Update, July 19: We've updated this page with the following video comparison of the cameras of the three phones. It covers the same things you will see on the following pages, so be warned, spoilers ahead.
In bright daylight, the OnePlus 5 captures the most detail, rendering both repeating textures like window blinds, and random high-intricacy foliage and stucco detail better than the other two. That said, noise is present even at low ISO in abundance of natural light. You can hardly split the iPhone 7 Plus and Galaxy S8 for resolved detail.
The OnePlus 5 takes a similar approach to the Galaxy S8 in terms of color rendition, with lively reds and greens that we don't think even the engineers could tell apart. The OP5 paints its blues differently, though, in a cooler way than the S8, and we're leaning towards the S8's tuning. Then there's the iPhone 7 Plus that is colors' enemy number one, its images downright lifeless.
There's more to that than color, though, as Apple's opted for a flatter tone curve, resulting in lower contrast, but better preservation of detail in the extremes. That approach does lend well to post processing, but straight out of the camera the iPhone's photos are easily the dullest. The OP5 and Galaxy S8's images are visibly more contrasty.
Here's a whole bunch of samples with those from the OnePlus 5 on the left, iPhone 7 Plus in the middle, and the Galaxy S8 on the right.
Daylight photos winner: Tie. To each their own. The OP5 leads in terms of detail, but is also the noisiest. The Galaxy S8's output is clean, but can't match the OP5's resolution. Both produce pleasing vivid colors. The iPhone has somewhat wider dynamic range, and its output is best suited to post processing.
The Galaxy S8 lacks a telephoto camera. The one on the OP5, however, isn't much use on its own, as a quick comparison against the iPhone 7 Plus reveals. The iPhone produces much cleaner images with superior dynamic range. On top of that, even if we're not super great fans of the iPhone 7 Plus' muted color rendition, it's still infinitely better to get consistent results between the two cams - the iPhone does it, while the OP5 pumps up the saturation higher on the tele cam than it does on the normal one.
The OnePlus 5 samples are on the left, the the iPhone's are on the right.
Telephoto camera winner: Apple iPhone 7 Plus, easily. The iPhone 7 Plus' telephoto cam produces cleaner, sharper images with an identical color rendition to the main camera, and it's a true hardware/optical 2x zoom. The OP5 resorts to software trickery to achieve the 2x magnification and it shows in its much noisier images. The different color saturation is also annoying.
The secondary function of the secondary cam is to enable depth effects - the much hyped portrait modes, we've been seeing more and more lately. That's one area where the OnePlus 5 is almost as good as the iPhone 7 Plus, or even better on occasion.
Better, because the OP5's portrait mode covers a wider FOV, so you can successfully use the rear cam in portrait mode to take selfies. On the iPhone 7 Plus the FOV is narrower and you'd struggle getting your face in the frame accurately when holding the phone at arm's length.
The iPhone does blur the background more, making for a clearer separation between subject and background. In terms of detecting the edges of the subject it's a toss-up between the two, and it depends a lot more on the hairstyle than the phone. Busy backgrounds can throw both phones off too - it's not like the iPhone is foolproof.
Portrait winner: Tie. The iPhone 7 Plus blurs the background more, but the wider coverage of the OP5 makes it better suited to portrait selfies. Both do the separation between subject and background with a similar level of success.
Gone are the days of out-of-this-world HDR shots - most makers now stick to a conservative rendition. The three phones have an Auto HDR mode freeing you worries on when to engage it, though you can always intervene by manually setting it to On.
The OnePlus 5 suffers from a drop in sharpness in its HDR samples. It does tend to brighten the shadow areas, but doesn't do much for salvaging the shadows.
The iPhone... Well, frankly, we can't tell what exactly the iPhone is doing in high-contrast scenarios like these - we don't see much of a difference.
The Galaxy S8's HDR mode makes more sense, boosting the shadows and midtones, though highlight preservation isn't its forte either. By the way, if you want the full strength of the HDR effect, do go for the HDR On option - Auto is more laid back. A great feature on the S8 is the live preview - you can tell in real time whether you like where things are going.
And here's a comparison between the photos produced by the three phones with HDR mode enabled.
HDR photos winner: Samsung Galaxy S8. While neither phone makes dramatic HDR shots, the ones from the S8 at least look like the algorithm has done something. There's also no change in sharpness, and the live preview is always great to have.
The Galaxy S8 is the phone that's best equipped to handle lowlight shooting scenarios - it's got large pixels, bright aperture and optical stabilization. The iPhone has OIS too, and its aperture is only slightly smaller, but the tinier individual photosites, and sensor overall, hinder its ability to gather light. OP5, on the other hand, may match the S8's aperture, but in its case the smaller sensor and pixels are also coupled with a lack of optical stabilization.
In the end, the Galaxy S8 produces the sharpest images in tough available-light conditions. It retains the most detail, while also keeping noise levels spectacularly low. The iPhone also manages to sharp, but loses fine detail to noise reduction. OnePlus' images are the softest and noisiest, but still quite usable, and with no dip in color saturation.
Shooting in low-light with the telephoto cameras is an interesting endeavor. Small sensors and/or apertures mean that the total gathered light won't be much. Thus, both the iPhone 7 Plus and the OnePlus 5 may determine that a better final image could be achieved by shooting with the primary cam, cropping and upscaling to match teh desired resolution. The iPhone 7 Plus is quicker to resort to that, while the OP5's tele cam has a higher tolerance for low light, so to speak.
In the first set of samples below, both phones shot with their actual secondary cameras. The iPhone's images are cleaner and sharper, but the noisier OnePlus 5 photo contains mostly the same amount of detail. In the second pair of images the iPhone chose to use the main camera, while the OP5 stuck to the telephoto one. We'd pick the iPhone's photo for detail, and the OP5's for colors, but that's hardly news at this point.
Lowlight photos winner: Samsung Galaxy S8. A combination of carefully chosen hardware components and mature processing secures the S8 the win in low light. The OP5's photos are very noisy, while the iPhone 7 Plus does an decent job despite a small sensor.
The three phones have panorama modes, but the one on the Galaxy S8 is the most versatile. It lets you capture panoramas left-to-right, right-to-left, top-to-bottom, or the other way around, as well as in portrait or in landscape. The iPhone can do left-to-right and right-to left, but that's it. The OP5 is even more limited - just left-to-right in portrait, and that's it. But what if you want to base the exposure of the shot on the right end of the frame? Well, tough luck.
But that's not all that's bad about the OP5's panoramas - they are also stitched rather poorly, resulting in wavy lines and ghosts.
The iPhone suffers from no stitching issues and produces sharp and detailed panoramas. We also didn't encounter the striping in the sky that we observed on previous occasions - perhaps it's been fixed with an update since.
Which is precisely the thing Samsung engineers need to address to achieve the S8's full panorama potential. Severral months into the flagship's existence, we can still see the borders between the different exposures - look at the sky in the right halves of both samples below. That aside, the S8's panoramas are very good.
Panorama photos winner: Apple iPhone 7 Plus. Apple's usual dominance in this field was disturbed at the 7's launch due to minor exposure issues and undersaturated colors. The former's been addressed, and while the colors aren't quite to our liking, the iPhone 7 Plus creates the sharpest panoramas here with flawless stitching. The Galaxy S8 needs to fix the same thing, and then it would be a tie. The OP5's stitching ruins its pano shots.
The OnePlus 5 has more pixels on its front-facing cam than the other two combined. It's got a 16MP sensor positioned behind an f/2.0 aperture lens. EXIF data reports its focal length at 20mm-equivalent, but we don't see it covering all that much - the Galaxy S8's 8MP cam has a 25mm-equiv. focal length, and the OP5 just about matches it in coverage. Or is it even a bit narrower, actually? Either way, the Galaxy's lens is brighter - its aperture is f/1.7 like on the main cam.
Meanwhile, the iPhone 7 Plus relies on a 7MP camera for selfies. It's coverage is even narrower, and the reported 32mm-equiv. focal length does look right. The lens is also the dimmest here - f/2.2.
All three phones take good selfies, though we're, again, not thrilled about the way the iPhone 7 Plus reproduces colors - what the other two phones would testify is a reasonably healthy subject looks sick and pale on the iPhone's selfies.
The OP5 captures the most detail, but the others aren't really too far back, the iPhone in particular aided by its narrower lens. OP's front cam has a similar take on colors as the Galaxy S8 - both produce more pleasing images than the iPhone.
Selfie photos winner: Tie between the OnePlus 5 and Samsung Galaxy S8. The OP5 has the more megapixels, while the S8 boasts a brighter lens and autofocus (even if you need to double check focus post-shot). The iPhone's tight lens and dull colors kill it for us.