The Galaxy M31 has a new quad camera system on the back. This includes a 64MP f1.8 primary camera with a Quad Bayer array (or as Samsung likes to call it, Tetracell). Next is an 8MP f2.2 camera for ultra-wide shots, which is identical to the one on the M30s. A new addition is the 5MP f2.4 macro camera. The fourth and final camera is a simple depth sensor for portrait images.
The Galaxy M31 ships with the updated Samsung Camera app that's part of the new One UI 2. The app is well-designed with a customizable and intuitive layout and a decent feature set, even for a budget device. The bottom bar to change camera modes can be customized to add or remove modes, and we recommend adding the macro and night mode here so you don't have to go hunting for them in the menu. The top bar also has handy controls for things like flash, timer, resolution and filters.
We do, however, have some complaints with the app. First of all, the HDR option is buried under Settings, which isn't ideal. Granted most people will never bother with this setting at all but if you do want to use it, you have to abandon the viewfinder screen and scroll through settings to find it. Secondly, we would have liked the resolution button to just be a toggle to enable 64MP mode instead of also being an aspect ratio control. We never found ourselves adjusting the aspect ratio even once but used the 64MP feature often.
Enabling 64MP mode also hides the option to switch to the ultra-wide lens. This means you cannot switch to the ultra-wide lens at all unless you switch the main camera resolution back to 16MP, which really makes no sense. Lastly, there is no zoom control on screen by default. The zoom presets (0.5x, 1x, 2x, 8x) only appear on screen when you pinch to zoom and promptly disappear. We understand this phone doesn't have any zoom lenses but if someone has to zoom anyway, it's easier to tap a button than to use two hands to pinch to zoom.
We will talk about the zoom more later but first, let's talk about the basic image quality. For the purpose of this test, we left the HDR mode to Auto and the Scene optimizer to On, which were the default settings. Both can be disabled from the Settings and the HDR can also be forced enabled all the time.
First, let's start with the main 64MP camera. As is usual for Quad Bayer sensors, the camera by default shoots in quarter resolution, which in this case is 16MP. Image quality in daylight is good but not excellent. Color accuracy is good but there is a slight tendency to over expose. Dynamic range is decent by default without HDR but you'll rarely see it as the HDR is almost always on, even in Auto mode. The depth of field is also quite shallow, owing to the large size of the sensor and the relatively wide aperture. When shooting things up close, often only part of the image is in focus. While this is better aesthetically, it's also possible to miss focus if you're not careful.
Where we would have liked to see the camera do better is in detail. It's decent but not 16MP decent, especially when you consider it's being downsampled from a 64MP sensor. The problem is that Samsung tends to overcook its JPEG images, particularly with the HDR, which causes fine detail to be smudged and then oversharpened. The oversharpening causes ringing, especially in high frequency detail regions, such as grass or foliage. This is most noticeable when you zoom in or crop into an image.
Speaking of 64MP, you can shoot in the sensor's native resolution. Now, Quad Bayer sensors aren't ideally suited to shooting in native resolution due to their pixel structure, so zooming in 100% in a native 64MP image will leave you unimpressed by the soft and blurry detail. However, the images still pack far more detail than the downsampled 16MP files and if you intend to crop and reframe the shot later, it's far better to shoot in 64MP than 16MP.
Shooting in 64MP also disabled most of Samsung's post processing. It's not the same as in Pro mode, where seemingly all processing is disabled, but you primarily lose out on HDR and also the scene recognition. However, in many cases, we found the image processing on the 64MP files more pleasing and although the dynamic range was worse in some cases, the images look more realistic with less crushed highlights and ringing artifacts. Plus, there's tons of additional details, so for daylight shooting, we actually recommend using the camera in 64MP mode.
We were not thrilled with the way the camera handles zoom. Instead of putting the surplus native resolution available on the sensor and just cropping in, the phone instead upscales the 16MP images when you zoom in. This results in far worse looking images than if you just captured a 64MP image and cropped in manually. Unfortunately, most people won't do that, which is why we wish Samsung had implemented it that way by default.
In low light, once again we were more impressed by the 64MP images. Sure, the default 16MP images look better at first glance due to the enhanced color processing and dynamic range but the 64MP images have so much more detail that if you are willing to edit the image manually you are once again better off shooting in full resolution.
The 64MP mode is really where the M31 trumps over the M30s. The default 16MP images are more detailed than the 12MP M30s images but it's really the 64MP images where the M31 shines.
The ultra-wide lens is identical on both phones. Once again, you are looking at relatively soft images with very little usable detail once you zoom in. You are really only using this lens for the additional coverage it offers and not for sharper images. The good thing about this camera is how well matched it is to the main camera in terms of color and exposure, at least when the subject filling the lenses are similar. However, since the ultra-wide can often expose additional areas, things such as the scene optimizer and HDR can occasionally change the color and exposure drastically from the main lens depending upon the subject.
Low-light image quality is even worse. The images are even softer and you can see the noise reduction algorithm had to try hard to keep things clean. The images are also darker because there really isn't much dynamic range to glean out of this sensor. Once again, you really need to crave that wider perspective to have to use this lens.
Finally, we come to the last usable lens on the rear, which is the new 5MP macro lens. Now, we aren't really big fans of macro lenses here as their value is dubious at best and the image quality often leaves a lot to be desired. So we approached the macro lens on the Galaxy M31 with some trepidation.
In terms of image quality, the macro lens on the M31 isn't bad. In fact, it's easily one of the best we have seen so far and doesn't make us cringe when we use it. However, there are some limitations with using this lens. When Samsung says macro, it really means Macro. The lens is usable only 3-5cm from the subject, which is really close. There's no autofocus so if you're a bit further away things are simply not in focus. This leaves a bit of a no man's land between the minimum focusing of the main camera and the maximum focusing distance of the macro camera, as the minimum focusing distance of the main camera is much larger than the maximum focusing distance of the macro camera. If you are in that range, you either have no choice but to move in closer or further away.
Getting that close to the subject also has problems. For one, you tend to cast shadow on the subject when you're that close. This makes the subject darker and less photogenic. You can use the flash, which in macro mode is permanently on as a lamp rather than a flash, but it looks far too unnatural and because you're so close to the subject, the light looks like it's coming from further away rather than where the lens is. If you're photographing a glossy subject, then you just have your own reflection on the subject and no amount of angling can fix that when you're this close. Lastly, 5MP is not really an impressive or usable resolution and you could very well just shoot from a distance from the main camera and crop in, which will also take care of the shadow and reflection issues.
All of this again puts the macro lens' usability in the dubious category. It's not unusable and can work quite well in some niche situations, especially since the actual image quality isn't terrible. But to have an entire camera dedicated to these niche situations seems wasteful. Oh well, at least the depth sensor now has some company in the category of relatively pointless cameras.
The video quality on the Galaxy M31 is decent. You can shoot in full 4K resolution at 30fps but that results in losing digital image stabilization. The image quality is good but the lack of stabilization and the jerky autofocus snapping can be distracting.
The 1080p video is the best option overall. You lose some of the detail and resolution but the image quality is still good and the stabilization helps out a lot.
The Galaxy M31 also has Samsung's Super Steady mode, which shoots using the ultra-wide lens and a heavy crop to get super stable footage. However, as we have already established, the ultra-wide camera on this phone isn't really good at all, so while you do get stable footage, the image quality takes a big hit and isn't really usable.
The phone also supports slow motion and super slow motion modes. The super slow motion mode mostly works well and has good image quality but the video does have some stuttering occasionally. The regular slow motion wasn't usable on our device; for whatever reason, it was stuttering a lot while capturing and in the final video. We restarted the device and tried again but it didn't help. The phone also doesn't support 60fps recording at any resolution so you can't even slow down that to get slow motion videos.