Loosing file quality

Discussion in 'macOS' started by Sgt.Pepper, Dec 17, 2008.

  1. Sgt.Pepper macrumors member

    Joined:
    Nov 23, 2008
    Location:
    Australia
    #1
    I wasn't sure where to post this, so I hope this is an okay location.

    I recently read that if you open up a jpeg file and then resave it, it loses quality. Is this true?
    Is it only Jpegs, or all compressed images? Or even yet, all images i.e. Raw?
    What other scenario must I be aware of where file quality can be lost? Any with music files, or video files?
     
  2. wrldwzrd89 macrumors G5

    wrldwzrd89

    Joined:
    Jun 6, 2003
    Location:
    Solon, OH
    #2
    Yes, this is true of anything that uses lossy compression. JPEG files, MP3 files, and AAC files are 3 examples. These all suffer from so-called generational losses. This occurs because, in a typical editor, the binary data must first be decompressed to work with it. This step incurs no data loss. However, when the file is next saved, the only way to re-save it is to re-encode it. This process incurs all the losses from the original encoding, AND additional losses in the re-encode. This is where the quality deterioration occurs.

    Not all compressed files have this problem. Anything that uses lossless compression, such as PNG images or Apple Lossless audio, does NOT suffer from generational loss each time it is saved.
     
  3. mongrol macrumors regular

    Joined:
    Jul 16, 2007
    #3
    No. But it can "lose" quality.
     
  4. Sgt.Pepper thread starter macrumors member

    Joined:
    Nov 23, 2008
    Location:
    Australia
    #4
    So I'd have to open the MP3, AAC file in someway where I'm resaving it for the file to degrade slightly? Not just say open it, play music, exit program?
     
  5. wrldwzrd89 macrumors G5

    wrldwzrd89

    Joined:
    Jun 6, 2003
    Location:
    Solon, OH
    #5
    Correct. Viewing a JPEG image or listening to MP3/AAC audio files doesn't degrade them. Editing these files DOES.
     

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