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JPEG and TIFF questions please....

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January 26, 2005 5:42:27 PM

Archived from groups: rec.photo.digital (More info?)

Being new I'm assuming 'saving' and 're-saving' JPEG images slowly
reduces quality right? Is this the same with TIFF? Thanks!

Kevin

More about : jpeg tiff questions

Anonymous
January 26, 2005 6:01:07 PM

Archived from groups: rec.photo.digital (More info?)

Kevin,

TIFF's are not affected and do not lose quality with multiple opening and
closings. Jpegs, as you assume, do.

Chris


On 1/26/05 2:42 PM, in article tdsfv0pthf0gd56v841rofl5f8hb15o3ca@4ax.com,
"Fred" <Pkevinf@hotmail.com> wrote:

>
> Being new I'm assuming 'saving' and 're-saving' JPEG images slowly
> reduces quality right? Is this the same with TIFF? Thanks!
>
> Kevin
>
Anonymous
January 26, 2005 6:33:46 PM

Archived from groups: rec.photo.digital (More info?)

Fred wrote:
> Being new I'm assuming 'saving' and 're-saving' JPEG images slowly
> reduces quality right? Is this the same with TIFF? Thanks!
>
> Kevin
>
No. TIFF is lossless.
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Anonymous
January 26, 2005 7:37:49 PM

Archived from groups: rec.photo.digital (More info?)

Chris Myers wrote:
> Kevin,
>
> TIFF's are not affected and do not lose quality with multiple opening and
> closings. Jpegs, as you assume, do.
>
Where do you get this info? What programs?

--
John McWilliams
Anonymous
January 26, 2005 10:43:54 PM

Archived from groups: rec.photo.digital (More info?)

Fred wrote:

> Being new I'm assuming 'saving' and 're-saving' JPEG images slowly
> reduces quality right?

Yes. Every time you save as JPEG, there is a loss of information (so
less details in the final photo).

> Is this the same with TIFF? Thanks!

No. TIFF format keeps all the info all the time (that's why is so much
bigger that a JPEG file).

--
chidalgo
January 26, 2005 10:44:13 PM

Archived from groups: rec.photo.digital (More info?)

Fred <Pkevinf@hotmail.com> wrote in
news:tdsfv0pthf0gd56v841rofl5f8hb15o3ca@4ax.com:

> Being new I'm assuming 'saving' and 're-saving' JPEG images slowly
> reduces quality right? Is this the same with TIFF? Thanks!
>
>

My tests in Photoshop 6 indicate that it is much less a problem with .jpgs
then most people would lead you to believe. In my case, even with a lot of
iterations of open, make edit, re-save, etc, I couldn't get photoshop to
make changes to the larger portion of the unedited photo, nor were the
reductions in quality such that they stood out in a print. ymmv.

With tiff there is not an issue. Same thing with photoshop or paint shop
pro native formats (.psd and .psp).

Bob
January 26, 2005 10:44:14 PM

Archived from groups: rec.photo.digital (More info?)

Thank you both! What test are you referring to in photoshop 6?


On Wed, 26 Jan 2005 19:44:13 GMT, bob <not@not.not> wrote:

>Fred <Pkevinf@hotmail.com> wrote in
>news:tdsfv0pthf0gd56v841rofl5f8hb15o3ca@4ax.com:
>
>> Being new I'm assuming 'saving' and 're-saving' JPEG images slowly
>> reduces quality right? Is this the same with TIFF? Thanks!
>>
>>
>
>My tests in Photoshop 6 indicate that it is much less a problem with .jpgs
>then most people would lead you to believe. In my case, even with a lot of
>iterations of open, make edit, re-save, etc, I couldn't get photoshop to
>make changes to the larger portion of the unedited photo, nor were the
>reductions in quality such that they stood out in a print. ymmv.
>
>With tiff there is not an issue. Same thing with photoshop or paint shop
>pro native formats (.psd and .psp).
>
>Bob
Anonymous
January 26, 2005 10:44:14 PM

Archived from groups: rec.photo.digital (More info?)

bob wrote:
> Fred <Pkevinf@hotmail.com> wrote in
> news:tdsfv0pthf0gd56v841rofl5f8hb15o3ca@4ax.com:
>
>
>>Being new I'm assuming 'saving' and 're-saving' JPEG images slowly
>>reduces quality right? Is this the same with TIFF? Thanks!
>>
>>
>
>
> My tests in Photoshop 6 indicate that it is much less a problem with .jpgs
> then most people would lead you to believe. In my case, even with a lot of
> iterations of open, make edit, re-save, etc, I couldn't get photoshop to
> make changes to the larger portion of the unedited photo, nor were the
> reductions in quality such that they stood out in a print. ymmv.
>
> With tiff there is not an issue. Same thing with photoshop or paint shop
> pro native formats (.psd and .psp).
>
> Bob

I agree. I recently did some testing with saving, editing, and resaving
jpgs (using Paint Shop Pro 8). In about the tenth generation I could
see a tiny bit of degradation.

Having said that, I still follow the practice of making a TIFF copy of
the original, and then doing all editing on the copy.
Anonymous
January 26, 2005 11:55:47 PM

Archived from groups: rec.photo.digital (More info?)

bob wrote:
> Fred <Pkevinf@hotmail.com> wrote in
> news:tdsfv0pthf0gd56v841rofl5f8hb15o3ca@4ax.com:
>
>> Being new I'm assuming 'saving' and 're-saving' JPEG images slowly
>> reduces quality right? Is this the same with TIFF? Thanks!
>>
>>
>
> My tests in Photoshop 6 indicate that it is much less a problem with
> .jpgs then most people would lead you to believe. In my case, even
> with a lot of iterations of open, make edit, re-save, etc, I couldn't
> get photoshop to make changes to the larger portion of the unedited
> photo, nor were the reductions in quality such that they stood out in
> a print. ymmv.
>
> With tiff there is not an issue. Same thing with photoshop or paint
> shop pro native formats (.psd and .psp).
>
> Bob

Maybe this is because when first saving in jpg, some of image info is lost
and after later re-saving that portion to be lost is not present anyway..so
not much damage is done.
But, still, doing this does loose some image quality, so it's at least
advised to leave originals intact and save corrected photos under different
name. You won't see difference in general photos, but if you shoot some text
from close, then save, re-save a few times, look in photoshop magnified,
you'll see the difference.
TIFF shouldn't suffer from any loss, though.
January 27, 2005 12:20:48 AM

Archived from groups: rec.photo.digital (More info?)

"SleeperMan" <SleeperMan@too.sleepy> wrote in
news:IASJd.8570$F6.1556921@news.siol.net:

> name. You won't see difference in general photos, but if you shoot
> some text from close, then save, re-save a few times, look in
> photoshop magnified, you'll see the difference.
>

Only if you make changes. To restate that in a way that will make it very
clear: If you edit a file, it will be different, but if you don't edit it,
then it will be the same. Further, if you edit only part of a .jpg, then
only part of it will be different. The exception being if you crop it on
other than an 8 pixel block boundary.

Bob
January 27, 2005 12:22:51 AM

Archived from groups: rec.photo.digital (More info?)

Fred <Pkevinf@hotmail.com> wrote in
news:2iufv05lmc8345qbaq4l90d34oqkt42eep@4ax.com:

> Thank you both! What test are you referring to in photoshop 6?
>

I opened a .jpg, and did 'save as' and 'close' and then 'open'. I repeated
that a number of times. No change in the .jpg. I then opened and made
changes to small parts of the .jpg, by, for instance bluring a selection.
The selection (and 0 to 7 adjcent pixel boundary) were altered, but the
remainder of the .jpg is not.

Bob
Anonymous
January 27, 2005 12:58:13 AM

Archived from groups: rec.photo.digital (More info?)

On Wed, 26 Jan 2005 21:20:48 GMT, bob <not@not.not> wrote:

>"SleeperMan" <SleeperMan@too.sleepy> wrote in
>news:IASJd.8570$F6.1556921@news.siol.net:
>
>> name. You won't see difference in general photos, but if you shoot
>> some text from close, then save, re-save a few times, look in
>> photoshop magnified, you'll see the difference.
>>
>
>Only if you make changes. To restate that in a way that will make it very
>clear: If you edit a file, it will be different, but if you don't edit it,
>then it will be the same.

Yep, presuming you don't re-save the file.

>Further, if you edit only part of a .jpg, then
>only part of it will be different.

This is only true if you don't adjust the quality setting in photoshop
from one save to the next, and that the original file was created by
the same version of photoshop in the first place.

For example, if photoshop opens a JPEG written by a D70, and then just
saves it again without edit, the whole file *does* get re-encoded.
This will be true for a JPEG created by any camera.

Secondly, even standard adjustments like warmup, levels, unsharp-mask,
color-temp, saturation etc *always* affect the entire image. So in
reality, nobody ever changes just 'a bit' of the image.

>The exception being if you crop it on
>other than an 8 pixel block boundary.

...or a 90degree rotation by software that is designed to do this
losslessly.

--
Owamanga!
January 27, 2005 1:19:39 AM

Archived from groups: rec.photo.digital (More info?)

On Wed, 26 Jan 2005 14:42:27 -0500, Fred <Pkevinf@hotmail.com> wrote:

>
>Being new I'm assuming 'saving' and 're-saving' JPEG images slowly
>reduces quality right? Is this the same with TIFF? Thanks!
>
>Kevin

Kevin:
You are correct.
JPEG is a "Lossy" format which discards some information. The amount
may be minimal at first, but I have noticed that repeated resaves
eventually cross a boundary and past that the image starts looking
like garbage pretty quickly.

TIFF is a "lossless" format and is not supposed to discard any data.

Personally I prefer using PNG which is lossless like TIFF format, but
has a generally better compression capability.


Drifter
"I've been here, I've been there..."
January 27, 2005 1:22:11 AM

Archived from groups: rec.photo.digital (More info?)

On Wed, 26 Jan 2005 15:01:07 -0500, Chris Myers <cmyers@virginia.edu>
wrote:

>Kevin,
>
>TIFF's are not affected and do not lose quality with multiple opening and
>closings. Jpegs, as you assume, do.
>
>Chris

Open and close has not effect. Open and re-save, now that has an
effect. The difference is subtle, but important to be clear about.


Drifter
"I've been here, I've been there..."
Anonymous
January 27, 2005 2:02:19 AM

Archived from groups: rec.photo.digital (More info?)

On Wed, 26 Jan 2005 21:20:48 GMT, bob <not@not.not> wrote:

>"SleeperMan" <SleeperMan@too.sleepy> wrote in
>news:IASJd.8570$F6.1556921@news.siol.net:
>
>Only if you make changes. To restate that in a way that will make it very
>clear: If you edit a file, it will be different, but if you don't edit it,
>then it will be the same.

Not exactly true. If you load a JPEG into an image editor, make no
edits (as you state) at all, and simply save it back to disk... you
can expect degradation of the image.
Anonymous
January 27, 2005 2:02:20 AM

Archived from groups: rec.photo.digital (More info?)

secheese wrote:
> On Wed, 26 Jan 2005 21:20:48 GMT, bob <not@not.not> wrote:
>
>
>>"SleeperMan" <SleeperMan@too.sleepy> wrote in
>>news:IASJd.8570$F6.1556921@news.siol.net:
>>
>>Only if you make changes. To restate that in a way that will make it very
>>clear: If you edit a file, it will be different, but if you don't edit it,
>>then it will be the same.
>
>
> Not exactly true. If you load a JPEG into an image editor, make no
> edits (as you state) at all, and simply save it back to disk... you
> can expect degradation of the image.
>
*You* might, but hundreds of others of us do not expect that, nor does
it happen.

Besides, the degradation of jpegs is frequently of the Chicken Little
nature.

--
John McWilliams
Anonymous
January 27, 2005 2:04:01 AM

Archived from groups: rec.photo.digital (More info?)

On Wed, 26 Jan 2005 21:22:51 GMT, bob <not@not.not> wrote:

>Fred <Pkevinf@hotmail.com> wrote in
>news:2iufv05lmc8345qbaq4l90d34oqkt42eep@4ax.com:
>
>I opened a .jpg, and did 'save as' and 'close' and then 'open'. I repeated
>that a number of times. No change in the .jpg. I then opened and made
>changes to small parts of the .jpg, by, for instance bluring a selection.
>The selection (and 0 to 7 adjcent pixel boundary) were altered, but the
>remainder of the .jpg is not.

No change? Or no perceivable change? I think we need your definition
of "no change".
Anonymous
January 27, 2005 6:02:58 AM

Archived from groups: rec.photo.digital (More info?)

On Wed, 26 Jan 2005 16:36:58 -0800, John McWilliams
<jpmcw@comcast.net> wrote:

>*You* might, but hundreds of others of us do not expect that, nor does
>it happen.
>
>Besides, the degradation of jpegs is frequently of the Chicken Little
>nature.

Okay...

I loaded a hi-res JPEG into PSP7, and made no edits to it. I then did
a "Save As" to a different name. And guess what? The new file was
different from the old file by 30Kbytes. "How do you explain that one
Mr. Fung?"
Anonymous
January 27, 2005 6:02:59 AM

Archived from groups: rec.photo.digital (More info?)

secheese wrote:
> On Wed, 26 Jan 2005 16:36:58 -0800, John McWilliams
> <jpmcw@comcast.net> wrote:
>
>
>>*You* might, but hundreds of others of us do not expect that, nor does
>>it happen.
>>
>>Besides, the degradation of jpegs is frequently of the Chicken Little
>>nature.
>
>
> Okay...
>
> I loaded a hi-res JPEG into PSP7, and made no edits to it. I then did
> a "Save As" to a different name. And guess what? The new file was
> different from the old file by 30Kbytes. "How do you explain that one
> Mr. Fung?"
>
>
I don't.

I was speaking of the top echelon of photo processors.

Photoshop and Graphic Converter, as well as iPhoto meet the criterion of
not changing jpegs just by changing the name.

I'd dump PSP on that ground alone.

--
John McWilliams
Anonymous
January 27, 2005 6:56:39 AM

Archived from groups: rec.photo.digital (More info?)

On Wed, 26 Jan 2005 19:16:15 -0800, John McWilliams
<jpmcw@comcast.net> wrote:

>secheese wrote:
>> On Wed, 26 Jan 2005 16:36:58 -0800, John McWilliams
>> <jpmcw@comcast.net> wrote:
>>
>>
>>>*You* might, but hundreds of others of us do not expect that, nor does
>>>it happen.
>>>
>>>Besides, the degradation of jpegs is frequently of the Chicken Little
>>>nature.
>>
>>
>> Okay...
>>
>> I loaded a hi-res JPEG into PSP7, and made no edits to it. I then did
>> a "Save As" to a different name. And guess what? The new file was
>> different from the old file by 30Kbytes. "How do you explain that one
>> Mr. Fung?"
>>
>>
>I don't.

Didn't think so.
Anonymous
January 27, 2005 6:58:15 AM

Archived from groups: rec.photo.digital (More info?)

On Wed, 26 Jan 2005 22:22:11 -0500, Drifter <zespectre@askme.com>
wrote:

>On Wed, 26 Jan 2005 15:01:07 -0500, Chris Myers <cmyers@virginia.edu>
>wrote:
>
>>Kevin,
>>
>>TIFF's are not affected and do not lose quality with multiple opening and
>>closings. Jpegs, as you assume, do.
>>
>>Chris
>
>Open and close has not effect. Open and re-save, now that has an
>effect. The difference is subtle, but important to be clear about.

Correct! Many don't understand this.
Anonymous
January 27, 2005 2:10:11 PM

Archived from groups: rec.photo.digital (More info?)

>>Being new I'm assuming 'saving' and 're-saving' JPEG images slowly
>>reduces quality right? Is this the same with TIFF? Thanks!

Non technical answer: re-saving jpegs slowly reduces quality. This is not
true of tiff.

Technical answer: it ain't that simple.

Jpeg is both a file format and an image compression mechanism.

Strictly speaking, the TIFF standard only defines the file structure. It
does not define whether, or how, the image data is compressed. Most camera
hardware and software uses TIFF structured files as a framework for storing
uncompressed image data. TIFF has therefore become synonymous with
"uncompressed" in common parlance. In practice, this is usually true but
doesn't have to be so. It is even possible to store a jpeg compressed image
in a TIFF file. If that's not bad enough, the image headers in a jpeg file
are actually in tiff format - but let's not go there.

The jpeg image compression mechanism is what's called a "lossy" compression
method. What that means is that if you jpeg-compress an image and then
reconstruct the image from the jpeg compressed data, the reconstructed image
is not identical to the original. It just looks very similar.

If you take your reconstituted image and jpeg compress it again, then
reconstruct, you end up with an image which is similar to the first
reconstructed image but not quite so similar to the original. Every time
you repeat the compress/reconstruct process, you move a little further away
from your original image.

Returning to the original question about re-saving a jpeg, it's not
re-saving that causes loss of information it's recompressing. Intelligent
image software will only re-compress if it has to. So if you open up a jpeg
image, make no changes then save to another file then the software _should_
just copy the original jpeg encoded data to the new file. It really should
not jpeg compress the decoded image. In fact, even some simple
transformations can be achieved without the need to recompress the image.
Rotating the image through 90 degrees is an example. There are well known
methods which allow software to achieve this without re-compressing, so
these operations can be performed without any loss of quality.

Unfortunately not all image software is this intelligent so, unless you
really understand how your software works and the circumstances under which
it will/will not recompress the image then it is safer to assume that every
new save represents a loss in quality.

Hope that makes sense.

Keith
Anonymous
January 27, 2005 2:10:11 PM

Archived from groups: rec.photo.digital (More info?)

>>Not exactly true. If you load a JPEG into an image editor, make no
>>edits (as you state) at all, and simply save it back to disk... you
>>can expect degradation of the image.

You can only expect that if you expect your image editor to be rubbish.
Mind you, given the general standard of software on the market that may not
be an unreasonable expectation.

I wrote my own a simple image editor which I have made available as
freeware. My software may be very simple and doesn't have a whole load of
features but I can assure you of one thing. If you open an image and then
save it back to disk then there will be NO image degradation.

You can change some of the header information or even rotate the image
through 90 degrees and still I guarantee NO image degradation. Unless you
actually change the pixels of the image itself, my software will always copy
the jpeg encoded data, unaltered, into the new file and I would assume that
any image editor worth its salt would do exactly the same.

Keith
January 27, 2005 2:10:12 PM

Archived from groups: rec.photo.digital (More info?)

In article <n_3Kd.597$gs6.36@newsfe3-win.ntli.net>, keith.sheppard@tesco.net
says...
> >>Not exactly true. If you load a JPEG into an image editor, make no
> >>edits (as you state) at all, and simply save it back to disk... you
> >>can expect degradation of the image.
>
> You can only expect that if you expect your image editor to be rubbish.
> Mind you, given the general standard of software on the market that may not
> be an unreasonable expectation.
>
> I wrote my own a simple image editor which I have made available as
> freeware. My software may be very simple and doesn't have a whole load of
> features but I can assure you of one thing. If you open an image and then
> save it back to disk then there will be NO image degradation.
>
> You can change some of the header information or even rotate the image
> through 90 degrees and still I guarantee NO image degradation. Unless you
> actually change the pixels of the image itself, my software will always copy
> the jpeg encoded data, unaltered, into the new file and I would assume that
> any image editor worth its salt would do exactly the same.
>
> Keith
>
>
>
>
>
>

If you open a JPG image in Photoshop CS an make no changes, the SAVE option
is not even available in the file menu, only SAVE AS (giving you the
oportunity to change the filename).

They structured it this way for a reason:

So you wont inadvertantly recompress your original image without knowing it.


I dont know whether the other popular software (specifically PaintShop Pro)
has this prohibition, as I dont currently have it installed.

Personally, I recomend saving as .TIF or some other non lossy format until
editing is finished. I dont know WHY this argument about jpg exists..

Once you have learned that JPG a lossy format, why would you use it for
anything intermediate (between shooting and finished product?). Some people
even save each intermediate step along the way, if they do their editing in
more than one session, using '(filename)a(b,c ect).tif along the way. I
think thats overkill, but it surely isnt harmfull, and saving a sucsession of
jpg images coud be harmfull, depending whether you re-load the image along
the way.

The easy answer is:

If you are doing your editing in more than one session, DONT save the
intermediate steps as JPG files, use .TIF or other non lossy filetypes.


--
Larry Lynch
Mystic, Ct.
Anonymous
January 27, 2005 2:14:58 PM

Archived from groups: rec.photo.digital (More info?)

>>No change? Or no perceivable change? I think we need your definition
>>of "no change".

Beware. It is possible for files not to be binary identical and still there
be "no change" in the image quality. The jpeg file format allows software a
great deal of flexibility, particularly in the storing of headers. Don't
assume that a change in file size necessarily means a quality loss (although
a _significant_ change probably does mean that).

The only way to determine scientifically whether there has been any change
is to perform a binary comparison of the decompressed image pixels.

Keith
Anonymous
January 27, 2005 2:18:52 PM

Archived from groups: rec.photo.digital (More info?)

>>> Kevin,
>>>
>>> TIFF's are not affected and do not lose quality with multiple opening
and
>>> closings. Jpegs, as you assume, do.
>>>
>>Where do you get this info? What programs?

I think Kevin is making the common assumptions that TIFF = uncompressed (it
ain't necessarily so) and that the jpeg save is performed either after
making changes to the image or that the saving software is dumb.

Given that the first assumption is usually correct and there's an awful lot
of dumb software out there, Kevin's assessment is not unreasonable as a
general guideline.

For a full discussion of the technicalities, see my response to the original
posting.

Keith
January 27, 2005 2:18:53 PM

Archived from groups: rec.photo.digital (More info?)

In article <w64Kd.599$gs6.447@newsfe3-win.ntli.net>, keith.sheppard@tesco.net
says...
> I think Kevin is making the common assumptions that TIFF = uncompressed (it
> ain't necessarily so) and that the jpeg save is performed either after
> making changes to the image or that the saving software is dumb.
>
> Given that the first assumption is usually correct and there's an awful lot
> of dumb software out there, Kevin's assessment is not unreasonable as a
> general guideline.
>
> For a full discussion of the technicalities, see my response to the original
> posting.
>
> Keith
>

..tif is NOT always uncompressed, but it USUALLY is compressed in a non-lossy
way (LZW?).

The only way to save a .tif (that I know of) is to actually CHOOSE a lossy
compression type when saving the file (PhotoShop CS allows this choice, but
it is several steps down the list of available compression styles, along with
..zip compression).


--
Larry Lynch
Mystic, Ct.
Anonymous
January 27, 2005 2:18:53 PM

Archived from groups: rec.photo.digital (More info?)

Keith Sheppard wrote:
>>>>Kevin,
>>>>
>>>>TIFF's are not affected and do not lose quality with multiple opening
>
> and
>
>>>>closings. Jpegs, as you assume, do.
>>>>
>>>
>>>Where do you get this info? What programs?
>
>
> I think Kevin is making the common assumptions that TIFF = uncompressed (it
> ain't necessarily so) and that the jpeg save is performed either after
> making changes to the image or that the saving software is dumb.
>
> Given that the first assumption is usually correct and there's an awful lot
> of dumb software out there, Kevin's assessment is not unreasonable as a
> general guideline.
>
> For a full discussion of the technicalities, see my response to the original
> posting.

You stripped out the attributions, and I was addressing Chris' post, not
Kevin's.

--
john mcwilliams

"Andre, a simple peasant, had only one thing on his mind as he crept
along the East wall: 'Andre creep ... Andre creep ... Andre creep'."
Anonymous
January 27, 2005 2:22:48 PM

Archived from groups: rec.photo.digital (More info?)

>>No. TIFF is lossless.

Now I'm going to spend the whole day being unable to get that darned song,
"It ain't necessarily so", out of my brain.

TIFF is a file structure which most manufacturers use for storing
uncompressed (or maybe losslessly compressed) images. It is possible to
store a jpeg compressed image in a TIFF file and still call it a TIFF. I
say "possible". I have no evidence that any camera hardware or image
software might ever do such a silly thing, but the pedant in me cannot allow
the possible misunderstanding to go by uncommented.

Keith
Anonymous
January 27, 2005 2:22:49 PM

Archived from groups: rec.photo.digital (More info?)

Keith Sheppard wrote:
>>>No. TIFF is lossless.
>
>
> Now I'm going to spend the whole day being unable to get that darned song,
> "It ain't necessarily so", out of my brain.
>
> TIFF is a file structure which most manufacturers use for storing
> uncompressed (or maybe losslessly compressed) images. It is possible to
> store a jpeg compressed image in a TIFF file and still call it a TIFF. I
> say "possible". I have no evidence that any camera hardware or image
> software might ever do such a silly thing, but the pedant in me cannot allow
> the possible misunderstanding to go by uncommented.
>
> Keith
>
>
> Yes, pedantic. Generally speaking, and unless you have very strange
(and stupidly written) software, TIFF files imply lossless storage, and
USUALLY uncompressed, although there is nothing to prevent a user, or
programmer, from applying LZW compression to the data (also lossless)
before writing the file.


--
Ron Hunter rphunter@charter.net
Anonymous
January 27, 2005 3:49:39 PM

Archived from groups: rec.photo.digital (More info?)

On Wed, 26 Jan 2005 19:16:15 -0800, John McWilliams
<jpmcw@comcast.net> wrote:

>secheese wrote:
>> On Wed, 26 Jan 2005 16:36:58 -0800, John McWilliams
>> <jpmcw@comcast.net> wrote:
>>
>>
>>>*You* might, but hundreds of others of us do not expect that, nor does
>>>it happen.
>>>
>>>Besides, the degradation of jpegs is frequently of the Chicken Little
>>>nature.
>>
>>
>> Okay...
>>
>> I loaded a hi-res JPEG into PSP7, and made no edits to it. I then did
>> a "Save As" to a different name. And guess what? The new file was
>> different from the old file by 30Kbytes. "How do you explain that one
>> Mr. Fung?"
>>
>>
>I don't.
>
>I was speaking of the top echelon of photo processors.
>
>Photoshop and Graphic Converter, as well as iPhoto meet the criterion of
>not changing jpegs just by changing the name.

John, the point is Photoshop *does* re-encode the entire image if it
wasn't previously saved by photoshop.

This is *always* true when the original jpeg came from a camera.

Lossy. Everything you do to it is lossy. No two ways about it.

>I'd dump PSP on that ground alone.

I'd dump JPEG on that ground alone.

--
Owamanga!
Anonymous
January 27, 2005 3:49:40 PM

Archived from groups: rec.photo.digital (More info?)

Owamanga wrote:
> On Wed, 26 Jan 2005 19:16:15 -0800, John McWilliams
> <jpmcw@comcast.net> wrote:
>
>
>>secheese wrote:
>>
>>>On Wed, 26 Jan 2005 16:36:58 -0800, John McWilliams
>>><jpmcw@comcast.net> wrote:
>>>
>>>
>>>
>>>>*You* might, but hundreds of others of us do not expect that, nor does
>>>>it happen.
>>>>
>>>>Besides, the degradation of jpegs is frequently of the Chicken Little
>>>>nature.
>>>
>>>
>>>Okay...
>>>
>>>I loaded a hi-res JPEG into PSP7, and made no edits to it. I then did
>>>a "Save As" to a different name. And guess what? The new file was
>>>different from the old file by 30Kbytes. "How do you explain that one
>>>Mr. Fung?"
>>>
>>>
>>
>>I don't.
>>
>>I was speaking of the top echelon of photo processors.
>>
>>Photoshop and Graphic Converter, as well as iPhoto meet the criterion of
>>not changing jpegs just by changing the name.
>
>
> John, the point is Photoshop *does* re-encode the entire image if it
> wasn't previously saved by photoshop.
>
> This is *always* true when the original jpeg came from a camera.
>
> Lossy. Everything you do to it is lossy. No two ways about it.
>
>
>>I'd dump PSP on that ground alone.
>
>
> I'd dump JPEG on that ground alone.
>
> --
> Owamanga!

'Dumping' jpg isn't feasible for many of us, since that is the format
the camera produces. Keeping that original (already lossy) image is the
best we can do. Multiple editing steps should be done using a non-lossy
format. I am not aware of a good photo editor program that doesn't have
some non-lossy method of storing intermediate editing steps.


--
Ron Hunter rphunter@charter.net
Anonymous
January 27, 2005 3:58:52 PM

Archived from groups: rec.photo.digital (More info?)

On Thu, 27 Jan 2005 11:10:11 GMT, "Keith Sheppard"
<keith.sheppard@tesco.net> wrote:

>>>Not exactly true. If you load a JPEG into an image editor, make no
>>>edits (as you state) at all, and simply save it back to disk... you
>>>can expect degradation of the image.
>
>You can only expect that if you expect your image editor to be rubbish.
>Mind you, given the general standard of software on the market that may not
>be an unreasonable expectation.
>
>I wrote my own a simple image editor which I have made available as
>freeware. My software may be very simple and doesn't have a whole load of
>features but I can assure you of one thing. If you open an image and then
>save it back to disk then there will be NO image degradation.

I'm sure this will be a useful tool for JPEG users, you should post
the link whenever you mention it.

>You can change some of the header information or even rotate the image
>through 90 degrees and still I guarantee NO image degradation. Unless you
>actually change the pixels of the image itself, my software will always copy
>the jpeg encoded data, unaltered, into the new file.

That's useful. 90 deg rotations are not uncommon.

>I would assume that
>any image editor worth its salt would do exactly the same.

So you consider Photoshop CS not worth it's salt?

:-)

There must have been a reason you had to write this loss-less
software? - Maybe it was because the vast majority of pro software
*will* re-encode it. Photoshop *definitely does*.

--
Owamanga!
Anonymous
January 27, 2005 3:58:53 PM

Archived from groups: rec.photo.digital (More info?)

Owamanga wrote:
>
> There must have been a reason you had to write this loss-less
> software? - Maybe it was because the vast majority of pro software
> *will* re-encode it. Photoshop *definitely does*.

You've lost the thread. Someone asserted that opening a jpeg and then
saving it (in PS, it'd be Save As, as Save is disabled when there's
nothing changed *to* save.) created a loss. It doesn't; it's merely
changing the name.

--
john mcwilliams

What if Bill Gates got a penny each and every time that Windows crashed?




Wait a minute!......He does!
Anonymous
January 27, 2005 4:02:18 PM

Archived from groups: rec.photo.digital (More info?)

On Thu, 27 Jan 2005 11:14:58 GMT, "Keith Sheppard"
<keith.sheppard@tesco.net> wrote:

>>>No change? Or no perceivable change? I think we need your definition
>>>of "no change".
>
>Beware. It is possible for files not to be binary identical and still there
>be "no change" in the image quality. The jpeg file format allows software a
>great deal of flexibility, particularly in the storing of headers. Don't
>assume that a change in file size necessarily means a quality loss (although
>a _significant_ change probably does mean that).

Yep.

>The only way to determine scientifically whether there has been any change
>is to perform a binary comparison of the decompressed image pixels.

This is something Photoshop can do by layering the two different JPEG
images together and then running some funky 'difference' filtration on
them:

Technique explained here:
http://www.ledet.com/margulis/ACT_postings/DailyLife/AC...


--
Owamanga!
Anonymous
January 27, 2005 4:05:27 PM

Archived from groups: rec.photo.digital (More info?)

On Thu, 27 Jan 2005 05:40:22 -0600, Ron Hunter <rphunter@charter.net>
wrote:

>Keith Sheppard wrote:
>>>>No. TIFF is lossless.
>>
>>
>> Now I'm going to spend the whole day being unable to get that darned song,
>> "It ain't necessarily so", out of my brain.
>>
>> TIFF is a file structure which most manufacturers use for storing
>> uncompressed (or maybe losslessly compressed) images. It is possible to
>> store a jpeg compressed image in a TIFF file and still call it a TIFF. I
>> say "possible". I have no evidence that any camera hardware or image
>> software might ever do such a silly thing, but the pedant in me cannot allow
>> the possible misunderstanding to go by uncommented.
>>
>> Keith
>>
>>
> Yes, pedantic. Generally speaking, and unless you have very strange
>(and stupidly written) software, TIFF files imply lossless storage, and
>USUALLY uncompressed, although there is nothing to prevent a user, or
>programmer, from applying LZW compression to the data (also lossless)
>before writing the file.

Apparently the Nikon D70 NEF (RAW) format is actually a TIFF container
and it's encoding is definitely lossy. So TIFF, like AVI (which has
ump-teen codecs) is not a standard per-se but is really just a
container standard. You can't say it's lossy or not, it's neither and
both.

99% of TIFFs people edit are either uncompressed, or use the LZW
lossless compression. Both are completely safe for multiple edits.

--
Owamanga!
Anonymous
January 27, 2005 4:21:17 PM

Archived from groups: rec.photo.digital (More info?)

On Thu, 27 Jan 2005 07:05:49 -0600, Ron Hunter <rphunter@charter.net>
wrote:

>Owamanga wrote:
>> On Wed, 26 Jan 2005 19:16:15 -0800, John McWilliams
>> <jpmcw@comcast.net> wrote:
>>
>>
>>>secheese wrote:
>>>
>>>>On Wed, 26 Jan 2005 16:36:58 -0800, John McWilliams
>>>><jpmcw@comcast.net> wrote:
>>>>
>>>>
>>>>
>>>>>*You* might, but hundreds of others of us do not expect that, nor does
>>>>>it happen.
>>>>>
>>>>>Besides, the degradation of jpegs is frequently of the Chicken Little
>>>>>nature.
>>>>
>>>>
>>>>Okay...
>>>>
>>>>I loaded a hi-res JPEG into PSP7, and made no edits to it. I then did
>>>>a "Save As" to a different name. And guess what? The new file was
>>>>different from the old file by 30Kbytes. "How do you explain that one
>>>>Mr. Fung?"
>>>>
>>>>
>>>
>>>I don't.
>>>
>>>I was speaking of the top echelon of photo processors.
>>>
>>>Photoshop and Graphic Converter, as well as iPhoto meet the criterion of
>>>not changing jpegs just by changing the name.
>>
>>
>> John, the point is Photoshop *does* re-encode the entire image if it
>> wasn't previously saved by photoshop.
>>
>> This is *always* true when the original jpeg came from a camera.
>>
>> Lossy. Everything you do to it is lossy. No two ways about it.
>>
>>
>>>I'd dump PSP on that ground alone.
>>
>>
>> I'd dump JPEG on that ground alone.
>>
>> --
>> Owamanga!
>
>'Dumping' jpg isn't feasible for many of us, since that is the format
>the camera produces. Keeping that original (already lossy) image is the
>best we can do. Multiple editing steps should be done using a non-lossy
>format. I am not aware of a good photo editor program that doesn't have
>some non-lossy method of storing intermediate editing steps.

Workflow. Use photoshop, do any global changes as adjustment layers
and keep this 'new master' saved as a PSD file. Create JPEG copies of
this only when you want to print or publish.

Given that sharpening has to be done based on what your output
resolution, size and viewing distance is going to be, I don't see the
need to keep intermediate versions in an 'open' format such as JPEG.

--
Owamanga!
January 27, 2005 5:41:00 PM

Archived from groups: rec.photo.digital (More info?)

secheese <sec@nbnet.nb.ca> wrote in
news:8h8gv0trfi6oo52obnqp0q4ln56r3uctld@4ax.com:

> No change? Or no perceivable change? I think we need your definition
> of "no change".
>

Use photoshop to subtract the final image from the first. If the value of
every pixel is 0,0,0, then there is "no change." If the values of the
pixels vary in the range of 0,0,0 to 1,1,1, then it is pretty unlikely that
anyone will be able to perceive a change, which from my point of view works
out the same in practice.

Bob
January 27, 2005 5:45:05 PM

Archived from groups: rec.photo.digital (More info?)

Owamanga <nomail@hotmail.com> wrote in
news:cd3gv0hg3r7ptja1utnp9tsfdbiolu434g@4ax.com:

> Secondly, even standard adjustments like warmup, levels, unsharp-mask,
> color-temp, saturation etc *always* affect the entire image. So in
> reality, nobody ever changes just 'a bit' of the image.
>

I dont' know why you think that. I frequently apply all of those
adjustments to selected parts of the image. But to address your point
directly: you are saying that you are changing the entire image with
adjustments. Is there any wonder that the image is different after you save
it?

Bob
January 27, 2005 6:27:28 PM

Archived from groups: rec.photo.digital (More info?)

Owamanga <nomail@hotmail.com> wrote in
news:D pohv0p1eeguo857ngkttdsuvrphp298rt@4ax.com:

> John, the point is Photoshop *does* re-encode the entire image if it
> wasn't previously saved by photoshop.
>

But if you make 8x10 prints, and look at them side by side, can you see any
difference? I can't. If I use PS to calculate the difference, it's all
black: Mean luminosity .29, std dev .46. If you can't see a difference,
does it make a difference?

Bob
Anonymous
January 27, 2005 7:20:49 PM

Archived from groups: rec.photo.digital (More info?)

On Thu, 27 Jan 2005 14:45:05 GMT, bob <not@not.not> wrote:

>Owamanga <nomail@hotmail.com> wrote in
>news:cd3gv0hg3r7ptja1utnp9tsfdbiolu434g@4ax.com:
>
>> Secondly, even standard adjustments like warmup, levels, unsharp-mask,
>> color-temp, saturation etc *always* affect the entire image. So in
>> reality, nobody ever changes just 'a bit' of the image.
>>
>
>I dont' know why you think that. I frequently apply all of those
>adjustments to selected parts of the image.

Do you care to explain when it is necessary to apply a levels
adjustment to just part of the image?

Color temp to just part of an image?

Saturation to just part of an image?

I'm not calling you a liar, but I don't believe you. ;-)

Even an unsharp mask, which would be applied to just edges within the
image, and therefore not the whole, usually affects a small bit of
*every part* of the image, so a jpeg re-encode is going to happen.

>But to address your point
>directly: you are saying that you are changing the entire image with
>adjustments.

Yes, for every image that gets used.

Exposure (90% of the cases, but usually a minor adjustment that could
be skipped), color temp (in about 30% of the cases), levels/curves
(about 25%), sharpening (200-300% of the cases [once for email, and
again for printing 6x4 and again for printing 8x10]), saturation boost
(about 90% of the cases - I use a D70).

Digital color filters (graduated warm-up usually) about 5% of the
cases. Digital vignetting (about 2% - some portraits), Digital
de-vignetting (about 25% - all wides get this). Digital channel-based
de-saturation to B+W or sepia (about 5% - mainly portraits).

Kodak digital GEM airbrush - (about 10% - all of them portraits),
affecting approximately half of the image area.

>Is there any wonder that the image is different after you save
>it?

Of course not, that was the whole point of doing the adjustments.

--
Owamanga!
Anonymous
January 27, 2005 7:45:03 PM

Archived from groups: rec.photo.digital (More info?)

On Thu, 27 Jan 2005 07:24:49 -0800, John McWilliams
<jpmcw@comcast.net> wrote:

>Owamanga wrote:
>>
>> There must have been a reason you had to write this loss-less
>> software? - Maybe it was because the vast majority of pro software
>> *will* re-encode it. Photoshop *definitely does*.
>
>You've lost the thread. Someone asserted that opening a jpeg and then
>saving it (in PS, it'd be Save As, as Save is disabled when there's
>nothing changed *to* save.) created a loss. It doesn't; it's merely
>changing the name.

John, you are either wrong, or my Photoshop is behaving differently to
yours.

Try this test:

Start Photoshop
Open a JPEG
Choose File/Save As... menu option

STARE AT THE DAMN DIALOG THAT COMES UP ASKING YOU ABOUT QUALITY
SETTINGS.

It has a title 'JPEG Options'.

A recode is just around the corner...

--
Owamanga!
Anonymous
January 27, 2005 7:45:04 PM

Archived from groups: rec.photo.digital (More info?)

Owamanga wrote:
> On Thu, 27 Jan 2005 07:24:49 -0800, John McWilliams
> <jpmcw@comcast.net> wrote:
>
>
>>Owamanga wrote:
>>
>>>There must have been a reason you had to write this loss-less
>>>software? - Maybe it was because the vast majority of pro software
>>>*will* re-encode it. Photoshop *definitely does*.
>>
>>You've lost the thread. Someone asserted that opening a jpeg and then
>>saving it (in PS, it'd be Save As, as Save is disabled when there's
>>nothing changed *to* save.) created a loss. It doesn't; it's merely
>>changing the name.
>
>
> John, you are either wrong, or my Photoshop is behaving differently to
> yours.
>
> Try this test:
>
> Start Photoshop
> Open a JPEG
> Choose File/Save As... menu option
<shouting removed>

> It has a title 'JPEG Options'.
>
> A recode is just around the corner...


Ooops. I am wrong. I do get the dialogue, even before the stare factor.
Ouch.

Now I wonder if PS ever operated the way I thought with JPEGs, or am
thinking of another program. IAE, it's moot in the sense that I never do
a Save As from a JPEG to a JPEG, at least that's the cop-out I choose.....

--
John McWilliams
January 27, 2005 8:48:00 PM

Archived from groups: rec.photo.digital (More info?)

Owamanga <nomail@hotmail.com> wrote in
news:D f4iv0lf1ohnpqvpn0tpcm4elbi6l5roee@4ax.com:

> Do you care to explain when it is necessary to apply a levels
> adjustment to just part of the image?
>

Example: I took a photo of Chicago at night out of my hotel. Each building
is illuminated differently. I selected the individual buildings and applied
levels, color adjustments, &c to each one. In short, anytime that various
parts of a scene are illuminated very differently, it might be useful to
adjust those parts independently.

Likewise, one may apply USM to a selection. Perhaps to make the letters on
a sign more legible.

Bob
January 27, 2005 10:51:18 PM

Archived from groups: rec.photo.digital (More info?)

On Thu, 27 Jan 2005 12:49:39 GMT
In message <dpohv0p1eeguo857ngkttdsuvrphp298rt@4ax.com>
Owamanga <nomail@hotmail.com> wrote:

> John, the point is Photoshop *does* re-encode the entire image
> if it wasn't previously saved by photoshop.
>
> This is *always* true when the original jpeg came from a camera.
>
> Lossy. Everything you do to it is lossy. No two ways about it.
>
> > I'd dump PSP on that ground alone.
>
> I'd dump JPEG on that ground alone.

Should we dump digital and revert to film?
We loose far to much information with sensors.

....no more problems with lossy formats... :) 

Jeff
Anonymous
January 27, 2005 10:51:19 PM

Archived from groups: rec.photo.digital (More info?)

Confused wrote:
> On Thu, 27 Jan 2005 12:49:39 GMT
> In message <dpohv0p1eeguo857ngkttdsuvrphp298rt@4ax.com>
> Owamanga <nomail@hotmail.com> wrote:
>
>
>>John, the point is Photoshop *does* re-encode the entire image
>>if it wasn't previously saved by photoshop.
>>
>>This is *always* true when the original jpeg came from a camera.
>>
>>Lossy. Everything you do to it is lossy. No two ways about it.
>>
>>
>>>I'd dump PSP on that ground alone.
>>
>>I'd dump JPEG on that ground alone.
>
>
> Should we dump digital and revert to film?
> We loose far to much information with sensors.
>
> ...no more problems with lossy formats... :) 
>
> Jeff

Yes, and perhaps you would like to revert to living in caves and walking
everywhere, and chasing down and killing your own food. Have fun.
Anonymous
January 27, 2005 11:37:09 PM

Archived from groups: rec.photo.digital (More info?)

On Thu, 27 Jan 2005 19:51:18 GMT, Confused
<somebody@someplace.somenet> wrote:

>On Thu, 27 Jan 2005 12:49:39 GMT
>In message <dpohv0p1eeguo857ngkttdsuvrphp298rt@4ax.com>
>Owamanga <nomail@hotmail.com> wrote:
>
>> John, the point is Photoshop *does* re-encode the entire image
>> if it wasn't previously saved by photoshop.
>>
>> This is *always* true when the original jpeg came from a camera.
>>
>> Lossy. Everything you do to it is lossy. No two ways about it.
>>
>> > I'd dump PSP on that ground alone.
>>
>> I'd dump JPEG on that ground alone.
>
>Should we dump digital and revert to film?
>We loose far to much information with sensors.
>
>...no more problems with lossy formats... :) 

Now there's an idea...

:-)

I wouldn't care if the recording medium is an array of bald-eagle's
eyeballs. As long as it gives me a decent picture down the USB cable a
few minutes afterwards, I'm a happy chappie.

--
Owamanga!
Anonymous
January 28, 2005 1:22:09 AM

Archived from groups: rec.photo.digital (More info?)

On Thu, 27 Jan 2005 11:14:58 GMT, "Keith Sheppard"
<keith.sheppard@tesco.net> wrote:

>(although a _significant_ change probably does mean that).

Thank you.
Anonymous
January 28, 2005 4:29:57 AM

Archived from groups: rec.photo.digital (More info?)

In message <Xns95EB637A5AAADj123w123x123@216.77.188.18>,
bob <not@not.not> wrote:

>secheese <sec@nbnet.nb.ca> wrote in
>news:8h8gv0trfi6oo52obnqp0q4ln56r3uctld@4ax.com:
>
>> No change? Or no perceivable change? I think we need your definition
>> of "no change".
>>
>
>Use photoshop to subtract the final image from the first. If the value of
>every pixel is 0,0,0, then there is "no change." If the values of the
>pixels vary in the range of 0,0,0 to 1,1,1, then it is pretty unlikely that
>anyone will be able to perceive a change, which from my point of view works
>out the same in practice.

Actually, this is not true. If all the pixels are higher in the
subtracted image, you will still get zeros.

You need to use an offset so that 0 is some other value, like 128. If
you can't see anything but grey, do a histogram/equalize.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
January 28, 2005 10:32:04 AM

Archived from groups: rec.photo.digital (More info?)

Owamanga <nomail@hotmail.com> wrote:

> >Should we dump digital and revert to film?
> >We loose far to much information with sensors.
> >...no more problems with lossy formats... :) 
>
> Now there's an idea...
>
> :-)
>
> I wouldn't care if the recording medium is an array of
> bald-eagle's eyeballs.

I don't see *that* happening anytime soon... heh

> As long as it gives me a decent picture down the USB
> cable a few minutes afterwards, I'm a happy chappie.

Me too! And then saved and verified on an internal hard drive. And
then saved and verified on an external hard drive. And then saved and
verified on DVD's. And then copied to a working area where editing,
printing and gallery making takes place. And then those results need
to be saved...

It is such a relaxing hobby...

:^)

Jeff
!