DxOMark Mobile Report: Apple iPhone 6s Plus

Summary

With a DxOMark Mobile score of 84 the Apple iPhone 6s Plus takes the number 3 spot in the DxOMark smartphone rankings, placing itself between the Samsung Galaxy S6 Edge and the Google Nexus 6P. The DxOMark team reports that the iPhone 6s Plus images show "very good overall exposure and good detail preservation in bright light". The testers also liked the "fast and generally accurate autofocus" and the "stable and pleasant white balance". 

On the downside, "some luminance noise is visible, especially in low light" and images show "color inaccuracies and visible color shading with indoor illuminants". The testers also found "occasional blue sky saturation and other artifacts" and flash images show noticeable vignetting.

In video mode the testers liked the "accurate and smooth autofocus, the effective stabilization and the good exposure and white balance". However, they also noted the "noise in low light conditions, especially in the corners, and visible color shading".

Still Photography

Color, Exposure and Contrast

The DxOMark team found that when shooting with the Apple iPhone 6s Plus images showed "very good overall exposure, stable white balance with a slight yellow cast and very nice colors when shooting outdoors". However, they also found "color inaccuracies and visible color shading with indoor illuminants".

Overall DxOMark awarded the Apple iPhone 6s Plus scores of:

  • 4.6 out of 5 for Exposure
  • 4.6 out of 5 for White Balance accuracy
  • 4.2 out of 5 for Color shading in low light*
  • 4.1 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 Apple iPhone 6s Plus images show "good detail preservation in bright light and low chroma noise". On the downside, "in low light conditions fine detail is lost and some luminance noise is visible, especially in low light".

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 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.

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.
Luminance texture acutance decreases in low light but is a touch better under tungsten light.
In terms of texture accutance the iPhone 6s Plus trails behind the competition. 

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.
In terms of edge acutance the iPhone 6s is on almost exactly the same level as the Nexus 6P but trailing behind the Samsung Galaxy S6. 
Edge acutance decreases noticeably in lower light.

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 increase noticeably in low light. 
The Apple iPhone 6s Plus produces a little more noise than most competitors across all light levels. 

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 Apple iPhone 6s Plus are:

Natural scene

  • Texture (bright light): 4.6 out of 5
  • Texture (low light): 3.7 out of 5
  • Noise (bright light): 4.0 out of 5
  • Noise (low light) 3.5 out of 5
Bright light sample shot
100% crop: well preserved detail
100% crop: fine noise noticeable
Low light (20 Lux) studio shot
100% crop: fine detail is being lost
100% crop: luminance noise 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 iPhone 6s Plus are shown below:

  • Blue sky saturation visible on some outdoor scenes
  • Slight ghosting occasionally visible in HDR mode 
  • Slight Moiré in some pictures
  • Slight ringing visible
Blue sky saturation is visible in some outdoor scenes.

Perceptual Scores

  • Sharpness 4.2 out of 5
  • Color fringing 3.2 out of 5

Measured findings

  • Ringing center 7.8%
  • Ringing corner 5.7%
  • Max geometric distortion -0.3%
  • Luminance shading 3.4%

Distortion and Chromatic Aberrations

The graph shows the magnification from center to edge (with the center normalized to 1). The Apple iPhone 6s Plus shows a slight pincushion distortion, which you are not going to notice in normal photography.
Some lateral chromatic aberration is noticeable in the 6s Plus images.

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 Apple iPhone 6s Plus performs very well at all light levels. The overall score is 94/100 in bright light and 89/100 in low light.

Pros: 

  • Fast and generally accurate autofocus in all conditions
  • Stable focus in preview

Cons: 

  •  Some irregularities in low light when touch-to-focus is used
Autofocus repeatability - average acutance difference with best focus: low light 6.14%, bright light 5.03%

Flash

The Apple iPhone 6s Plus comes with a dual-LED flash and DxOMark scored the camera 83/100 overall for its flash performance. 

Pros: 

  • Good exposure with and without additional light sources
  • Stable exposure and white balance in all conditions

Cons:

  • Visible noise, especially near the corners
  • Visible attenuation in the corners without additional light sources

Overall DxOMark Mobile Score for Photo: 84 / 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 Apple iPhone 6s Plus video footage to be well exposed, with good stabilization and white balance. AF is smooth and accurate in all situations but noise and color shading are noticeable in low light. 

Pros: 

  • Fast, accurate and smooth autofocus
  • Good overall exposure and white balance
  • Effective stabilization in all conditions

Cons: 

  • Noise noticeable in low light, especially in the corners
  • Sometimes tremors are visible
  • Visible color shading in all conditions

Overall DxOMark Mobile Score for Video: 82 / 100