DxOMark Mobile Report: Sony Xperia Z
Touted as Sony's new "superphone" and leading the charge as one of the first to foster a growing trend toward 13MP camera phones, the Xperia Z certainly piqued the interest of mobile photography enthusiasts when it was launched at the start of this year. We know we were eager to see how the phone fared under DxOMark's rigorous scientific testing.
The DxOMark Mobile Report includes DxO Lab's usual industrial-quality scientific measurements. Its imaging experts have analyzed 14 aspects of mobile imaging including detailed image quality assessment, flash performance, autofocus reliability and more to calculate a final score. This report will be integrated into our full review once it is finished. We do not yet have a review unit at the DPR Connect offices but will start working on our own evaluation as soon as we get one. For now scroll down to find out how the Sony Xperia Z's camera performed in the DxO lab tests.
Sony Xperia Z headline features:
- 13-megapixel camera with Exmor RS sensor
- 2MP front-facing camera
- 5-inch touchscreen (1920 x 1080 pixels, 441ppi)
- 1.5GHz quad-core CPU
- 2GB RAM
- 16GB of internal storage
- MicroSD card slot, up to 64 GB
With a DxOMark Mobile score of 61 the Sony Xperia Z is ranked low among DxO smartphone rankings. It came in only two points above Apple's New iPad and the only other devices it left behind are older phones like the Samsung Galaxy SII or the Apple iPhone 4. However, it's far below the best in class such as the Nokia 808, Apple iPhone 5 and Samsung Galaxy S3. In particular, it exhibited a poor performance in low light conditions.
The DxOMark team report that the Sony Xperia Z captures images with "good overall exposure," "nice colors in every lighting conditions" and "low noise level in low light without chromatic component."
On the downside: DxOMark reports that many pictures were out of focus. Images show "very strong low frequency chroma noise in the shade in bright light conditions" and "some white balance errors outdoors." In low light, the camera demonstrated poor texture preservation, a strong loss of texture, poor autofocus repeatability and excessive exposure time, even when the image stabilizer is off. Color shading occurs under a tungsten light source.
In video mode, the Xperia Z redeemed itself a bit. DxOMark's engineers reported that the Sony produced video with "excellent contrast and dynamic: best device tested to date" and "good noise reduction."
However, the report also found the Xperia Z video testing showed "loss of texture, even in bright light," "artifacts such as aliasing (staircase effect on straight lines) and flickering" and "inefficient video stabilization." Autofocus was not very reactive to scene change without moving the device.
Color, Exposure and Contrast
The DxOMark team found that the Sony Xperia Z images show "good overall exposure" and "nice colors in every lighting conditions."
However, the Xperia Z also displayed "excessive exposure time in low light, even when the image stabilizer is off." In difficult lighting conditions, contrast can be lost in the shadows. The Xperia Z shows color shading under tungsten light and some white balance errors outdoors. Because of this, DxOMark scored the Sony Xperia Z at 78/100 for color in bright light and 67/100 in low light.
Overall DxOMark awarded the Sony Xperia Z scores of:
- 4.2 out of 5 for Exposure
- 3.5 out of 5 for White Balance accuracy
- 4.0 out of 5 for Color shading in low light*
- 3.8 out of 5 for Color shading in bright light*
- 3.0 out of 5 for Color Rendering in low light
- 4.0 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 Sony Xperia Z image output shows "low noise levels in low light without chromatic component." However, the Xperia Z also showed "poor texture preservation in all lighting conditions," "strong loss of texture in low light conditions" and "strong low frequency chroma noise in the shade in bright 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 (textures such as fine foliage, hair, 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 is 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 its edges are sharp and if fine details are visible, but in-camera processing means 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 a 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 a 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.
- Texture (bright light): 3.0 out of 5
- Texture (low light): 2.5 out of 5
- Noise (bright light): 2.0 out of 5
- Noise (low light) 2.0 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 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 Z are shown below:
- Slight color fringing but at an acceptable level
- Sharpness 4.0 out of 5
- Color fringing 4.0 out of 5
- Ringing center 7.2%
- Ringing corner 5.4%
- Max geometric distortion -0.31%
- Luminance shading 14%
Distortion and Chromatic Aberrations
DxOMark also tests autofocus accuracy and reliability by measuring how much the accutance -- 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 dependant 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 condition the Sony Xperia Z results are especially poor in low light. The overall score is 67/100 in bright light and 26/100 in low light.
- Few oscillations
- Poor repeatability in low light conditions. Many pictures are out of focus.
DxOMark scored the Sony Xperia Z 64/100 overall for its flash performance.
- Exposure and color results are good with flash
- White balance is stable
- Poor texture preservation.
- Autofocus sometimes lacks repeatability.
- Red color cast with tungsten light source.
Overall DxOMark Mobile score for Photo: 62 / 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. We'll simply summarize for you. DxOMark found the Sony Xperia Z's exposure to be the best in any device it's tested to date. However, results exhibit loss of texture, artifacts and flickering, and image stabilization performance is inefficient.
- Good exposure: best device tested to date.
- Good noise reduction.
- Loss of texture, even in bright light.
- Artifacts such as aliasing (starcaise effect on straight lines) and flickering.
- Inefficient video stabilization.
- Autofocus not very reactive to scene change without phone motion.
Overall DxOMark Mobile score for Video: 61 / 100
DXOMark Image Quality Assessment
The Sony Xperia Z achieves a DxO Mark score of 61 which means it can only place itself in front of older phones such as the Samsung Galaxy SII or Apple iPhone 4. However, it is far below the best in class such as the Nokia 808, Apple iPhone 5 and Samsung Galaxy S3. In particular, it exhibited a poor performance in low light conditions.
The Sony Xperia Z offers "good overall exposure," "nice colors in every lighting conditions" and "low noise level in low light." On the downside: DxOMark reports that many pictures were out of focus. Images show chroma noise in shadow areas and in low light the camera preserved textures poorly, with poor autofocus repeatability and excessive exposure time, even with the image stabilizer switched off. Color shading occurs under tungsten light sources.
In video mode, the Xperia Z captured footage with "excellent contrast and dynamic range" and "good noise reduction" but also showed a "loss of texture, even in bright light" and "artifacts such as aliasing (staircase effect on straight lines) and flickering." Image stabilization in video mode was found to be inefficient and the AF was not very reactive to scene changes without moving the device. For a more detailed analysis, visit www.dxomark.com.
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