The Google Pixel XL Review: Life After Nexusby Matt Humrick & Brandon Chester on November 8, 2016 8:00 AM EST
Google’s Pixel phones use a 1/2.3" Sony IMX378 Exmor RS sensor that captures 12.3MP images with a native 4:3 aspect ratio. Its large 1.55µm pixels have a larger full-well capacity than the 1.12µm pixels found in most smartphone camera sensors, which should improve dynamic range and gather more light per pixel. While similar in many ways to the Sony IMX377 Exmor R sensor in last year’s Nexus 5X and Nexus 6P, the Pixels’ IMX378 offers two key improvements. First, it uses a stacked CMOS topology that moves some of the circuitry to the support substrate below the backside-illuminated pixels. Second, it adds support for phase detect autofocus (PDAF), which greatly improves AF speed and accuracy in well-lit scenes.
The Pixels combine PDAF with laser and contrast AF to create a hybrid autofocus system that works well in most lighting conditions. The laser-ranging module sits next to the rear camera and its time-of-flight sensor is supposed to work in lower-light conditions at distances up to 2 meters (6.5 feet).
One feature the Pixels lack is optical image stabilization (OIS), which was MIA on the previous Nexus phones too. OIS helps improve low-light camera performance by removing the small vibrations caused by shaky hands that can lead to blurry images during long exposures. Google claims OIS is unnecessary, partly because of the sensor’s larger pixels and partly because of its HDR+ feature.
Google’s HDR+ processing works a little differently than other HDR capture modes. Instead of taking two or more images at different exposures—a fast exposure to capture bright areas and a slow exposure to capture darker areas—Google’s HDR+ mode combines multiple fast exposures. Using fast exposures avoids clipping bright areas, while combining multiple shots reduces image noise in dark areas by the square root of the number of shots taken. For example, taking four shots would reduce noise by a factor of two and nine shots would reduce noise by a factor of three. Tone mapping and other post-processing can then be used to further brighten and fine tune the final image.
The primary drawback to using HDR+ on previous Nexus phones, however, was the slow image capture rate. Depending on the phone it could take anywhere from one to three seconds to capture and process a single picture. Thanks to the processing speed of the Snapdragon 821 SoC (the HDR+ algorithm takes advantage of vector instructions when running on the Hexagon 680 DSP to improve performance and reduce power consumption) and some capture trickery (the camera is already taking pictures before the shutter button is pressed), this is not as big of an issue for the Pixels. Google claims its new phones have zero shutter lag when using HDR+, implying you can snap pictures as quickly as you can press the button, which is true when using the “HDR+ auto” setting; however, after snapping four to five HDR+ images as fast as possible, the Pixel’s camera slows down and can only take a picture about once per second, although this is not a typical scenario. Also, when the camera is set to “HDR+ on,” it does not appear to take exposures continuously, which introduces about a 0.5-1.0 second delay between shots, which is still pretty good, while it captures several exposures and processes the image.
|Google Pixel & Pixel XL||Huawei Nexus 6P|
|Front Camera: Resolution||8MP||8MP|
|Front Camera: Sensor||Sony IMX179 Exmor R
|Sony IMX179 Exmor R
|Front Camera: Focal Length||3.38mm (26mm equivalent)||3.41mm (26mm equivalent)|
|Front Camera: Aperture||f/2.4||f/2.4|
|Rear Camera: Resolution||12.3MP||12.3MP|
|Rear Camera: Sensor||Sony IMX378 Exmor RS
|Sony IMX377 Exmor R
|Rear Camera: Focal Length||4.67mm (26mm equivalent)||4.67mm (26mm equivalent)|
|Rear Camera: Aperture||f/2.0||f/2.0|
The Pixels use a 6-element lens array with an f/2.0 aperture. Increasing the aperture area (decreasing f-stop value) allows more light to reach the camera sensor, but it also increases the design complexity and z-height of the camera module. The Pixels end up with the same aperture area as the Nexus 6P and are competitive with, but a little behind, other flagships. Their aperture area is 10% smaller than the LG G5’s camera, 13% smaller than the Galaxy S7’s and Moto Z Force’s, and 16% smaller than the HTC 10’s.
The Pixels inherit their front-facing cameras from the Nexus 6P, an 8MP Sony IMX179 Exmor R sensor with 1.4µm pixels and an f/2.4 lens. The Pixels do not have a dedicated LED flash for the selfie camera like Motorola’s Moto Z phones, and there’s no screen flash feature with the default camera app either.
Google is very proud of the Pixels’ camera. Its marketing materials prominently proclaim that it’s the “highest rated” smartphone camera based on the tests of a particular camera testing site. This certainly piqued our curiosity, so we took a bunch of pictures with the Pixel XL in various lighting conditions to see just how well it performs. Normally, we leave HDR turned off except for specific scenes that serve as good tests for HDR image quality; however, Google recommends leaving HDR+ on all the time, and the Pixels are fast enough to do so, so we’re including photos with HDR+ both disabled and enabled for each scene.
Even though the Nexus 6P’s camera is very similar to the Pixel XL’s, we’re including it in our roundup to see how the Pixel’s software processing has evolved. The Samsung Galaxy S7 edge has one of the better cameras currently available, and it looks similar to the Pixel XL on paper (12MP, 1/2.6" Sony IMX260, 1.4µm pixels, f/1.7), so it will be interesting to see if the Pixel XL’s larger sensor and HDR+ processing translate to better image quality. Motorola’s Moto Z Play costs significantly less than the Pixel XL and comes with a decent camera, so it will serve as our value comparison. Unfortunately, the iPhone 7 Plus, HTC 10, and OnePlus 3 were all unavailable for testing. All of the images were taken using the stock camera app's Auto mode unless noted.
|Daylight Photo Comparison 1|
In this first daylight scene, the sun is almost directly overhead, providing excellent light and casting some shadows. Right away we see the Pixel XL produce better photos than the Nexus 6P. With HDR+ turned off, the Nexus 6P produces the darkest image of the group but still manages to clip the bright clouds. Its white balance is good, but its colors look a bit too saturated. The Pixel’s exposure is better (but still a little dark), and its white balance and colors look good too.
The Pixel, with HDR+ turned off, captures an image that looks almost identical to the Galaxy S7 edge’s: similar exposure, similar white balance, similar colors. One obvious difference, however, is how much more dynamic range the Pixel’s image has, showing far more detail in the shadows beneath the tree. And while the Pixel does apply an unsharp mask filter to make edges appear sharper, it’s not as aggressive as the S7’s filter and produces more natural looking results.
Activating HDR+ produces some notable changes for both the Nexus 6P and the Pixel. The images are a little brighter overall. White balance and color look good, although the sky turns a shade of blue that’s a bit darker than natural. The white clouds are no longer overexposed and some areas in shadow are brighter, as we would expect; however, some shadowy areas under the tree actually get darker, which is odd and undesirable. The images still maintain a natural-looking appearance at least.
The Pixel’s photos show very little noise, noticeably less than the Nexus 6P’s photos, and even a little better than the S7, especially shot noise in the sky. The HDR+ images from both the Pixel and 6P show a bit more noise than the non-HDR+ images in busy areas where there is not a lot of constant color like the sky, which is surprising given Google’s explanation of how HDR+ works. This is most obvious on the plants and rocks in the foreground, and the net result is a perceived loss of sharpness.
While this issue is pretty minor, I’m concerned by how blurry the left edge appears in both of the Pixel’s photos, an issue that does not show up in the 6P’s images. As we’ll see below, this is a problem that persists across all of the pictures taken with this Pixel XL. We recently received a second Pixel XL review unit that shows some softening on the extreme left edge and a little in the corners, but it’s nowhere near as bad. Both Pixel XL review units perform the same otherwise, so this issue seems to be specific to our first review unit.
|Daylight Photo Comparison 2|
The second daylight photo replaces green grass with brick and concrete, which highlights some differences in exposure. The Moto Z Play overexposes its image a little bit, while the Nexus 6P underexposes, producing a darker image that still looks alright but does not accurately reflect the brightness of the scene. The photos from the Pixel XL (HDR+ off) and S7 edge show the best exposure. Using HDR+ on both the Nexus 6P and Pixel XL reduces brightness across the entire frame. Without any highlights on the building, the photos look like they were taken under a cloudy sky rather than in direct sunlight, which is not accurate.
Each phone’s auto white balance routine works well, and there’s no major issues with color after accounting for the differences in exposure, although the Nexus 6P and Pixel XL (with HDR+ on) produce a darker blue sky again.
Both the Nexus 6P or Pixel XL (the Moto Z Play did not focus correctly) capture more detail than the S7 edge, whose more aggressive noise reduction processing wipes away texture on the bricks and sidewalk. The 6P and XL clearly perform more noise reduction when HDR+ is turned off; however, even when HDR+ is turned on, noise is still minimal with a very fine grain, making it about the same or even a bit less noticeable than in the S7’s image.
When comparing the photos of the parking garage with the camera’s HDR modes turned off, we again see that the Nexus 6P produces more saturated colors than the Pixel XL. Also, just like in the first daylight image above, the S7 edge shows less dynamic range than the Pixel XL and other two phones, capturing less detail in the shadows inside the garage. The S7 edge and Pixel XL are almost identical again when it comes to exposure and white balance.
All of the phones perform well after turning HDR on, reducing the glare on the white sign on the far left, significantly brightening the dark area inside the garage, and leaving properly exposed areas alone. The Pixel XL’s HDR+ mode shows some subtle differences—it does not brighten the garage’s interior as much as the S7 edge or Moto Z Play, but it does a better job bringing out the concrete’s detail in the foreground—although there’s no clear winner in this scene.
The second series of images of the bush largely reinforce previous observations. In this scene, the sun was just outside the frame, with the cameras facing into the sun. This scenario finally trips up the Pixel XL’s auto white balance routine, resulting in a yellow cast to both of its images.
|Evening Photo Comparison 1|
This first low-light scene was taken just after sunset when there was still a bit of light left in the sky. Without HDR turned on, all of the phones overexpose the sky, which is really the best solution for this tricky scene when faced with capturing an image with a single exposure. The Moto Z Play opts for a brighter exposure again, completely blowing out the sky and washing out some color. The S7 edge handles this situation the best, with a decent exposure and good white balance. The Pixel XL comes very close to matching the S7’s performance, but its colors are not as rich and warm, there’s some flares around the lights on the ground, there’s less detail on the bricks and walls, and there’s more noise grain.
Activating HDR+ on the Nexus 6P and Pixel XL improves image quality dramatically. The sky is no longer overexposed, the foreground is clearer and brighter, and colors are accurate and rich. Image noise is also reduced and there’s more detail in the bricks. There’s still flares around the lights on the ground, however, and the S7’s image still shows less noise. The Pixel XL’s HDR+ image also shows some odd, speckled artifacts around the brightest edges that are not present in its non-HDR+ image or in the S7’s. Unfortunately, I did not take a picture using the S7’s HDR mode for an apples-to-apples comparison. If I had, I suspect the S7 would have the edge after combining its lower noise and sharper detail in this image with the improvements we saw earlier when using its HDR mode.
|Evening Photo Comparison 2|
This second image was taken after the first just before the sky went completely black. Comparing the non-HDR images, the Moto Z Play clearly produces the worst image of the group. It overexposes again, the green in the trees and bushes is too saturated, and its autofocus had issues, resulting in a blurry image. The best image goes to the S7 edge. Its colors look natural, avoiding the yellow cast in the Pixel XL’s image, and it captures sharper detail with less visible noise than the Pixel XL and Nexus 6P.
Turning on HDR+ once again boosts image quality, although the Pixel XL produces a better image than the Nexus 6P. The biggest changes occur at the front of the building where the overexposed highlights are eliminated, making colors look richer. The Pixel XL uses much less noise reduction in its HDR+ mode, resulting in much sharper detail over its non-HDR+ image. The side effect is more visible noise, but it’s a fine pattern and not that noticeable, except for artifacts that show up around bright edges again (lights along building’s roof). The S7 edge captures more detail with less noise along the front of the building, although detail and noise are similar to the Pixel XL with HDR+ along the side of the building where there’s less light.
The Pixel XL certainly has a very good camera, but I would not crown it the best. In good lighting, it equals or surpasses the S7 edge’s image quality, but in low-light situations the S7 edge performs better, capturing sharper detail with less noise even when the Pixel XL uses its HDR+ mode. Overall, the Pixel’s auto exposure and white balance routines perform admirably, and colors appear saturated but natural. I also did not notice any vignetting (darkening in the corners), an optical issue the Nexus 6P suffers from pretty strongly, or chromatic aberration. Our first review unit shows pretty severe softening along the left edge of the frame, but a second unit only shows mild softening in the corners, so this might not be a widespread problem.
There’s no doubt that Google’s HDR+ mode performs well, improving exposure and detail while producing natural looking results. There are a few cases where turning HDR+ off will produce a better image, but given how well it performs, both in terms of image quality and capture speed, it’s best to take Google’s advice and leave it turned on all the time.