DxOMark Mobile Report: Apple iPhone 6 Plus
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."
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 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): 4.5 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
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
- Sharpness 3.9 out of 5
- Color fringing 3.4 out of 5
- Ringing center 1.9%
- Ringing corner 0.5%
- Max geometric distortion -0.3%
- Luminance shading 20.0%
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 Apple iPhone 6 Plus performs very well. The overall score is 91/100 in bright light and 92/100 in low light.
- Very fast autofocus in both low and bright light
- No oscillation when focusing at infinity
- Lack of repeatability
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.
- Good exposure, stable white balance, good color rendering, low noise levels and good detail
- Stable white balance in mixed light situations with tungsten light
- Without any other light sources vignetting is visible in flash shots
Overall DxOMark Mobile Score for Photo: 84 / 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 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.
- 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
- 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 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.
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