We usually use our resolution chart to test a camera's ability to capture details, but we've already seen that result in the Image Clarity & Noise page (and in any case, the One's 4MP won't give you much resolution to write home about). This time, we'd like to use the chart to test the One's lens and see its corner to corner performance.
We've already mentioned that the first HTC One given to us produced obvious softness in the corners. But the second HTC One we received, with updated firmware for the camera, cleared up this issue. Now, we have to admit, we don't understand how a firmware upgrade could have resolved an issue with - what we assume to be - the lens, but our experience with the updated One is noticeably different after. It's not just a matter of stopping down either, both images were shot by the camera at f/2. It might be a little hard to spot in these thumbnails, but you can just about see that the upper left and bottom right of the image shot by the first One are soft.
The HTC One XL's lens behaved oddly, it would sometimes produce an image with consistent focus across the entire chart, and sometimes have only the center in focus (we selected the center as our focal point in all test images) with almost everything else out of focus. And this was for a flat focal plane - very odd.
The Nokia 920 looked a hair soft to us, while the Nokia 808 and the iPhone 5 produced consistently sharp results.
We didn't find any evidence of barrel distortion from any of the cameras' images.
When it comes to color reproduction, we didn't notice any significant deviation between the different cameras, except that in this instance taken in daylight, the iPhone 5 and Nokia 920 prefer a warmer white balance, while the rest of the phones run cooler. But even in this simple shot with ample light, you can clearly see that the limited resolution of the HTC One takes a hit in terms of detail levels, which diminishes the photo's vibrancy.