Does Compress Old Files in Disk Cleanup affect photos?

Discussion in '35mm Cameras' started by Donald Specker, Dec 25, 2007.

  1. Was wondering if this function in Windows affects photo files.

    Thanks.
     
    Donald Specker, Dec 25, 2007
    #1
    1. Advertisements

  2. Donald Specker

    Scott W Guest

    It is a losses compression so no detail is lost, but they will take
    longer to load.
    Also jpeg photos will really not compress any more then they are so
    there is little point in using window to compress them.

    Scott
     
    Scott W, Dec 25, 2007
    #2
    1. Advertisements

  3. It is a losses compression so no detail is lost, but they will take
    longer to load.
    Also jpeg photos will really not compress any more then they are so
    there is little point in using window to compress them.

    Scott

    I don't understand the above. If I take a jpeg photo that was saved with
    moderate compression so the file size is say, one megabyte, and I resave it
    with more severe compression, so the file size is say, 1/2 megabyte, isn't
    that compressing it more?
     
    William Graham, Dec 26, 2007
    #3
  4. Donald Specker

    Scott W Guest

    The OP was talking about Windows routine to compress files, this is a
    lossless compression and since jpeg files have already gone through a
    final stage of lossless compression there is nothing to be gained.
    Try making a zip file out of a jpeg image and you will see that it
    does not shrink the file much very much, only a very small part of a
    jpeg file is not already compressed. A quick test shows that I am
    seeing much less then a 1% reduction in the size of the file when I do
    this.

    Scott
     
    Scott W, Dec 26, 2007
    #4
  5. The OP was talking about Windows routine to compress files, this is a
    lossless compression and since jpeg files have already gone through a
    final stage of lossless compression there is nothing to be gained.
    Try making a zip file out of a jpeg image and you will see that it
    does not shrink the file much very much, only a very small part of a
    jpeg file is not already compressed. A quick test shows that I am
    seeing much less then a 1% reduction in the size of the file when I do
    this.

    Scott

    Ah.....Thank you....The key phrase here is, "Lossless compression"......I
    never expected any compression to be lossless. This seems to me to be like
    getting something for nothing....I'm always glad to get a free lunch....:^)
     
    William Graham, Dec 26, 2007
    #5
  6. Donald Specker

    Matthew Winn Guest

    Lossless compression works by discarding unnecessary information and
    encoding what's left. For example, normal English text can be written
    with 52 letters, a space and a few punctuation characters: perhaps 60
    characters in total. A byte contains 8 bits and allows for up to 256
    characters, but if you're using only 60 characters you can represent
    that with 6 bits, which means you can cram one and a third characters
    into a byte or four characters into three bytes. The text ends up
    taking only 3/4 as much space, but no information has been lost.

    Real lossless compression is more complex than that: a good algorithm
    would recognise the frequent use of the sequence "compress" in this
    message and replace it with a single shorter code, and that means that
    some popular compression algorithms can compress text by around 80%.
    However, if something has already been compressed there's little or
    no redundant information left to remove so a second compression is
    ineffective.

    One of the features of lossless compression is that for every lossless
    algorithm there will always be some data that can't be compressed at
    all. This doesn't stop people from trying to find a way around this
    restriction even though it's been proven impossible. See section 9.2
    of http://www.faqs.org/faqs/compression-faq/part1/section-8.html for
    details.
     
    Matthew Winn, Dec 27, 2007
    #6
  7. 5-level Baudot gets it done in 32 characters - well 2 sets of 32 with a
    shift character to get between sets. With 5 character words it
    works out to ~25 bits/word.

    Static dictionary compression gets it down to ~14 bits/word
    using a 16,000 word vocabulary.
     
    Nicholas O. Lindan, Dec 27, 2007
    #7
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.