Rotation & aspect ratio

Could someone please explain why, when I rotate a picture 90° degrees in a
viewing/editing program, the picture is stretched so that long faces appear
rounder? The actual change (as measured with a ruler on the monitor screen)
is from 1:1.25 in normal view to 1:1.43 in rotated view.

This happens with pictures from Kodak, Pentax, and Ricoh digital cameras,
when opened and rotated in Irfanview, Kodak, Adobe Elements, or The Gimp .

--
Jeff
(cut "thetape" to reply)

On Sun, 12 Aug 2007 10:24:25 +0100, "Jeff Layman"
wrote:

Could someone please explain why, when I rotate a picture 90° degrees in a
viewing/editing program, the picture is stretched so that long faces appear
rounder? The actual change (as measured with a ruler on the monitor screen)
is from 1:1.25 in normal view to 1:1.43 in rotated view.

I suspect you are using an inappropriate resolution that
doesn't match the aspect ratio of your monitor. Monitors may
be 5:4, 4:3, or other formats like 16:9. My guess is that
your monitor is physically 5:4 but you're using a resolution
intended for 4:3 displays.

--
John Bean

k. harvey wrote:
On Sun, 12 Aug 2007 10:24:25 +0100, "Jeff Layman"
wrote:

Could someone please explain why, when I rotate a picture 90°
degrees in a viewing/editing program, the picture is stretched so
that long faces appear rounder? The actual change (as measured with
a ruler on the monitor screen) is from 1:1.25 in normal view to
1:1.43 in rotated view.

This happens with pictures from Kodak, Pentax, and Ricoh digital
cameras, when opened and rotated in Irfanview, Kodak, Adobe
Elements, or The Gimp .

It means that your monitor is not correctly adjusted for a 1:1 aspect
ratio. Just because you can select various desktop resolutions for
display doesn't mean that they are all supposed to be stretched to
the very edges of your monitor.

To correct for this use any editing program and use the vector
graphic tools to draw a perfect circle (or square). Make sure you use
a "lock aspect-ratio" function so that you are not drawing an ellipse
or rectangle when doing this. Then measure the vertical axis and the
horizontal axis of the object on your screen. Adjust the vertical and
horizontal height of your monitor display until the horizontal and
vertical distances of the circle or square are equal. Now your images
from all cameras in any software will display as they should no
matter how you rotate them.

Be prepared to see all your familiar faces in the photos as rounder
than you have been seeing them. The new and correct aspect ratio will
be halfway between what you have been seeing before and after
rotating.

Many thanks for this explanation and simple correction! OK, I lose a little
of the screen top & bottom, but at least the images are identical when
rotated.

Out of interest, do different printers suffer from this effect, too?

--
Jeff
(cut "thetape" to reply)

Jeff Layman added these comments in the current discussion du
jour ...

Could someone please explain why, when I rotate a picture 90°
degrees in a viewing/editing program, the picture is stretched
so that long faces appear rounder? The actual change (as
measured with a ruler on the monitor screen) is from 1:1.25 in
normal view to 1:1.43 in rotated view.

This happens with pictures from Kodak, Pentax, and Ricoh
digital cameras, when opened and rotated in Irfanview, Kodak,
Adobe Elements, or The Gimp .

You're doing something wrong, Jeff. Simple rotations, whether small
degree or 90 deg. increments will neither elongate nor foreshorten
an image, they simply rotate the pixels. Please explain more of
what you're doing and the results you're getting. e.g., if you're
using some sort of deform tool to do your rotates, you may be
stretching a corner of the image and elongating it. Pure rotates
shouldn't cause a change in aspect ratio.

--
HP, aka Jerry

k. harvey added these comments in the current discussion du jour
....

Could someone please explain why, when I rotate a picture 90°
degrees in a viewing/editing program, the picture is stretched
so that long faces appear rounder? The actual change (as
measured with a ruler on the monitor screen) is from 1:1.25 in
normal view to 1:1.43 in rotated view.

This happens with pictures from Kodak, Pentax, and Ricoh
digital cameras, when opened and rotated in Irfanview, Kodak,
Adobe Elements, or The Gimp .

It means that your monitor is not correctly adjusted for a 1:1
aspect ratio. Just because you can select various desktop
resolutions for display doesn't mean that they are all
supposed to be stretched to the very edges of your monitor.

How does this affect anything? I have my screen resolution in
Windows set to 1280 x 960 on a normal 4:3 monitor. Are you
talking about a wide-screen monitor where the graphics app or
Windows is doing the stretching to fill the screen, the way that
a normal TV show elongates when viewed incorrectly on a 16:9 HDTV
screen?

To correct for this use any editing program and use the vector
graphic tools to draw a perfect circle (or square). Make sure
you use a "lock aspect-ratio" function so that you are not
drawing an ellipse or rectangle when doing this. Then measure
the vertical axis and the horizontal axis of the object on
your screen. Adjust the vertical and horizontal height of your
monitor display until the horizontal and vertical distances of
the circle or square are equal. Now your images from all
cameras in any software will display as they should no matter
how you rotate them.

Be prepared to see all your familiar faces in the photos as
rounder than you have been seeing them. The new and correct
aspect ratio will be halfway between what you have been seeing
before and after rotating.

I simply do not understand your recommendation, unless it is
related to the aspect ratio of the monitor and how the image is
zoomed. There are some settings for my video card/monitor
combination that WILL change aspect ratio because they are
designed for other than a standard 4:3 aspect ratio.

As to "lock aspect ratio", that sounds more to me what needs to
be done generally when resizing up or down, not rotating which is
the OP's problem. There are also situations where you WANT to
change the aspect ratio, but that's a different discussion than
this one, to me at least.

--
HP, aka Jerry

John Bean added these comments in the current discussion du jour
....

Could someone please explain why, when I rotate a picture 90°
degrees in a viewing/editing program, the picture is stretched
so that long faces appear rounder? The actual change (as
measured with a ruler on the monitor screen) is from 1:1.25 in
normal view to 1:1.43 in rotated view.

I suspect you are using an inappropriate resolution that
doesn't match the aspect ratio of your monitor. Monitors may
be 5:4, 4:3, or other formats like 16:9. My guess is that
your monitor is physically 5:4 but you're using a resolution
intended for 4:3 displays.

That sounds right to me, John. Some people are buying the new wide-
screen LCD monitors and have video adapters that support them.
Improperly used, they WILL mess up the aspect ratio of an image
that was created at 4:3 or the typical DSLR 3:2. BTW, I've never
heard of 5:4 aspect ratio. 4:3 is a throwback to TVs and became the
PC standard in the earliest days of CGA/EGA/VGA adapters. I've
therefore never seen a 5:4 monitor. I see either 4:3 "standard"
monitors or the new wide-screen kind, which may be 16:9 or
something less for Windows vs. HDTV use.

--
HP, aka Jerry

On Sun, 12 Aug 2007 12:10:50 GMT, "HEMI-Powered"
wrote:

BTW, I've never
heard of 5:4 aspect ratio.

Ordinary LCDs (not widescreen) are typically 5:4, like the
1280x1024 display I'm using right now. A similar sized CRT
would have been set to 1280x960 (4:3) instead.

I suspect that is the problem the OP has.

--
John Bean

k. harvey writes:

You can also try different desktop resolutions to see if you like one more than
another so that the visible area fits your monitor's screen more accurately.
Each one produces slightly different aspect ratios. I do well with a 1280x1024
resolution desktop on my monitor with little to no distortion and being able to
use most of the space.

If you are using a typical 4:3 CRT display I recommend using a
resolution of 1280x960 instead - it's got the same aspect ratio as
your display, and you will get square pixels. If you want a higher
resolution, the next step up is 1600x1200, though some display
adapters may offer some in-between options as well - just make sure
that width/height is 1.33333.

(typical 17" LCD's are confusing in that their 1280x1024 resolution actually
does have square pixels. That's because their aspect ratio is 5:4, not 4:3.)

John Bean added these comments in the current discussion du jour
....

BTW, I've never
heard of 5:4 aspect ratio.

Ordinary LCDs (not widescreen) are typically 5:4, like the
1280x1024 display I'm using right now. A similar sized CRT
would have been set to 1280x960 (4:3) instead.

I suspect that is the problem the OP has.

Still never heard of 5:4. My Samsung 213T 21" LCD is clearly 3:2
and I run at 1280 x 1024. Apparently, there are other monitor types
I'm not familiar with. I agree, this may be the OP's problem. But,
they should know what they bought, yes?

--
HP, aka Jerry

HEMI-Powered wrote:
k. harvey added these comments in the current discussion du jour
...


As to "lock aspect ratio", that sounds more to me what needs to
be done generally when resizing up or down, not rotating which is
the OP's problem. There are also situations where you WANT to
change the aspect ratio, but that's a different discussion than
this one, to me at least.

I'm not very interested in this post, but even for my casual perusal of
the threads it was very clear that the word 'lock' was used in
explaining how to draw a perfect circle (which may or may not display as
a perfect circle). A square might perform same function and be a little
easier to measure.
Dave Cohen