quality of jpeg images with different
    > levels of jpeg compression? What do you lose by using a lower level
    > jpeg compression to save the files? You do save disk space but do
    > you lose anything else?


    It's a quality vs. size equation: the more compression, the less quality.

    JPEG is a lossy compression that works by making various assumptions about
    the way we see images and colors. For example, say you took a picture of
    the sky - no clouds, just plain blue sky. If you zoomed down to the pixel
    level, you'd find very small changes in the exact shade of blue from one
    area to the next. JPEG compression assumes that you won't notice
    differences of, say, 1% (this will vary with the compression level set), and
    so defines anything that falls within that range as a single blue. This can
    cause a "mottling" effect if you have a gradient where the color changes
    gradually and you end up with "jumps" in color.

    If you have one pixel of red within a region of blue, that may also be
    discarded outright under the assumption that it wouldn't be noticeable or
    missed. In some cases this may be desireable; in others it may have adverse
    effects.

    The higher the compression level you set, the broader and more forceful the
    assumptions become... and the more noticeable their effect.

    > I have a canon powershot and the options are superfine (very large
    > files), fine (large files), and normal. I guess the normal has the most
    > compression and the superfine has the least compression. Please
    > correct me if I'm wrong.


    Probably correct. Some cameras will use such definitions for different
    image resolutions, and some may refer to a combination of resolution and
    compression - one camera I used once, don't remember what kind, defined
    highest quality as low compression at the maximum image size, mid-quality as
    higher compression at maximum image size, and lowest quality at the same
    compression as mid, but with a smaller image.
     
    Matt Ion, Jul 27, 2004
    #19
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