One of the best things I love about the OnePlus 3T main camera is its low-light and high ISO performance. No one will doubt it's amazing image quality in daylight, but I was surprised that it was able to maintain such high-quality output at very high ISO speeds. The OnePlus 3T rear camera uses the Sony IMX298. It is a small 1/2.8" sensor, the pixels size is very small (1.12-micron) but even with all what seems like average specs, the 3T camera manage to deliver excellent results.
The Sony IMX298 sensor uses Sony's Exmor RS Stacked BSI technology that is renowned for its impressive light sensitivity and image quality. This sensor also boasts high single to noise ratio (SNR) and boasts advanced chroma noise reduction processing which translates to image with less noise and more clarity, even when shooting in low-light conditions.
I usually judge the low-light performance based on sample images that were taken in dim light, rather than one that were taken at night but with strong ambient light in the background or on directed on the subject. This allows me to see how the sensor performs in those non-optimal lighting conditions and see how much noise the sensor produce in mid-tone and shadow areas. You can capture a ISO1000 and notice very little noise in the bright areas of the image. You might think that you've got a winner here, until you get the next shot relatively dark place without a strong light source and then you start to comprehend the camera's poor performance.
I've viewed and analyzed many sample images shot with the OnePlus 3T. At ISO 100 and ISO 200 there is still little noise, but it's well under control, nothing to worry about. At ISO 500 you can clearly see the noise but it has a dine grained luminance noise characteristic. TheOnePlus 3T image processing engine does not apply strong noise reduction algorithms in the background to minimize noise. Now this is a good thing. What most cameras do in this situations is that employ a strong Noise Reduction (NR) processing that makes the image look smoother and with less noise, but this comes at a cost of image detail loss. It also makes the image look smudgy, like an oil painting when you look at the image in full size. Some cameras do it better than others, but I personally love to see the image with the least amount of processing.
Why do you ask? well, because I personally enjoy processing the images myself and I used advanced noise reduction software that works really well with this type of grainy image noise.
If you are like me and enjoy processing some of your photos yourself, you probably will be glad to here that the OnePlus 3T does offer a DNG Raw support. This means that you can obtain a unprocessed image data directly from the sensor. This image file contains the color data without any post processing that is usually applied to the JPEG image to improve its appearance (e.g. sharpening, white balance saturation, contrast and other adjustments). However, the camera still save the camera settings in the metadata of the file, but the adjustment is not applied on the pixel color data itself.
Images like this one shot by dpreview at ISO 6500 without flash, clearly shows how good the OnePlus 3T performance is in low-light. Just look how well the details and color are maintained. There is definitely stronger NR going on there, but the implications on fine details is relatively very low . Decrease the image size a bit and it's very hard to notice any noise. The fast f/2.0 aperture lens and the optical image stabilization really help here. That image was shot at 1/17s shutter speed, below the recommended one (1/focal length of the lens) and you can see that the window texture details are still sharp. The slight blurriness that you see isn't caused by hand movement, but due to the NR that kicks in stronger this time. Let me remind you that it's not ISO 1000 image, but ISO 6400 and taken with a sensor with 1.12-micron pixels, it's really very impressive performance considering those specs.
The OnePlus 3T also has a HQ shooting mode that has a very high impact on the image quality when shooting in dim lighting environments. In this mode the camera is forced to capture the image in a slower shutter speed and with less aggressive noise reduction. I love this mode because it helps maintain the fine grain noise. There is a huge difference between images taken with or without this mode. Images taken with HQ off will have the noise appear more smudgy and soft and images taken with the HQ shooting mode on will help preserve the details much better with more fine grained noise pattern. This is a very useful shooting mode when shooting pictures of subjects with fine textures and many fine details. It helps maintaining details of sharp lines and text. This is definitely the best mode to shoot at in low-light if you care about image quality.
I dislike HDR mode in low-light, it just make pictures look unnatural and increase noise levels. The OnePlus 3T camera does have an Auto HDR modeI which is good to maintain good details in shadow and bright areas in high contrast images taken in good lighting conditions.
There is an excellent post on forums.oneplus.net with sample images taken with the HQ mode off and on. Just look at the texture quality between the two shots there and you can see what shooting in HQ mode is the preferred mode of the two.
Oh, I almost forgot, if you are searching for a great noise reduction software, I highly recommend downloading Noise Ninja 4 by PictureCode. Their noise reduction algorithm is just superb for reducing/removing fine grained image noise like the one that you get with the HQ mode. I tried it many times before when it was a standalone product and it worked amazingly well. I think there is an Adobe Photoshop plugin for it, but I am not sure it's currently being maintained. You can download their Photo Ninja RAW converter software that comes with Noise Ninja 5 built in, at least that what I understand from their website.
So overall, the OnePlus 3T can capture really impressive low-light pictures, especially when the HQ mode is turned on, which I believe it should be turned on most of the time.