Quality loss using ZIP files?

Discussion in 'Digital Darkroom' started by jasonsmith, Aug 28, 2004.

  1. I have a Nikon Coolscan 4000 which at 16 Bit produces 100MB files.

    I like to keep a master scan of all trannies / negs before doing any
    adjustments / levels etc. The problem is that this quickly erodes
    space on the hard drive.

    I am wondering if I ZIP the original scans and burn them to DVD
    would there be any loss in quality of the original scan.


    Jason Smith
  2. Are you asking about files with extension ".tif". LZW is a compression commonly associated with tiffs. If you are using Vuescan, you can specify lzw compression when outputting tiffs, either the finished gamma tiffs, or "Vuescan Raw File" tiffs.

    In my case, I output Vuescan raw files (tiff format) that range between 35~45 megs, with lzw compression. Without lzw, they would be around 55 megs. In the course of working these files in Photoshop, the compression ratio erodes, with each re-save. Sometimes, they end up bigger than uncompressed!

    After completion of PS editing, I'll use these to output a fresh raw file, within Vuescan, getting the compression ratio back, and then delete the PS edited version (after checking the new ones are ok).

    I don't think zip would compress any better than lzw. I've tried it, and it is ponderously slow. As to Zip integrity, I believe it is safe. But lzw has two advantages:

    1. The file is still a tiff, accessable as is, albeit a little slower to open.

    2. If you do a multiple file zip, you are making it more difficult to access/use your files. And, if the zip were to somehow become corrupted, you have all your eggs in one basket.
  3. ZIP is a non-lossy compression algorithm and hence will not loose anything. however a consideration for archiving of course is being able to use it sometime in the future. Not to mention the media, the format and I guess in an instance of ZIP, the operating system. Lossy as it is, JPEG has been around and continues to show compatibility. I think TIF has also shown some resilience over the years. I just make sure my film is put away safely as it seems to have survived the longest.
  4. ZIP is fine and has been around for quite sometime. IF one is concerned about the program going away it would suffice to put the program file along the pix on the same CD/DVD. If, one is concerned about the distant future PC not being able to run the ZIP program...I'd say not to worry as it is such a widely used standard that whatever comes up next most likely will be able to open (unzip) ZIP files.
  5. Or self-extracting zip. Still, I think lzw gets them just as small, and leaves them usable.
  6. The ZIP algorithm unmodified probably desn't compress an uncompressed TIFF all that well. However the specialized implementation of ZIP compression used in the PNG format generally gives better compression ratios than LZW TIFF and doesn't have the software patents associated with it.
  7. ZIP won't lose any quality (as noted above). However, there will of course be a loss of covenience -- you won't be able to open the files directly from the DVD, instead you'll have to decompress them first. Therefore I would recommend as above, and use some sort of LZW compression on the TIFFs themselves (or use PNG).
  8. 4000 * 6000 * 6 = 144 MB, not 100MB. If you have already saved
    these files as JPEG, all the answers above are wrong. ZIP will do
    little to further compress a JPEG file. Insufficient information in
    your original question, sorry.
  9. Thanks for all your answers. Bill just to clarify - I have been saving the original 'raw' (16 bit / 4000 dpi) scan as an uncompressed TIFF. I might be a little anal but I like to store an original 16 bit scan that I havent modified in any way. From there I do levels/ curves adjustments and scale down to 8 bit where I make any further changes. I store that file as an LZW compressed TIFF.

    So I guess what most of you are saying is best option might be to save the raw 16 bit scan as an LZW TIFF which should be completely lossless - ?
  10. Yes, compressed TIFF sounds like your best bet. PNG would be a bit
    smaller but most software can't do 48-bit PNG. Lossless JPEG 2000,
    if you have it, would be even more compact and theoretically supports
    16-bits per color. ZIP is about as compact as LZW TIFF and much less
    convenient. Another thing you could do is edit now and convert to
    8-bit, because 16-bit is mostly useful for post-scan chromatic and
    luminance corrections. Then you could store PNG, or Photoshop format.
  11. What about non Tiff files? specifically Photoshop PSD files? I am in the habit of converting my jpegs to PSD immediately after downloading from the camera since ACDSee and my editors (ACDSee FotoCanvas,PSE2, and Corel PhotoPaint - since retired) all handle PSD files quite readily. I only convert to a different format when I want to distribute the photo.

    I've noticed that the zip format won't compress jpegs at all (which makes sense, they are already compressed) Zip will compress PSD files anywhere from 3% to around 18%. Is the zip format non lossey ALL the time or does it depend on the source file or other conditions?

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