I always batch change my photos in iPhoto to change both the date stamp on the filename, I never had any issues with my photos being out of order on the Apple TV. I have now been doing this for several years and because of this time I cannot remember 100% which of these affects the order of the slideshow on the Apple TV, but rather suspect it is the date stamp.
Are you sure that it is simply that photos in portrait are put to the end of the slideshow, or could it be that you take all your portrait photos on one particular camera and that cameras time setting are slightly adrift from the date setting on the other camera.
I am also curious as to why you import using image capture and then move the photos to iPhoto rather than importing directly into iPhoto itself.
Thank you for the fast response. I am sure that all my portrait photos are displayed last, but also some other photo's are. You put me on track to investigate the naming of the photo files. I didn't pay any attention to that as it didn't matter to iPhoto. I left the default names as they were on the camera (both iPhone and Cannon use the format IMG_xxxx.jpg). Because of that and the fact that I took more than 10.000 pictures, during import usually a sequence number is added to that name like IMG_xxxx 1.jpg, IMG_xxxx 2.jpg. But I do not think that influences the sequence.
However looking through the content of the iPhoto library on the Mini I found that in the Masters directory all photo's are more or less in the correct sequence, but I also discovered a Previews directory with files for the Canon portrait photos and as it turns out also the landscape iPhone photos, each in a separate folder with a long name, consisting of random characters. The files are all dated around the time of the import into iPhoto.
So it is likely that AppleTV gets it Previews from these directories when browsing through the events.
Can that be changed in some way? I prefer stepping through the photos manually instead of starting a slide show.
For your information: I started using the two step import years ago when iPhoto asked me each time after an import if I wanted to remove the imported photos from the camera. At that time I didn't want to accidentely choose "Yes" , ending up with only one copy of the photos, with the risk of loosing the photo's when something went wrong with iPhoto at that point. It is also convienent to import photos from multiple cameras into one event without the need to manually join them afterwards.
Propably this not necessary any more, but you know what they say about old habits.... :-)
I crop all my photos for the Apple TV to 16:9, so I didn't have any first hand knowledge about using portrait photos and decided to investigate. It turns out my photos are out of order on the Apple TV too. Not having noticed this until now, my suspicions are drawn to a recent change rather than an older one, but couldn't be 100% sure of that.
Time to do some investigating.
I've been trying a few things out here. It appears the Apple TV may be viewing photos by modification date rather than creation dates (there are a few different dates that photos can be tagged with at the same time). As I modified photos they were placed at the end of a sequence on the Apple TV regardless of orientation.
My only explanation for portrait photos being placed at the end is that perhaps these photos are imported in landscape and then rotated in iPhoto according to flags set by the camera and as such their modification dates are after the landscape photos modification date.
Batch changing the date in iPhoto doesn't help, possibly because it changes the creation date rather than the modification date. However selecting all the photos in an album, rotating them one way and then the other, seems to get them to display on the Apple TV.
If you try it, be sure to remove the album from the homeshare list and add it back again, to make sure it has refreshed.
Thank you very much for the extra testing and verification. It is completely consistent with my experience and indeed it is likely that the modification date is the problem. I will send feedback to Apple to register a bug report. I hope they can solve this easily, the code to make that happen is already present in iPhoto, so it wouldn't be that hard to port it to iTunes and/or AppleTV, where ever the problem resides.
If they do not, I will have to resort to your manual work-around, but with 12K + photos in my library that may take a while...
I filed a bug report with Apple regarding this behaviour.
I noticed today that when browsing through the photo's of an event on AppleTV it displays a date of the picture in the left upper corner of the screen just below the Event name. And the date shown on the modified photos is the actual date the picture was taken and not the modification date! So the software has the correct date (and time I presume) available and it does not use it to sort the list!