DxOMark Mobile Report: Apple iPhone 6

Summary

The iPhone 6 is one half of Apple's brand new duo of high-end smartphones. It shares most of its specification with the iPhone 6 Plus but at 4.7 inches comes with a smaller screen (versus the Plus version's 5.5 inches) and has to make do without an optical image stabilization system in the camera module that, like in the predecessor 5S, captures its images on a 1/3-inch 8MP sensor and through a F2.2 maximum aperture lens. 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 takes the number one spot in the DxOMark smartphone rankings and shares it with its sister model iPhone 6 Plus. The Samsung Galaxy S5 and Sony Xperia Z3 are following in positions three and four respectively. 

The DxOMark team reports the iPhone 6 shows "very good overall exposure, impressive autofocus performance in both low and bright light, good color rendering and nice detail preservation outdoors and indoors". The engineers were also impressed with the new device's flash behavior which resulted in "good exposure, stable white balance, good color rendering, low noise level and good detail preservation."

On the downside there is "luminance noise visible in low light conditions and color quantification, ghosting and fringing noticeable on HDR pictures."

In the iPhone 6's video mode "autofocus is very fast, accurate and repeatable" and at the time of testing the iPhone 6 AF is the best on a smartphone ever tested by the DxOMark Mobile team. The testers also found that "in good lighting condition videos are very well stabilized, color is very nice in all tested light conditions and the noise grain is pleasantly fine". However, during testing also "some cases of exposure instabilities" were observed.

Still Photography

Color, Exposure and Contrast

The DxOMark team found that the Apple iPhone 6 images show "very good overall exposure, good detail preservation in dark areas even in difficult outdoor conditions, stable white balance with a slight yellow cast" and nice colors outdoors. 

On the downside "skin colors are not accurate under tungsten light" and there is a "slight color shading noticeable with some indoor light sources."

Overall DxOMark awarded the Apple iPhone 6 scores of:

  • 4.6 out of 5 for Exposure
  • 4.5 out of 5 for White Balance accuracy
  • 3.8 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 images show "nice detail preservation in bright light", that "detail is still visible in low light conditions" and that noise is finely grained with low chroma noise levels. However, "luminance noise is noticeable 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 is a touch better in daylight than tungsten light and increases as light sources get brighter.  
In terms of texture acutance, the iPhone 6 is roughly on the same level as its predecessor 5S in good light but improved in lower light. It is trailing behind the Samsung Galaxy S5 and Nokia Lumia 1020 at all light levels though.

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 is at or near the top at all light levels. 
The Apple iPhone 6's ability to retain sharp edges is very good and remains the same 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 increase visibly in low light.
Noise levels in low daylight are a touch higher than under artificial tungsten light.
The iPhone 6's noise levels are in line with the competition in bright light but slightly higher in lower light scenes.

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 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) 3.1 out of 5
Bright light sample shot. 
100% crop: A lot of detail is visible in the iPhone 6 images.
Low light (20 Lux) studio shot.
100% crop: Luminance noise in areas of plain color
100% crop: Some fine 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 Apple iPhone 6 are shown below:

  • Color quantification visible in HDR mode
  • Ghosting and color fringing noticeable in high dynamic range scenes
  • Slight moiré pattern in some images
HDR sample shot
100% crop: color quantification visible

Perceptual scores

  • Sharpness 4.2 out of 5
  • Color fringing 3.0 out of 5

Measured findings

  • Ringing center 3.1%
  • Ringing corner 0.9%
  • Max geometric distortion -0.3%
  • Luminance shading 19.5%

Distortion and Chromatic Aberrations

The graph shows the magnification from center to edge (with the center normalized to 1). The Apple iPhone 6 shows a slight pincushion distortion, which you are not going to notice in normal photography.
The Apple iPhone 6 shows some lateral chromatic aberrations which won't be noticeable in any normal 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 is the best device tested so far. The overall score is 97/100 in bright light and 92/100 in low light.

Pros: 

  • Very fast and precise autofocus in both low and bright conditions
  • No oscillation when focusing at infinity.

Cons: 

  • n/a
Autofocus repeatability - average acutance difference with best focus: low light 4.62%, bright light 2.82%

Flash

DxOMark scored the Apple iPhone 6 84/100 overall for its flash performance which is one point above the iPhone 5S.

Pros: 

  • Good exposure, stable white balance, good color rendering, low noise levels and good detail preservation in flash mode
  • Stable white balance when flash is mixed with tungsten light

Cons:

  • Without any other light sources vignetting is visible on flash images

Overall DxOMark Mobile Score for Photo: 83 / 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's 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 light videos are very well stabilized.
  • Very nice color in all lighting conditions 
  • Noise is finely grained

Cons: 

  • Some exposure instabilities

Overall DxOMark Mobile Score for Video: 80 / 100

DXOMark Mobile Score
82

DXOMark Image Quality Assessment

With "very good overall exposure, impressive autofocus performance in both low and bright light, good color rendering and nice detail preservation outdoors and indoors" the Apple iPhone 6 takes the number one spot in DxOMark's smartphone ranking. The DxO engineers could not identify any major image quality problems but noticed some luminance noise in in low light and artifacts in HDR mode.

The iPhone 6's performance in video mode is equally impressive, with a very fast and precise AF, good stabilization and and nice colors. However, some exposure instabilities were observed during testing. For a more detailed analysis, visit www.dxomark.com.

Photo Mobile Score 83   Video Mobile Score 80
Exposure and Contrast 90   Exposure and Contrast 76
Color 84   Color 89
Autofocus 94   Autofocus 86
Texture 71   Texture 82
Noise 73   Noise 78
Photo Artifacts 85   Video Artifacts 85
Flash 84   Stabilization 61