Archived posting to the Leica Users Group, 2005/02/11

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Subject: [Leica] Can you really JPEG a JPEG?
From: aaron.sandler at duke.edu (Aaron Sandler)
Date: Fri Feb 11 14:04:57 2005
References: <005101c51060$c20eecb0$833b6d18@ted> <2b.6c8e6565.2f3d89ea@aol.com> <005101c51060$c20eecb0$833b6d18@ted>

Hi Alex,

I support you in your new workflow.  You described basically what I've been 
doing for the last year or so.  The photofinisher develops and scans to CD 
(1524x1024 700kb jpg) for me to sort on my computer.  Almost all of my PAWs 
that are shot on C-41 film come from those commercial scans, which I adjust 
in PS then save as 700pixel wide jpgs, aiming for 50-100kb files.  At some 
point I scan the good ones myself for printing.  It seems like a nice 
marriage of film and digital for those of us who aren't (currently) 
interested in shooting digitally but like using the web +/- digital darkroom.

As far as your question: It makes sense that the more repetitions of 
compressing you do, and the greater each compression is, the worse the 
final outcome.  In this case you may have started with a not-too-compressed 
jpg and only compressed it one additional time without a big effect on the 
screen image.  I think the more salient fact is that web display is soooooo 
low resolution...it'll take much longer to see the multi-compression 
problems on the web then it would if you were making prints.  As you're 
scanning separately for printing, I wouldn't worry about a couple of rounds 
of compression for web jpgs.

Best,
Aaron

>As I was getting overwhelmed by proof prints, I instructed my friendly 
>photo processors to simply develop the film and provide a CD with a 
>reference print. This means I can review what I've got very quickly on the 
>Mac, find the average 3 or 4 keepers per roll, and scan the relevant negs 
>to produce decent prints.
<snip>
>My question is this: the hi-res disk files have a JPEG (jpg) handle, and 
>received wisdom is that quality deteriorates rapidly if you try to 
>re-compress an existing JPEG. So are these hi-res files really JPEGs?
>
>I took a deep breath and saved the adjusted and resized PS files as small 
>JPEGs, and, as you can see, the results seem pretty good - in fact more or 
>less on a par with what I would expect from a Net-ready JPEG  where the 
>original data came from film. Am I missing something here?


In reply to: Message from tedgrant at shaw.ca (Ted Grant) ([Leica] WAS: and my remarks NOW: Sympathy.)
Message from SonC at aol.com (SonC@aol.com) ([Leica] your dog and my remarks)
Message from corkflor at iol.ie (Alex Hurst) ([Leica] Can you really JPEG a JPEG?)