Is jpeg rotation loseless?

[Florian Lindner]

Hello,
is the jpeg rotation in digikam loseless or not?

Thanks,

Florian
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Florian Lindner wrote:

> Hello,
> is the jpeg rotation in digikam loseless or not?
>
> Thanks,
>
> Florian
> _______________________________________________
> Digikam-users mailing list
> [hidden email]
> https://mail.kde.org/mailman/listinfo/digikam-users
>
>

I can only quote from an email from 2 days ago:

*************
 >>> About the rotation: Is it done in a "losless" way? Or with
 >>> > > > recompression?
 >> > >
 >> > > The CameraUI is lossless. The image editor is pixel-based and thus
 >> > > lossless if you save back to JPEG. For already downloaded images, use the
 > >
 > > Sorry, thats of course not true what I wrote here. Corrected version:
 > > "The image editor is pixel-based and thus lossy if you save back to JPEG"
 > >
 > > kipiplugin and cameraUI rotation is lossless, but JPEG specific. The image
 > > editor supports lossless PNG.

And tiff of course.
***************

Regards,
Gabor
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[Florian Lindner]

Am Samstag, 10. Juni 2006 16:23 schrieb Dudas Gabor:

> Florian Lindner wrote:
> > Hello,
> > is the jpeg rotation in digikam loseless or not?
> >
> > Thanks,
> >
> > Florian
> > _______________________________________________
> > Digikam-users mailing list
> > [hidden email]
> > https://mail.kde.org/mailman/listinfo/digikam-users
>
> I can only quote from an email from 2 days ago:
>
> *************
>
>  >>> About the rotation: Is it done in a "losless" way? Or with
>  >>>
>  >>> > > > recompression?
>  >> > >
>  >> > > The CameraUI is lossless. The image editor is pixel-based and thus
>  >> > > lossless if you save back to JPEG. For already downloaded images,
>  >> > > use the
>  > >
>  > > Sorry, thats of course not true what I wrote here. Corrected version:
>  > > "The image editor is pixel-based and thus lossy if you save back to
>  > > JPEG"
>  > >
>  > > kipiplugin and cameraUI rotation is lossless, but JPEG specific. The
>  > > image editor supports lossless PNG.
>
> And tiff of course.

And how can I tell when I use the image editor rotating feature and when the
feature from a KIPI plugin? The rotation I can do from a thumbnails context
menu. Is this done by a plugin or by the image editor?

Thanks,

Florian
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[Gilles Caulier-2]

Le Samedi 10 Juin 2006 18:04, Florian Lindner a écrit :

> Am Samstag, 10. Juni 2006 16:23 schrieb Dudas Gabor:
> > Florian Lindner wrote:
> > > Hello,
> > > is the jpeg rotation in digikam loseless or not?
> > >
> > > Thanks,
> > >
> > > Florian
> > > _______________________________________________
> > > Digikam-users mailing list
> > > [hidden email]
> > > https://mail.kde.org/mailman/listinfo/digikam-users
> >
> > I can only quote from an email from 2 days ago:
> >
> > *************
> >
> >  >>> About the rotation: Is it done in a "losless" way? Or with
> >  >>>
> >  >>> > > > recompression?
> >  >> > >
> >  >> > > The CameraUI is lossless. The image editor is pixel-based and
> >  >> > > thus lossless if you save back to JPEG. For already downloaded
> >  >> > > images, use the
> >  > >
> >  > > Sorry, thats of course not true what I wrote here. Corrected
> >  > > version: "The image editor is pixel-based and thus lossy if you save
> >  > > back to JPEG"
> >  > >
> >  > > kipiplugin and cameraUI rotation is lossless, but JPEG specific. The
> >  > > image editor supports lossless PNG.
> >
> > And tiff of course.
>
> And how can I tell when I use the image editor rotating feature and when
> the feature from a KIPI plugin? The rotation I can do from a thumbnails
> context menu. Is this done by a plugin or by the image editor?
>

By a kipi plugin.

Gilles
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[Florian Lindner]

Am Samstag, 10. Juni 2006 19:21 schrieb Gilles Caulier:

> Le Samedi 10 Juin 2006 18:04, Florian Lindner a écrit :
> > Am Samstag, 10. Juni 2006 16:23 schrieb Dudas Gabor:
> > > Florian Lindner wrote:
> > > > Hello,
> > > > is the jpeg rotation in digikam loseless or not?
> > > >
> > > > Thanks,
> > > >
> > > > Florian
> > > > _______________________________________________
> > > > Digikam-users mailing list
> > > > [hidden email]
> > > > https://mail.kde.org/mailman/listinfo/digikam-users
> > >
> > > I can only quote from an email from 2 days ago:
> > >
> > > *************
> > >
> > >  >>> About the rotation: Is it done in a "losless" way? Or with
> > >  >>>
> > >  >>> > > > recompression?
> > >  >> > >
> > >  >> > > The CameraUI is lossless. The image editor is pixel-based and
> > >  >> > > thus lossless if you save back to JPEG. For already downloaded
> > >  >> > > images, use the
> > >  > >
> > >  > > Sorry, thats of course not true what I wrote here. Corrected
> > >  > > version: "The image editor is pixel-based and thus lossy if you
> > >  > > save back to JPEG"
> > >  > >
> > >  > > kipiplugin and cameraUI rotation is lossless, but JPEG specific.
> > >  > > The image editor supports lossless PNG.
> > >
> > > And tiff of course.
> >
> > And how can I tell when I use the image editor rotating feature and when
> > the feature from a KIPI plugin? The rotation I can do from a thumbnails
> > context menu. Is this done by a plugin or by the image editor?
>
> By a kipi plugin.

So can you take it the way that every rotation that is not done by "left click
on an image -> transformations -> rotate" is loseless?

Thanks,

Florian
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[Marcel Wiesweg]

> > > And how can I tell when I use the image editor rotating feature and
> > > when the feature from a KIPI plugin? The rotation I can do from a
> > > thumbnails context menu. Is this done by a plugin or by the image
> > > editor?
> >
> > By a kipi plugin.
>
> So can you take it the way that every rotation that is not done by "left
> click on an image -> transformations -> rotate" is loseless?

Remove the "not".

You are using the image editor if you have opened the image in the image
editor, rotated, and clicked on save. The image editor is operating on raw
RGB data, and rotating there is no difference to applying any effect, it's
changing pixels. It can load from a variety of image formats, not only JPEGs,
it works on raw data, and it can save back to a variety of formats, some of
them are lossless (PNG, TIFF), but JPEG is not lossless.

Lossless rotation is a special feature of the JPEG compression format, at a
level above raw image data.

Marcel
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[Florian Lindner]

Am Sonntag, 11. Juni 2006 19:48 schrieb Marcel Wiesweg:

> > > > And how can I tell when I use the image editor rotating feature and
> > > > when the feature from a KIPI plugin? The rotation I can do from a
> > > > thumbnails context menu. Is this done by a plugin or by the image
> > > > editor?
> > >
> > > By a kipi plugin.
> >
> > So can you take it the way that every rotation that is not done by "left
> > click on an image -> transformations -> rotate" is loseless?
>
> Remove the "not".

"left click on image" opens the image editor. So I guess my statement is
correct, isn't?
As soon as I enter the image editor I perform lossy changes.
Right click -> rotate or "Picture Menu" -> Rotate is loseless. Correct?

Regards,

Florian

>
> You are using the image editor if you have opened the image in the image
> editor, rotated, and clicked on save. The image editor is operating on raw
> RGB data, and rotating there is no difference to applying any effect, it's
> changing pixels. It can load from a variety of image formats, not only
> JPEGs, it works on raw data, and it can save back to a variety of formats,
> some of them are lossless (PNG, TIFF), but JPEG is not lossless.
>
> Lossless rotation is a special feature of the JPEG compression format, at a
> level above raw image data.
>
> Marcel
> _______________________________________________
> Digikam-users mailing list
> [hidden email]
> https://mail.kde.org/mailman/listinfo/digikam-users

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Marcel Wiesweg wrote:
> You are using the image editor if you have opened the image in the image
> editor, rotated, and clicked on save. The image editor is operating on raw
> RGB data, and rotating there is no difference to applying any effect, it's
> changing pixels. It can load from a variety of image formats, not only JPEGs,
> it works on raw data, and it can save back to a variety of formats, some of
> them are lossless (PNG, TIFF), but JPEG is not lossless.
>
> Lossless rotation is a special feature of the JPEG compression format, at a
> level above raw image data.

Can the Image Editor tell that the image currently loaded has been
modified by a user operation (e.g. effect etc.)? If so, could a feature
be added to the Rotate option in the Image Editor that:

Checks to see if the image is unmodified, is a jpeg and the rotate
amount is a multiple of 90 degs and if so, uses a lossless rotation of
the raw image file and then reverts to that saved version (effectively
reload the (now modified) saved image).

If the conditions are not met, the current rotating methods are used?

That would be kinda nice.

Col.

--

+------------------------+
|     Colin Guthrie      |
+------------------------+
| kde(at)colin.guthr.ie  |
| http://colin.guthr.ie/ |
+------------------------+

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