rotating thumbnails

[DanR]

WinXP and ME both have the ability to rotate pictures as you view them within
their folder. This is nice for viewing pictures shot vertically. And I like the
fact that the thumbnail is rotated. But... after rotating them they stay that
way. My question is... how does Windows do this? If the picture is a jpg... is
the picture opened (expanded) and then re-saved. If so is there generation loss?
If so... how much? In Photoshop and other image editors I have a choice of the
jpg quality when saving. What settings does Windows use when doing this in the
background?
I'm hoping that only some header information is changed. Does anyone know?

 

[Kenny S]

by default xp warns you before jpg rotation that image quality may be
reduced.. but there is an option there that you can select to not show that
message again.. perhaps you did that so now you dont see the warning.

Yes xp opens and resaves the image and quality is lost.
There is no way to adjust the quality.
there are some programs available that offer lossless jpg rotation like
acdsee (www.acdsystems.com)
.. Or you can convert your images in to bmp or tif files that do not have
this problem since they are lossless formats
(this takes up more space... even though there is an option to use LZW
lossless compression in tiff files).

kenny

 

[DanR]

Thanks for the reply, Kenny. My WinME machine gives no warning about diminished
quality and my WinXP in filmstrip mode does not warn me. I don't think the XP
machine ever did warn me. I'm very cautious about resaving JPGs and It's
unlikely I would have turned this off.
But you answered my question. Thanks.

 

[Kenny S]

read here:

http://www.indospectrum.com/articles/photography/manage_digital_library.html

and

http://groups.google.com/[email protected]&rnum=1

(seems tha xp does support losless rotation on some sizes but not all)
(Windows Picture and Fax Viewer provides lossless
rotation for certain sizes...(must be an exact multiple
of 16 and probably 8. So if your image is, say, 2048 x
1360 it will be lossless.)


also irfanview (free) now supports lossless jpeg rotation
if you download and install the additional pluggins.

http://www.irfanview.com/history_old.htm

Version 3.25 (Release date: 02.09.2000)
- Support for lossless JPG rotation/flip (Menu: Options->JPG
Transformation):
http://www.irfanview.com/plugins.htm

Kenny

 

[DanR]

I notice that the file size does NOT change at all after rotating a jpg file.
(WinXP) That seems strange. Seems if Windows opens the image file and re-saves
it that the file size would change.