A straight-forward answer to this might be out there, but I haven't
found it yet. (All file sizes are approximations, but representative of
actual experience.)

When saving JPEG's, the Quality drop-down menu gives you the choice of
Low, Medium, High, Maximum. Choosing Maximum gives a setting of 10.
However, you can increase the setting to 12. I've noticed that if I open
a JPEG that is, say, about 1.3mb and save it at the "default" Maximum
setting of 10, it compresses it to, say, about 900k. If I save it at the
"maximum" Maximum setting of 12, I actually end up with a larger file
than I started out with of about 3mb. Apparently it is uncompressing the
original compressed jpeg?

What's up with this, and practically speaking, should I be saving at 10
or 12?

(Take it as read that I know about tif being non-lossy, and jpeg being
lossy, etc. I'm just wondering about this Photoshop jpeg Quality thing.)

Thanks!!

--
Carl Miller
carl_miller23@hotmail.com
http://www.ezinfocenter.com/8557444

carl_miller23@hotmail.com (Carl Miller) writes:

> A straight-forward answer to this might be out there, but I haven't
> found it yet. (All file sizes are approximations, but representative of
> actual experience.)
>
> When saving JPEG's, the Quality drop-down menu gives you the choice of
> Low, Medium, High, Maximum. Choosing Maximum gives a setting of 10.
> However, you can increase the setting to 12. I've noticed that if I open
> a JPEG that is, say, about 1.3mb and save it at the "default" Maximum
> setting of 10, it compresses it to, say, about 900k. If I save it at the
> "maximum" Maximum setting of 12, I actually end up with a larger file
> than I started out with of about 3mb. Apparently it is uncompressing the
> original compressed jpeg?

Of course it is; that's what loading it into photoshop does.  And then
if you save it, it recompresses it at whatever level you select.

> What's up with this, and practically speaking, should I be saving at 10
> or 12?

I find essentially no use for either.  For screen resolution, 8 is
plenty, or even 5.  For printing, I wouldn't use jpeg.
--
David Dyer-Bennet, <mailto:dd-b@dd-b.net>, <http://www.dd-b.net/dd-b/>
RKBA: <http://noguns-nomoney.com/> <http://www.dd-b.net/carry/>
Pics: <http://dd-b.lighthunters.net/> <http://www.dd-b.net/dd-b/SnapshotAl.../dragaera.info/>

Carl Miller <carl_miller23@hotmail.com> wrote:

> A straight-forward answer to this might be out there, but I haven't
> found it yet. (All file sizes are approximations, but representative of
> actual experience.)
>
> When saving JPEG's, the Quality drop-down menu gives you the choice of
> Low, Medium, High, Maximum. Choosing Maximum gives a setting of 10.
> However, you can increase the setting to 12. I've noticed that if I open
> a JPEG that is, say, about 1.3mb and save it at the "default" Maximum
> setting of 10, it compresses it to, say, about 900k. If I save it at the
> "maximum" Maximum setting of 12, I actually end up with a larger file
> than I started out with of about 3mb. Apparently it is uncompressing the
> original compressed jpeg?

Photoshop (or any other program) cannot edit images in compressed
format, so yes, when you open an image it will be uncompressed.

>
> What's up with this, and practically speaking, should I be saving at 10
> or 12?

All the information you've lost on the first compression, is lost
forever. On the next compression you will loose information again, so if
you insist in subsequent JPEG saves and you want to retain as much
information as you can, you'll have to use 12.


--
Johan W. Elzenga            johan<<at>>johanfoto.nl
Editor / Photographer      http://www.johanfoto.nl/

carl_miller23@hotmail.com (Carl Miller) wrote in
news:00040823235949.OUI15.carl_miller23@hotmail.com:

> On September 24 2004, Eric Gill <ericvgill@yahoo.com> wrote: 
> "default"  >> Maximum setting of 10, it compresses it to, say, about
> 900k. If I  >> save it at the "maximum" Maximum setting of 12, I
> actually end up  >> with a larger file than I started out with of about
> 3mb. Apparently  >> it is uncompressing the original compressed jpeg? 
> whatever you need it for. 
>
> Thank you mr. expert for totally NOT ansering my question. Didn't I SAY
> I KNEW about lossy vs non-lossy compressions? Don't you think that
means
> I KNOW about saving my "work copy" in a non-lossy format?

That was, of course, why you asked about multiple saves in JPEG.

> Now, re-read
> my post and if you can answer the question I asked, please do, but
> otherwise stop being a total lack of help. (Hint: The question is in
one
> of the sentences that ends with a question mark.)
>
> Sorry to sound pissy,

Oh, I'm sure.

> but you gave me the exact type of NON-ANSWER I've
> been getting to this question for practically six months now.
Apparently
> NO ONE knows the answer.

The answer is simply that you shouldn't be re-saving in JPEG format.

It's not my problem that you don't like the answer, and getting pissy
because you hold a misconception is stupid.

carl_miller23@hotmail.com (Carl Miller) wrote in
news:00040823211103.OUI90.carl_miller23@hotmail.com:

> A straight-forward answer to this might be out there, but I haven't
> found it yet. (All file sizes are approximations, but representative of
> actual experience.)
>
> When saving JPEG's, the Quality drop-down menu gives you the choice of
> Low, Medium, High, Maximum. Choosing Maximum gives a setting of 10.
> However, you can increase the setting to 12. I've noticed that if I open
> a JPEG that is, say, about 1.3mb and save it at the "default" Maximum
> setting of 10, it compresses it to, say, about 900k. If I save it at the
> "maximum" Maximum setting of 12, I actually end up with a larger file
> than I started out with of about 3mb. Apparently it is uncompressing the
> original compressed jpeg?

Of course. It has to, to work on it.

> What's up with this, and practically speaking, should I be saving at 10
> or 12?

You shouldn't be re-saving a JPEG at all. Save your working copy in a
lossless format, then use save for web to optimize the JPEG output for
whatever you need it for.

> (Take it as read that I know about tif being non-lossy, and jpeg being
> lossy, etc. I'm just wondering about this Photoshop jpeg Quality thing.)
>
> Thanks!!
>

On September 24 2004, Eric Gill <ericvgill@yahoo.com> wrote: 
"default"  >> Maximum setting of 10, it compresses it to, say, about
900k. If I  >> save it at the "maximum" Maximum setting of 12, I
actually end up  >> with a larger file than I started out with of about
3mb. Apparently  >> it is uncompressing the original compressed jpeg?
>
> Of course. It has to, to work on it.
> 
>
> You shouldn't be re-saving a JPEG at all. Save your working copy in a
> lossless format, then use save for web to optimize the JPEG output for
>
whatever you need it for.
> 

Thank you mr. expert for totally NOT ansering my question. Didn't I SAY
I KNEW about lossy vs non-lossy compressions? Don't you think that means
I KNOW about saving my "work copy" in a non-lossy format? Now, re-read
my post and if you can answer the question I asked, please do, but
otherwise stop being a total lack of help. (Hint: The question is in one
of the sentences that ends with a question mark.)

Sorry to sound pissy, but you gave me the exact type of NON-ANSWER I've
been getting to this question for practically six months now. Apparently
NO ONE knows the answer.

--
Carl Miller
carl_miller23@hotmail.com
http://www.ezinfocenter.com/8557444

"Rick" <me@privacy.net> wrote in message n 
if 
>
> Exactly.  To put it another way, when you save a file in
> JPEG format, the compression routine doesn't know or
> care about any previous compression(s).
>
> Rick
Why do they even bother with an adjustable scale then? I would think that
there is not a soul who would want to save a file with less quality!

>> When you set it to "12", the result is closer to the original file 


>From: "Scraphead" Watashee@{deletethis}one.net
>
>Why do they even bother with an adjustable scale then? I would think that
>there is not a soul who would want to save a file with less quality!

Every "soul" who saves jpegs for the web will soon discover that at moderate
mid-level settings well below 10 or 12 you have a much smaller file size wit
h
acceptable quality, so people can look at your images without lengthy waits 
for
downloads.

>Why do they even bother with an adjustable scale then? I would think that
>there is not a soul who would want to save a file with less quality!

Yes, there are many times when you want to save a JPEG with less quality--fo
r
example, for the Web.

The JPEG file format was created for situations where file size is critical 
and
file quality is not important. The Web is one such situation. There are many
times when a JPEG saved at maximum quality is just plain too big for a Web
site.

Only use JPEG if you *have to*--if you absolutely must have a small file, an
d
quality isn't important. Never save a JPEG if you do not have to have a JPEG
.
("JPEG is the only kind of file I know about" does not qualify as "have to."
)

--
Art, literature, shareware, polyamory, kink, and more:
http://www.xeromag.com/franklin.html

Carl Miller wrote:
> If I save it at the "maximum" Maximum setting of 12, I actually end up
> with a larger file than I started out with of about 3mb. Apparently
> it is uncompressing the original compressed jpeg?
>
> What's up with this, and practically speaking, should I be saving at
> 10 or 12?
>
> (Take it as read that I know about tif being non-lossy, and jpeg being
> lossy, etc. I'm just wondering about this Photoshop jpeg Quality
> thing.)

You say that you _know_ about lossy file formats, but your comments seem to
suggest you have only a very basic understanding. Every time you open a
JPEG, it's decompressed. When it's saved, it must be compressed again. No
matter what compression level you set it to, you are losing information.
When you set it to "12", the result is closer to the original file than if
you set it to "10"

Cheers,
nicholas Sherlock