Hello, Mr13r4n.
I understand that when you attempt to take a photo with your iPhone 7, your display becomes blank, and you often need to restart your iPhone to be able to use it. I love taking pictures with my iPhone, and I can see how this would be bothersome. I am glad to have a chance to help you.
I first wanted to make sure you had access to the Apple Support article, If the camera on your iPhone, iPad, or iPod touch isn't working. A key callout from the article is to see if the issue occurs without a case or screen protector.
I noticed that you specifically mentioned that this happens when you take a regular photo and with Portrait Mode. Is this not occurring when you take a video? Does it happen when you are using the camera with a different app such as Facebook, Instagram, or Twitter? If it occurs across all apps, I would, per the support article I linked earlier, "take your device to an Apple Retail Store or Authorized Service Provider for more help."
If it doesn’t happen in other apps, that points to a software issue. I see that you already reinstalled iOS. That was a significant troubleshooting step. What I would do next, if you haven’t already, is back up your iPhone and restore it to its factory condition. Then, before adding any of your personal data back to your iPhone, test for the behavior. If the issue is still present, go ahead and contact Apple Support. If the issue is resolved, you will want to be careful about how you bring your data back onto your iPhone. If you use iCloud to sync your information, there should be no issue in signing back in and bringing your photos, contacts, and messages back to your device. What you might want to avoid is restoring a full backup as the issue may "live" in your iPhone's backup.
I hope this information helps!
Restore your iPhone, iPad, or iPod to factory settings
Best Regards.
