JPEG saving options

JPEG saving options

Post by Carl Mill » Sat, 25 Sep 2004 10:18:53



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

http://www.ezinfocenter.com/8557444

 
 
 

JPEG saving options

Post by Eric Gil » Sat, 25 Sep 2004 10:56:23




Quote:> 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.

Quote:> 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.
Quote:> (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!!


 
 
 

JPEG saving options

Post by Carl Mill » Sat, 25 Sep 2004 12:59:57



Quote:>> 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?
Quote:

> 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.

Quote:

>> (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!!

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

http://www.ezinfocenter.com/8557444

 
 
 

JPEG saving options

Post by Nicholas Sherloc » Sat, 25 Sep 2004 13:08:25



> 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

 
 
 

JPEG saving options

Post by Rick » Sat, 25 Sep 2004 16:26:47




> > 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"

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

 
 
 

JPEG saving options

Post by David Dyer-Benne » Sat, 25 Sep 2004 16:55:21



> 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.

Quote:> 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.  
--

RKBA: <http://noguns-nomoney.com/> <http://www.dd-b.net/carry/>
Pics: <http://dd-b.lighthunters.net/> <http://www.dd-b.net/dd-b/SnapshotAlbum/>
Dragaera/Steven Brust: <http://dragaera.info/>
 
 
 

JPEG saving options

Post by Johan W. Elzen » Sat, 25 Sep 2004 17:08:31



> 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.

Quote:

> 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/

 
 
 

JPEG saving options

Post by Eric Gil » Sat, 25 Sep 2004 21:37:14





>>> 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!!

> 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.

Quote:> 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.

Quote:> 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.

 
 
 

JPEG saving options

Post by Andrew Morto » Sat, 25 Sep 2004 22:20:09


The higher the setting, the more accurately it records the image,
including the distortions caused by the previous jpeg encoding. Higher
setting=>more detail will be recorded=>bigger file.

Andrew

 
 
 

JPEG saving options

Post by Taci » Sat, 25 Sep 2004 23:53:53


Quote:>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.

Yes, of course.

You open a JPEG. It is now uncopressed. it is impossible to display or edit a
JPEG without uncompressing it.

You save it. Now it is compressed as though it had never been compressed to
begin with. The higher the quality, the bigger the file.

Quote:>Apparently it is uncompressing the
>original compressed jpeg?

Yes, of COURSE it is! If it didn't uncompress it, how could it show you the
image on the screen?

Quote:>What's up with this...

Let's say you have a JPEG compressed at the lowest possible quality. it's a
tiny file. You open it and it's uncompressed. You Save As. You set the highest
possible quality. It will be a bigger file, because it has been uncompressed,
and then recompressed again with higher qualiy setting.

Of course, when you open and then re-save a JPEG, you lose more information.
You open and re-save again, you lose still more information. Every time you
open and re-save, the quality goes down, and down, and down; the loss is
cumulative.

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

 
 
 

JPEG saving options

Post by Mart » Tue, 28 Sep 2004 01:57:43



> 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!!

I've had the exact questions. I was hoping for a straight forward
answer, but I must agree with Carl, no one directly answered the
questions; e.g. what about Max = 10 but 12 is available. Why is 12
larger that the original (details)? If someone who really understand
P/Shop JPEG save routing could/would answer it would be appreciated.
 
 
 

JPEG saving options

Post by Arti » Tue, 28 Sep 2004 02:32:34


FWIW I don't know exactly either

Urban myths are:
resaving JPEG to JPEG at low levels cummulatively reduces (?) image size and
hence quality
JPEG compression algorithms are independent steps
for example
(a)image save at JPEG level 5 then image reopened and saved at JPEG level 12
=> this will not return the image to its original appearance because JPEG is
lossy BUT saving and resaving at JPEG level 12 will not cummulatively reduce
(?) image quality

(b) image saved a JPEG level 5 then image reopned and saved at JPEG level 5
=> a second application of the JPEG compression algorithms => a further loss
in image quality

I suppose (a) and (b) may be tested empirically (I can be bothered at the
mo')

My own preference on working images is to take JPEG to PSD and keep
everytthing in PSD form flattening out into JPEG at level 12 setting until I
am pleased with result.  Mike will probably confirm that I am easily pleased
with results - possibly too easily pleased LOL

Saving to JPEG at anyother setting - I try to do this from the PSD file
rather than JPEG to JPEG (I can't remember why tho :-)

Artie




>> 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!!

> I've had the exact questions. I was hoping for a straight forward
> answer, but I must agree with Carl, no one directly answered the
> questions; e.g. what about Max = 10 but 12 is available. Why is 12
> larger that the original (details)? If someone who really understand
> P/Shop JPEG save routing could/would answer it would be appreciated.

 
 
 

JPEG saving options

Post by Rick » Tue, 28 Sep 2004 03:25:15




> > 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!!

> I've had the exact questions. I was hoping for a straight forward
> answer, but I must agree with Carl, no one directly answered the
> questions; e.g. what about Max = 10 but 12 is available. Why is 12
> larger that the original (details)? If someone who really understand
> P/Shop JPEG save routing could/would answer it would be appreciated.

It's been explained to you in plain English. What part of this
do you not understand:

The JPEG compression routine doesn't know or care whether
an image has been previously compressed.  In other words,
when you JPEG compress an image, the routine doesn't know
or care what the original file size was, or what quality settings
were used for previous compressions.  At quality 12 you're
getting a less compressed image, therefore larger in size,
although it will still be compressed, and will still be lossy
relative to the original.

Rick

 
 
 

JPEG saving options

Post by Taci » Tue, 28 Sep 2004 07:33:19


Quote:> Why is 12
>larger that the original (details)?

Very, very simple.

You have an image. Let us say for the sake of example that the image, when
UNCOMPRESSED, is one megabyte.

You save it as a JPEG. You use quality, say, 4. It saves to about 200
kilobytes.

You open the JPEG, It uncompresses. The image is 1 megabyte uncompressed.

You save it as JPEG with quality 12. It compresses again. You saved it with a
higher quality so this time it compresses to 500 kilobytes.

Make sense?

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

 
 
 

JPEG saving options

Post by Taci » Tue, 28 Sep 2004 07:35:51


Quote:>Why is 12
>larger that the original (details)? If someone who really understand
>P/Shop JPEG save routing could/would answer it would be appreciated.

It's very, very simple, and has already been explained.

Let us say you have an image that is 1 megabyte in size uncompresssed. Let's
say you save it as a JPEG with quality 4. So it saves to a file that's, for
instance, about 150 K in size.

Now you open that 150 K JPEG. It uncompresses. Now it is 1 megabyte again.

Now you save it again. You save as JPEG with quality 12. So it compresses
again, this time to 500 kilobytes.

Make sense?

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