Export Quality

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This has probably been asked before. If so, here it comes again. In the export dialogue box, under File Settings, there is a slider called Quality ranging from ' to 1''%. What exactly does this mean? I mean, what do I loose by using 5'%? Please don't answer "5'% of the quality".
 
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I won't answer 5'% of the quality because that's not the answer!

The quality slider affects the amount of compression used in creating a JPG. More compression (closer to zero on the Quality scale) implies lower quality (more artifacts), less compression (closer to 1'' on the quality scale) implies higher quality (few artifacts). The scale is non-linear, so if you selected ', you wouldn't get a file that is compressed down to nothing (although it is probably so compressed that you wouldn't like it), and if you select 1'' you get a file that is most likely going to be larger than the JPG original (if you started with JPG originals), but even at 1'', there is still some compression and artifacts, most likely invisible to the human eye.

The practical impact of this isn't particularly damaging in LR, but in other photographic editors, repeated opening and saving of a JPG photograph continually causes compression and artifacts, which build upon each other and accumulate. So repeated opening and saving of a JPG is a no-no. LR normally doesn't do repeated opening and saving.
 
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Firstly, the slider is not percentage (although this is an easy assumption to make). I'm not even sure the slider is linear..
Second, unless there is a compelling reason to compress jpegs, I would recommend leaving it on 1'' and not compress. Once a JPEG is compressed, it is no longer able to be decompressed and returned to the same 8-bit color state. i.e. image data is lost forever.

If you have to compress, then keep in mind that a setting of 8' will produce an image file that is smaller than one produced at 1'' and it is still acceptable for viewing on a website. The reasons that you might need to compress are external requirements such as from a website that might limit uploads. For instance, attachments to this post can be no larger than 256KB. Any image that I include need to be either cropped down in size or compressed before it is accepted for upload.
 
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WHCC recommends a value of 1' on the Photoshop JPG Quality Scale. At the same time they recommend 84 on the Lightroom JPG quality scale. I don't know where they get their information but the Lightroom Team is in the same city as WHCCC...
 
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FYI - While the scale runs from ' to 1'', I believe there was a previous post discussing that changes in file size seemed to coour about every 5 or so units. On the informal tests that I recently ran, this seemed to hold merit. So, it is possible that there are actually only four to five possible output options between 8' and 1''. I do not know this for certain, but the file sizes being similar seem to support this theory.

--Ken

P.S. Rikk, I was not aware that the LR Team was in one city. Can you elaborate?
 
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The LR team is split between at least 4 offices, if not more. San Jose, San Francisco, Minneapolis and Seattle spring to mind.
 
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[quote author=Victoria Bampton link=topic=8899.msg59832#msg59832 date=126332'465]
The LR team is split between at least 4 offices, if not more. San Jose, San Francisco, Minneapolis and Seattle spring to mind.
[/quote]I think Rikk was implying the WHCC in Minneapolis might be in communication with the LR team in that city. It would be a reasonable assumption, but speculation surely unless Rikk is in contact with one or both parties.
 
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[quote author=Victoria Bampton link=topic=8899.msg59832#msg59832 date=126332'465]
The LR team is split between at least 4 offices, if not more. San Jose, San Francisco, Minneapolis and Seattle spring to mind.
[/quote]

This is what I remembered. Thanks for the clarification, Victoria.

--Ken
 
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It is true that the LR Team is located in multiple cities (as are most software teams these days). A number of the LR Team Members are in Arden Hills, (MSP suburb) only about 2' miles from WHCC located in Eagan. To clarify, I am in contact with both parties but do not have direct knowledge of their being in contact with one-another.
 
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That would really confuse people! The '-1'' scale is not specific to Lightroom - it's the scale most use - Photoshop's '-12 is the odd one out.
 
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[quote author=Victoria Bampton link=topic=8899.msg59913#msg59913 date=1263391439]
Photoshop's '-12 is the odd one out.
[/quote]

Yes, but at least it "goes to 11"! ;)

--Ken
 
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[quote author=Victoria Bampton link=topic=8899.msg59913#msg59913 date=1263391439]
That would really confuse people! The '-1'' scale is not specific to Lightroom - it's the scale most use - Photoshop's '-12 is the odd one out.[/quote]But two '-1'' scales in different applications can use the same numbers to represent different compression ratios. Same file saved at 1'' in LR is 1' MB and in DPP is 8.5 MB
 
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So the long and the short of it is find a setting you like and stick with it.
 
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