Photo filters have changed the least of most of the features in the iOS photography apps. When you edit a photo in the Photos app there are still eight filters, all quite good without being over the top. The behavior for saving edited photos has changed, at least in the latest iOS 8 beta, and I personally don't think the change is an improvement.
If you added a filter to an image in iOS 7 and then saved it, the photo went to your camera roll as a new photo, while the original image remained unchanged. When I tried this in iOS 8 beta 5, the original had the filter applied. To me, that's a no-no. You can get back the original by bringing it up in the editor and tapping 'revert', but some people may miss that option.
In fact, in iOS 8 the concept of the 'camera roll' is gone. You won't find it at all. All your photos are in the Photos app in collections sorted by date with photos grouped by location. If you save an image from the web with no EXIF date data, it is saved with the date and time that you saved it. I liked the old way better, but unfortunately I think the change is permanent. One could argue that the changes are better or worse, but they will certainly confuse people who expect the iOS 7 behavior and now get something else. I expect a lot of "where's my camera roll?" questions when the update comes out.
Users will also see the iCloud Photo Library replace Photo Stream. That means that every photo you take goes to the cloud at original resolution and is available on every device you have. The feature can be turned off in settings.
iOS 8 Camera filters
Another change is that third-party developers of editing tools and filters are now able to integrate their software into the Apple Photos app editing process. That could be a big deal for people who want more flexibility in adding tools and filters but feel more comfortable with the familiar Apple tools. I haven't personally seen any of these third-party tools working in the iOS 8 beta, but I think it is an important enhancement.
Still, the overall Apple Photos editing package is much improved. Third party filters, adjustments for light and color, and auto-straightening of photos are an improvement. These changes allow users to stay in the Apple-supplied apps for a lot of their photo editing, but rest assured that third parties will continue to bring more sophisticated tools to the App Store. Some will be included through Apple's extension architecture, while others will still require separate apps.
Apple iPad Air 2
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