Computer Graphics with Photoshop - Re: JPEG saving options

Author

Re: JPEG saving options

Martin

2004-09-28, 7:14 am

carl_miller23@hotmail.com (Carl Miller) wrote in message 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?
>
> 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.

Artie

2004-09-28, 7:14 am

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

"Martin" <metpx3c@hotmail.com> wrote in message
news:3a16084b.0409260857.646fd4de@posting.google.com...
> carl_miller23@hotmail.com (Carl Miller) wrote in message
> news:<00040823211103.OUI90.carl_miller23@hotmail.com>...
>
> 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.

Rick

2004-09-28, 7:14 am

"Martin" <metpx3c@hotmail.com> wrote in message news:3a16084b.0409260857.646fd4de@posting.google.com...
> carl_miller23@hotmail.com (Carl Miller) wrote in message news:<00040823211103.OUI90.carl_miller23@hotmail.com>...
>
> 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

Tacit

2004-09-28, 7:14 am

> 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

Tacit

2004-09-28, 7:14 am

>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

David Dyer-Bennet

2004-09-28, 7:14 am

metpx3c@hotmail.com (Martin) writes:

> 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.

That second question *was* specifically answered, I thought, but I'll
go through it again.

When you open an image in Photoshop, it reads whatever format the
image file is originally in and decodes it into computer memory where
it's stored as an uncompressed bitmap. (Yes, if any of the Photoshop
programmers hang out here I know there are additional complexities,
not nearly well enough to explain them, so I'm not trying.) This is
the *full-sized* bitmap -- if it's a 1600x1200 digital original in
24-bit color, that's a 5,760,000 byte image, even though the jpeg
might have been 512KB.

So, there's this bitmap image in memory. Big. You edit it some,
change various bits, whatever. (Or just leave it alone, not change
any bits).

Now you tell Photoshop to save the image. It pops up the dialog for
you to select the quality level, and then starts coding the image into
a jpeg using the setting you gave it and writing the result to disk.

If the new quality level you give is the same as was used in the
original jpeg, the resulting file will be about the same size (if you
haven't changed the bitmap extensively). If you pick a higher quality
level, the resulting file will be larger -- it won't compress it as
much. If you pick a lower quality level, the resulting file will be
smaller -- it will compress more.

(The photoshop quality levels are a layer above the actual parameters
to the jpeg compression algorithm, by the way; that's why every
program has a different way of expressing degree of jpeg compression,
and they're not easy to compare to each other.)

Have I managed to make it make sense? Sorry if I still haven't.

As to your *first* question, about the "level 12" quality, I think I
know a tiny bit about why that's so. I believe that the range was
1-10 in earlier versions. They decided to add some options at the
top, and rather than changing the meaning of the previous options,
they just added more numbers (11 and 12) to describe the new options.
I *don't* really know exactly how those differ from 10, though.
--
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/SnapshotAlbum/>
Dragaera/Steven Brust: <http://dragaera.info/>

Carl Miller

2004-09-28, 7:14 am

On September 24 2004, Eric Gill <ericvgill@yahoo.com> wrote:
> The answer is simply that you shouldn't be re-saving in JPEG format.

Not ever?

So how about explaining this to most of the printing services that
PREFER you submit your digital files in JPEG. (MPIX for instance, a
division of Miller, a HIGHLY RESPECTED company in the professional
photography world.)

See, I LOVE the internet because people who DON'T KNOW the answer to the
question always seem to feel the need to phrase something that they DO
KNOW so that it SOMEHOW REMOTELY RELATES to the original question,
thereby SEEMING TO PROVE to themselves and everyone listening that they
DO INDEED KNOW SOMETHING!

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

Clyde

2004-09-28, 7:14 am

Tacit wrote:
>
>
> 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?
>

No problem, as long as you understand that Photoshop isn't restoring any
of that lossy information that JPEG got rid of when it compressed. PS is
only opening what is there.

However, it opens everything the same. So, this shade of red takes up
just as much memory as that shade of red. That is true even if the
shades of red are the same. That's why the memory size is the big size,
not the little file size. The file size makes certain shades of red all
the same and then treats them as one small piece of data rather than all
of them separately. [Highly simplified]

So, if PS were just cutting down the number of reds when it resaves in
JPEG, the theory it wouldn't change a thing. Of course, YOU may have
changed something in the picture. Then it isn't changing the same thing.
So, it compresses on top of the previous.

Also, you don't know what settings were used for the first JPEG
compression. The odds are that yours won't be the same. So, PS will be
compressing it differently. That means that it's likely to add to lossiness.

Now, if those losses mean anything or are actually visible are another
question completely. You will have to test that to your own satisfaction.

Clyde

Xalinai

2004-09-28, 7:14 am

Carl Miller wrote:

> On September 24 2004, Eric Gill <ericvgill@yahoo.com> wrote:
>
> Not ever?
>
> So how about explaining this to most of the printing services that
> PREFER you submit your digital files in JPEG. (MPIX for instance, a
> division of Miller, a HIGHLY RESPECTED company in the professional
> photography world.)
>
> See, I LOVE the internet because people who DON'T KNOW the answer to
> the question always seem to feel the need to phrase something that
> they DO KNOW so that it SOMEHOW REMOTELY RELATES to the original
> question, thereby SEEMING TO PROVE to themselves and everyone
> listening that they DO INDEED KNOW SOMETHING!

Whatever you do, you should handle the decision whether it is time to
save as JPG with the same care as you would the decision to save a text
document in a printer's native format.

You surely would keep a text version - so keep an uncompressed version
of your images.

When you save an image that is in your computer's memory as a JPG image
the compression algorithm does not know anything about the image expect
that it is a rectangular array of pixels.

IF your image was overcompressed earlier, saving at a lower compression
setting will take care to represent all detail fount in the currently
loaded image - including the artifacts created by the earlier save
process. So your image file may become bigger - it won't become better.

If you use very low compression you can be lucky that untrained eyes do
not see the degradation even avter several saves - and if you send
images to printing services that are sufficiently large for a high
number of pixels per inch then artifacts will be small enough to become
invisible. As JPG artifacts occur in blocks of 8x8 pixels, with 300dpi
your artifact size will be 37.5 blocks per inch - not everybody will
notice them.

Printing services love JPG as it reduces their transfer volume.

Michael

Tacit

2004-09-28, 7:14 am

>So how about explaining this to most of the printing services that
>PREFER you submit your digital files in JPEG. (MPIX for instance, a
>division of Miller, a HIGHLY RESPECTED company in the professional
>photography world.)

MPIX is a consumer-level printing service that takes images online. They prefer
JPEG because it's easiest to transfer JPEG images over the Web, and as a
consumer-level service, they know that the JPEG artifacts will probably not be
noticeable or objectionable to their clients.

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

Artie

2004-09-28, 7:15 am

Nice concise & nto the point

good answer!

Artie

"David Dyer-Bennet" <dd-b@dd-b.net> wrote in message
news:m24qlkcnsz.fsf@gw.dd-b.net...
> metpx3c@hotmail.com (Martin) writes:
>
>
> That second question *was* specifically answered, I thought, but I'll
> go through it again.
>
> When you open an image in Photoshop, it reads whatever format the
> image file is originally in and decodes it into computer memory where
> it's stored as an uncompressed bitmap. (Yes, if any of the Photoshop
> programmers hang out here I know there are additional complexities,
> not nearly well enough to explain them, so I'm not trying.) This is
> the *full-sized* bitmap -- if it's a 1600x1200 digital original in
> 24-bit color, that's a 5,760,000 byte image, even though the jpeg
> might have been 512KB.
>
> So, there's this bitmap image in memory. Big. You edit it some,
> change various bits, whatever. (Or just leave it alone, not change
> any bits).
>
> Now you tell Photoshop to save the image. It pops up the dialog for
> you to select the quality level, and then starts coding the image into
> a jpeg using the setting you gave it and writing the result to disk.
>
> If the new quality level you give is the same as was used in the
> original jpeg, the resulting file will be about the same size (if you
> haven't changed the bitmap extensively). If you pick a higher quality
> level, the resulting file will be larger -- it won't compress it as
> much. If you pick a lower quality level, the resulting file will be
> smaller -- it will compress more.
>
> (The photoshop quality levels are a layer above the actual parameters
> to the jpeg compression algorithm, by the way; that's why every
> program has a different way of expressing degree of jpeg compression,
> and they're not easy to compare to each other.)
>
> Have I managed to make it make sense? Sorry if I still haven't.
>
> As to your *first* question, about the "level 12" quality, I think I
> know a tiny bit about why that's so. I believe that the range was
> 1-10 in earlier versions. They decided to add some options at the
> top, and rather than changing the meaning of the previous options,
> they just added more numbers (11 and 12) to describe the new options.
> I *don't* really know exactly how those differ from 10, though.
> --
> 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/SnapshotAlbum/>
> Dragaera/Steven Brust: <http://dragaera.info/>

Eric Gill

2004-09-28, 7:15 am

carl_miller23@hotmail.com (Carl Miller) wrote in
news:00040827111716.OUI13.carl_miller23@hotmail.com:

> On September 24 2004, Eric Gill <ericvgill@yahoo.com> wrote:
>
> Not ever?

Not ever, really golly-gosh. Not if you have any control over the
situation.

> So how about explaining this to most of the printing services that
> PREFER you submit your digital files in JPEG.

Are they forcing you to make multiple JPEG saves, or have you simply not
thought this through?

> (MPIX for instance, a
> division of Miller, a HIGHLY RESPECTED company in the professional
> photography world.)
>
> See, I LOVE the internet because people who DON'T KNOW the answer to the
> question always seem to feel the need to phrase something that they DO
> KNOW so that it SOMEHOW REMOTELY RELATES to the original question,
> thereby SEEMING TO PROVE to themselves and everyone listening that they
> DO INDEED KNOW SOMETHING!

Yes, it seems you have a serious issue there.

If a beer doesn't help, perhaps you should seek therapy.

Rick

2004-09-28, 7:15 am

"Nicholas Sherlock" <n_sherlock@hotmail.com> wrote in message news:cj06jm$mgb$1@lust.ihug.co.nz...
> Carl Miller wrote:
>
> 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

Carl Miller

2004-09-28, 7:15 am

On September 26 2004, David Dyer-Bennet <dd-b@dd-b.net> wrote:
> I believe that the range was
> 1-10 in earlier versions. They decided to add some options at the
> top, and rather than changing the meaning of the previous options,
> they just added more numbers (11 and 12) to describe the new options.
> I *don't* really know exactly how those differ from 10, though.

THANK YOU! Whether that is actually correct or not (I REALLY APPRECIATE
the "I believe" disclaimer. Most people would just proceed on as if they
knew it as Truth.) that is the MOST DIRECT AND APPLICABLE ANSWER in well
over 6 months!

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

bigbopper

2004-09-28, 7:15 am

in article 00040827112109.OUI10.carl_miller23@hotmail.com, Carl Miller at
carl_miller23@hotmail.com wrote on 09/27/2004 8:26 PM:

> that is the MOST DIRECT AND APPLICABLE ANSWER in well
> over 6 months!

What a cry baby you are.

David Dyer-Bennet

2004-09-28, 7:15 am

Eric Gill <ericvgill@yahoo.com> writes:

> carl_miller23@hotmail.com (Carl Miller) wrote in
> news:00040827111716.OUI13.carl_miller23@hotmail.com:
>
>
> Not ever, really golly-gosh. Not if you have any control over the
> situation.

Even *I* will call that excessive. Slightly.

In particular, if your camera produces JPEG output, then to really
follow that rule would mean you never produced a JPEG for web
display. Which is obviously dumb.

>
> Are they forcing you to make multiple JPEG saves, or have you simply not
> thought this through?

The point is *sequences* of jpeg saves. Other than in emergencies,
*I'll* save to jpeg exactly *once*, and never touch that file again (I
might *replace* it with a new version, reworked from the original or a
losslessly-saved intermediate). If I started with a jpeg file from
the camera, that's a "resave", though.
--
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/SnapshotAlbum/>
Dragaera/Steven Brust: <http://dragaera.info/>

Rick

2004-09-28, 7:15 am

"Carl Miller" <carl_miller23@hotmail.com> wrote in message news:00040827112109.OUI10.carl_miller23@hotmail.com...
> On September 26 2004, David Dyer-Bennet <dd-b@dd-b.net> wrote:
>
> THANK YOU! Whether that is actually correct or not (I REALLY APPRECIATE
> the "I believe" disclaimer. Most people would just proceed on as if they
> knew it as Truth.) that is the MOST DIRECT AND APPLICABLE ANSWER in well
> over 6 months!

Actually four different people have given you the exact same
answer. David simply phrased it in a way your little pea brain
could wrap itself around.

Rick

Scraphead

2004-09-28, 12:14 pm

>MPIX is a consumer-level printing service that takes images online. >They
prefer
>JPEG because it's easiest to transfer JPEG images over the Web, and as a
>consumer-level service, they know that the JPEG artifacts will probably not
be
>noticeable or objectionable to their clients.
Rinky Dink

How hard is it to do all of your photo reworks in psd format and then save
the final that goes to the printer in jpg, so it doesn't have to be resized
at all?
And, if you use Corel Draw or a program that will import psd files and
supply the printer with a hi-res pfd file of your final project, you should
never even have to see a jpg. To some, this may even be rinky dink, but a
hell of a lot better than what is described above!

Scraphead

2004-09-28, 12:14 pm

"David Dyer-Bennet" <dd-b@dd-b.net> wrote in message
news:m2oejreyak.fsf@gw.dd-b.net...
> The point is *sequences* of jpeg saves. Other than in emergencies,
> *I'll* save to jpeg exactly *once*, and never touch that file again (I
> might *replace* it with a new version, reworked from the original or a
> losslessly-saved intermediate). If I started with a jpeg file from
> the camera, that's a "resave", though.
Once out of the camera, I convert it to a psd file for working on. Am I
losing anything there? I've been doing that since last year when this had
been brought up, for the millionth time

<http://dragaera.info/>