# LR 5.3 unable to use LZW compression when doing "Edit in Photoshop".



## Sunny16 (Feb 16, 2014)

Running Lightroom 5.3 on a Win7 PC.



I go EDIT > PREFERENCES > EXTERNAL EDITING > FILE FORMAT = TIFF, COMPRESSION = LZW.
I press ctrl+E to edit in Photoshop CS2.
After the edit, I go EDIT > PREFERENCES > EXTERNAL EDITING, and COMPRESSION has been set to NONE by Lightroom.
 
IOW, LR 5.3 changed the compression selection to "NONE" all by itself so there is no LZW compression possible.  However if I set COMPRESSION = ZIP, then zip compression occurs and that setting is retained.

Any ideas why LR is changing LZW compression to NONE?

Thanks,
Sunny


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## johnbeardy (Feb 16, 2014)

It's because LZW can't handle 16 bit and LR really shouldn't offer the possibility.

TIF began as 8 bit with  LZW, and you would be OK if your files were 8 bit, but LZW was never intended for 16 bit. The underlying problem is that most image compression takes advantage of groups of identical pixels. Once you push resolution up to 16 bit, neighbouring pixels are most unlikely to be identical.

John


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## Sunny16 (Feb 16, 2014)

johnbeardy said:


> It's because LZW can't handle 16 bit and LR really shouldn't offer the possibility.
> 
> TIF began as 8 bit with  LZW, and you would be OK if your files were 8 bit, but LZW was never intended for 16 bit. The underlying problem is that most image compression takes advantage of groups of identical pixels. Once you push resolution up to 16 bit, neighbouring pixels are most unlikely to be identical.
> 
> John


Hi John,

That was a fast and very informative reply.  Had no idea that LZW could only handle 8bits.

Thanks so much for solving my headache,
Sunny


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## Bryan Conner (Feb 16, 2014)

For some reason, the first time you set your preferences to 16 bit Tiff, you are given the option to choose LZW when that option is in fact disabled.  If you set your preferences to 8 bit tiff with lzw for example and then export an image with these settings, when you go back to preferences (external editor) you are not given the option of LZW.  This is something that should be corrected to avoid confusion. 

16 bit LZW compression is not a real option in Lightroom:
http://forums.adobe.com/message/1402822  is a link to thread that contains an answer from Thomas Knoll himself: "_*Using LZW with 16-bit TIFF files (of actual photographs--not computer  graphics) most often results in the file size increasing from what it  would be if no compression at all was used. So that combination of  settings (LZW was 16-bit) was disabled.*_"

LZW compression on 16 or 32 bit images results in *larger *file sizes than both zip compression as well as uncompressed zip files.  

Is there a reason (I can not think of one) that you want or need to use LZW compression?  ZIP compression is the best if the images will not have layers.  If you have layers, uncompressed is my choice as the file sizes are usually smaller than uncompressed.

LZW on 16 bit images is an option in Photoshop because Photoshop can generate graphics that are not actual photographic images.  Lightroom can not do this...therefore LZW is not an option with 16 bit images.

I did a quick save test on 16 bit and 8 bit images (no layers) in CS5 using the same file:

8 bit uncompressed:          35.196 mb
8 bit zip compression         13.804 mb
8 bit LZW compression      15.360 mb

16 bit uncompressed         70.350 mb
16 bit zip compression       64.696 mb
16 bit LZW compression    83.149 mb


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## Sunny16 (Feb 16, 2014)

Bryan Conner said:


> For some reason, the first time you set your preferences to 16 bit Tiff, you are given the option to choose LZW when that option is in fact disabled.  If you set your preferences to 8 bit tiff with lzw for example and then export an image with these settings, when you go back to preferences (external editor) you are not given the option of LZW.  This is something that should be corrected to avoid confusion.
> 
> 16 bit LZW compression is not a real option in Lightroom:
> http://forums.adobe.com/message/1402822  is a link to thread that contains an answer from Thomas Knoll himself: "_*Using LZW with 16-bit TIFF files (of actual photographs--not computer  graphics) most often results in the file size increasing from what it  would be if no compression at all was used. So that combination of  settings (LZW was 16-bit) was disabled.*_"
> ...


Hi Bryan,

Thanks for the in-depth info regarding LZW compression.  I wanted to try TIFF LZW compression since the Faststone Image Viewer does not support TIFF zip compression.  No biggie.  I'll just use TIFF with no compression.

BTW, I would try using the PSD format but Windows 7 Explorer won't display thumbnail images in the .PSD format.  Know of any Win7 plugin that will make Explorer display .PSD thumbnail images?

Thanks,
Sunny


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