DxOMark Mobile Report: Google Nexus 6P
With its 5.7-inch QHD AMOLED display the Nexus 6P is a little smaller than last year's Nexus 6 in terms of both display size and overall dimensions. It comes with an aluminium shell and overall high-end specs. In the camera department the new model features a 12.3MP Sony sensor and an F2.0 aperture. The lack of optical image stabilization should be made up for by large pixels with a size of 1.55 microns, while more phase detection sensors and a laser "time of flight" sensor allow for faster and more precise focusing.
With a DxOMark Mobile score of 84 the Google Nexus 6P is the new number three in the DxOMark smartphone rankings, placing itself between the Samsung Galaxy S6 and the LG G4. The DxOMark team reports that the Nexus images show "impressive detail preservation in low light conditions, by far the best tested to date and good detail preservation in outdoor conditions". The AF is "accurate and fast in all conditions" and image output shows "good white balance and color rendering in outdoor conditions". Flash behavior is good as well, with "good detail preservation, white balance and color rendering".
On the downside, there are "visible irregularities in exposure, color, texture and noise due to HDR+ mode activation in low light conditions" and "in high-contrast scenes, image highlights are occasionally blown out". The testers also criticized that the camera captures an image when the shutter is pressed, even though the AF has not locked on yet.
In video mode the DxO team liked the "good global exposure, white balance and color rendering, the fast and accurate AF and the low noise levels in all conditions". On the downside, the stabilization causes a strong jello effect, the camera tends to refocus when illumination changes and focus can be lost when tracking. The testers also found that "fine detail is lost in low light conditions and color shading is visible in low light and indoor conditions".
Color, Exposure and Contrast
The DxOMark team found that when shooting with the Google Nexus 6P images "are mostly well exposed, with generally accurate white balance". On the downside, white balance is "slightly pinkish with tungsten illuminants" and in "high-contrast scenes image highlights are occasionally blown out".
Overall DxOMark awarded the Google Nexus 6P scores of:
- 4.5 out of 5 for Exposure
- 4.4 out of 5 for White Balance accuracy
- 3.5 out of 5 for Color shading in low light*
- 4.5 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 the Google Nexus 6P images show "good detail preservation in outdoor conditions and in low light". However, "slight noise is visible in both low light and bright light conditions".
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.
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 contrasted 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.
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 and Detail Perceptual scoring
- Texture (bright light): 4.8 out of 5
- Texture (low light): 4.1 out of 5
- Noise (bright light): 4.1 out of 5
- Noise (low light) 4.1 out of 5
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 6P are shown below:
- Visible irregularities in exposure, color, texture and noise due to HDR+ mode activation in low light conditions
- Strong moiré
- Visible ringing in outdoor conditions
- Blue sky saturation occurs in sunny scenes
- Slight color fringing noticeable
- Sharpness 3.8 out of 5
- Color fringing 3.1 out of 5
- Ringing center 7.8%
- Ringing corner 3.0%
- Max geometric distortion -0.4%
- Luminance shading 19.7%
Distortion and Chromatic Aberrations
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 6P puts in a decent performance in all light levels. The overall score is 95/100 in bright light and 81/100 in low light.
- Generally accurate and fast autofocus in all conditions
- Very stable autofocus in low light conditions
- When triggered, shot is taken before autofocus has converged
- Some instabilities in very bright light, both in macro and infinity position
The Nexus 6P comes with a dual-LED flash and DxOMark scored the camera 80/100 overall for its flash performance.
- Good detail preservation
- Strong attenuation in corners
- Some autofocus irregularities
- Strong noise in the corners
Overall DxOMark Mobile Score for Photo: 86 / 100
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 Nexus 6P's video footage to be well exposed, with good AF and low noise levels. However, stabilization caused a strong jello effect and color shading is noticeable in low light.
- Good global exposure, white balance and color rendering
- Fast and accurate autofocus
- Low noise level in all conditions
- Strong jello effect caused by stabilization
- Visible refocusing during illuminant changes and loss of focus during tracking
- Fine detail is lost in low light conditions
- Color shading visible in low light and indoor conditions
Overall DxOMark Mobile Score for Video: 79 / 100
DXOMark Image Quality Assessment
With a DxOMark Mobile score of 84 the Google Nexus 6P is the new number three in the DxOMark smartphone rankings, slotting in between the Samsung Galaxy S6 and the LG G4. The DxOMark testers particularly liked the impressive detail preservation in low light and the accurate and fast autofocus. Points of criticism were highlight clipping in high-contrast scenes and some exposure and color irregularities introduced by the HDR+ mode in low light.
In video mode the footage shows good color and exposure and noise levels are low. However, a strong jello effect is caused by the stabilization algorithm. For a more detailed analysis, visit www.dxomark.com.
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