Photos Change Orientation

[pbyrne]

Hi all

 

I am just starting out in astrophotography.  Last night I was imaging Cassiopeia using a Canon 1100D, 50mm f/1.8 lens and iOptron Sky Guider Pro.  I had set it up to take 100, 45 second exposures starting at 8.30 local time.  When I checked the images tonight, I noticed that after 35 images the orientation changed from landscape to portrait.  Can anyone tell me why this is happening and how do I prevent it?

 

Thanks in advance.

 

Paul 

[Cornelius Varley]

The camera has a function to automatically rotate the images between landscape and portrait depending on the orientation of the camera. This can be switched off to avoid the rotation.

[pbyrne]

Cornelius, thank you very much.

 

Paul

[wimvb]

I would think that the raw image files, while containing the orientation information in the image header, shouldn't be rotated.

[ollypenrice]

1 hour ago, wimvb said:

I would think that the raw image files, while containing the orientation information in the image header, shouldn't be rotated.

Indeed. It will just be the camera screen display which has changed otherwise the captured file would have to be 'cropped and padded.'

Olly

[Cornelius Varley]

45 minutes ago, ollypenrice said:

Indeed. It will just be the camera screen display which has changed otherwise the captured file would have to be 'cropped and padded.'

Olly

The captured file is also rotated, it isn't just on the camera's screen. This is fine for conventional photography but not so good for astro. If the rotated images are loaded into DSS the landscape and portrait mode images won't match. Switch rotation off and all the images will be in landscape mode.

[wimvb]

The jpeg conversion routine in the camera will use the header information  to create a rotated jpeg image, but as I wrote before, the raw, uncompressed image files won’t be rotated.

[Cornelius Varley]

5 hours ago, wimvb said:

The jpeg conversion routine in the camera will use the header information  to create a rotated jpeg image, but as I wrote before, the raw, uncompressed image files won’t be rotated.

I choose to disagree. The image size, for example (Eos 5D mkII) is 5616 (x axis)x 3744 (y axis) pixels in landscape. In portrait mode this becomes 3744 (x) x5616 (y). DSS would load all the images in their original orientation (5616 (x) x 3744 (y)/ 3744 (x) x 5616 (y))  which obviously will cause problems if the x and y values don't match through a batch of image files. The image rotation option can be switched off to avoid this and all the images will be saved with the x axis always being the higher value. There are threads in the beginners imaging and imaging sections were this has been discussed. If the camera is on an eq mount and image rotation is on then the rotation of the images will change over time as the camera becomes more vertical / horizontal. Hence the question from the OP.

 

[wimvb]

1 hour ago, Cornelius Varley said:

I choose to disagree

It seems strange to me that the raw files are also rotated. But it's a long time since I've used a dslr for imaging, so I won't argue.

[sharkmelley]

The raw file format is completely unchanged by the rotation to portrait.  This can easily be verified by RawDigger, for instance, where the image width (in the raw file EXIF) is greater than the image height even in Portrait mode.  The only thing that changes in the raw file is a "rotation" flag in EXIF header.   DSS might be choosing to respect this flag under certain circumstances (or maybe under all circumstances).

Mark

Edited October 8, 2021 by sharkmelley

[Cornelius Varley]

2 hours ago, sharkmelley said:

The raw file format is completely unchanged by the rotation to portrait.  This can easily be verified by RawDigger, for instance, where the image width (in the raw file EXIF) is greater than the image height even in Portrait mode.  The only thing that changes in the raw file is a "rotation" flag in EXIF header.   DSS might be choosing to respect this flag under certain circumstances (or maybe under all circumstances).

Mark

Rawdigger appears to ignore to rotational information in the EXIF data and displays all images in landscape irrespective of the photographer's intentions. The camera, DSS and image processing programmes will use the EXIF data to display the image file as landscape or portrait as required. The OP wanted to know why their photos rotated over a period of time and how to avoid it in future. If image rotation is turned off the camera will display all images in landscape.

[sharkmelley]

18 minutes ago, Cornelius Varley said:

The OP wanted to know why their photos rotated over a period of time and how to avoid it in future. If image rotation is turned off the camera will display all images in landscape.

Yes, that is the answer to the question raised by the OP.  But for the avoidance of any doubt, changing the "image rotation" flag in the camera menu makes no difference at all to the layout of the raw data file saved by the camera (unlike the JPG saved by the camera).  The only difference in the raw file is the "rotation" flag in the EXIF header.  Some astro-software (including DSS) respects this value, other astro-software (e.g. PixInsight) ignores it.

Mark

Edited October 8, 2021 by sharkmelley