exif -- orientation and rotation

I'm fighting a problem that involves the display of rotated images.

Looking in the EXIF stuff (using XnView MP on a Mac), I see a field
called "Orientation" which might be something like "top-left (1)" or
"left-bottom (8)" and also a field called "Rotation" that might be
"Horizontal (normal)" or "Rotate 270 CW".

What is the difference between these fields (seems redundant), and how
do they interact within the image display app to control the way the
image is displayed?

Isaac

isw wrote:
I'm fighting a problem that involves the display of
rotated images.

Looking in the EXIF stuff (using XnView MP on a Mac), I
see a called "Orientation" which might be something
like "top-left (1)" or "left-bottom (8)" and also a
field called "Rotation" that might be "Horizontal
(normal)" or "Rotate 270 CW".

What is the difference between these fields (seems
redundant), and how do they interact within the image
display app to control the way the image is displayed?

Isaac

Sounds like a Nikon D810 camera. I have not been able
to actually discover what that particular tag relates
to, but there is a lot of perhaps (or not) interesting
information.

What you really want is probably the Orientation tag in
the Exif data. That can have specific integer values
from 1 to 8, with these meanings:

1 = Horizontal (normal)
2 = Mirror horizontal
3 = Rotate 180
4 = Mirror vertical
5 = Mirror horizontal and rotate 270 CW
6 = Rotate 90 CW
7 = Mirror horizontal and rotate 90 CW
8 = Rotate 270 CW

In fact though, the only values I have ever seen used by
Nikon were 1, 3, 6, and 8.

Now, as to the "Rotation" tag, it is actually not in the
Exif data, but instead is part of the proprietary
MakerNotes data. That is a problem because Nikon just
doesn't bother telling us what everything there means.

What I've seen is what appears to be randomly varying
values. That was with handheld shots, so I don't know
what happens if the camera is held rock steady.

I use the Orientation tag to "correct" the orientation
of images automatically, using a bash script.

--
Floyd L. Davidson http://www.apaflo.com/
Utqiagvik (Barrow, Alaska)

In article ,
(Floyd L. Davidson) wrote:

isw wrote:
I'm fighting a problem that involves the display of
rotated images.

Looking in the EXIF stuff (using XnView MP on a Mac), I
see a called "Orientation" which might be something
like "top-left (1)" or "left-bottom (8)" and also a
field called "Rotation" that might be "Horizontal
(normal)" or "Rotate 270 CW".

What is the difference between these fields (seems
redundant), and how do they interact within the image
display app to control the way the image is displayed?

Isaac

Sounds like a Nikon D810 camera.

Panasonic, in fact.

Now, as to the "Rotation" tag, it is actually not in the
Exif data, but instead is part of the proprietary
MakerNotes data.

Same section heading on mine. Sounds like I don't need to mess with that
one, anyhow.

So, if I just set Orientation to "1" and look at the image, and then
losslessly rotate it so it's "right", that's it?

Isaac

isw wrote:
In article ,
(Floyd L. Davidson) wrote:

isw wrote:
I'm fighting a problem that involves the display of
rotated images.

Looking in the EXIF stuff (using XnView MP on a Mac), I
see a called "Orientation" which might be something
like "top-left (1)" or "left-bottom (8)" and also a
field called "Rotation" that might be "Horizontal
(normal)" or "Rotate 270 CW".

What is the difference between these fields (seems
redundant), and how do they interact within the image
display app to control the way the image is displayed?

Isaac

Sounds like a Nikon D810 camera.

Panasonic, in fact.

Interesting! That does suggest there might be some universal
definition for it. The D810 is the only higher end Nikon that
has that tag. I don't know about any of the DX or entry level
cameras.

Now, as to the "Rotation" tag, it is actually not in the
Exif data, but instead is part of the proprietary
MakerNotes data.

Same section heading on mine. Sounds like I don't need to mess with that
one, anyhow.

So, if I just set Orientation to "1" and look at the image, and then
losslessly rotate it so it's "right", that's it?

Isaac

That is essentially the way that I use it.

--
Floyd L. Davidson http://www.apaflo.com/
Utqiagvik (Barrow, Alaska)

In article ,
(Floyd L. Davidson) wrote:

isw wrote:
In article ,
(Floyd L. Davidson) wrote:

isw wrote:
I'm fighting a problem that involves the display of
rotated images.

Looking in the EXIF stuff (using XnView MP on a Mac), I
see a called "Orientation" which might be something
like "top-left (1)" or "left-bottom (8)" and also a
field called "Rotation" that might be "Horizontal
(normal)" or "Rotate 270 CW".

What is the difference between these fields (seems
redundant), and how do they interact within the image
display app to control the way the image is displayed?

Isaac

Sounds like a Nikon D810 camera.

Panasonic, in fact.

Interesting! That does suggest there might be some universal
definition for it. The D810 is the only higher end Nikon that
has that tag. I don't know about any of the DX or entry level
cameras.

Now, as to the "Rotation" tag, it is actually not in the
Exif data, but instead is part of the proprietary
MakerNotes data.

Same section heading on mine. Sounds like I don't need to mess with that
one, anyhow.

So, if I just set Orientation to "1" and look at the image, and then
losslessly rotate it so it's "right", that's it?

Isaac

That is essentially the way that I use it.

thx

Isaac