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In Picasa2, Is Rotating A Vertical JPEG Image Lossy Or Los..

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Anonymous
September 17, 2005 11:27:59 PM

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

Hi,

I have several types of image software, and seem to prefer Picasa2 for
my simple needs. Picasa2 maintains the original image with all its
pixels (5 million in my case), and edited pix can have the editing undone.

My question is this: If I rotate a vertical JPEG image to make it stand
up on screen, is this rotation process lossy or lossless? Knowing the
correct answer will allow me to decide how to maintain my vertical images.

Thank you.

Morton
Anonymous
September 18, 2005 5:26:19 AM

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

"Morton Linder" <mort@cloud9.net> wrote in message
news:5E1Xe.7562$IC3.5778@fe12.lga...
> Hi,
>
> I have several types of image software, and seem to prefer Picasa2 for my
> simple needs. Picasa2 maintains the original image with all its pixels (5
> million in my case), and edited pix can have the editing undone.
>
> My question is this: If I rotate a vertical JPEG image to make it stand up
> on screen, is this rotation process lossy or lossless? Knowing the correct
> answer will allow me to decide how to maintain my vertical images.
>
> Thank you.
>
> Morton

I can not see the reason why any programmer would want or need to change the
values stored in the memory representing a pixel location when the image is
rotated 90 Deg. because the pixel is moving relative its neighbor. No
advanced algorithm is needed. But don't take my word for it.

Also, JPEG is a file compression standard. When the file is open, the
operations performed on the image is independent of the file type.

John
Anonymous
September 18, 2005 5:26:20 AM

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

JohnR66 wrote:
> "Morton Linder" <mort@cloud9.net> wrote in message
> news:5E1Xe.7562$IC3.5778@fe12.lga...
>
>>Hi,
>>
>>I have several types of image software, and seem to prefer Picasa2 for my
>>simple needs. Picasa2 maintains the original image with all its pixels (5
>>million in my case), and edited pix can have the editing undone.
>>
>>My question is this: If I rotate a vertical JPEG image to make it stand up
>>on screen, is this rotation process lossy or lossless? Knowing the correct
>>answer will allow me to decide how to maintain my vertical images.
>>
>>Thank you.
>>
>>Morton
>
>
> I can not see the reason why any programmer would want or need to change the
> values stored in the memory representing a pixel location when the image is
> rotated 90 Deg. because the pixel is moving relative its neighbor. No
> advanced algorithm is needed. But don't take my word for it.
>
> Also, JPEG is a file compression standard. When the file is open, the
> operations performed on the image is independent of the file type.
>
> John
>
>
Thanks for your reply. In a different image software, (I forgot which),
when clicking on to rotate an image there is an on-screen warning that
carrying out the rotation will permanently deteriorate the image.
Therefore, I want to be certain one way or the other, before I rotate
all my vertical images.
Morton
Anonymous
September 18, 2005 11:55:29 AM

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

Morton Linder wrote:

> My question is this: If I rotate a vertical JPEG image [in Picasa]
> to make it stand up on screen, is this rotation process lossy or
> lossless?

Can't say for sure, but Picasa does not seem to appear on this
list of applications implementing lossless JPEG rotation:
<http://sylvana.net/jpegcrop/losslessapps.html&gt;.

--
znark
Anonymous
September 18, 2005 12:32:34 PM

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

JohnR66 wrote:

>> My question is this: If I rotate a vertical JPEG image to make it
>> stand up on screen, is this rotation process lossy or lossless?

> I can not see the reason why any programmer would want or need to
> change the values stored in the memory representing a pixel location
> when the image is rotated 90 Deg. because the pixel is moving
> relative its neighbor. No advanced algorithm is needed. But don't
> take my word for it.
> Also, JPEG is a file compression standard. When the file is open, the
> operations performed on the image is independent of the file type.

The point is specifically that the OP wants to rotate images that are in
JPEG format.

If rotated the conventional way - by opening the JPEG file in an image
editor, rotating it, then saving it as a JPEG file again, the image has
now been through _two_ lossy JPEG compression cycles: one in the camera
and another one when saving after rotation.

However, a special algorithm exists that allows rotating (and mirroring)
JPEG images in a lossless fashion, without subjecting the image to
another compression cycle. For this to work, a JPEG-specific rotation
functionality needs to be implemented.

On the following web page, there is a list of programs that implement
this kind of lossless JPEG rotation:

<http://sylvana.net/jpegcrop/losslessapps.html&gt;

You might also want to see this page:

<http://graphicssoft.about.com/cs/digitalimaging/f/rotat...;

--
znark
September 18, 2005 2:16:06 PM

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

I haven't used Picasa at all. The list on the Sylvana site includes
Irfanview, so I just tried a rotation in it and then saved the file. There
was a save options dialog box for me to make some choices. I would have
thought if the rotation were lossless that a dialog box wouldn't be
necessary. I gave up on Irfanview.

Then I copied some original files taken yesterday on my CP5700 to a scratch
directory.
I opened the lame Nikon PictureProject, which is not listed on the Sylvana
site, and imported these files. I rotated one of them, which was instant
and then checked in Windows Explorer. PictureProject saves the change
without asking! The original file in it's original directory is 1757184
bytes and the rotated file is 1753088 bytes.

I opened both the original and the rotated file in Photoshop enlarged them
both to 300% then rotated back the rotated image.

I can't see any difference.


--
Joan

"Morton Linder" <mort@cloud9.net> wrote in message
news:5E1Xe.7562$IC3.5778@fe12.lga...
> Hi,
>
> I have several types of image software, and seem to prefer Picasa2 for my
> simple needs. Picasa2 maintains the original image with all its pixels (5
> million in my case), and edited pix can have the editing undone.
>
> My question is this: If I rotate a vertical JPEG image to make it stand up
> on screen, is this rotation process lossy or lossless? Knowing the correct
> answer will allow me to decide how to maintain my vertical images.
>
> Thank you.
>
> Morton
Anonymous
September 18, 2005 3:03:05 PM

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

Joan wrote:
[]
> I opened the lame Nikon PictureProject, which is not listed on the
> Sylvana site, and imported these files. I rotated one of them, which
> was instant and then checked in Windows Explorer. PictureProject
> saves the change without asking! The original file in it's original
> directory is 1757184 bytes and the rotated file is 1753088 bytes.

A small file change in file size is possible, with the rotation still
being lossless.

> I opened both the original and the rotated file in Photoshop enlarged
> them both to 300% then rotated back the rotated image.
>
> I can't see any difference.

Better to do image arithmetic, and subtract the two images to make a
difference image. Using something like "Count number of image colours"
ensure that the difference image has just one colour.

David
Anonymous
September 18, 2005 5:59:26 PM

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

Morton Linder wrote:
> Thanks for your reply. In a different image software, (I forgot which),
> when clicking on to rotate an image there is an on-screen warning that
> carrying out the rotation will permanently deteriorate the image.

Windows Pictures and Fax Viever.

Cheers,
Antonio
--
http://www.E-Photographers.com
The Photographers Directory: Submit your site!
Anonymous
September 18, 2005 8:47:47 PM

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

"Joan" <Joan@home.tosh> wrote in news:G7bXe.55016$FA3.49836@news-
server.bigpond.net.au:

> I haven't used Picasa at all. The list on the Sylvana site includes
> Irfanview, so I just tried a rotation in it and then saved the file

How did you rotate it? It seems that you didn not use the lossless rotation
option (Options > Jpeg lossless rotation).

--
Onno Voors
Anonymous
September 18, 2005 10:54:14 PM

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

Morton Linder wrote:
> Hi,
>
> I have several types of image software, and seem to prefer Picasa2 for
> my simple needs. Picasa2 maintains the original image with all its
> pixels (5 million in my case), and edited pix can have the editing undone.
>
> My question is this: If I rotate a vertical JPEG image to make it stand
> up on screen, is this rotation process lossy or lossless? Knowing the
> correct answer will allow me to decide how to maintain my vertical images.
>
> Thank you.
>
> Morton

why not first save it in a lossless form, e.g. .psd, do your
manipulation, THEN save ir as .jpg.?
Anonymous
September 19, 2005 12:42:00 AM

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

Morton Linder wrote:
> JohnR66 wrote:
>
>> "Morton Linder" <mort@cloud9.net> wrote in message
>> news:5E1Xe.7562$IC3.5778@fe12.lga...
>>
>>> Hi,
>>>
>>> I have several types of image software, and seem to prefer Picasa2
>>> for my simple needs. Picasa2 maintains the original image with all
>>> its pixels (5 million in my case), and edited pix can have the
>>> editing undone.
>>>
>>> My question is this: If I rotate a vertical JPEG image to make it
>>> stand up on screen, is this rotation process lossy or lossless?
>>> Knowing the correct answer will allow me to decide how to maintain my
>>> vertical images.
>>>
>>> Thank you.
>>>
>>> Morton
>>
>>
>>
>> I can not see the reason why any programmer would want or need to
>> change the values stored in the memory representing a pixel location
>> when the image is rotated 90 Deg. because the pixel is moving relative
>> its neighbor. No advanced algorithm is needed. But don't take my word
>> for it.
>>
>> Also, JPEG is a file compression standard. When the file is open, the
>> operations performed on the image is independent of the file type.
>>
>> John
>>
>>
> Thanks for your reply. In a different image software, (I forgot which),
> when clicking on to rotate an image there is an on-screen warning that
> carrying out the rotation will permanently deteriorate the image.
> Therefore, I want to be certain one way or the other, before I rotate
> all my vertical images.
> Morton
>
Thanks to all for the helpful replies. They are all appreciated.

Morton
Anonymous
September 19, 2005 1:31:36 AM

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

mike o'sullivan wrote:

>> [rotating JPEG images the lossless way]

> why not first save it in a lossless form, e.g. .psd, do your
> manipulation, THEN save ir as .jpg.?

Supposing there's nothing to edit in the image (besides fixing the
orientation), that'll still give him yet another (lossy) compression
cycle, whereas using a lossless JPEG rotation algorithm won't.

--
znark
September 19, 2005 12:33:15 PM

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

Onno, I didn't know about those options. I still get a jpeg options window
when saving, though.

--
Joan

"Onno Voors" <ov-NOSPAMww1@SVPxs4all.nl> wrote in message
news:Xns96D5BFFDFE858qpweoi480@194.109.133.133...
> "Joan" <Joan@home.tosh> wrote in news:G7bXe.55016$FA3.49836@news-
> server.bigpond.net.au:
>
>> I haven't used Picasa at all. The list on the Sylvana site includes
>> Irfanview, so I just tried a rotation in it and then saved the file
>
> How did you rotate it? It seems that you didn not use the lossless
> rotation
> option (Options > Jpeg lossless rotation).
>
> --
> Onno Voors
Anonymous
September 19, 2005 12:48:58 PM

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

Hi Morton,
I have Picasa 2 installed and checked your query.
On a bush scene which was 5119 kb in the folder was the same size when
exported from Picasa 2 as landscape (original format) and 5414 kb when
rotated and exported.

As I understand how Picasa 2 works all the modification details done
on the original file are stored in the "ProcessmultipleFiles.Txt" file
stored in the same folder as the designated picture file. The original
file is not modified in any way.

However when a picture is exported the modifications are then done.

Hope this makes sense
Allan




On Sat, 17 Sep 2005 19:27:59 -0400, Morton Linder <mort@cloud9.net>
wrote:

>Hi,
>
>I have several types of image software, and seem to prefer Picasa2 for
>my simple needs. Picasa2 maintains the original image with all its
>pixels (5 million in my case), and edited pix can have the editing undone.
>
>My question is this: If I rotate a vertical JPEG image to make it stand
>up on screen, is this rotation process lossy or lossless? Knowing the
>correct answer will allow me to decide how to maintain my vertical images.
>
>Thank you.
>
>Morton
Anonymous
September 19, 2005 1:23:20 PM

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

Jukka Aho wrote:
> mike o'sullivan wrote:
>
>>> [rotating JPEG images the lossless way]
>
>
>> why not first save it in a lossless form, e.g. .psd, do your
>> manipulation, THEN save ir as .jpg.?
>
>
> Supposing there's nothing to edit in the image (besides fixing the
> orientation), that'll still give him yet another (lossy) compression
> cycle, whereas using a lossless JPEG rotation algorithm won't.
>
Would it do that? I always save my pix in psd format before doing any
adjustments. Do you mean that the mere act of saving as psd causes
information loss?
September 19, 2005 3:50:36 PM

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

[posted and mailed]

Morton Linder <mort@cloud9.net> wrote in news:yPnXe.9124$gE7.3736
@fe08.lga:

> Morton Linder wrote:
>> JohnR66 wrote:
>>
>>> "Morton Linder" <mort@cloud9.net> wrote in message
>>> news:5E1Xe.7562$IC3.5778@fe12.lga...
>>>
>>>> Hi,
>>>>
>>>> I have several types of image software, and seem to prefer Picasa2
>>>> for my simple needs. Picasa2 maintains the original image with all
>>>> its pixels (5 million in my case), and edited pix can have the
>>>> editing undone.
>>>>
>>>> My question is this: If I rotate a vertical JPEG image to make it
>>>> stand up on screen, is this rotation process lossy or lossless?
>>>> Knowing the correct answer will allow me to decide how to maintain
my
>>>> vertical images.
>>>>
>>>> Thank you.
>>>>
>>>> Morton
>>>
>>>
>>>
>>> I can not see the reason why any programmer would want or need to
>>> change the values stored in the memory representing a pixel location
>>> when the image is rotated 90 Deg. because the pixel is moving
relative
>>> its neighbor. No advanced algorithm is needed. But don't take my
word
>>> for it.
>>>
>>> Also, JPEG is a file compression standard. When the file is open,
the
>>> operations performed on the image is independent of the file type.
>>>
>>> John
>>>
>>>
>> Thanks for your reply. In a different image software, (I forgot
which),
>> when clicking on to rotate an image there is an on-screen warning
that
>> carrying out the rotation will permanently deteriorate the image.
>> Therefore, I want to be certain one way or the other, before I rotate
>> all my vertical images.
>> Morton
>>
> Thanks to all for the helpful replies. They are all appreciated.
>
> Morton

Since no one gave you a simple yes or no answer, I will tell you that
rotating photos in Picasa2 is definitely lossless. Any changes you make
in Picasa are only made in Picasa. The original photo image is
unchanged.
Jack
Anonymous
September 19, 2005 9:12:43 PM

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

Its lossless because it only happens inside of Picasa. If you view your
images in another browser they will not be rotated. So your original image
wasn't touched by Picasa.


"Morton Linder" <mort@cloud9.net> wrote in message
news:5E1Xe.7562$IC3.5778@fe12.lga...
> Hi,
>
> I have several types of image software, and seem to prefer Picasa2 for my
> simple needs. Picasa2 maintains the original image with all its pixels (5
> million in my case), and edited pix can have the editing undone.
>
> My question is this: If I rotate a vertical JPEG image to make it stand up
> on screen, is this rotation process lossy or lossless? Knowing the correct
> answer will allow me to decide how to maintain my vertical images.
>
> Thank you.
>
> Morton
Anonymous
September 19, 2005 10:20:37 PM

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

"Joan" <Joan@home.tosh> wrote in
news:fJuXe.328$4f3.52@news-server.bigpond.net.au:

> Onno, I didn't know about those options. I still get a jpeg options
> window when saving, though.
>
(Please reply underneath the text you're quoting)

It is not necessary to go through the save file procedure, after you have
used the lossless rotation. The picture has already been saved rotated.


--
Onno Voors
Anonymous
September 20, 2005 2:13:43 AM

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

mike o'sullivan <mike@nowhere.com> writes:

>Would it do that? I always save my pix in psd format before doing any
>adjustments. Do you mean that the mere act of saving as psd causes
>information loss?

No, there's no loss as long as the image remains in PSD format. But
supposed you ultimately want a JPEG output image? To convert from your
PSD to a new JPEG, the image will undergo a JPEG compression step which
is lossy. This is in addition to the original in-camera JPEG
compression, so your final image data has undergone two JPEG
compression steps.

In comparison, if all you want to do is rotate the image, a lossless
JPEG rotation merely re-arranges the coefficient data in the JPEG file
*without* any further loss. The result has been compressed only once,
not twice.

On the other hand, if you keep the image in PSD or TIFF format always,
never generating a new JPEG, there's no advantage.

Dave
September 20, 2005 3:48:45 AM

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

Interesting. I hadn't looked.
The image rotated in Irfanview became about 4K smaller and the image rotated
in PictureProject became about 4K larger. Both images were similar in that
they were landscapes with bushes in the foreground then water and then sky.

--
Joan

"Onno Voors" <ov-NOSPAMww1@SVPxs4all.nl> wrote in message
news:Xns96D6CFC183751qpweoi480@194.109.133.133...
>
> It is not necessary to go through the save file procedure, after you have
> used the lossless rotation. The picture has already been saved rotated.
>
>
> --
> Onno Voors
Anonymous
September 20, 2005 5:24:29 AM

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

mike o'sullivan wrote:

>>>> [rotating JPEG images the lossless way]

>>> why not first save it in a lossless form, e.g. .psd, do your
>>> manipulation, THEN save ir as .jpg.?

>> Supposing there's nothing to edit in the image (besides fixing the
>> orientation), that'll still give him yet another (lossy) compression
>> cycle, whereas using a lossless JPEG rotation algorithm won't.

> Would it do that? I always save my pix in psd format before doing any
> adjustments. Do you mean that the mere act of saving as psd causes
> information loss?

The problem is not the "saving in psd format" part of the procedure, but
the "saving in jpeg format" part. (See the above comments again.)

When using an image viewer/manipulator that has a lossless JPEG rotation
algorithm (such as XnView), the original JPEG file and the rotated JPEG
file share identical quality - nothing was lost in the process; the
original image data inside the file was just rearranged.

When using an image viewer/manipulator that does _not_ have a lossless
JPEG rotation algorithm, the on-screen rotation itself is lossless, but
saving back to JPEG format isn't. That's the difference.

* * *

To put it in another way, lossless JPEG rotation algorithms operate
directly on the (already-compressed) JPEG data. They know how the JPEG
images are constructed and how the data is stored inside the file. That
allows them to do their rotation or mirroring magic without invoking
another lossy decompression-compression cycle.

Traditional (non-JPEG-aware) image rotation tools, however, do not know
anything about the internals of the JPEG format, but insist of
decompressing the JPEG image first, then rotating, and finally
recompressing the rotated data back to JPEG format again. In this
process, information is lost. (Lossless JPEG rotation algorithms bypass
this decompression-recompression cycle entirely.)

--
znark
Anonymous
September 20, 2005 11:14:43 PM

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

Jukka Aho wrote:
>
> The problem is not the "saving in psd format" part of the procedure, but
> the "saving in jpeg format" part. (See the above comments again.)
>
> When using an image viewer/manipulator that has a lossless JPEG rotation
> algorithm (such as XnView), the original JPEG file and the rotated JPEG
> file share identical quality - nothing was lost in the process; the
> original image data inside the file was just rearranged.
>
> When using an image viewer/manipulator that does _not_ have a lossless
> JPEG rotation algorithm, the on-screen rotation itself is lossless, but
> saving back to JPEG format isn't. That's the difference.

> To put it in another way, lossless JPEG rotation algorithms operate
> directly on the (already-compressed) JPEG data. They know how the JPEG
> images are constructed and how the data is stored inside the file. That
> allows them to do their rotation or mirroring magic without invoking
> another lossy decompression-compression cycle.
>
> Traditional (non-JPEG-aware) image rotation tools, however, do not know
> anything about the internals of the JPEG format, but insist of
> decompressing the JPEG image first, then rotating, and finally
> recompressing the rotated data back to JPEG format again. In this
> process, information is lost. (Lossless JPEG rotation algorithms bypass
> this decompression-recompression cycle entirely.)
>
Thanks for that guys. What about my favourite, Irfanview. Is this
lossless of lossy?
Anonymous
September 20, 2005 11:17:32 PM

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

Dave Martindale wrote:

> On the other hand, if you keep the image in PSD or TIFF format always,
> never generating a new JPEG, there's no advantage.
>
Thanks for that. My camera records images as JPEG, but I always save the
files as PSD before doing any manipulation, only then re-saving as JPEG.
Anonymous
September 21, 2005 1:54:28 AM

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

mike o'sullivan wrote:

> Thanks for that guys. What about my favourite, Irfanview. Is this
> lossless of lossy [as regards to JPEG rotation]?

The built-in rotation function in Irfanview ("Image" -> "Rotate left" /
"Rotate right") does not have any special considerations for the JPEG
format, so it can be considered lossy _if_ you save the rotated image
back to JPEG format.

Of course, no loss will occur if you save the rotated image using a file
format that does _not_ use lossy compression (such as BMP or PNG.)
However, if the original image already was in JPEG format, saving to
another format (for just being able to change from landscape orientation
to portrait, or vice versa, without any loss in image quality) is, in
most cases, neither practical nor reasonable. For one thing, when
changing file formats, you will usually lose whatever EXIF information
(and other metadata) there might have been in the original JPEG file.
For another thing, saving to a lossless format (such as BMP or PNG) will
almost without exception make the file size considerably larger.

Using the lossless JPEG rotation (where available) makes sense: you will
not lose any image quality due to superfluous lossy compression cycles,
the file size will stay the same as the original (there may be a slight
difference due to how programs reconstruct the file headers or optimize
the JPEG data, but the actual image stays the same), and you get to keep
all the original metadata.

Fortunately, Irfanview _does_ have a lossless JPEG rotation algorithm as
well - but not as a built-in feature: it has been implemented as a
plugin. You will need to download and install the plugin package from
Irfanview's site in order to use it. Once the plugin is installed, it
will show up in the "Options" menu, under the label "JPEG lossless
operations... (PlugIn) Shift+J".

--
znark
Anonymous
September 21, 2005 6:19:04 PM

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

Jukka Aho wrote:
>
> Fortunately, Irfanview _does_ have a lossless JPEG rotation algorithm as
> well - but not as a built-in feature: it has been implemented as a
> plugin. You will need to download and install the plugin package from
> Irfanview's site in order to use it. Once the plugin is installed, it
> will show up in the "Options" menu, under the label "JPEG lossless
> operations... (PlugIn) Shift+J".

Jukka, I have just done exactly that. Thanks very much for the tip. It
works well.

Mike
!