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Old 2nd of July 2007 (Mon)   #1
sapearl
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Default JPG Quality Level 12 Compression Loss?

I realize that saving a RAW, PSDF, Tiff, DNG, etc. file as a jpg will result in loss of information through the compression nature of the jpg process. But will there always be significant (noticable?) "loss" even if you save at Quality level 12 in PhotoShop?

I am assuming that at Quality Level 12 in CS2 it will be minimal since in CS2 it shows "12" as MAXIMIUM qualityl. My starting point is always a RAW file, and I can see the file size shrink when I do a before and after comparison. So obviously there is loss going on.. I just wonder if it's only something that a mathematician will notice as compared to a person looking at an 11x14 print. - Stu
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Old 2nd of July 2007 (Mon)   #2
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Default Re: JPG Quality Level 12 Compression Loss?

There is some detail loss at Jpeg Level 12, but it's very negligible, and almost impossible to see with the naked eye.
As I've said in other threads, Jpeg is absolutely fine for a final save - eg to send to a client, or a lab, or whatever. But for your working files - the ones that you'll be opening and re-saving several times - you're better off choosing a non-compressed format.
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Old 2nd of July 2007 (Mon)   #3
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Default Re: JPG Quality Level 12 Compression Loss?

I completely agree with you Damo - my starting point is always the RAW file, and after making general tweaks there I'll save it as a PSD for final adjustments when I'm doing my attempts at "fine art" prints . But for most of my wedding JPGs that end up as 4x6, 5x7, 8x10 prints, (starting as a 12-14MB RAW) I'll save at Quality level 10 prior to sending to the lab. Thanks Damo.

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..... But for your working files - the ones that you'll be opening and re-saving several times - you're better off choosing a non-compressed format.
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Old 3rd of July 2007 (Tue)   #4
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Default Re: JPG Quality Level 12 Compression Loss?

Not to take this off on a tangent, but I've noticed that when I start with a jpg (my first digital only shot jpg's) and save it as a jpg with quality level 12, the resulting file is larger than what I started with. Why would the file be larger? Is this helping me or hurting me (any more than a re-save of a jpg would)?
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Old 3rd of July 2007 (Tue)   #5
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Default Re: JPG Quality Level 12 Compression Loss?

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Originally Posted by mabas9395 View Post
Not to take this off on a tangent, but I've noticed that when I start with a jpg (my first digital only shot jpg's) and save it as a jpg with quality level 12, the resulting file is larger than what I started with. Why would the file be larger? Is this helping me or hurting me (any more than a re-save of a jpg would)?
Because you are editing the uncompressed file, which is actually quite large, when you go to save it the program will re-compress the file to the new compression level, which could be higher or lower.
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Old 3rd of July 2007 (Tue)   #6
René Damkot
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Default Re: JPG Quality Level 12 Compression Loss?

The 'out of camera' jpg is probabely a higher compression jpg. (Say: comparable to PS jpg quality 8 or so)
If you use 'Save' it gets saved at the same compression level. If you 'Save as' you set the compression level. If you set 12, the rsulting file will be larger, and compressed less. (Have better IQ)
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Old 3rd of July 2007 (Tue)   #7
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Default Re: JPG Quality Level 12 Compression Loss?

Which is what I'd been doing on a number of files.... using SAVE AS and selecting Quality level 12.

I guess what I'm still a little confused about is, if it was already compressed DOWN to a file of some smaller size, and then I saved it at 12, and the resultant is larger file, what is being added to it? Are more "filler" one's and zero's being pumped into it to make it larger? Obviously something I'm missing here.....

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..........If you use 'Save' it gets saved at the same compression level. If you 'Save as' you set the compression level. If you set 12, the rsulting file will be larger, and compressed less. (Have better IQ)
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Old 3rd of July 2007 (Tue)   #8
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Default Re: JPG Quality Level 12 Compression Loss?

If the jpg is opened, it is 'decompressed'. That's why a jpg out of an 8Mp camera of, say, 2Mb opens to a file that is roughly 23Mb according to Photoshops file info.
If you save it as a tiff, all individual pixels are saved, resulting in a large file (n pixels x 8bpc x 3 channels for an RGB file). If you save a s a jpg, the file is compressed again.
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Last edited by René Damkot : 3rd of July 2007 (Tue) at 16:36.
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Old 3rd of July 2007 (Tue)   #9
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Default Re: JPG Quality Level 12 Compression Loss?

Sapearl-this is from a neophyte, but why don't you save your "best" as a "smart object"?
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Old 3rd of July 2007 (Tue)   #10
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Default Re: JPG Quality Level 12 Compression Loss?

OK, I'm confused here...If the initial image is a jpg out of a camera that is saved at PS equivelant of "8", then hasn't the lossy compression already thrown away the information required to make it a "12"? I understand that we can save-as a "12", but that can't return any image info that has already been discarded by the original jpeg compression. Aren't we just saving an "8" as a "12" and doing the least degradation of the "8" image on the resave? We're still stuck with the original "8" quality, aren't we?
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Old 3rd of July 2007 (Tue)   #11
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Default Re: JPG Quality Level 12 Compression Loss?

Bingo! Yes, you can never get that detail back. That is why Raw photography is preferable in some cases.

In my experience, the highest quality jpeg setting in my wife's 5D is about equivalent to Photoshop's quality level 10. Perhaps somebody out there can confirm/contradict this.

Re: file sizes after compression - you have to remember that every photo is different. Large areas of low detail will compress a lot. Eg a photo of sky with one bird in it will compress a long way, whereas a complex photo of trees won't compress as far.

Likewise, if you apply sharpening to an image, the compressed size will be larger. This is why a lot of people recommend not too much sharpening on photos that you post on web sites - the bigger the file, the slower the viewing speed.
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Old 3rd of July 2007 (Tue)   #12
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Default Re: JPG Quality Level 12 Compression Loss?

Ah, Rene - I know I can always count on you for a simple but thorough and comprehensible explanation. In addition to your impressive photographic talents, you must also write for a living.

Quote:
Originally Posted by René Damkot View Post
If the jpg is opened, it is 'decompressed'. That's why a jpg out of an 8Mp camera of, say, 2Mb opens to a file that is roughly 23Mb according to Photoshops file info.
If you save it as a tiff, all individual pixels are saved, resulting in a large file (n pixels x 8bpc x 3 channels for an RGB file). If you save a s a jpg, the file is compressed again.
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Old 3rd of July 2007 (Tue)   #13
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Default Re: JPG Quality Level 12 Compression Loss?

Hello there Chauncey - well, I must confess my ignorance here as I don't know what a smart object is at it relates to Photoshop. BTW, is CRNA some flavor of RN? My wife is one of those .

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Sapearl-this is from a neophyte, but why don't you save your "best" as a "smart object"?
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Old 4th of July 2007 (Wed)   #14
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Default Re: JPG Quality Level 12 Compression Loss?

A smart object looks at the original source and works with that, not the current view. Say you take a 3000x2000 pixel image into photoshop, resize it to 3x2 pixels, then back to 3000x2000 pixels, you'll have almost a solid color with NO detail. The image will be 6 HUGE pixels. If you made it a smart object to start with, then do the same thing, when you take it back to 3000x2000 it will look fine. The easy way to explain it is to say photoshop remembers the original image, and checks back with it as needed. The disadvantage is it's a little slower and your files are larger. It'd be a handy technique for someone who designs wedding albums in PS and does lots of resizing.
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Old 4th of July 2007 (Wed)   #15
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Default Re: JPG Quality Level 12 Compression Loss?

Also, to make a layer a smart object you right click, or I think there's a menu command "paste as smart object" somewhere.
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