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Undo LZW compression

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Fing Fang Foom
Undo LZW compression
on Apr 11, 2007 at 1:29:43 am

Hi Y'all

Is there any way to undo compression? I stupidly compressed (LZW) some tiff files, put weeks of work into them and just realized I don't want any compression. I'm laying out a book in Photoshop - illustrations and text.
Can anyone help me or at least tell me the harsh reality that i have to redo all the files?

Thanks!




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Mike Gondek
Re: Undo LZW compression
on Apr 11, 2007 at 2:55:53 pm

You can do a Photoshop Save AS save as back to Tiff and remove the LZW , and your image most likley will still print very good. Many RIPS hang if LZW is on the file, so they may fail to print the file. LZW is a lossy compression though, so you cannot get the quality back you lost.

There is a filter reduce noise in phothsop which is uspposed to get rif of jpeg artifact, though I have nto had good results with it, you may want to try it on you un LZWed file. Median may also help.

PSD is a format that has compresison, but is not lossy, I use it all the time as many Adobe apps InDesign/After Effects/Illustrator let you place PSD.


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Vincent Rosati
Re: Undo LZW compression
on Apr 11, 2007 at 8:00:04 pm

Hey Mike-
I've read the specifications of the LZW algorithm and it states that LZW compression is lossless. I save much of my work in TIFF LZW format, and am concerned by you post.
Could you elaborate on the lossy attributes of LZW or direct me to some documentation?

Thanks


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Mike Gondek
Re: Undo LZW compression
on Apr 11, 2007 at 8:18:19 pm

Vince is right, my memory slippd on that one. LZW is a 100% a non-lossless compression. You should only have to do a save as and uncheck LZW, and your file will be back to original quality.

Sorry for the scare, but alteast a happy ending.



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pixelmeister
Re: Undo LZW compression
on Apr 12, 2007 at 1:52:03 pm

Yeah, LZW goes back to the days where computers were struggling with a "50 MB" file. Now computers are so much more powerfull that there's no reason to use lzw compression any It causes more trouble on some RIPs than there is benefit . I think designers just check that LZW button, because they've done it for years this way...just a bad habit ;)
Adi



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Vincent Rosati
Re: Undo LZW compression
on Apr 12, 2007 at 4:13:12 pm

I use LZW compression to save disc space. It is not a bad habit, when you can save up to 90% of your disc space by using LZW.


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Fing Fang Foom
Re: Undo LZW compression
on Apr 14, 2007 at 4:21:33 pm

Thanks a bunch!



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Mike Gondek
Re: Undo LZW compression
on Apr 13, 2007 at 2:02:22 pm

Have you tried printing your image as an RGB file. Wanting to make sure you had received my post as it will make a world of difference.


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Mike Gondek
Re: Undo LZW compression
on Apr 13, 2007 at 2:04:27 pm

my last post wound up under the wrong topic somehow. This was supposed to be a reply to rgb -vs- cmyk. Sorry again.


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