10-08-2018 03:01 PM - edited 10-09-2018 05:51 AM
If you run Accuracy Assessment, open the same image file you uploaded, then Report > Accuracy Report. Your accuracy report should show the result Ian posted, even starting at older versions 2014 and later.
If you run Accuracy Assessment and use Edit options (e.g. Edit > Create/Add Random Points...), the accuracy report could list blank classes.
If the previous posts do not explain what you are observing, you should submit a Support ticket to investigate this more thoroughly.
10-09-2018 07:48 AM
Thank you both for the advice. I sort of combined the two. If I add points and add reference classes and save the table, close and re-add the image, then run Accuracy Assessment, it works. The only trouble then is it doesn't use the Class_Names but 'Class 1', etc. But I can live with that - easier than scrolling through multiple lines/pages of values. thanks again for the help.
10-09-2018 08:47 AM
are you you sure it isn't using Class_Names? The file you sent had an attribute column called Class_Name (no "s"), which wouldn't be recognized as a column to use for the names.
10-09-2018 09:03 AM
Fairly certain. The 'Class_Name' field has names in it. As you say, it didn't use the names but if I run without saving and reopening (the one with 256 values), it does put class names in. But it won't be a big deal. Even if the classification goes to more classes, they'll be aligned by rows and it's easy enough to refer back to the attribute table. Thank you again for your help.