DxOMark Mobile Report

Summary

The Nexus 6 is Google's showcase phone for Android 5.0 "Lollipop" and the first Nexus device made by Motorola. It comes with the same dual-LED ring flash as the new Moto X, a 13MP imaging sensor with a fast F2.0 aperture and optical image stabilization. Like the Moto X, the Nexus 6 is capable of recording 4K video. With its 5.96-inch QHD AMOLED screen it is a fairly large device and fully qualifies as a phablet. Under the hood the Nexus 6 is powered by Qualcomm's latest high-end system chip, the Snapdragon S805, and users can choose between versions with 32 or 64GB of storage. Unfortunately, like on previous Nexus models, there is no microSD-slot for memory expansion.

With a DxOMark Mobile score of 78 the Google Nexus 6 easily makes it into the top 10 of the DxOMark smartphone rankings and takes the number six spot, right behind the Sony Xperia Z2 and directly ahead of the Nokia Pureview 808. The DxOMark team reports that the Nexus 6 images are showing "good overall exposure" and that "fine detail in bright light conditions is preserved better than on most smartphones". The testers also noted the "good color rendering" and found that flash images showed "good detail preservation, color rendering and stable exposure". The DxOMark team also liked the "stable and repeatable" autofocus.

On the downside the testers found that "in cloudy conditions the white balance is slightly pink", the autofocus takes a long time to detect a change of scene and that the "uniformity of sharpness across the frame is not as good as most other smartphones."

In the Google Nexus 6's video mode the recorded footage shows "very good texture preservation, good colors and low noise levels." However, the testers found the image stabilization to be inefficient when shooting while walking and noticed rolling shutter artifacts. The AF tends to "overshoot when refocusing".

Still Photography

Color, Exposure and Contrast

The DxOMark team found that the Google Nexus 6 images show "good overall exposure and good color rendering" but "white balance is slightly pink in cloudy conditions" and "in low light (20 Lux) pictures are slightly underexposed compared to most smartphones".

Overall DxOMark awarded the Google Nexus 6 scores of:

  • 4.4 out of 5 for Exposure
  • 4.0 out of 5 for White Balance accuracy
  • 4.2 out of 5 for Color shading in low light*
  • 4.4 out of 5 for Color shading in bright light*
  • 3.0 out of 5 for Color Rendering in low light
  • 4.5 out of 5 for Color Rendering in bright light

*Color Shading is the nasty habit cellphone cameras have of rendering different areas of the frame with different color shifts, resulting in pictures with, for example, pinkish centers and greenish corners.

Noise and Details

DxOMark's engineers reported that on the Google Nexus 6 images show "good detail preservation in bright light" but "in daylight conditions slight luminance noise is noticeable in areas of plain color." Luminance noise is also visible in low light conditions.

Texture Acutance

Texture acutance is a way of measuring the ability of a camera to capture images that preserve fine details, particularly the kind of low contrast detail (such as fine foliage, hair or fur) that can be blurred away by noise reduction or obliterated by excessive sharpening.

Sharpness is an important part of the quality of an image, but while it's easy to look at an image and decide visually whether it's sharp or not, the objective measurement of sharpness is less straightforward.

An image can be defined as "sharp" if edges are sharp and if fine details are visible. In-camera processing means that it's possible to have one of these (sharp edges) but not the other (fine details). Conventional MTF measurements tell us how sharp an edge is, but have drawbacks when it comes to measuring fine detail preservation. Image processing algorithms can detect edges and enhance their sharpness, but they can also find homogeneous areas and smooth them out to reduce noise.

Texture acutance, on the other hand, can qualify sharpness in terms of preservation of fine details, without being fooled by edge enhancement algorithms.

A dead leaf pattern is designed to measure texture acutance. It's obtained by drawing random shapes that occlude each other in the plane, like dead leaves falling from a tree. The statistics of this model follow the distribution statistics in natural images.

In this example from a DSLR without edge enhancement, sharpness seems equal on edge and on texture. Many details are visible in the texture.

In this second example, edges have been digitally enhanced, and the edge looks over-sharp, with visible processing halos ("ringing"). On the texture part, many details have disappeared.

At first sight, the images from these two cameras may appear equally sharp. A sharpness measurement on edges will indeed confirm this impression, and will even show that the second camera is sharper. But a closer examination of low contrast textures shows that the first camera has better preservation of fine details than the second. The purpose of the texture acutance measurement is to qualify this difference.

Note: Acutance is a single value metric calculated from a MTF result. Acutance is used to assess the sharpness of an image as viewed by the human visual system, and is dependent on the viewing conditions (size of image, size of screen or print, viewing distance). Only the values of texture acutance are given here. The measurements are expressed as a percentage of the theoretical maximum for the chosen viewing condition. The higher the score, the more details can be seen in an image. 
 
For all DxOMark Mobile data presented on connect.dpreview.com we're only showing 8MP equivalent values, which gives us a level playing field for comparison between smartphone cameras with different megapixel values by normalizing all to 8MP (suitable for fairly large prints). DxOMark also offers this data for lower resolution use-cases (web and onscreen). For more information on DxOMark's testing methodology and acutance measurements please visit the website at www.dxomark.com.
In low light luminance texture acutance is a touch lower under tungsten light than under daylight but you are unlikely to notice the difference in normal shooting. 
In terms of texture acutance, the Google Nexus 6 is among the best in bright light but falls slightly behind in low light conditions.

Edge Acutance

Edge acutance is a measure of edge sharpness in images captured by the phone's camera. Again we're only looking at the most demanding of the three viewing conditions that DxOMark reports on - the 8MP equivalent.
At 100 and 700 Lux measured edge acutance on the Nexus 6 is among the best, it drops slightly lower in dim conditions.
Edge acutance is at a high level in bright light but drops noticeably in darker conditions.

Visual Noise

Visual noise is a value designed to assess the noise in an image as perceived by the human visual system, depending on the viewing condition (size of image, size of screen or print, viewing distance). The measurements have no units and can be simply viewed as the weighted average of noise standard deviation for each channel in the CIE L*a*b* color space. The lower the measurement, the less noise in the image.

Noise levels drop noticeably as the illumination gets brighter.
Daylight noise values are very similar to the measurements under tungsten light.
Compare to most competitors the Nexus 6 noise levels are low in all light conditions.

Noise and Detail Perceptual scoring

DxOMark engineers don't just point camera phones at charts, they also take and analyze scores of real-world shots and score them accordingly. Their findings for the Google Nexus 6 were:

Natural scene

  • Texture (bright light): 4.6 out of 5
  • Texture (low light): 3.4 out of 5
  • Noise (bright light): 3.8 out of 5
  • Noise (low light) 3.2 out of 5
Bright light sample shot. 
100% crop: fine detail is well preserved
Low light (20 Lux) studio shot.
100% crop: luminance noise is noticeable
100% crop: detail is still visible

Artifacts

Phone cameras, like entry-level compact cameras, tend to suffer from artifacts such as sharpening halos, color fringing, vignetting (shading) and distortion, which can have an impact on the visual appeal of the end result. DxOMark engineers measure and analyze a range of artifacts. Their findings after testing the Google Nexus 6 are shown below:

  • Uniformity of sharpness across the frame not as good as some rivals
  • Ringing and fringing noticeable

Perceptual scores

  • Sharpness 3.3 out of 5
  • Color fringing 4.0 out of 5

Measured findings

  • Ringing center 9.8%
  • Ringing corner 5.6%
  • Max geometric distortion -0.4%
  • Luminance shading 27.3%

Distortion and Chromatic Aberrations

The graph shows the magnification from center to edge (with the center normalized to 1). The Google Nexus 6 shows very slight complex distortion, which is not going to be noticeable in normal photography.
The Nexus 6 images show slight lateral chromatic aberrations which can be just about noticeable in very high-contrast shooting situations.

Autofocus

DxOMark also tests autofocus accuracy and reliability by measuring how much the acutance - or sharpness - varies with each shot over a series of 30 exposures (defocusing then using the autofocus for each one). As with other tests these results are dependent on the viewing conditions (a little bit out of focus matters a lot less with a small web image than a full 8MP shot viewed at 100%). Using the 8MP equivalent setting, the Google Nexus 6's AF is very stable and repeatable. The overall score is 85/100 in bright light and 80/100 in low light.

Pros: 

  • Stable and repeatable autofocus 

Cons: 

  • AF slow to detect a change of scene
Autofocus repeatability - average acutance difference with best focus: low light 3.83%, bright light 3.01%

Flash

DxOMark scored the Google Nexus 6 85/100 overall for its flash performance which is one point higher than the iPhone 6 and 6 Plus.  

Pros: 

  • Good detail preservation, good color rendering and no color shading

Cons:

  • When flash is mixed with low tungsten light white balance turns slightly red but image retains overall pleasant color response

Overall DxOMark Mobile Score for Photo: 81/ 100


Video Capture

DxOMark engineers put phone cameras through a similarly grueling set of video tests, and you can read their full findings on the DxOMark website here. Overall DxOMark found the Google Nexus 6's video performance to be decent, with good textures and color. However, the stabilization is inefficient and causes rolling shutter artifacts. 

Pros: 

  • Very good texture preservation
  • Good color
  • Good noise performance.

Cons: 

  • Inefficient stabilization, especially for walking movements: only a slight correction of the overall frame translation is noticeable and rolling shutter artifacts are visible.
  • Overshoot during refocusing

Overall DxOMark Mobile Score for Video: 74 / 100

DXOMark Mobile Score
78

DXOMark Image Quality Assessment

With strong photo performance the Google Nexus 6 can compete with the best in class. The DxOMark team reports that its images show good exposure and color, and detail preservation is among the best. The testers also liked the good flash performance and reliable AF behavior. However, the white balance can produce slightly pink results in cloudy conditions and the lens shows some softness towards the edges of the frame. 

The Nexus 6 video mode cannot quite keep up with the performance in stills mode. The recorded footage shows very good texture and color with low noise levels but the testers found the image stabilization to be inefficient and to introduce rolling shutter artifacts. For a more detailed analysis, visit www.dxomark.com.

Photo Mobile Score 81   Video Mobile Score 74
Exposure and Contrast 85   Exposure and Contrast 84
Color 80   Color 82
Autofocus 83   Autofocus 50
Texture 76   Texture 82
Noise 76   Noise 84
Photo Artifacts 82   Video Artifacts 93
Flash 85   Stabilization 53