HTC have taken a fair bit of flak over their continued use of the 4 MP "UltraPixel" branded camera in both the 2013 HTC One and the 2014 HTC One M8. The theory behind the UltraPixel camera is that it has larger pixels, which allows it to capture more light and so performs better when it's dark. The disadvantage of this technique is that with only four million pixels, the camera loses detail compared with those cameras offering 8, 13, 16 or even 20.7 MP resolution. As to where I sit on the argument: I use the HTC One M8 as my daily driver but my expectations of a smartphone camera are that it takes a clear, in-focus picture when I want it to, which I'll only be sharing online. I don't need higher numbers of pixels and so I've found the M8's camera to be perfectly serviceable. I've taken some great pictures using it and I've also taken some poor pictures too!
The above written, I'm fortunate enough to have reviewed all manner of smartphones in the past. When it comes to the camera, my expectations remain the same: I use my smartphone to capture the moment and I don't necessarily want to take time to compose the shot (even if really I should). I'll use a "proper" camera if I want to take a "proper" picture, my smartphone is for larking around. Devices such as the Sony Xperia Z1 (and later) haven't changed my mind on this. But still: I have wondered how well the One's camera would be if it were a normal unit... and HTC have given customers the opportunity to find out thanks to releasing the HTC One (M8 EYE) handset. Here, the HTC M8 EYE is almost the exact same handset as the Asian-specification HTC One M8. It uses the same 2.5 GHz quad core Qualcomm Snapdragon 801 processor (in most markets, the M8 uses a 2.3 GHz processor), 2 GB of RAM, 16 GB of storage plus a MicroSD card slot, 5.0-inch, 1080p screen and 2,600 mAh battery. The key difference is that the M8 EYE's rear camera array consists of the same duo-camera arrangement but the main camera now uses a 13 MP assembly rather than the 4 MP unit. Unleash the Phones put together an extensive gallery with sample images from both the vanilla M8 and the new M8 EYE models, under a variety of lighting conditions.
I've added a few example pictures in the gallery here but there are many more available on the source. And my conclusion... In bright light, the M8 EYE takes a better picture. In low light, the UltraPixel M8 takes a better picture. There's not so much in it until we start to zoom in. Neither model makes a big enough case to sway me personally... wouldn't it be nice if HTC used a 13 MP UltraPixel camera for their M9, though? We'll probably know in a few months.