DxOMark Mobile Report: Apple iPhone 6 Plus

Summary

The iPhone 6 Plus is the phablet version of the new iPhone 6. With its 5.5-inch 1080p screen (vs the standard model's 4.7-inch variant) it is noticeably larger and thanks to a little more space in the body the camera module comes with optical image stabilization. Otherwise the specifications of the two devices are pretty much identical. Like the predecessor iPhone 5S the camera uses a 1/3-inch 8MP sensor and F2.2 aperture. However, among other improvements there is now a phase detection AF system and an 8x slow-motion video mode at 720p resolution. 

With a DxOMark Mobile score of 82 the Apple iPhone 6 Plus shares the number one spot in the DxOMark smartphone rankings with its sister model iPhone 6. The two Apple devices place themselves in front of the Samsung Galaxy S5 and Sony Xperia Z3.  

The DxOMark team reports the iPhone 6 Plus shows "very good overall exposure, very fast autofocus in both low and bright light, good color rendering, nice detail preservation and low noise levels outdoors and indoors". The DxO testers also liked the iPhone 6 Plus' flash output which shows "good exposure, stable white balance, good color rendering, low noise levels and good detail preservation". On the downside some color quantification was noticed when shooting in HDR mode. 

In the iPhone 6 Plus' video mode "autofocus is very fast, accurate and repeatable and, at the time of testing, the best smartphone AF tested by the DxOMark Mobile team. The testers also found that "in good lighting videos are very well stabilized" and colors are nice in all conditions. Noise grain in video footage is very fine. On the downside exposure can be a little unstable and "some stabilization artifacts were noticed" with the device mounted on a support. Those artifacts could be described as "occasional sudden jitter across a horizontal line."

Still Photography

Color, Exposure and Contrast

The DxOMark team found that the Apple iPhone 6 Plus images show "very good overall exposure, good detail preservation in dark areas, even in difficult outdoor conditions". They also noticed the "stable white balance with a slight yellow cast" and very nice colors outdoors. On the downside "skin colors are not accurate under tungsten light."

Overall DxOMark awarded the Apple iPhone 6 Plus scores of:

  • 4.6 out of 5 for Exposure
  • 4.5 out of 5 for White Balance accuracy
  • 4.2 out of 5 for Color shading in low light*
  • 4.2 out of 5 for Color shading in bright light*
  • 2.5 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 Apple iPhone 6 Plus images show "good detail preservation in bright light" and that "detail is still visible in low light conditions". Noise is finely grained and chroma noise levels are low. However, "slight luminance noise is noticeable 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 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 is pretty much identical in daylight and tungsten light. It is also on similar levels as the iPhone 6 but a touch better in low light.
In terms of texture acutance, the iPhone 6 Plus has improved over the 5S but in medium level and bright light is trailing behind some competitors such as the Samsung Galaxy S5 and Nokia Lumia 1020. 

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 Apple iPhone 6 Plus is only beaten by the Samsung Galaxy S5 in this comparison.  
Like the iPhone 6 the 6 Plus retains sharp edges across all light levels. 

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 under tungsten illumination are a touch lower in low light than on the unstabilized iPhone 6.
Daylight noise values are similar to the tungsten measurements.
The iPhone 6 Plus noise levels are slightly higher than the competition in low and bright light but on par at 100 Lux. 

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 6 Plus were:

Natural scene

  • Texture (bright light): 4.5 out of 5
  • Texture (low light): 3.6 out of 5
  • Noise (bright light): 3.9 out of 5
  • Noise (low light) 3.4 out of 5
Bright light sample shot. 
100% crop: a lot of detail is visible in the iPhone 6 Plus images
Low light (20 Lux) studio shot.
100% crop: Fine grained luminance noise in areas of plain color
100% crop: still good detail in this low-light shot

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 Apple iPhone 6 Plus are shown below:

  • Color quantification visible in HDR mode
  • Slight moiré in some pictures
HDR sample shot
100% crop: color quantification visible

Perceptual scores

  • Sharpness 3.9 out of 5
  • Color fringing 3.4 out of 5

Measured findings

  • Ringing center 1.9%
  • Ringing corner 0.5%
  • Max geometric distortion -0.3%
  • Luminance shading 20.0%

Distortion and Chromatic Aberrations

The graph shows the magnification from center to edge (with the center normalized to 1). Like the standard model the Apple iPhone 6 shows a slight pincushion distortion, which you are not going to notice in normal photography.
Like its sister model the Apple iPhone 6 Plus shows a small amount of lateral chromatic aberration which you won't normally notice in any 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 6 Plus performs very well. The overall score is 91/100 in bright light and 92/100 in low light.

Pros: 

  • Very fast autofocus in both low and bright light
  • No oscillation when focusing at infinity

Cons: 

  • Lack of repeatability
Autofocus repeatability - average acutance difference with best focus: low light 4.53%, bright light 6.11%

Flash

DxOMark scored the Apple iPhone 6 Plus 84/100 overall for its flash performance which is the same as the iPhone 6 and one point higher than the iPhone 5S.

Pros: 

  • Good exposure, stable white balance, good color rendering, low noise levels and good detail
  • Stable white balance in mixed light situations with tungsten light

Cons:

  • Without any other light sources vignetting is visible in flash shots

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 6 Plus' video performance to be very good, with very fast and precise AF, good color and stabilization. However, exposure was occasionally a little unstable.  

Pros: 

  • Autofocus is very fast, accurate and repeatable
  • In good lighting conditions videos are very well stabilized
  • Nice color in all light conditions
  • Noise grain is fine

Cons: 

  • Occasionally slightly unstable exposure
  • Some stabilization artifacts when mounted on tripod (occasional jitter across a horizontal line)

Overall DxOMark Mobile Score for Video: 79 / 100

DXOMark Mobile Score
82

DXOMark Image Quality Assessment

The iPhone 6 Plus comes with an optical image stabilization system but otherwise the camera hardware is identical to the iPhone 6 sister model and unsurprisingly the test results are very similar as well. In stills mode the iPhone 6 Plus images show "very good overall exposure, very fast autofocus in both low and bright light, good color rendering, nice detail preservation and low noise levels outdoors and indoors". The DxO testers were also impressed by the flash performance.  

In video mode the iPhone 6 Plus autofocus is the best ever tested by the DxOMark Mobile Team and the engineers found the footage to be "well stabilized" with good color. However, exposure can be a little unstable and a "horizontal jitter" was observed with the device mounted on a support. For a more detailed analysis, visit www.dxomark.com.

Photo Mobile Score 84   Video Mobile Score 79
Exposure and Contrast 90   Exposure and Contrast 76
Color 85   Color 89
Autofocus 92   Autofocus 86
Texture 70   Texture 82
Noise 79   Noise 78
Photo Artifacts 87   Video Artifacts 85
Flash 84   Stabilization 59