DxOMark Mobile Report: Apple iPhone 6s
From a design point of view the iPhone 6s is pretty much identical to its predecessor the iPhone 6 but there have been a number of improvements under the hood, including in the camera department. Sensor resolution has been upped to 12MP and with the total number of pixels the number of phase detection sensors on the chip (the so-called 'focus-pixels) has been increased by 50%. 'Deep trench' isolation technology has been used to reduce cross-talk between the light-gathering photosites and image noise.
The camera is now also capable of recording 4K video and the FaceTime camera at the front comes with an increased resolution of 5MP. As we've seen on the LG G4 and some new Motorola devices the iPhone 6S also uses the display as a light source in low light conditions. For this purpose the screen can light up three times brighter than normal and the color of the emitted light is matched to ambient light sources for natural skin tones and colors. Panorama mode has been improved as well. It can now capture even larger images up to 63MP and as before uses dynamic exposure for avoiding extreme jumps in brightness across the frame.
With a DxOMark Mobile score of 82 the Apple iPhone 6s delivers a solid performance but cannot place itself among the very best of current smartphone cameras. It takes the number ten spot in the DxOMark smartphone rankings, placing itself between its own predecessor, the iPhone 6, which achieved the same score last year, and the Samsung Galaxy S5. The DxOMark team reports that the iPhone's autofocus is "fast and generally accurate in all conditions", and that images show "stable and pleasant white balance in most conditions" and "good detail preservation in bright light".
On the downside, "some luminance noise is visible, especially in low light" and "color shading is visible indoors". Images also show a "slightly yellow cast in outdoor conditions" and "occasional ghosting and other artifacts".
In video mode the DxO team liked the "fast, accurate and smooth autofocus, good overall exposure and white balance and effective stabilization in good lighting conditions". As negatives they noted "noticeable noise in low light conditions, especially in corners" and "slight color shading in low light conditions".
Color, Exposure and Contrast
The DxOMark team found that when shooting with the Apple iPhone 6s images showed "very good overall exposure" and "stable and pleasant white balance in most conditions". On the downside, the testers noted "some exposure irregularities due to HDR activation", "a slightly yellow cast in outdoor conditions" and "some color shading indoors".
Overall DxOMark awarded the Apple iPhone 6s scores of:
- 4.6 out of 5 for Exposure
- 4.6 out of 5 for White Balance accuracy
- 3.9 out of 5 for Color shading in low light*
- 4.2 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 images show "good detail preservation in bright light and low chroma noise". However, "in low light conditions fine detail is lost and some luminance noise is visible, especially in low light".
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): 4.6 out of 5
- Texture (low light): 3.6 out of 5
- Noise (bright light): 4.0 out of 5
- Noise (low light) 2.9 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 iPhone 6s are shown below:
- Occasional ghosting with HDR mode activated
- Blue sky saturation visible in some outdoor scenes
- Slight Moiré in some pictures
- Slight ringing
- Sharpness 4.2 out of 5
- Color fringing 3.1 out of 5
- Ringing center 8.1%
- Ringing corner 6.1%
- Max geometric distortion -0.3%
- Luminance shading 9.2%
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 6s performs well at all light levels. The overall score is 92/100 in bright light and 92/100 in low light.
- Fast and generally accurate autofocus in all conditions
- Stable focus in preview
- Some irregularities in low light when touch-to-focus is used
The Apple iPhone 6s comes with a dual-LED flash and DxOMark scored the camera 84/100 overall for its flash performance.
- Good exposure with and without additional light sources
- Stable exposure and white balance in all conditions
- Visible noise, especially near the corners
- Visible attenuation in the corners without additional light sources
Overall DxOMark Mobile Score for Photo: 83 / 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 6s's video footage to be well exposed, with good white balance. AF is quick and precise in all situations but noise and color shading can be an issue in low light.
- Fast, accurate and smooth autofocus in all conditions
- Good overall exposure and white balance
- Effective stabilization in good light
- Noise noticeable in low light, especially in the corners
- Slight color shading visible in low light
Overall DxOMark Mobile Score for Video: 80 / 100
DXOMark Image Quality Assessment
With a DxOMark Mobile score of 82 the Apple iPhone 6s cannot quite keep up with the best in class and takes the number ten spot in the DxOMark smartphone rankings, slotting in between its predecessor the iPhone 6, which achieved the same score last year, and the Samsung Galaxy S5. The DxOMark testers liked the good exposure and fast AF in all situations but were less impressed by noise and color shading in low light. Occasional ghosting was observed as well.
In video mode the camera shows good exposure and AF but as in stills mode, noise and color shading in dimmer conditions. For a more detailed analysis, visit www.dxomark.com.
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