Are you talking the actual picture is degraded when it is taken or the screen distort the picture when it comes up on the phone screen after it has been taken?
I personally don't see any screen distortion at all with my TechArmor protector on my s4. Sure it holds fingerprints better (which is not a good thing) than the glass itself, but nothing a quick wipe couldn't fix. To each their own though.
In the past screen protectors did interfere with display quality a bit. However, as I mentioned, today's screen protectors are top notch and don't interfere/distort the display of your phone, in my opinion. There have been countless times where a friend or family member has taken a look at my phone and had no idea a screen protector was on it, but were still very impressed with the display quality of my s4.
Just like the phones from 2 years ago being compared to today's phones, the difference is night and day.