DxOMark Mobile Report: Sony Xperia Z1

The Sony Xperia Z1 was launched in September at the IFA consumers electronics trade show in Berlin and replaces the Xperia Z, which itself was only launched at CES in January, as Sony's top-of-the-line smartphone. The new model comes with the same impressive build-quality and waterproof body as its predecessor. With Qualcomm's Snapdragon 800 processor and a 5-inch 1080p screen the Z1 offers top-end specs all-around.

However, for photo-centric users the really big news is the Z1's camera.  At 1/2.3-inch the sensor in the Sony's camera module is the same size as you would find in most consumer level compact cameras and therefore larger than the 1/3-inch sensors that are common in the current crop of smartphones. 

The comparatively large sensor is combined with a high pixel count of 20.7MP, a fast F2.0 lens and a physical shutter button indicating that Sony, like Nokia and HTC with their latest high-end models, has identified camera performance as a key differentiator in the highly competitive smartphone market.

Our partners at DxOMark have put the Sony Xperia Z1's through their comprehensive image quality testing regime. Read on to find out if the Z1's impressive specs translate into great image quality. For a more more hands-on evaluation of the Xperia Z1 also have a look at our smartphone shootout.

Specifications

  • 20.7 MP 1/2.3 Exmor RS CMOS sensor
  • F2.0 lens
  • 1080p/30 fps video
  • HDR video
  • Snapdragon 800 quad-core 2.2GHz processor
  • 5-inch 1080p Sony TRILUMINOS display (441ppi)
  • Android 4.2
  • 2GB of RAM
  • Waterproof body (IP55/58)
  • 16 GB internal memory
  • microSD up to 64GB
  • 3,000 mAh battery, non-removable

Summary

With a DxOMark Mobile score of 76 the Sony Xperia Z1 takes the number two spot in the DxO smartphone rankings, just above the Apple iPhone 5s and the Samsung Galaxy S4. With a score of 77 only the Nokia 808 has done better so far.

The DxOMark team reports that the Xperia Z1 images show "good overall exposure, excellent detail preservation outdoors, pleasant colors and low noise levels in all situations". "Noise is pleasant (no chroma component) with a very small grain size". The autofocus was found to be "fast and precise in most situations". The Z1's also performed well when using its flash, with "precise autofocus, good exposure, good color rendering and white balance and good detail preservation".

On the downside: "Slight color shading is sometimes noticeable" and "excessive exposure times in low light under 20 lux can be a source of motion blur". Images show "strong ringing" (halos around high-contrast edges) and "low-contrast detail is slightly smeared in low light conditions.

In video mode the Xperia Z1 displayed a good overall performance, with "good noise reduction especially in low-light conditions". However, the "autofocus lacks stability and a residual high frequency motion is visible in indoor conditions for walking movements".

Still Photography

Color, Exposure and Contrast

The DxOMark team found that the Sony Xperia Z1 images show "good overall exposure, nice colors in all situations and stable white balance"

However, the Xperia Z1 also displayed "very slight color shading, sometimes noticeable both indoors and outdoors" and "in extreme low light, exposure time is too long (1/10s under 20 lux when other camera phones do not use longer exposure than 1/15s)".

Overall DxOMark awarded the Sony Xperia Z1 scores of:

  • 4.4 out of 5 for Exposure
  • 4.3 out of 5 for White Balance accuracy
  • 3.5 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
  • 4.5 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 Sony Xperia Z1 image output shows "very low noise levels with a small grain size, even in low light conditions, and very good detail preservation. Outdoors, more details are visible than with other current 8 Mp mobile cameras". "Most noise is luminance noise".

On the downside "low-contrast detail is slightly smoothed out compared to the edges and noise levels are not constant in the image: edges are noisier than areas of plain color; image corners are noisier than the center".

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 (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.

A detail of  target made of a dead leaves pattern, designed to measure Texture Acutance. It is 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 of the same 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 a 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 showing only the 8MP equivalent values, which gives us a level playing field for comparison between phone cameras with different megapixel values by normalizing all to 8MP, suitable for fairly large prints. DxOMark also offer this data for lower resolution use-cases (web and on-screen). For more information on DxOMark's testing methodology and Acutance measurements please visit the website at www.dxomark.com.
Luminance texture acutance is very similar under daylight and tungsten illuminant and pretty much constant across light levels. 
In terms of texture acutance the Xperia Z1 scores well at low light levels but lags behind the competition in brighter conditions. 
Edge Acutance
Edge acutance is a measure of the sharpness of the edges in images captured by the phone's camera, and again we're only looking at the most demanding of the three viewing conditions that DxOMark reports on, "8MP equivalent."
The Sony Xperia Z1's ability to retain sharp edges in images is excellent across all light levels. 
In terms of edge acutance the Sony Xperia Z1 is up there with the very best..
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 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.

Noise levels in daylight conditions are low across all light levels.
Noise levels under tungsten light are similar to daylight conditions.
The Sony Xperia Z1's noise levels are lower than its competitors' at all light levels. 

Noise and Detail Perceptual scoring

DxOMark engineers don't just point camera phones at charts, they also take and analyse scores of real-world shots and score them accordingly. Their findings for the Sony Xperia Z1 were:

Natural scene

  • Texture (bright light): 4.8 out of 5
  • Texture (low light): 3.0 out of 5
  • Noise (bright light): 3.8 out of 5
  • Noise (low light) 3.8 out of 5
Bright light sample shot 
100% crop: "a lot of very fine detail is noticeable everywhere in the frame, more than for other 8MP mobile cameras."
Low light (20 Lux) studio shot
100% crop shows "low-contrast detail is slightly less visible than in bright light conditions and noise is more visible near edges."
100% crop 20 lux: "noise level is low compared to other cameras and noise grain is very small." 

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 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 Z1 are shown below:

Pros:

  • n/a

Cons 

  • Strong ringing noticeable near edges
  • Slight color fringing sometimes visible

Perceptual scores

  • Sharpness 4.0 out of 5
  • Color fringing 4.0 out of 5

Measured findings

  • Ringing center 15.3%
  • Ringing corner 8.6%
  • Max geometric distortion -0.3%
  • Luminance shading 30.8%

Distortion and Chromatic Aberrations

The graph shows the magnification from center to edge (with the center normalized to 1). The Sony Xperia Z1 shows a slight pincushion distortion, which you are not going to notice in normal photography.
The Xperia Z1 shows some lateral chromatic abberations which is slightly visible in some pictures.

Autofocus

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 Z1 is much better, especially in low light, than its predecessor, the Xperia Z. The overall score is 72/100 in bright light and 73/100 in low light.

Pros: 

  • Fast and reactive autofocus
  • Good overall repeatability and precision.

Cons: 

  • Occasionally pictures are completely out of focus in outdoor conditions
Autofocus repeatability - average acutance difference with best focus: low light 6.4%, bright light 11.35%

Flash

DxOMark scored the Sony Xperia Z1 84/100 overall for its flash performance.

Pros: 

  • Good flash performance: precise autofocus, good exposure, good color rendering and white balance, good detail preservation

Cons: 

  • Slight change of white balance in presence of tungsten lighting.
  • Some noise noticeable

Overall DxOMark Mobile score for Photo: 77 / 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. We'll simply summarize for you. DxOMark found the Sony Xperia Z1's overall video performance to be good, with good noise reduction in low light. However, the autofocus exposure to be the best of any device which the lab has tested to date. However, some instability of the autofocus was observed. 

Pros: 

  • Good overall video performance
  • Good noise reduction, especially in low-light conditions

Cons: 

  • Autofocus lacks stability
  • A residual high frequency motion is visible in indoor conditions for walking movements

Overall DxOMark Mobile score for Video: 74 / 100

DXOMark Mobile Score
76

DXOMark Image Quality Assessment

The Sony Xperia Z1 has improved in almost all areas over its predecessor, the Xperia Z, and with a DxOMark Mobile score of 76 is taking the number two spot in the DxO smartphone rankings, between the Nokia 808 on the top spot and the Apple iPhone 5s at number three.

In still image mode the DxOMark team found the Xperia Z1 to get the exposure right and produce excellent detail and color in good light. Noise levels are low across all light situations. The autofocus is reliable and the testers were also pleased with the  Z1's flash performance.

However, slight color shading is sometimes noticeable and slow shutter speeds in low light can lead to motion blur. Images also show some artifacts and low-contrast detail is being smeared in low light.

In video mode the Xperia Z1 showed a good overall performance but the autofocus lacks stability and a residual high frequency motion is visible in indoor conditions for walking movements". For a more detailed analysis, visit www.dxomark.com.

Photo Mobile Score 77   Video Mobile Score 74
Exposure and Contrast 85   Exposure and Contrast 92
Color 77   Color 85
Autofocus 73   Autofocus 60
Texture 66   Texture 64
Noise 84   Noise 85
Photo Artifacts 74   Video Artifacts 75
Flash 84   Stabilization 59