DxOMark Mobile Report: Sony Xperia Z2
The Xperia Z2 is Sony's latest flagship smartphone and replaces the Z1. The full-HD display measures 5.2 inches and offers better viewing angles than its predecessor's 5-inch equivalent. While a new Snapdragon 801 processor and 3GB of RAM offer plenty of power, the camera specification is nearly identical to the Z1's. Images are captured by a 20.7MP 1/2.3-inch CMOS sensor on a F2.0 lens. Nevertheless, Sony has managed to improve the image quality of its new flagship.
The DxOMark team reports the Xperia Z2 images show "impressive detail preservation outdoors" and "in low light, a lot of detail is still visible, even if a loss of details is noticeable compared to outdoors." Noise levels are reasonable at all light levels, with small grain size and no chroma noise. The autofocus works in a fast and responsive manner, with only very few focus errors. The DxO team found the Z2 to deliver "good overall exposure," "nice colors in all conditions" and a "good overall flash performance."
On the downside, DxO says the "white balance is sometimes unstable indoors" and "outdoors, some images show a slight blue cast." They also report "slight color shading is also noticeable under tungsten light." Aside from the white balance issues the Z2 images show "noticeable fringing, ringing and maze artifacts."
In video mode the Xperia Z2 displayed "good stabilization, especially on walking movements, good texture reproduction and low noise levels." However, the "autofocus moves step-by-step rather than continuously, and is unstable." DxO has also found "white balance failures on vegetation scenes under daylight illuminant, visible color shading and aliasing."
Color, Exposure and Contrast
The DxOMark team found that the Sony Xperia Z2 images show "good overall exposure and nice colors" and "in extreme low light conditions, images are better exposed than most other camera phones." The DxO testers also noticed the exposure adapts intelligently to the scene or shooting conditions - for example when shooting portraits or mounting the Z2 on a tripod.
However, DxO also found "contrast is not very good in shadows, white balance is slightly cold outdoors" and there is "slight color shading noticeable under tungsten light."
Overall DxOMark awarded the Sony Xperia Z2 scores of:
- 4.5 out of 5 for Exposure
- 4.0 out of 5 for White Balance accuracy
- 3.5 out of 5 for Color shading in low light*
- 4.0 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 the Sony Xperia Z2 shows "impressive detail preservation outdoors" and in this respect is "one of the best smartphones tested to date." In the Z2 image output "noise is only in the luminance channel and the grain is small." Good detail is maintained in low light (20 lux) but a slight reduction is noticeable.
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 that can be blurred away by noise reduction or obliterated by excessive sharpening (such as fine foliage, hair or fur).
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): 5.0 out of 5
- Texture (low light): 3.5 out of 5
- Noise (bright light): 3.8 out of 5
- Noise (low light) 3.8 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 Sony Xperia Z2 are shown below:
- Noticeable fringing outdoors
- Strong ringing
- Some flare in challenging light situations
- Maze artifacts
- Sharpness 4.0 out of 5
- Color fringing 4.0 out of 5
- Ringing center 22.6%
- Ringing corner 16.0%
- Max geometric distortion 0.2%
- Luminance shading 25.1%
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 Sony Xperia Z2 is quite a bit better than its predecessor, the Xperia Z1. The overall score is 87/100 in bright light and 81/100 in low light.
- Fast and reactive autofocus
- Good overall repeatability and precision
DxOMark scored the Sony Xperia Z2 85/100 overall for its flash performance which is one point more than the Xperia Z1.
- Precise autofocus, good exposure, good color rendering and white balance, good detail preservation
- White balance slightly inaccurate in when mixing flash with tungsten light
- Some noise
- Slight vignetting
Overall DxOMark Mobile Score for Photo: 81 / 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. Bottom line: DxOMark found the Sony Xperia Z2's overall video performance to be good, with decent stabilization, nice textures and low noise levels. However, the AF tends to be a little unstable and white balance can be unreliable in some shooting situations.
- Good stabilization, especially on walking motion
- Good texture reproduction
- Low noise level
- Autofocus moves step-by-step rather than continuously, and is unstable
- White balance failures on vegetation scenes in daylight
- Visible color shading
Overall DxOMark Mobile Score for Video: 73 / 100
DXOMark Image Quality Assessment
The Xperia Z2's images show good detail and comparatively low noise levels in all light conditions. The autofocus is reliable, fast and responsive. The the DxO team found the Z2 to deliver "good overall exposure," "nice colors in all conditions," and a "good overall flash performance."
On the downside the white balance can occasionally struggle outdoors and in mixed-light, flash scenarios. Close-up, the images also show "noticeable fringing, ringing and maze artifacts."
In video mode the Xperia Z2 displayed good overall performance with "decent stabilization, nice textures and low noise levels." However, the AF tends to be a little unstable. Like in stills mode, the video white balance can produce color casts when shooting in daylight. For a more detailed analysis, visit www.dxomark.com.
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